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Nuclear Physics NewsInternational

Volume 22, Issue 2April–June 2012

FEATURING:ALICE on Duty • Experimental Nuclear Astrophysics

in Underground Laboratories • Neutron-Rich Hypernuclei

Vol. 22, No. 2, 2012, Nuclear Physics News 1

Editor: Gabriele-Elisabeth Körner

Editorial Board Maria José Garcia Borge, Madrid (Chair) Eugenio Nappi, Bari Rick Casten, Yale Hideyuki Sakai, Tokyo Reiner Krücken, Vancouver Hans Ströher, Jülich Jan Kvasil, Prague and EPS/NPB James Symons, Berkeley Douglas MacGregor, Glasgow and EPS/NPB Marcel Toulemonde, Caen

Editorial Office: Physikdepartment, E12, Technische Universitat München,85748 Garching, Germany, Tel: +49 89 2891 2293, +49 172 89 15011, Fax: +49 89 2891 2298,

E-mail: [email protected]

Correspondents (from countries not covered by the Editorial Board and NuPECC)Argentina: O. Civitaresse, La Plata; Australia: A. W. Thomas, Adelaide; Brasil: M. Hussein, São Paulo; India: D. K. Avasthi, New Delhi; Israel: N. Auerbach, Tel Aviv; Mexico: J. Hirsch, Mexico DF; Russia: Yu. Novikov, St. Petersburg; Serbia: S. Jokic, Belgrade; Shanghai: Yu-Gang Ma; South Africa: S. Mullins, Cape Town.

Nuclear Physics NewsVolume 22/No. 2

Nuclear Physics News is published on behalf of the Nuclear Physics European Collaboration Committee (NuPECC), an Expert Committee of the European Science Foundation, with colleagues from Europe, America, and Asia.

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2 Nuclear Physics News, Vol. 22, No. 2, 2012

Editorial .......................................................................................................................................................... 3

Facility PortraitALICE on Duty

by Karel Safarik ........................................................................................................................................... 5

Feature ArticlesExperimental Nuclear Astrophysics in Underground Laboratories

by Marialuisa Aliotta ................................................................................................................................... 13

Facilities and MethodsPresent Status and Future Evolution of Inter-University Accelerator Centre

by Amit Roy .................................................................................................................................................. 18Beihang University ( ) Research Center for Nuclear Science and Technology (RCNST) ( )

by Isao Tanihata .......................................................................................................................................... 21Neutrino Investigation in Daya Bay

by Rupert Leitner and Vít Vorobel ............................................................................................................... 25Heavy Hadrons and Nuclear Physics at the SuperB

by Vincenzo Lucherini and Alessandro Feliciello ....................................................................................... 29

Meeting ReportsInternational Summer School on Subatomic Physics 6th Course: New Frontiers of Nuclear Physics

by Haozhao Liang, Lulu Li, and Lang Liu .................................................................................................. 34Fourth International Conference on Proton-Emitting Nuclei PROCN2011

by Bertram Blank ......................................................................................................................................... 36Report on the XXXV Symposium on Nuclear Physics in Mexico

by Elizabeth Padilla-Rodal and Jorge G. Hirsch ........................................................................................ 37BORMIO-2012: The First Topical Workshop on Modern Aspects in Nuclear Structure

by Silvia Leoni ............................................................................................................................................. 39

Calendar................................................................................................................................. 41???? (Cover 3)?

NuclearPhysicsNews

Cover Illustration: The ALICE experiment open for maintenance during the winter shutdown 2011–2012 (CERN Photo by Antonio Saba).

Volume 22/No.2

Contents

editorial


In the last 3 years as chair of the Nuclear Science Advisory Commit-tee (NSAC), I have attended a num-ber of international planning activities and as a result realize that NSAC is somewhat different from other groups. NSAC is a committee formed jointly by the U.S. Department of Energy and the U.S. National Science Foun-dation to provide consensus advice or guidance to the federal government. NSAC is neither a lobbying group nor a community advocacy group. Its members are selected by the Federal agencies, and it acts solely in response to charges presented to it by the gov-ernment.

The major activity of NSAC has always been to provide the govern-ment with advice on the scientific op-portunities and priorities within the field of nuclear physics. This is done to fit within expectations for the U.S. budget for nuclear physics, and almost always considers the plans of the in-ternational scientific community. This advice can be broad, as when a Long Range Plan is called for, or it can be more specific, for example, asking ad-vice for priorities within a sub-field. The government also uses NSAC to give it advice on setting and evaluat-ing metrics for the field, or to evaluate the effectiveness of the government departments administering the nuclear physics program.

A long range plan (LRP) is gener-ally called for every 5–7 years. The last was completed and published in 2007. The start of the LRP process is to develop input from the broad nuclear

physics community through a series of white papers and Town Meetings organized by the Division of Nuclear Physics of our American Physical So-ciety. Our present LRP articulates the focus of our national program on three broad and interrelated areas: (1) QCD and its implications and predictions for the state of matter in the early uni-verse, quark confinement, the role of gluons, and the structure of the proton and neutron; (2) the structure of atomic nuclei and nuclear astrophysics, which addresses the origin of the elements, the structure and limits of nuclei, and the evolution of the cosmos; and (3) developing a New Standard Model of nature’s fundamental interactions, and understanding its implications for the origin of matter and the properties of neutrinos and nuclei. Within each of these areas a number of overarch-ing scientific questions are articulated. A key feature of the plan development is that it is developed in the context of possible budget scenarios that are established by the agencies; this mo-tivates serious debate on relative pri-orities because tough choices must be made when budgets are limited.

The 2007 LRP contained four high-level recommendations (http://science. energy.gov/~/media/np/nsac/pdf/docs/NuclearScienceHighRes.pdf):

1. We recommend completion of the 12 GeV CEBAF Upgrade at Jeffer-son Lab.

2. We recommend construction of the Facility for Rare Isotope Beams, FRIB, a world-leading facility for

the study of nuclear structure, reac-tions, and astrophysics.

3. We recommend a targeted program of experiments to investigate neu-trino properties and fundamental symmetries.

4. We recommend implementation of the RHIC II luminosity upgrade, together with detector improve-ments, to determine the properties of a new state of matter, the quark-gluon plasma.

In the 5 years since that plan was issued, enormous progress has been made on the goals of the plan. The 12 GeV upgrade at Jefferson Lab has made substantial progress: two of ten planned new cryomodules have been installed and are delivering high qual-ity beam and the new experimental Hall D is complete with equipment installation underway. At RHIC, an R&D breakthrough has allowed the luminosity upgrade to be accom-plished via previously unattained bunched-beam stochastic cooling, several years earlier and at about one seventh the projected cost of the origi-nal plan to achieve these luminosities through electron cooling. At MSU, the preliminary civil design for FRIB is complete, final design has started, and the project will be ready to start civil construction in May 2012. Many fore-front projects are underway as part of the New Standard Model Initia-tive: progress is being made in double beta decay, collaborating in Cuore and leading the Majorana demonstra-tor which plans to go underground at

The United States Nuclear Science Advisory Committee

The views expressed here do not represent the views and policies of NuPECC except where explicitly identified.

editorial


Sanford lab this spring with a natural Ge detector. The nEDM experiment is addressing technological risk in a number of areas in order to make a world-leading search for a non-zero neutron electric dipole moment and the UCNA experiment has achieved a competitive sensitivity in the neutron spin-electron A correlation measured for the first time using ultra cold neu-trons at the Los Alamos Ultra Cold Neutron Source.

Much focus goes into the estab-lishment of priorities for major in-vestment, and facilities take a large piece of the budget, but all of this is supported by a vigorous principal investigator (PI) driven program at universities and national laboratories. Funding decisions are based on peer review that includes the strength of the PI and the merit of the science being proposed. Work is funded at facilities

around the world in addition to U.S. facilities. The alignment of the work with the LRP is a factor as well.

The progress in the field over the last 5 years was enabled by robust budgets that resulted from the U.S. government commitment to invest-ment in science and technology to achieve innovation as articulated in the “America Competes” Act. The present financial situation is not as positive as we have seen in science over the last 5 years. NSAC will likely be called on to provide recommendations for how to achieve the most important scien-tific results within more constrained budgets. Although difficult choices might be necessary, the strong strate-gic planning that the community has engaged in has the potential to enable U.S. nuclear physics to make signifi-cant investments even in a period of constrained budgets.

