eRHIC: Science and Perspective
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Transcript of eRHIC: Science and Perspective
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
eRHIC: Science and Perspective
• Introduction• Science of eRHIC• Realization• Summary
Study of the Fundamental Structure of Matter with an Electron-Ion ColliderA. Deshpande, R. Milner, R. Venugopalan, W. Vogelsanghep-ph/0506148, to appear in Ann. Revs. Nucl. Part. Sci.
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
The study of the fundamental structure of matter
• QCD tells us that the nucleon and atomic nuclei are made of pointlike constituents bound by powerful gluon fields
• The valence quark region is well explored experimentally and reasonably well understood theoretically
• Frontier research in QCD demands a concerted experimental effort directed at the role of the gluons and sea quarks
• A new accelerator which directly probes the quarks and gluons is required
Lepton probeHigh center of mass energyHigh luminosity precisionPolarized lepton, nucleonOptimized detectors
• This accelerator is urgently needed to make progress in this field of research and has substantial discovery potential
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Deep inelastic scattering – the experimental cornerstone of
QCD
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Running of the strong coupling αs
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Quark and gluon momentum in proton
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Lattice QCD making significant progress
quenchedapproximation
full QCD
agreement with experiment at level of few percent
HPQCDhep-lat/0304004
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Nucleon axial charge in full lattice QCD
LHPC Collaborationhep-lat/0510062
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Why a Collider ?
• High Ecm (20 to 100 GeV)
large range of x, Q2
x range (10-4 to 1): valence, sea quarks,
glue
Q2 range ( 1 to 1000 GeV2): utilize
evolution equations of QCD
• High luminosity ~ 1033 cm-2 s-1
• High polarization ( ~ 70%) of lepton, nucleon achievable
• Complete mass range of nuclear targets
• Collider geometry allows complete reconstruction of final state
Qmax2 = ECM
2 · x
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Why eRHIC?
• RHIC is the world’s first and only polarized proton collider
• In addition, RHIC accelerates heavy ion beams to 100 GeV/nucleon
• eRHIC would capitalize on ~ $ 1 billion investment in RHIC
• RHIC scientific program strongly motivates eRHIC • Leadership from BNL in evolution of lepton-ion
collider since 1999• eRHIC is viewed at BNL as a necessary and
natural upgrade of RHIC after 2010 as the heavy ion and spin programs mature
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
The Electron-Ion Collider (EIC)• A high luminosity (~1033cm-2s-1) polarized lepton-ion collider is
the QCD machine hadronic physicists worldwide require for future research
• Workshops Seeheim, Germany 1997 MIT 2000
IUCF 1999 BNL 2002 BNL 1999 JLab 2003 Yale 2000
• Electron Ion collider (EIC) received very favorable review of science case in US 2001 Nuclear Physics Long Range Plan, with strong endorsement for R&D
• NSAC in March 2003, declared EIC science `absolutely central’ to Nuclear Physics
• DOE Office of Science 20 Year Strategic Plan in 2004: eRHIC
identified as a long term (realized ~ 2015) priority
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
EIC Steering Committee
• A. Caldwell (MPI Munich)• A. Deshpande (StonyBrook)• R. Ent (JLab)• G. Garvey (LANL)• R. Holt (ANL)• E. Hughes (Caltech)• K.-C. Imai (Kyoto Univ.)• R. Milner (MIT)• P. Paul (BNL)• J.-C. Peng (Illinois)• S. Vigdor (Indiana Univ.)
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
eRHIC will be a unique accelerator
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Scientific Highlights• nucleon structure
sea quarks and gluespin and flavor structurenew parton distributions
• Meson structure, K are Goldstone Bosons of QCDessential to nuclear binding
• hadronizationevolution of parton into hadronprocess in nuclei of fundamental interest
• nucleirole of partonsinitial conditions for relativistic heavy ion
collisions• matter under extreme conditions
saturation of parton distributionsnew phenomena, e.g. colored glass condensate
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
The Spin Structure of the Nucleon
•Bjorken Sum Rule
• From NLO-QCD analysis of DIS measurements …ΔG = 1.0±1.2
•quark polarization Δq(x)first 5-flavor separation from
HERMES
• transversity δq(x)a new window on quark spinazimuthal asymmetries from
HERMES and JLab
•gluon polarization ΔG(x)RHIC-spin and COMPASS will
provide some answers!
•orbital angular momentum Lhow to determine? GPD’s ?