SuSan J. SeeStromNSAC Chair 2009–2011

facility portrait


The first ideas about a heavy-ion experiment at the Large Hadron Col-lider (LHC) at CERN were formed in the early nineties (in the last cen-tury). The motivation was to study strongly interacting matter at extreme conditions of high density and tem-perature, presumably in a new phase called quark–gluon plasma (QGP) in which quarks and gluons would be de-confined. Expectations from the suc-cessful theory of strong interactions, quantum chromodynamics (QCD), and from experiments at lower ener-gies were that the LHC would pro-vide ideal conditions to carry on these studies at unprecedented volumes, temperatures, and densities. After a few years with different designs the proposal started to converge on a solu-tion based on a very large cylindrical time-projection chamber (TPC) with a multi-layer silicon tracker inside,

both placed in a huge solenoid mag-net with a moderate field. A suitable solenoid, with 12 m aperture and 12 m length, was in use in the L3 experi-ment running at that time at the Large Electron–Positron collider (LEP), the predecessor of the LHC in the same underground tunnel. When the choice of this magnet, providing the field of 0.5 T, was confirmed, it became clear that it could house additional detec-tors for particle identification (PID), calorimetry, and even some end-cap devices. This was the time to give it a name, and that is how ALICE (A Large Ion Collider Experiment) was born. However, the collision energy achieved at contemporary heavy-ion machines was a few hundred times lower and the heaviest nuclei acceler-ated at the CERN SPS, which at that time gave the highest energies, were sulphur ions. Thus enormous extrapo-

lations were needed in the preparation work on this new experiment.

ALICE DetectorDuring the years, the ALICE col-

laboration benefited from the results coming from the heavy-ion programs at the SPS and at Brookhaven’s Rela-tivistic Heavy-Ion Collider (RHIC), allowing a much better idea of what to look for, as well as the kind of de-tectors and the precision needed. The detector design evolved continuously during these years of development. It was clear that nuclear collisions at the LHC will have produced events of enormous complexity with thousands of tracks, thus a robust tracking was from the start the design priority. The ALICE detector [1], operating at the LHC since 2009, is shown in Figure 1, and it has the following main parts: central barrel, muon arm, and forward detectors. The central barrel provides measurements of particles produced within about ±45° with respect to a plane perpendicular to the beam axis. The six-layer silicon inner tracking system (ITS), surrounding the beryl-lium vacuum beam pipe 6 cm in diam-eter, begins with pixel detectors at ra-dii 4 and 8 cm, continues with silicon drift detectors at 14 and 22 cm, and ends with double-sided strip detectors at 39 and 43 cm. The ITS measures the particle tracks with position precision of a few tens of microns. In addition, the four outer layers participate in PID by determining the specific ionization energy loss (dE/dx). The excellent spatial resolution of the innermost sili-con pixel layers results in outstanding capabilities of primary and secondary vertex reconstruction. This is illus-trated in Figure 2, showing the resolu-tion in measuring the distance of clos-

ALICE on Duty

Figure 1. Schematic layout of the ALICE detector, indicating the main subsystems.

facility portrait


est approach to the primary vertex for tracks coming from secondary decays. The values below 100 microns clearly demonstrate the ability to detect weak decays of charm and beauty particles.

The main particle tracking device is the TPC, the largest such detector built at this time. It has a cylindrical shape, more than 5 m along the beam axis, and 5 m in outer diameter. The TPC continues the tracking from the ITS at a radius of 88 cm and carries on till the end of its sensitive volume. The TPC volume, filled with neon-based gas mixture, is divided into two halves by a thin central high-voltage electrode providing an electrostatic field of about 0.4 kV/cm. Electrons created by ionization in the gas drift toward one of the end-plates equipped with multi-wire proportional chambers with cath-ode-pad readout. Altogether the TPC is read out with more than 600 thou-sands pads, which gives, taking into account the sampling along the drift direction, an effective granularity in

the TPC volume of more than half a billion three-dimensional pixels. Con-sequently, this results in very efficient track-finding down to low transverse momenta, about 100MeV/c, even at the highest particle densities in central lead–lead collisions at LHC energies. In addition, the ALICE TPC has an ex-cellent resolution for the measurement of dE/dx, between 5 and 6%, depend-ing on particle density. Figure 3 (left side) demonstrates the separation of different particle species utilizing the TPC dE/dx and the particle momen-tum measurement with ITS and TPC.

The curves representing momen-tum dependence of dE/dx for different particles cross when approaching their minima for ionization energy losses. This makes particle identification us-ing the dE/dx method impossible in that momentum region. To distinguish particle species in this region, AL-ICE installed a time-of-flight detector (TOF) at a radius of about 3.7 m from the beam axis. This detector deter-

mines the arrival time of charged par-ticles with a precision better than 100 ps, exploiting multi-gap resistive plate chambers—an innovative technology developed specifically for ALICE. The TOF measurement (Figure 3b) is able to separate π and K mesons up to 2.2 GeV/c, K mesons and protons up to 3.5 GeV/c, and can be used for elec-tron identification at lower momenta. To further increase the momentum reach for charged hadron identifica-tion, a smaller detector, the High-Momentum PID (HMPID), covering about 10% of the solid angle of the other central barrel detectors and us-ing Čerenkov ring-imaging technique, is placed about 1 m behind the TOF.

To improve the electron identifica-tion, ALICE uses a transition radia-tion detector (TRD) situated between the TPC and TOF detectors. Particles traverse six radial drift chambers, each consisting of a transition radia-tor followed be a volume containing a xenon-based gas mixture, allow-ing the detection of X-ray photons in addition to charged tracks. The TRD drift chambers are read out with cathode-pad wire chambers. Electrons are separated from π mesons by dis-criminating on signal amplitude of last samples, where the electron transition radiation contributes. This detector is also used in the tracking system; an increase of the track length in mag-netic field improves the momentum resolution at high transverse momenta (to about 5% around 100 GeV/c). At low momenta, 100 MeV/c to 1 GeV/c, the momentum resolution of ALICE tracking system is better than 1%.

The central barrel part of ALICE is completed with electromagnetic calorimeters. The larger one, EMCal, covers 120° in azimuthal angle and in longitudinal direction a little less than the barrel detectors in front of it. It is used to trigger on jets and to improve the jet energy determination measured

Figure 2. Transverse momentum dependence of resolution in distance of closest approach to primary vertex (projection in bending plane) for pions, kaons, and protons. Comparison between data and simulation (MC) is shown.

facility portrait


with tracking detectors. The much smaller photon spectrometer (PHOS) has significantly better energy resolu-tion and granularity, and is dedicated to the isolation of a direct photon sig-nal in heavy-ion collisions.

The ALICE detector can detect and trigger on muons in the forward region on one side of the central barrel using its muon arm, between 2° and 9° from the beam axis. A conical absorber be-gins at only 90 cm from the nominal interaction point, in order to suppress the background from decaying π and K mesons. Behind the absorber, the five tracking stations detect the fil-tered out muons. The first two stations are still inside the main solenoid mag-net; the third one is in the middle of the ancillary dipole magnet with 3 Tm of field integral used for muon mo-mentum analysis; the remaining two measure deflected muon tracks be-hind the dipole. Each tracking station consists of two planes of multi-wire chambers with cathode-pad readout, giving a coordinate precision of about 100 microns in the bending plane, thus giving a mass resolution of 1% at the ϒ mass, needed for the separation of different ϒ states.

Behind the last muon tracking sta-tion a second absorber shields the muon trigger detectors from remain-ing background. The full length of the muon arm, from the interaction point to the end of the trigger system, is about 20 m. Two trigger planes of resistive plane chambers (RPC) detect the position and direction of penetrat-ing muons. Using this information the muon trigger electronics select events having muons with transverse momentum above a predetermined threshold.

On the side opposite to the muon arm the Photon Multiplicity Detector (PMD) measures the yield of π0 me-sons by counting the number of pho-tons. The Forward Multiplicity Detec-tor (FMD), with silicon strip planes on both sides of the interaction region, determines the density of charged par-ticles emitted at angles closer to the beam axis than those covered by the central barrel. Scintallator tile arrays (called VZERO), covering similar ac-ceptance as that of the FMD, are used to trigger on LHC collisions, in heavy-ion collisions also selecting different centrality classes with corresponding thresholds. Small quartz counters on

both sides (T0 detector) are employed in time-of-flight measurements. The Zero Degree Calorimeters are placed more than 100 m from the interaction region in both directions; on each side there is one for the detection of pro-ton spectators and second for neutron spectators.

First CollisionsAfter many years of preparation, in-

stallation, and commissioning the AL-ICE experiment detected the first col-lisions at the LHC in November 2009. These were interactions of protons at injection energy, corresponding to center-of-mass energy of 900GeV in pp system. The ALICE collaboration was the first to submit a publication [2] on the analysis of about 300 events recorded during this first burst of col-lisions, thus demonstrating the readi-ness of the entire experiment, from the detectors and the online systems to the data analysis software. It presents the results on charged-particle density in central region and compares the mea-surement on proton–proton collisions at the LHC with those from earlier ex-periments, including UA1 and UA5 at CERN, which collected data for pro-

Figure 3. Performance of the ALICE particle identification systems. (a) Dependence of specific ionization energy loss on transverse momentum as measured by TPC. (b) Particle velocity as a function of rigidity (momentum over charge) as measured by TOF detector.

(a) (b)

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Figure 4. Event display of lead–lead collision at center-of-mass energy 2.76TeV per nucleon pair from the ALICE detector.

ton–antiproton collisions at the same energy. The last such comparison was done at the CERN ISR at 15 times lower energy. Subsequently, the LHC increased the collision energy for pro-ton–proton interactions, before the end of 2009 the world record energy of 2.36 TeV in center of mass was es-tablished, and in March 2010 the cen-ter-of-mass energy reached 7 TeV. The ALICE collaboration has measured the yields of charged particles pro-duced at these different energies and the results confirm that the charged-particle multiplicity appears to be ris-ing with energy faster than expected from calculations with the commonly used models [3]. In addition, the shape of the multiplicity distribution is not reproduced well by the standard simu-lations.

During most of 2010 the LHC con-tinued to collide proton beams. ALICE collected data on more than half a bil-lion proton–proton collisions at 7TeV energy. These were analyzed and various results on basic characteristics of particle production in pp interac-tions were published and presented

at conferences. Specifically, ALICE measured the momentum spectra of identified charged hadrons, strange and multi-strange particles, charmed mesons, the J/ψ cross-section and po-larization. One such analysis done in ALICE was the measurement of the antiproton-to-proton production ration in central region. This is especially interesting at the LHC because it col-lides baryons with baryons, where the production of baryons and antibaryons can be asymmetric even in the central region. An asymmetry is predicted in models allowing for baryon-number transport from incident particles over large distances. However, ALICE found [4] a value close to unity at 0.9TeV collision energy, and compat-ible with unity at the highest center-of-mass energy of 7TeV, setting a tight limit on the possibility for large-dis-tance baryon-number transport.

Less than a year after the first pro-ton–proton collisions, the LHC pro-ceeded to the first heavy-ion operation for experiments. At the beginning of November 2010 two lead-ion beams were put into collisions, and the LHC

became the world’s most energetic heavy-ion accelerator, reaching a cen-ter-of-mass energy of 2.76 TeV per colliding nucleon pair. This is an en-ergy nearly 14 times higher than that of the previous record holder, RHIC at Brookhaven National Laboratory. The first events “seen” by the ALICE detector are presented in Figure 4. A hundred thousand of these were used to calibrate our tools; to measure the density of produced charged particles in the most central lead–lead colli-sions [5], a crucial ingredient to esti-mate the energy density achievable in LHC heavy-ion collisions. These re-sults are then utilized to tune theoreti-cal models, on which an interpretation of the complex interaction of heavy-ions relies.

ALICE Heavy-Ion ResultsThe first LHC heavy-ion results

were already published during the 2010 lead–lead run, lasting for a month. In fact, there were three papers submitted almost simultaneously: the above mentioned multiplicity mea-surement [5] and the measurement of v2 coefficient of the azimuthal anisot-ropy [6] by ALICE, and by the ATLAS collaboration a paper on jet-energy imbalance [7]; these appeared to-gether in one issue of Phys. Rev. Lett. One of the most spectacular findings at RHIC was that the matter generated in heavy-ion collisions flows like a liquid with very low viscosity, almost at the limit of what is allowed for any material in nature. This tells us that the constituents of this QGP are quite dif-ferent from freely interacting quarks and gluons. The first LHC azimuthal anisotropy measurement [6] confirms the RHIC results: elliptic flow of parti-cles with the same transverse momenta is almost identical at the two ener-gies. The nearly perfect fluid has been found to be opaque to even the most energetic partons (quarks and gluons),

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which appear as jets of particles from the collisions, an effect known as jet quenching. This is an interpretation of the reported strong jet-energy imbal-ance [7]. However, the physical mech-anisms underlying these phenomena are not well understood. Jet quench-ing manifests itself also in a reduced high-transverse-momentum-particle yield in central collisions compared to that expected from the measurements in proton–proton reactions. To express such reduction a properly normalized ratio of yields in heavy-ion and in pro-ton–proton interactions—the nuclear modification factor RAA—is used. The suppression pattern observed by AL-ICE [8] gives factor about 7 (= 1/RAA) lower charged-particle production in lead–lead collisions at transverse mo-mentum around 6GeV/c, and less re-duction at higher momenta.

The size of the pion-emitting source in central lead–ion collisions is deduced from the shape of the Bose-Einstein peak in the two-pion correla-tion functions [9]. The collective flow makes the size of the system appear smaller with increasing momentum of the pair. This behavior is clearly visible for the radii measured in the ALICE experiment. The results for measurements of the radius of the pion source in three dimensions indicate a short duration for the emission, hence an “explosive” emission. Time when the emission reaches its maximum is 10–11 fm/c, significantly longer than it is at RHIC, see Figure 5(a). More-over, the product of the three compo-nents at low pair-momentum, an esti-mate of the homogeneity volume of the system at decoupling, is twice as large as at RHIC, see Figure 5(b).

One of the crucial measurements for the characterization of the fire-ball produced in heavy-ion collisions focuses on the spectra of identified hadrons, which encode the collective expansion velocity developed in the

QGP and in hadronic stages. More-over, the overall abundances of identi-fied hadrons are believed to be fixed at hadronization, thus they indicate the temperature when chemical composi-tion was established. The measured spectra [10] show an increase of about 10% in the radial-flow velocity when compared to RHIC results. At present, however, the yield ratios observed by ALICE seem to challenge both previ-ous experiments and theory. While the K/π, Ξ/π, and Ω/π ratios are compat-ible with the expectations from the thermal model with temperature about 165 MeV, as in previous observations, the p/π ratio points to a significantly lower temperature. On the experimen-tal side, there are indications of a simi-lar effect at lower energies, which call for further investigations. On the theo-retical side, a number of different pos-sibilities are being investigated, none of them conclusive at the moment.

As mentioned earlier, the first re-sults on elliptic flow were published [6] during the initial Pb–Pb run. Flow is an interesting observable because it provides information on the equation of state and the transport properties of matter created in a heavy-ion col-lision. This observable relates final state anisotropies with features of the initial one, thus allowing study of the medium response and charac-teristics. The azimuthal anisotropy in particle production is a clear experi-mental signature of collective flow. It is caused by multiple interactions be-tween the constituents of the created matter and the initial asymmetries in the spatial geometry of a non-central collision. The amount of elliptic flow measured by the v2 coefficient, inte-grated over transverse momentum, increases by 30% compared to RHIC energies. However, this increase is entirely a consequence of the growth in transverse momenta. ALICE also measured the higher harmonic coef-

ficients of azimuthal distribution [11]; they exhibit much shallower central-ity dependence than v2, and the sym-metry planes of v2 and v3 coefficients are uncorrelated (Figure 6a). These observations point to fluctuations in the initial geometry as the origin of higher-order azimuthal asymmetries. The flow coefficients can also be stud-ied in another way, using two-particle correlations in azimuthal angle [12]. A Fourier decomposition of the correla-tion function gives squares of differ-ent v coefficients, and describes well the structures seen in azimuthal cor-relations, see Figure 6b, such as the “long-range ridge” (a small angle cor-relation between particles distanced in longitudinal direction) and the “Mach cone” (a correlation on two sides of

Figure 5. Bose–Einstein pion-inter-ferometry results from different ex-periments [9]. (a) Estimate of lifetime of emitting source as a function of cube root of particle density. (b) Vol-ume of homogeneity region as a func-tion of particle density.

(a)

(b)

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back-to-back direction). The collec-tive response to initial spatial anisot-ropy that causes elliptic flow econom-ically explains these puzzling features, once event-by-event initial-state den-sity fluctuations are considered. The ALICE experiment has analyzed azimuthal asymmetry also separately for different particle species, which constrains models incorporating a re-alistic initial state and hydrodynamic evolution.

The two-particle azimuthal corre-lations at higher transverse momenta measure particle-yield modifications in jet-like structures [13]. When com-pared to the expectation from proton–proton interactions, the observed yield around high-transverse-momentum particle is slightly higher, while the yield on the opposite side is reduced. This measurement assists the under-standing of jet-quenching phenomena. The ALICE collaboration continues to contribute to this topic by studying reconstructed jets, underlying event fluctuations, modifications of jet-frag-mentation function and jet-particle composition.

Heavy-flavor particles are recog-nized to be effective probes of a very

dense and hot medium formed in nucleus–nucleus collisions; they are expected to be sensitive to its energy density, through the mechanism of in-medium energy loss. In addition, at LHC energies, heavy-flavor par-ticles are copiously produced and thus provide ideal tools for QGP studies. The nuclear modification factor RAA is well established as a sensitive ob-servable for the study of the interac-tion of hard partons with the medium. Parton energy-loss is caused by the strong interaction, hence the amount of energy loss depends on color charge of parton. Therefore, quarks are predicted to lose less energy than gluons. In addition, heavy quarks (up to some high momentum), which are slower than light, cannot emit glu-ons within the so-called “dead-cone” around their trajectory; this effect is expected to reduce the energy loss of heavy quarks with respect to light ones. Thus, a pattern of gradually de-creasing suppression (i.e., increasing RAA) should emerge when going from the light-flavor hadrons (e.g., pions), which mainly come from gluons, to the heavier D and B mesons: RAA(π) < RAA(D) < RAA(B). The measurement

and comparison of these different probes provides, therefore, a test of the color-charge and mass dependence of parton energy-loss. The ALICE col-laboration has measured the produc-tion of the charmed mesons D0 and D+, detecting their hadronic decays in lead–lead collisions [14]. In cen-tral collisions a large suppression with respect to expectations at large trans-verse momentum was found, indicat-ing that charm quarks undergo a strong energy loss in the hot and dense state of strongly interacting matter formed at the LHC. This is the first time that D meson suppression has been measured directly in central nucleus–nucleus collisions. The results show a suppres-sion by a factor 4–5, almost as large as for charged pions, above 5 GeV/c (Fig-ure 7). At lower momenta, there is an indication of smaller suppression for D than for π mesons.