½ = ½ + G + Lq + Lg
ΔΣ ≈ 0.2
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Inclusive spin-dependent DIS
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
QCD Test: Bjorken Sum Rule
• Γ1p - Γ1
n = 1/6 gA [1 + Ο(αs)]
• Sum rule verified to ±10%
• eRHIC can approach ±1% G. Igo
Precision QCD test
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Polarized parton densities of the proton
Blümlein and Böttcher
SU(3) flavorsymmetryassumed
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HERMES Flavor Decomposition of Quark Spin
Semi-inclusiveDIS
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Gluon polarization data from COMPASS
2002+3 data analysis; as much again in 2004 on disk
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Gluon polarization from STAR
STAR preliminary 2003+4 results for double longitudinal spin asymmetry ALL versus jet pT in p + p → jet + X, compared with NLO pQCD
New more precise data from PHENIX
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Spin structure function gp1 at low
xx = 10-4 0.7Q2 = 0 104 GeVeRHIC 250 x 10 GeV
Lumi=85 inv. pb/day
x = 10-3 0.7Q2 = 0 103 GeVFixed target experiments1989 – 1999 Data
10 days of eRHIC runAssume: 70% Machine Eff. 70% Detector Eff.
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eRHIC determination of polarized quarks and anti-
quarks
Kinney and Stösslein
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Gluon polarization from di-jets in LO for eRHIC
Deshpande et al.
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Parity violating lepton scattering
• requires a positron beam• determines new combinations of Δu, Δd, Δs etc.• analog sum rule to Bjorken
A. Deshpande
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Saturation: the Color Glass Condensate
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Using Nuclei to Increase the Gluon Density
• Parton density at low x rises as• Unitarity saturation at some• In a nucleus, there is a large enhancement of the parton
densities / unit area compared to a nucleon
•
ExampleQ2=4 (GeV/c)2
< 0.3 A = 200
Xep=10-7 for XeA = 10-4
1x
2sQ
2 1 13 3
2
/
/
6 for 200
A A A
N N N
G R GA A
G r AG
A
2
21
134
3
eA s
ep s
X Qx Q
A
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Gluon Momentum Distribution from DIS
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RHIC Data consistent with Gluon Saturation
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Longitudinal structure function FL
• Extracted from scaling violations of F2 • Experimentally can be determined directly• Highly sensitive to effects of gluon• With precise enough F2 and FL one can extract the coefficient λ of the saturation scale• Logarithmic derivatives of F2 and FL with Q will be sensitive to CGC
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Quarks in a Nucleus“EMC Effect”
Space-Time Structure of Photon
F2A/F2
D
10-4 10-3 10-2 10-1 1 x
Can pick apart the spin-flavor structure of EMC effect by technique of flavor tagging, in the region where effects of the space-time structure of hadrons do not interfere (large !)
Nuclear attenuation negligiblefor > 50 GeV hadrons escapenuclear medium undisturbed
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eRHIC projections for nuclear quark distributions
T. Sloan1 pb-1
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Sea-Quarks and Gluons in a NucleusDrell-Yan No Nuclear Modifications to
Sea-Quarks found at x ~ 0.1 Where is the Nuclear Binding?
Flavor tagging can also (in principle)disentangle sea-quark contributions
Constraints on possible nuclearmodifications of glue come from1) Q2 evolution of nuclear ratio of F2 in Sn/C (NMC)2) Direct measurement of J/Psi production in nuclear targets
Compatible with EMC effect?Precise measurements possible of Nuclear ratio of Sn/C (25 GeV) J/Psi production (ELIC)
F2
G
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Nuclear Binding Natural Energy Scale
of QCD: O(100 MeV) Nuclear Binding Scale
O(10 MeV) Does it result from a
complicated detail of near cancellation of strongly attractive and repulsive terms in N-N force, or is there another explanation?
How can one understand nuclear binding in termsof quarks and gluons?
Complete spin-flavor structureof modifications to quarks andgluons in nuclear system may bebest clue.