Suppression of charmonium pro-duction was for a long time consid-ered as one of the main probes for a deconfined medium. At large enough temperatures bound charm–anticharm states are supposed to be dissolved due to Debye screening. However, at LHC energies, new mechanisms of

Figure 6. Measurements of azimuthal anisotropy in lead–lead collisions at LHC. (a) Dependence of different vn coefficients (see legend) on collision centrality [11]. (b) Fourier decomposition of two-particle azimuthal correlation function in 2% most central collisions [12].

(a) (b)

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charmonium production in the QGP could occur because of a large number of charm quarks. Around one hundred charm–anticharm pairs are expected to be produced in a central lead–lead collision. Several dynamical transport models predict that charm and anti-charm quarks could combine at later stages of the interaction, leading to an enhancement of charmonium pro-duction in the most central collisions. ALICE detects charmonium down to very low transverse momentum in two different regions: the central barrel in the dielectron channel and the forward muon arm in the dimuon channel. The detection at low transverse momen-tum is crucial because the recombi-nation of the charm and anticharm quarks is expected to be the main pro-duction mechanism for charmonium below 3 GeV/c. The different regions allow for the study of QGP with dif-ferent charm densities. ALICE has studied the nuclear modification fac-tor RAA for J/ψ mesons as a function of collision centrality [15]. The results

indicate that the J/ψ nuclear modifi-cation factor shows little dependence on centrality (Figure 8), a trend that is different from that observed at lower energies. For central and mid-central collisions the J/ψ RAA is larger at the

LHC than that measured at RHIC. In a complementary study, the CMS col-laborations at the LHC have measured a smaller value for the J/ψ nuclear modification factor at transverse mo-menta above 6.5 GeV/c. These ob-servations hint at the recombination of charm and anticharm quarks in the QGP as the main mechanism for J/ψ production in central lead–lead colli-sions at LHC energies.

This was a glimpse on the first heavy-ion results published by the ALICE collaboration. There are many other analyses at various stages of progress, which will be presented soon, and for certain will enlarge our insight into the matter produced in col-liding heavy-ions at the new energy.

Future of ALICEIn 2010 the ALICE detector col-

lected with a minimum-bias trigger about 30 million of lead–lead col-lisions at center-of-mass energy of 2.76TeV per nucleon pair. Last year there was a short period of proton–pro-ton running at the same energy at the start of the LHC operation, to gather

Figure 7. Charmed-meson nuclear modification factor as a function of trans-verse momentum compared to that of charged hadrons and of non-prompt (most-ly from B-decays) J/ψ mesons (as measured by CMS).

Figure 8. Nuclear modification factor for J/ψ as a function of collision central-ity, expressed as number of participants. ALICE data are compared to those from the PHENIX experiment at RHIC.

facility portrait


comparison data; these were used for normalization in practically all mea-surements described above. The rest of the proton running proceeded at (a standard) energy of 7TeV. At the end of the year, the LHC switched again to the heavy-ion mode. This time the instant luminosity grew to above 1026cm–2s–1, and was above the design value for energy 2.76TeV per nucleon pair. ALICE used triggers for different types of lead–lead collisions: central, semi-central, dimuons, photons, jets, ultraperipheral, and others, and col-lected about 100 million events, in-specting over 0.1 nb–1 of integrated luminosity. These data are currently being analyzed and the results will be presented at upcoming conferences.

The coming end-of-year period will be dedicated to proton–lead col-lisions, to improve the baseline com-parison, taking into account modifica-tions of structure functions in nuclei. We expect to collect at least 30 nb–1 of luminosity in the four weeks of pA running. Then the LHC operation will be paused for an upgrade necessary to increase the collision energy. After the restart the ALICE collaboration aims to complete its approved program, collecting 1 nb–1 of heavy-ion colli-sions at the higher collision energy

(5.5 TeV per nucleon pair in the center of mass, being the design value). The intention is to achieve a significant part of this agenda before the second long shutdown for the preparation of the LHC luminosity increase, planned for 2018. Under discussion is an AL-ICE detector upgrade allowing for high-luminosity heavy-ion running after this period. The extended phys-ics program justifying the LHC opera-tion in heavy-ion mode beyond 2020, which would imply collecting over 10 nb–1 of data, is being prepared.

After having confirmed the main discoveries obtained at RHIC, AL-ICE has entered an exciting phase of new measurements, allowing a much broader and deeper study of the QGP. At the same time, ALICE is already preparing, on the basis of what has been learnt so far, a next step in more detailed characterization of the extreme state of matter produced at LHC; new discoveries may come!

References 1. K. Aamodt et al. (ALICE collabora-

tion), JINST 3 (2008) S08002. 2. K. Aamodt et al. (ALICE collabora-

tion), Eur. Phys. J. C65 (2010) 111. 3. K. Aamodt et al. (ALICE collabora-

tion), Eur. Phys. J. C68 (2010) 345.

4. K. Aamodt et al. (ALICE collabo-ration), Phys. Rev. Lett. 105 (2010) 072002.



7. G. Aad et al. (ATLAS collaboration), Phys. Rev. Lett. 105 (2010) 252303.

8. K. Aamodt et al. (ALICE collabora-tion), Phys. Lett. B696 (2011) 30.


10. M. Floris for the ALICE collabora-tion, J. Phys. G38 (2011) 124025.




14. A. Dainese for the ALICE collabora-tion, J. Phys. G38 (2011) 124032.

15. G. Martinez Garcia for the ALICE collaboration, J. Phys. G38 (2011) 124034.

Karel SafariKCERN

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IntroductionStars generate energy and synthesize elements through

nuclear reactions during stages of quiescent evolution and during fierce catastrophic explosions. The detailed descrip-tion of the processes that account for a star’s lifetime is a truly multi-disciplinary effort that requires input from as-tronomical observations, theoretical stellar modeling, and experimental nuclear physics.

Despite impressive progress in the last few decades, many open questions still remain: What are the final stages in the evolution of a massive star? What determines if the remnant of a supernova explosion is a neutron star or a black hole? How, when, and where do stars synthesize the heavy elements that form much of our everyday environment?

How can we explain the isotopic abundances observed in novae ejecta? Answering these and similar questions is at the heart of Nuclear Astrophysics and invariably requires accurate measurements of key nuclear reactions at the ener-gies at which they take place in stars [1]. Unfortunately, this is an extraordinarily difficult task.

Thermonuclear reactions in stars take place over a nar-row energy region, the so-called Gamow peak, well below the repulsive Coulomb barrier between the interacting nu-clei. At these extremely low energies, characteristic cross-sections range between 10–18 barn < σ < 10–9 barn [1]. Although the nuclear cross-section is a useful concept to determine the probability at which a given reaction takes place in the astrophysical plasma, what is measured in the laboratory is not the cross-section, but rather the reaction yield that is proportional to the cross-section, as well as to the number of projectile and target nuclei, and to the detec-tion efficiency. For typical stable-beam experiments (beam currents i = 10–100 μA, target thicknesses Nt = 10

19 atoms/cm2, and detection efficiencies ԑ = 1–100%) characteristic reaction yields range between about 0.1–10 counts/day (for a representative cross-section σ = 10–13 barn).

Measuring such low yields poses extreme challenges to even the most experienced of experimentalists and finding ways to improve the signal-to-noise ratio becomes vital. Typically, one needs a combination of both improving the “signal” and reducing the “noise.” Improving the signal requires maximizing beam currents, using thicker targets, and increasing detection efficiencies wherever possible. Clearly, there are limits on the extent to which each of these can be accomplished and improvements in this direction have mostly been exhausted at surface laboratories. Reduc-

Experimental Nuclear Astrophysics in Underground Laboratories

Marialuisa aliottaSUPA, School of Physics and Astronomy, University of Edinburgh, Edinburgh, Scotland, UK

“Some people are so crazy that they actually venture into deep minesto observe the stars in the sky.”

—C. Plinii Secundi, Naturalis Historiae, AD 77–79

Figure 1. Characteristic g-ray background spectrum ob-tained at a surface laboratory.

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ing the noise can be even more challenging and how suc-cessfully this can be achieved depends of the sources of background.

Why Underground?There are two main sources of background: beam-in-

duced and ambient. The former is produced by reactions induced by the beam as it interacts with components of the beam-lines (e.g., collimators and apertures) and/or with impurities in the target. This source of background is dif-ficult to minimize and the greatest care is devoted to the experimental setup design and to the production of the pur-est targets possible. The ambient background arises from a combination of three components, as illustrated in Figure 1. At high energies (Eγ > 3 MeV), the background is rather flat and mostly due to neutron-induced reactions and to in-teraction of cosmic rays (muons and high-energy charged particles from outer space) with the experimental setup. By contrast, the strong contribution at Eγ < 3MeV is associated with the ambient natural radioactivity (mainly from U and and Th decay chains and from Rn contained in the labora-tory building materials) and displays intense characteristic lines.

Partial reduction of the ambient background in surface laboratories, particularly at high energies, can be obtained by a proper shielding of the detectors. However, major improvements can only be achieved in deep underground laboratories, where the flux of cosmic muons can be re-duced by several orders of magnitude, depending on the depth of the location.1 Suppression of the background at lower energies is more difficult and the level of background will clearly depend on the geology of the underground site. Specifically, salt mines are particularly well suited because of the low U and Th content in the salt rocks compared to ordinary rocks.

As an example, a comparison between γ-ray background spectra in surface and underground laboratories is shown in Figure 2. The ambient background at Eγ < 3 MeV is re-duced by a factor of 5–30 in the salt and potash mine at Boulby (UK) compared to both surface and LNGS (Gran Sasso, Italy) laboratories. At higher γ-ray energies, a back-ground suppression of up to three orders of magnitude is obtained both at Boulby and at Gran Sasso, thus showing the great advantage of underground locations.

LUNA: A Pioneering ProjectThe potential of underground measurements of key reac-

tions for astrophysics has been demonstrated in the last two decades by the pioneering work performed at the Labora-tory for Underground Nuclear Astrophysics (LUNA) fa-cility located at the Laboratori Nazionali del Gran Sasso (LNGS), Italy. Here, the Gran Sasso massif provides 1,400 m of rock overburden (3,800 meters of water equivalent, m.w.e.) leading to a million-fold reduction in the cosmic-ray flux compared to a surface laboratory. Such a strong background reduction has enabled, for first time, the mea-surement of key reaction cross-sections of astrophysical importance directly in their Gamow energy regions.

Initial investigations at LUNA included two fundamental reactions in the pp-chain, 3He(3He,2p)4He [2] and d(p,γ)3He [3], which were measured directly at solar Gamow-peak energies for the first time. Both measurements were car-ried out using a “homemade” 50 kV accelerator capable of delivering protons and 3He+ beams of 300 to 500 μA at energies between 10 and 50 keV.

Following the early success of these measurements, the LUNA facility was upgraded by the acquisition of a com-mercial 400 kV machine that became operational in 2002. Since then, LUNA has carried out investigations of other key reactions relevant to hydrogen burning in the pp-chain,

1Further background reduction can be achieved by active or passive shielding of the detection system and in general the shielding is more ef-fective underground than on the surface because of the already reduced cosmic ray–induced interactions.

Figure 2. Comparison of γ-ray background spectra ob-tained with the same (unshielded) detector in three differ-ent laboratories. The ambient background at Eγ < 3 MeV is reduced by a factor of 5–30 in the Boulby Mine because of the lower content of U and Th in the salt rock, compared to both surface and LNGS (Gran Sasso) laboratories. At higher γ-ray energies, a background suppression of up to three orders of magnitude is observed both at Boulby and at Gran Sasso (Courtesy: F. Strieder).

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the CNO cycles, the MgAl and NeNa cycles, and to the Big Bang nucleosynthesis [4, 5].

Perhaps the most impressive achievements of this exten-sive experimental program are exemplified by the results on the 14N(p,γ)15O reaction, the slowest of the CNO cycles reactions. The new improved data obtained at LUNA [6, 7] led to a reduction in the previously accepted reaction rate by a factor 2 with a number of impressive consequences for many astrophysical scenarios. These include: a delay in the onset of the CNO cycle in massive stars; a reduction in the flux of CNO solar neutrinos (to the level of 2% instead of 4% as previously assumed) with important implications for the Borexino detector; and, most notably, an increase of about one billion years in the age of globular clusters (the oldest objects in our galaxy) [8], and hence a corresponding increase in the age of the universe.

While the success of these measurements testifies to the enormous potential of underground environments, present capabilities at LUNA are limited both in the ion species (mostly protons and helium isotopes) and energies that can be attained. Yet, several open questions of stellar evolution depend on reactions involving heavier nuclei (see below) and higher interaction energies than can be achieved at LUNA. Thus, new upgraded facilities are clearly needed. The following section highlights some of the key reactions for which underground investigations could lead to major breakthrough.

Key Open Questions in Nuclear Astrophysics

Carbon BurningCarbon burning represents the third stage of stellar evo-

lution for massive stars (M ≥ 8 Mʘ) and proceeds mainly through the 12C(12C,p)23Na and the 12C(12C,α)20Ne chan-nels. As the rates of these reactions govern the timescale of the carbon burning and influence later stages of stellar evolution, they are essential to the understanding of, for example, type Ia supernovae explosions and accreting neu-tron stars. Experimental data on these reactions display pro-nounced resonance features that persist down to the lowest energies measured so far (Ecm ~ 2.1 MeV) [9]. As a result, the extrapolation of existing data into the Gamow region is largely unconstrained, as shown in Figure 3, and this leads to uncertainties in the actual reaction rate up to a few orders of magnitude. Direct measurements at lower energies are essential, but are severely hampered by both cosmic-ray and beam-induced backgrounds. It is expected that major improvements can be achieved in underground measure-ments, ideally with advanced detectors, such as Compton suppressed HPGe detector arrays.

Neutron SourcesApproximately 50% of all the elements beyond iron

are synthesized through slow neutron-capture reactions (s-process) along the valley of beta stability. The most likely reactions to produce the required neutron fluxes are the 13C(α,n)16O, 22Ne(α,n)25Mg, and possibly the 17O(α,n)20Ne reaction. However, no experiment has yet been able to reach the relevant astrophysical energies. For the 13C(α,n)16O re-action, direct data extend only down to 270 keV [10] (i.e., well above the energies of astrophysical interest 170–200 keV). Similarly, the 22Ne(α,n)25Mg reaction yield at Eα ≤ 800 keV (i.e., the relevant astrophysical energies) is entirely dominated by cosmic-ray induced background [11] and its reaction rate remains uncertain by an order of magnitude below T ≤ 0.3 GK, which significantly affects nucleosynthesis predictions. Further low-energy measure-ments in underground laboratories thus hold the potential for major advances on the current state of the art.

Galactic NucleosynthesisRadiative capture reactions such as 22Ne(p,γ)23Na,

23Na(p,γ)24Mg and 26Al(p,γ)27Si significantly influence the production of Ne, Na, Mg, and Al in Asymptotic Giant Branch stars [12]; while processes such as 17,18O(p,γ)18,19F, 33S(p,γ)34Al and many other proton-induced reactions on A = 20–40 nuclei are crucial to the production of key isotopes often observed in novae ejecta [13]. Once again, essential improvements in the measurement of these reactions could be achieved by using advanced detection systems in under-ground laboratories.

Figure 3. Astrophysical S-factor versus center-of-mass en-ergy for the 12C+12C reaction. Current extrapolations of the S-factor to the energy region of interest (shaded area) differ by up to three orders of magnitude [Adapted from: F. Strie-der et al., J. Phys. G35 (2008) 14009].

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Future Underground FacilitiesSeveral underground laboratories exist worldwide for the

investigation of rare physical phenomena, such as neutrino-less ßß decay, proton radioactivity, gravitational waves, as well as for the detection and investigation of neutrino’s properties and for dark matter search [14]. However, only a few of these would meet the requirements for easy access, dedicated space, and suitable geology required for nuclear astrophysics experiments. Thus, LUNA remains at present the only underground facility in the world dedicated to nu-clear astrophysics. Given the importance of further under-ground measurements, various projects are being proposed for future facilities both in Europe and elsewhere. Here, I will present a brief overview of some relevant proposals, but the map of underground science is rapidly evolving and further facilities may be proposed in the next few years.

Europe

LUNA MVThis project foresees the upgrade of the existing LUNA

facility by the acquisition of a MV machine capable of ac-celerating light ion species (protons, deuteron, and helium isotopes) at the energies required for the study of some key reactions, mostly occurring in helium-burning stars. The development of a full project for the preparation of the site inside LNGS (floor sealing, ventilation, power supply, etc.) is almost complete and the shielding of the experimental hall from the rest of the laboratory is under study. Simu-lations on the expected neutron fluxes generated by some of the reactions to be studied have been carried out and technical solutions are currently being considered [15, 16]. Recently, a proposal in support of the LUNA MV program was submitted [17] as part of the “Progetti Premiali INFN” scheme to the Italian Research Ministry.

CanfrancThe Canfranc Underground Laboratory (LSC) is located

under the Pyrenees, where the rock overburden provides 2,500 meters-water-equivalent shielding from cosmic rays and offers a low background environment for experiments in particle and astro-particle physics. The nuclear astro-physics project foresees the installation of a 3.5 MV accel-erator coupled with a RF source for beams of protons and alpha particles. However, the possibility of a future upgrade to an ECR source for the acceleration of heavier nuclei (e.g., 12C and 16O) is also being considered [18]. The proj-ect requires the construction of an independent and well-isolated cave, for which an engineering design has recently been completed. Permission for excavation is expected during 2012, after which excavation work may start. Neu-

tron background measurements and simulations have re-cently been completed. Funds for the accelerator are be-ing sought in parallel. A full Letter of Intent should be presented to the LSC Scientific Committee in the next few months [18].