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
eRHIC - machine design aspects– First detailed document (252
pages) reporting on the eRHIC accelerator and interaction region (IR) design studies
– Collaborative effort between BNL, MIT-Bates, BINP and DESY
– Goal:• Develop an initial design for
eRHIC• Investigate accelerator physics
issues most important to its design
• Evaluate luminosities that could be achieved with minimal R&D effort including IR design
• Identify specific R&D extensive accelerator aspects which could lead to significantly higher luminosities
– Review planned in June 2005http://www.bnl.gov/eic/http://www.bnl.gov/eic/
See talk by V. Ptitsyn
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
eRHIC: ring-ring design•Collisions at 12 o’clock interaction region•10 GeV, 0.5 A e-ring with 1/3 of RHIC circumference (similar to PEP II
HER)•Inject at full energy 2 – 10 GeV•Existing RHIC interaction region allows for typical asymmetric
detector (similar to HERA or PEP II detectors)
AGS
BOOSTER
TANDEMS
RHIC
2 – 10 GeV e-ring
e-cooling
2 -10GeV Injector
LINAC
Required modifications of RHIC:• Electron cooling• Increase of total current 120 → 360 bunches•Additional spin rotators
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
eRHICeRHIC
e-/e+ Ring e-/e+ Ring ParametersParameters
10 GeV electrons – 250 GeV 10 GeV electrons – 250 GeV protonsprotons
Ion beam Energy p 250 GeV
Circumference(m) 1278
Electron Energy (GeV) 10
Bending radius(m) 81
Bunch spacing(m) 10.6
Number of bunches 120
Bunch population 1.00E+11
Beam current(A) 0.45
Energy loss/turn (MeV) 11.7
Accelarting voltage(MV) 25
Total rad. Power(MW) 5.27
Syn. Rad. Power/m (KW) in Arc 9.63
Self-pola. Time at 10GeV(minutes) 22.03
Emittance-x, no coupling (n m.rad) 56.6
Beta function at IP (cm) y*/x
*19.2/26.6
Emittance Ratio (y/x) 0.18
Beam size at IP(um) σx 104
Beam size at IP(um) σy 52
Momentum spread σE 9.61E-04
Bunch length (cm) σz 1.17
S.R. damping time(x) (mS) 7.3
Beta tune x 26.105
Beta tune y 22.145
Natural chromaticity ξx/ξy -35.63/-33.84
Luminosity (10^33/cm^2/s) 0.44
• Luminosity limited by beam-beam tune shifts:ξi = 0.0065 ξe = 0.08 •Luminosity assumes collisionsat two other IPs• Dedicated operations yields Luminosity ~ 1033 cm-2 s-1
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
eRHIC: linac-ring design – Two possible designs are
presented in the ZDR– Electron beam is
transported to collision point(s) directly from superconducting energy recovery linac (ERL)
– Features:• Higher luminosity (~ X 5)
possible• Rapid reversal of
electron polarization• Machine elements free
region approx. 5m• Simpler IR region design:
Round beams possible• Multiple interaction
regions• No positrons
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
eRHIC: interaction region design - ZDR assumes IR region with zero
crossing angle
– Crab-crossing scheme considered (rotate ion bunch into direction of electron beam): However, required
deflecting RF voltage: V=14.4MV
factor 10 larger then for KEKB crab cavities so excluded for now.
– Initial design: dipole winding in the superconducting electron low- quadrupoles
– Limitation: 1m machine element free region
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Review of eRHIC ZDR• Detailed technical review of both ring-ring and linac-ring
designs by Machine Advisory Committee in June 2005• Excellent technical criticism• Status of the present design studies is not yet advanced
enough to make a decision• Ring-ring: challenging project, can be extrapolated from to-
day’s experience and technology. Suggests pursuing ring-ring design as first priority with goal to develop a CDR
• Linac-ring: much more attractive regarding luminosity. Requires successful extrapolations on a number of fronts that are beyond what can be achieved to-day. Requires intensive R&D.
• Concentrate first on R&D which is useful to ring-ring and ring-linac options, e.g. ERL prototype, cooling of ion beams, and beam dynamics.
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
eRHIC lepton ring vs. PEP-II rings
• Ring type: all are collider lepton rings• Energy range: 5~10 GeV vs. 3-9 GeV• Beam currents: 0.5 ~1A vs. 1.5 ~ 3 A
similar bunch current, PEP-II has more bunches• Beam dimensions: comparable
emit.: ~50 nm rad, beta_ave: ~15 m (arc, rf)• Collective effects:similar
In general, technical approaches are very similar.
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
• RF : 90% from PEP-II with minimum modifications
• Magnet/power supply: ~ 50 % from PEP-II• Feedback: 100%• Beam diagnostics / control: ~ 50%• Vacuum: now we count it as 20% ~ 30% • Injector: design not clear at this point.
• A large amount of PEP-II components could be used for the eRHIC lepton ring.
• A preliminary estimate shows that we may save 20% to 30% of cost by using PEP-II components. More detailed studies underway.
D. Wang/BatesPreliminary conclusions
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
eRHIC - Detector design • General purpose
unpolarized/polarized ELECTRon-A- compact central detector with
specialized forward/rear tagging detectors- required free region ± 3m
Ae
eA
• Forward detector unpolarized eA- specialized detector system to detect complete final state in eA collisions- Require dfree region ± 5 m• Common detector subsystems• R&D coherent with heavy ion detector upgrades
See talk by B. Surrow
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
eRHIC realization• Science case must be strengthened and sharpened• Accelerator case must be developed so that the
science can be made to happen in a timely fashion • eRHIC must be presented coherently in the context of
future RHIC plans • It is essential to energize and organize the hadronic
community worldwide in support of eRHIC• We expect a new Long Range planning exercise
within the next several years• We have to be ready to argue for eRHIC in the
context of other communities arguing strongly for other priorities
Richard G. Milner RHIC Planning Meeting October 29-20, 2005
Summary• A high luminosity lepton-ion collider offers
a very exciting future for the study of the fundamental structure of matter
• eRHIC appears to be a very attractive means to realize it in a cost-effective and timely way
• It is essential to develop the most powerful eRHIC case with a sense of urgency