FelsenkellerThe Felsenkeller underground site, near Dresden, Ger-

many, consists of nine tunnels dug in the 1850s to host the ice cellar of the nearby Felsenkeller brewery. The aver-age rock overburden is 47 m, equivalent to 110 m water (m.w.e.), and provides a factor of 30–50 reduction in the muon flux. Felsenkeller could be used as part of a staged approach by installing a used accelerator in one of the already-existing tunnel, greatly speeding up progress and reducing cost. However, the background at Felsenkeller is a factor of 3–10 higher than at Gran Sasso [19], meaning that the most challenging measurements would still have to be done deep underground.

BoulbyFor completeness of information, it is worth mention-

ing that a proposal [20] for a feasibility study to create a dedicated underground facility in the salt and potash mine at Boulby, UK, was submitted to the Science and Technol-ogy Facilities Council (STFC, UK) in 2009. Unfortunately, following major financial cuts to science in recent years, the proposal was not funded despite receiving extremely positive evaluation by international referees. However, the features of the mine (1.1 km depth; low U and Th content in the salt and potash layer; availability of large areas for the construction of a dedicated underground laboratory) still make it an ideal location for underground nuclear as-trophysics.

United States: DIANAIn the United States, plans to construct an underground

facility at the site of the former gold mine of Homestake in South Dakota are under way. Specifically, the Dakota Ion Accelerators for Nuclear Astrophysics (DIANA) project is a collaboration between the University of Notre Dame, University of North Carolina, Western Michigan Univer-sity, and Lawrence Berkeley National Laboratory to build a nuclear astrophysics accelerator facility 1.4 km below ground as part of the Deep Underground Science and En-gineering Laboratory (DUSEL) proposal. DIANA would consist of two high-current accelerators: a 30 to 400 kV variable, high-voltage platform; and a dynamitron accelera-tor with a voltage range of 350 kV to 3 MV. The project foresees the development of a high-density super-sonic jet-

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gas target capable of delivering up to 100 mA on the low energy accelerator and several mA on the high-energy ac-celerator. As a unique feature, both accelerators are planned to be equipped with either high-current microwave ion sources or multi-charged ECR ion sources producing ions from protons to oxygen. The design work is underway for both the accelerator and jet-gas target [21]; however, the funding situation is somewhat unclear at present [22].

Rest of the World In addition to the projects and proposals already men-

tioned, a number of other underground laboratories are currently being planned or built at several other locations worldwide. Here, we just mention the proposal for the AN-DES laboratory that may potentially be suitable to host an accelerator for nuclear astrophysics studies. The project exploits the construction of a low altitude tunnel as part of a strategic improvement of the Agua Negra pass in the Andes, near the Argentina-Chile border. The ANDES un-derground laboratory would be the only such laboratory in the southern hemisphere. The laboratory would consist of 3 halls shielded by 1,750 m of rock from cosmic rays. A linear access tunnel would be available for the installa-tion of the accelerator. If the proposed project goes ahead, the opening of the laboratory would be concurrent with the opening of the Agua Negra tunnel in 2018 [22, 23].

ConclusionsThermonuclear reactions provide the engine that makes

stars shine and the means by which all elements beyond primordial hydrogen and helium are synthesized. The di-rect investigation of these reactions in terrestrial laborato-ries is severely hampered by the background induced by cosmic rays as they interact with the experimental detection systems. Often, the only way to significantly improve the signal-to-noise ratio characteristic of nuclear astrophysics reactions consists in measuring nuclear cross-sections in deep underground laboratories where the cosmic-ray flux can be reduced by several orders of magnitude compared to surface laboratories.

The potential for underground measurements has been demonstrated by the pioneering work performed at LUNA, in Gran Sasso, Italy. Yet, despite the major advances ob-tained so far, many important astrophysical reactions re-main beyond current capabilities at LUNA. Here, an outline of key open questions in nuclear astrophysics has been pre-sented together with an overview of current plans for future next-generation underground facilities both in Europe and elsewhere. It is hoped that some of the proposed facilities

will be realized in the near future so as to open up new and unprecedented opportunities for major breakthroughs in this fascinating research field.

References 1. C. Iliadis, Nuclear Physics of Stars (New York: Wiley-VCH,

2007). 2. R. Bonetti et al., Phys. Rev. Lett. 82 (1999) 5205. 3. C. Casella et al., Nucl. Phys. A 706 (2002) 203. 4. C. Broggini et al., Annu. Rev. Nucl. Part. Sci. 60 (2010) 53. 5. H. Costantini et al., Rep. Prog. Phys. 72 (2009) 086301. 6. A. Formicola et al., Phys. Lett. B 59 (2004) 61. 7. A. Lemut et al., Phys. Lett. B 634 (2006) 483. 8. G. Imbriani et al., Astron. & Astrophys. 420 (2004) 625. 9. T. Spillane et al., Phys. Rev. Lett. 98 (2007) 122501.10. M. Heil et al., Phys. Rev. C 78 (2008) 025803.11. M. Jaeger et al., Phys. Rev. Lett. 87 (2001) 202501.12. R.G. Izzard et al., Astron. & Astrophys. 466 (2007) 641.13. C. Iliadis et al., ApJ. S134 (2001) 151; and ApJ. S142 (2002)

105.14. E. Coccia, Journ. Phys. Conference Series 203 (2010) 012023.15. A. Guglielmetti, Private communication (2012).16. A. Guglielmetti, Proceedings of Science (2012): VI Euro-

pean Summer School on Experimental Nuclear Astrophysics, ENAS 6, 18–27 September 2011, Italy.

17. http://www.presid.infn.it/premiali/LUNA.pdf (accessed 12 March 2012).

18. L. M. Fraile, Private communication (2012); and http://www.lsc-canfranc.es/ (accessed 2 March 2012).

19. T. Szücs et al., Eur. Phys. J. A48 (2012) 8.20. M. Aliotta (for the ELENA Collaboration): Proposal for a fea-

sibility study and design (2009).21. D. Leitner et al., Proceedings of 2011 Particle Accelerator

Conference, New York, NY USA; and http://www.jinaweb.org/dusel/DIANA/rpt76801.pdf (accessed 26 January 2012).

22. M. Wiescher, Private communication (2012).23. http://fisica.cab.cnea.gov.ar/particulas/andes/main.php (ac-

cessed 28 January 2012).

Marialuisa aliotta

facilities and methods


The laboratory portrait of Inter-University Accelerator Centre (IUAC) was published in Nuclear Physics News in 2003 [1]. Since then, devel-opment of both the accelerator fa-cilities and the experimental facilities have grown hand in hand. The booster superconducting linac is now in op-eration providing higher energy heavy ions into four beam-lines. New target stations house a neutron array and an-other the Hybrid Recoil Analyser that can work in either gas filled mode or in vacuum mode. The Indian National Gamma Array consisting of a maxi-mum of 24 Ge clover detectors also uses this beam-line. One beam-line is dedicated for experiments on ion beam interaction in materials, having in-situ x-ray diffractometer, a micro Raman facility, and an elastic recoil detector set-up. The fourth beam-line is for atomic physics studies.

Accelerator DevelopmentsThe 15 UD Pelletron Accelera-

tor has been running smoothly since 1991, providing a multitude of heavy ion beams to the users. The machine was upgraded with a multi-cathode SNICS source and new design of column resistor mountings allowing smoother changes of energy. A 1.7 MV Pelletron with RBS and chan-neling set-up was commissioned last year as an additional facility for users. The Low Energy Ion Beam Facility provides multiply charged ions in the energy range 30 keV–2 MeV for ex-periments in atomic physics and ma-terials science into three recently laid beam-lines.

The superconducting linac system of IUAC consists of five cryostats,

the first one is the superbuncher (SB) cryostat housing a single niobium resonator, the next three accelerating cryomodules house eight resonators each and the last cryostat has two res-onators to be used as re-buncher. Two modules of the linac are operational and the remaining eight resonators in the last linac module will be installed by the end of the year. In the high cur-rent injector project, an electron cy-clotron resonance ion source (ECRIS) has been developed, which will be fol-lowed by radio frequency quadrupole (RFQ), drift tube linac (DTL), and low velocity (low b) resonant cavities. Prototypes of the RFQ and DTL have been tested and the low beta cavity has been designed.

Work on the construction of two single spoke resonators for Project-X at Fermi National Accelerator Labora-tory is nearing completion. IUAC and RRCAT, Indore, have jointly fabri-cated two Tesla-type single cell cavi-ties in niobium, with an aim to even-tually build a 9-Cell Cavity as part of collaboration toward the International Linear Collider.

Research Facilities

Nuclear PhysicsThe Indian National Gamma Array (INGA) [2] was developed as a na-tional facility for γ-spectroscopy con-sisting of Compton-suppressed Clover detectors with nearly 4π coverage. Three campaigns with a smaller num-ber of Clover detectors were carried out in 2001, 2003, and 2005 at TIFR, IUAC and VECC, respectively, with existing infrastructure. The first big campaign, with INGA having 18 Ge

Clover detectors, took place at IUAC during March–June 2008, and the sec-ond cycle took place April–October 2009. The electronics and data-acqui-sition used at IUAC was developed in-house. Currently the detectors have been moved to TIFR, Mumbai. Some of the interesting problems that were addressed recently are (i) search for band termination in magnetic rotation band in A~140 region (ii) role of pro-ton and neutron orbits in magnetic ro-tation for A~137 nuclei (iii) high spin structure in A~110 region and search for chiral bands and band termination (iv) spectroscopy of magnetic rotation bands near Z~64 N~82 shell closure (v) spectroscopy of neutron-rich nu-clei near 132Sn produced by heavy-ion induced fission (vi) spectroscopy of trans-lead nuclei 210–212Ra, 208–211Fr and (vii) study of octupole correlation in 239–241Pu, 237–240Np.

Fission fragment mass distribution has been determined in 238U(18O,f) reaction from the on-line measure-ment of individual even-even frag-ment yields by analyzing the in-beam g-g matrix. Fine structure dips corre-sponding to fragment shell closures at Z = 50 and N = 82 are observed, indi-cating the effect of nuclear structure in the dynamical evolution of fissioning nucleus.

The first phase of Hybrid Recoil Mass Analyzer (HYRA) [3], has been used in the gas filled mode (GFS) for several experiments. The recoil mass spectrometer (RMS) mode would be commissioned by the end of 2012. A photograph of INGA and HYRA in the same beam-line is shown in Figure 1. In collaboration with TIFR, a 4-pi spin spectrometer developed at TIFR has

Present Status and Future Evolution of Inter-University Accelerator Centre



been coupled with the HYRA spec-trometer for study of spin distributions in fusion reactions and in coincidence with GDR decays.

At present an array of 26 neutron detectors are being used in another beam-line and funding has been re-ceived for upgrading this to a National Array of Neutron Detectors (NAND) consisting of 100 organic liquid scin-tillators of 5ʺ diameter and 5ʺ thick-ness. Target chamber also has provi-sion to put charged particle detectors like large area position sensitive mul-tiwire proportional counters (MWPC) and silicon detectors to detect neutron emitting sources (heavy ions and fis-sion fragments) and other associated light charged particles in coincidence with neutrons. It would be a versa-tile tool for separating out fission and quasi-fission components through measurement of variance of pre-scis-sion multiplicity distributions.

Materials Science Facilities at IUAC provide a unique opportunity for studies in the field of ion induced materials engineering and character-ization. There are two beam-lines in the two beamhalls for irradiation stud-ies with accelerated ions from Pelle-tron and Linac. The beam-line in Pelle-tron beamhall includes two irradiation chambers with on-line ERDA, on-line QMA and ionoluminiscence facilities. Low flux irradiation facility for materi-als science is also available in another beam-line. The beam-line in Linac beamhall has two irradiation chambers with on-line ERDA and in-situ XRD facility (Model D8 Advance) from Bruker AXS, Germany. The XRD set-up was used for in-situ measurement of growth of Au nanoparticles with ion beam irradiation.

An in-situ Raman facility is also installed. A Pfeiffer QMA 422 quadru-pole mass analyzer system with SIMS option operating at 2.25MHz that can mass analyze in the range 1–1024 amu

with mass separation (ΔM/M) better than 0.01 is installed in materials sci-ence beam-line.

Besides the above, the center has many-offline characterization facilities including XRD, AFM/MFM/C-AFM, SEM, Raman, photoluminescence setup, transport/noise measurement setup, low temperature cryostat with 8T superconducting magnet, FTIR, and UV-Vis absorption spectroscopy setup. Formation of nanostructures with ion beam bombardment has been identified as a thrust area and is draw-ing a large number of users.

The Atomic and Molecular phys-ics program at IUAC addresses basic

fundamental aspects of ion–atom in-teraction as well as processes of as-trophysical and plasma interests and applications, using beam foil spectros-copy with X-ray and ion detectors. At the low energy facility, a reaction mi-croscope is installed for the study of molecular dissociation dynamics us-ing a position sensitive time of flight setup. A deceleration set up has been developed for very low energy highly charged ions from an ECR source. The molecular dissociation studies on sev-eral molecules by highly charged ions showed evidence for bond rearrange-ment and alignment in the dissociation process.

Figure 1. A photograph of the INGA and HYRA detector systems in the beam-line.



The facility for Heavy Ion Radia-tion Biology provides a laboratory for pre and post irradiation treatment of samples. The computer controlled ir-radiation system ASPIRE (Automatic Sample Positioning for Irradiation in Radiation Biology Experiments) en-ables one to irradiate cells placed on 35 mm petri dishes kept in medium in a sterile condition in quick succession with predetermined ion dose. IUAC radiation biology program is based on in-vitro studies of different effects of heavy ion irradiation on prokaryotic and eukaryotic cells.

Accelerator Mass Spectrometry (AMS) using 10Be and 26Al is opera-tional on geological samples. A clean chemistry laboratory has been set-up for preparation of 10Be samples. In fu-ture a dedicated AMS system for 14C is also being planned.

The computing power available at the Centre got a big boost with com-missioning of the high-performance computing center consisting of a distributed memory cluster with 96

nodes. Preliminary tests of the first phase showed that the system is ca-pable of operating at 6.5 terraflops. It will be upgraded to the level of ~40 terraflops shortly.

In addition to the regular Ph.D. and M.Sc. training programs, IUAC has initiated a program to help improve the laboratory facilities in the classroom. In this program, (a) a low cost radia-tion detection and analysis system has been developed which is useful to carry out some of the Nuclear Physics experiments at the M.Sc. level. (b) a simple and cost effective PC interface (called Phoenix) has been designed that will encourage many computer-aided experiments and data analysis [4].

Future ProspectsThe availability of accelerated

LINAC beam in Beamhall II, along with the major experimental facilities under construction (INGA, HYRA, and NAND), opens up new areas of research in nuclear physics. With the

High Current Injector, many more ion species at higher fluxes would be available allowing study of processes having lower cross-sections.

International CollaborationsSeveral groups from laboratories

outside India use the IUAC facilities at present and others who want to propose experiments are welcome. In accelera-tor development, IUAC has collabora-tions with many laboratories world-wide (e.g., ANL, MSU, TRIUMF, Fermilab, LNL, and GANIL).

References1. K. Asokan and Amit Roy, Nucl. Phys.

News 13(1) (2003) 4.2. S. Muralithar et al., Nucl. Inst. and

Method A622 (2010) 281.3. N. Madhavan et al., Pramana 75(2)

(2010) 317.4. www.iuac.res.in/~elab/phoenix/

Amit RoyInter-University Accelerator Centre



On November 1, 2011, the inau-guration ceremony was held for “Re-search Center for Nuclear Science and Technology (RCNST)” in Bei-hang University (Beijing University of Aeronautics and Astronautics, also written as BUAA) (Figure 1). The Chinese name 北京航空航天大学 is pro-nounced as “Beijing hang kong hang tian da xue.” The university is located north west of Beijing city near Olym-pic Park and Peking University. Please refer to http://www.buaa.edu.cn/ for university information, where some English pages are also prepared.

The nuclear physics theory group has been led by Professor Jie Meng in

the School of Physics and Nuclear En-ergy Engineering. A new group in ex-perimental nuclear physics was started last year, led by Isao Tanihata after the award of “Thousand-Talented Proj-ect” scholars of China. After one year of preparation, the Research Center for Nuclear Science and Technology become reality.

At the occasion, the steering com-mittee of the center was formed and the first meeting was held. The steer-ing committee was formed by interna-tional scientists and chaired by an aca-demician, Huanqiao Zhang of CIAE (China Institute of Atomic Energy) (Figure 2). Members are:

Chai, ZhifangIHEP, Beijing, China

Choi, SeonhoSNU, Seoul, Korea

Gales, SydneyGANIL, Caen, France

Geissel, HansGSI, Darmstadt,Germany

Kishimoto, TadafumiRCNP, Osaka, Japan

Liu, WeipingCIAE, Beijing, China

Ma, Yugang SIAP/CAS, Shanghai, China

Meng, JieBeihang U. and Peking U.

Figure 1. Inauguration ceremony of the Research Center for Nuclear Science and Technology in Beihang University.

Beihang University ( ) Research Center for Nuclear Science and Technology (RCNST) ( )



Sakurai, HiroyoshiRIKEN, Saitama, Japan

Sherrill, BradleyNSCL/MSU, East Lansing, USA

Tamura, HirokazuTohoku U., Sendai, Japan

Tanihata, IsaoBeihang and RCNP, Osaka

Toki, HiroshiOsaka U., Osaka, Japan

Xu, HushanIMP/CAS, Lanzhou, China

Ye, YanlinPeking U., Beijing, China

Zhang, HuanqiaoCIAE, Beijing, China

Zhou, ShanguiITP/CAS, Beijing, China

After the opening of the inaugura-tion ceremony by Professor Zhiming Zheng (vice president of Beihang Uni-versity) the director and the members of the steering committee were intro-duced. Then the appointment certifi-cates were given, first to the director, Isao Tanihata, and then the chairman of the Steering Committee, Huanqiao

Zhang, by Jinpeng Huai (the president of the Beihang University). The cer-tificates of the steering committees were then given to the members of the committee (Figure 3).

After unveiling the name plate of the center, the RCSNT was introduced by I. Tanihata and then the president, J.-P. Huai, delivered speeches ex-pressing their hope for the future of the center.

This new center is not a facility-based research center but based on the international collaboration scheme. The planned operation structure of the RCNST is shown in Figure 4.

The aims of the RCNST at Beihang University are:

1. To incubate scientific ideas and promote next generation researches in nuclear science with a broad view, and

2. To promote applications of nuclear science, in particular detector tech-nology and accelerator sciences.

The RCNST at Beihang University would like to become a world center to gather expertise and ideas and to create a nest where new ideas can be incubated. As part of this mission the RCNST will promote the development of collaborations to address targeted opportunities. The center could be a starting place for a person who has a new idea, or a place to spend a sabbat-ical leave where the environment ex-

Figure 2. Certificates were given to the director and the chairman of the steer-ing committee. From left to right: Professor Lingyun Hu (Secretary of the Par-ty Committee of BUAA, Professor Isao Tanihata, Professor Hunquiao Zhang (CIAE), Jinpeng Huai (President of BUAA).

Figure 3. University and ministry personnel and RCNST committee at Beihang University.



ists for creating new ideas. Under such conditions, top scientists from all over the world will gather here at RCNST and form a world-unique think tank.

For the realization of such aims the center will include an in-house pro-gram and the incubation program.

In-House ProgramThe in-house research groups will

promote leading edge research and technical development. The groups will promote the research in the field of nuclear science by development of worldwide collaborations. National and international collaborations are one of the key objectives of the center. Five groups are planned and some of the scientists from the School of Phys-ics and Nuclear Energy Engineering (SPNEE) have expressed their inter-est. Nuclear physics and astrophysics are the main initial focus areas but the effort will also include a group for the application of the radiation tech-niques. In particular, the development of radiation detectors has critical im-portance for applications and thus will be strongly promoted.

An important function of the re-search groups is to educate young stu-

dents and scientists. This will benefit the wider field of nuclear physics and related applications.

The list of the in-house groups for the start of the RCNST is:

1. Theoretical nuclear physics a. Researches on nuclear structure

and hadron structure. b. Researches on nuclear structure

from the view of tensor and three body forces.

2. Experimental nuclear physics a. Presently on going program is

the study of Tensor and three body forces in nuclei. Also the study of charge radii of unstable nuclei.

b. Researches on nuclear structure and reaction studies using world wide accelerator facilities.

c. Ultra-cold-neutron. 3. Cosmonuclear physics a. Study of big bang nucleosyn-

thesis and subsequent nucleo-synthesis in stars.

4. Application of nuclear technology a. Detector laboratory for devel-

opment of radiation detectors. b. Development of radiation detec-

tors for astronomical research, medical, and industrial use.

c. Development of environmental radiation monitoring system.

5. Accelerator science a. Provide both special and general

educational programs in nuclear science, including an accel-erator science school course in-cluding hands-on training at the facility at RCNP.

Presently, the SPNEE has the the-ory group with five staff members and the experimental group has six staff members. All of them are joint mem-bers of the RCNST but several posi-tions are now open. The position could be a permanent position in Beihang or could be a temporary position. Also, positions for post doc research fellows are open.

Incubation ProgramIn nuclear physics and in an ap-

plication of nuclear science, most of the research is based on the large-size facilities. Advances in experimental nuclear science now routinely require an extremely advanced facility such as the accelerator facility in IMP/Lan-zhou. Such a large facility can only be constructed at limited places in the world. Forefront research is done by users from around the world traveling to these facilities. Because scientists are scattered in many universities, many times with limited staff, they have to form collaboration teams to use such facilities. To form such a col-laboration requires a series of steps: (i) a new idea, (ii) incubation of the new idea, (iii) forming a group, (iv) devel-opment of a proposal to be submitted to a research facility, (v) and so on.

The RCNST will provide a place for promoting such development of collaborations and incubation of ideas. The BUAA does not have any large-size accelerator facility but it would be an advantage as a center for such development purposes. Any idea

Figure 4. Organization structure of RCNST.



without one-to-one connection to a facility can be brought to the center and incubated. The completed idea as a proposal would be sent to the most relevant facility in the world and will be realized.

With this principle, RCNST would become a world center of gathering knowledge and ideas, in experiment and theory, and become a nest to incu-bate new ideas.

The RCNST would be a starting place for the person who has a new idea, or be a place to spend sabbatical leave for creating a new idea. Young students and scientists in BUAA may join in such a program and thereby benefit from the exposure to visiting scientists. It will be a major benefit for them to be involved in research from the early stage of a project.

To realize such a purpose the center offers visiting researchers positions as well as post-doctoral positions.

The program proceeds in the fol-lowing steps:

1. Proposal for an incubation program (theory, experiment, and/or techni-cal) is open to interested scientists from all over the world. This pro-gram will be accepted from Janu-ary 2012.

2. After acception of the incubation program, the RCNST will invite the researcher in a short term (a few months) and small research group may be formed around him or her by inviting additional appropriate secinetists. At the beginning a few programs will be possible to be ac-tivated under the present budgetary conditions. The steering committe comments on the program in rela-tion to the acceptance.

3. The steering committee comments on the program and suggests the appropriate researches and facili-ties for this program.

4. The incubation group can invite ac-tive and influential researchers for a short term to give them time for promoting researches freely under the aim of the group.

5. The incubation group can hold workshops related to new ideas to promote them to proposals for projects at facilities worldwide.

6. A research proposal is expected to be submitted to some facility or in-stitute, or already a research paper may appear.

We hope that this system will pro-vide new opportunities to nuclear sci-entists all over the world and also help

to promote Chinese nuclear science overall.

“The Second International Sympo-sium on Frontiers in Nuclear Physics ‘Tensor Interaction in Nuclear and Hadron Physics’” was held on No-vember 2–3 in Beihang University’s Ruxin conference center (Figure 5). About 60 scientists attended the meet-ing. It has been known that the tensor force plays an essential role for bind-ing of lightest nuclei d and 4He, for ex-ample. More than half of the potential energies are due to the D-wave mixing through tensor forces. It is also known from recent ab-initio type calculations that the tensor forces are important for the binding of light nuclei below mass 10. However, in nuclear models for heavier nuclei, it was treated as a per-turbation in spite of a possible large contribution to the structure of nuclei just because this interaction cannot be treated as a mean field. Due to recent studies of radioactive beams as well as of excited states of stable nuclei, the necessity of the tensor force becomes clear. In the symposium, presentations and discussions are made for recent theoretical studies to include tensor force explicitly and for recent experi-mental studies to observe effects of tensor forces in low-lying states. Bei-hang University plans to hold the sym-posium on various subjets on nuclear science regularly.

We hope that the world researchers in nuclear science will recognize this new endeavor and help us by propos-ing and/or joining the programs in the RCNST.

More information on the inaugura-tion ceremony can be seen in http:// news.buaa.edu.cn/dispnews.php? type=1&nid=84609&s_table=news_txt

Isao TanIhaTaBeihang University and

RCNP Osaka UniversityFigure 5. The Symposium on Tensor Interaction in Nuclear and Hadron Physics held in Beihang University also help to promote Chinese nuclear sciences overall.



IntroductionAfter several years of construc-

tion, the first pair of detectors of the Daya Bay Reactor Neutrino Experi-ment began taking data in August of 2011. Daya Bay is a neutrino oscilla-tion experiment designed to determine the value of the mixing angle q13 by measuring, at different locations, the fluxes and energy spectra of electron antineutrinos produced in the reactors of the Daya Bay and Ling Ao Nuclear Power Plants in southern China. The experiment is an international effort of countries and regions including China, the United States, Czech Republic, Russia, Hong Kong, and Taiwan.

The neutrino was proposed by W. Pauli in 1930 to preserve the conser-vation of energy and angular momen-tum in nuclear beta decays. Since its first experimental detection by Cowen and Reines 55 years ago, our knowl-edge of neutrinos has progressed enormously but is still incomplete. Neutrinos are unique among other el-ementary fermions because they inter-act with matter only via weak interac-tions by exchanging either the charged intermediate bosons W± or the neutral Z0. There are three different flavor types of neutrinos produced in pairs with either an electron, muon, or tau lepton.

Recent discoveries have shown that neutrinos are massive. Neutrinos of specific flavor type: νe (electron), νµ (muon) and ντ (tau) are linear su-perpositions of three different mass states ν1, ν2, and ν3. This mixing re-sults in an experimentally observed phenomena known as neutrino oscil-lation where neutrinos of one flavor type can change into another on the fly. Neutrino oscillations are described by six parameters, two mass-squared differences, three mixing angles, and

one complex phase. Mass-squared dif-ferences determine oscillation lengths, mixing angles account for oscillation amplitudes, and the complex phase is responsible for violation of the com-bined charge

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