Ⅱ-1. Nuclear Physics

- 43 -

RIKEN Accel. Prog. Rep. 49 (2016)

First commissioning results for SπRIT-TPC

M. Kurata-Nishimura,∗1 G. Jhang,∗3 J. Barney,∗2 J. Estee,∗2 M. Kaneko,∗4 Y. Zhang,∗6∗2 J. W. Lee,∗3

P. Lasko,∗5 G. Cerizza,∗2 C. Santamaria,∗2 K. Pelczar,∗5 Y. Kim,∗7 H. Lee,∗7 J. Lukasik,∗5 P. Pawlowski,∗5

D. Suzuki,∗1 T. Isobe,∗1 T. Murakami,∗4 W.G. Lynch,∗2 M.B. Tsang,∗2 and for SπRIT-TPC collaboration

The aim of the SAMURAI Pion-Reconstruction andIon-Tracker Time-Projection Chamber (SπRIT-TPC)1) project is to constrain the symmetry energy term inthe nuclear-matter equation of state (EOS) at super-saturation density. It is proposed to compare π+/π−

production ratio among various isospin asymmetry en-vironments combining different unstable Sn beams andstable Sn targets in SAMURAI.

The first commissioning run using 79Se beam wasperformed outside of the SAMURAI magnet in fall2015. The performance of SπRIT-TPC and triggersystems were evaluated. Results revealed necessarymodifications for upcoming physics campaign.

For the commissioning, the SπRIT-TPC was placedabout 7 m away from the center of the SAMURAImagnet and lined up on 60 deg with the 79Se secondarybeam. Two targets of 0.5 mm natural Sn foil and 9 mmaluminum plate were mounted on a ladder in front ofthe TPC field cage window.

The overall readout system3) was prepared and threetypes of trigger arrays composed by plastic countersread by MPPCs were installed for opening a gating griddriver. (1) KATANA (KrAkow Trigger Array with am-plitude discrimiNAtion) was placed at the exit windowto reject the non reacting beam. (2) The MultiplicityTrigger Array4) was placed on the both sides of TPC toselect high multiplicity events. (3) The active collima-tors was mounted in front of the target to reject beamshitting the target frame. The reaction trigger was pro-vided by a start counter signal, no hit on the activecollimator, low energy deposit in KATANA, and mul-tiple hits on Multiplicity Trigger Array. The triggercondition was controlled through a trigger logic board.

The analysis framework, SπRITROOT5), has beendeveloped for SπRIT-TPC experiment. Using thiscode, a typical high multiplicity 3D event display isshown in Fig.1. The straight tracks were reconstructedeven in dense track regions just after the target.

The total number of reconstructed tracks per eventwas plotted for two different multiplicity selectionswith KATANA and Multiplicity Trigger Array inFig.2. Higher multiplicity requirement resulted inhigher multiplicity track events corresponding to cen-

∗1 RIKEN Nishina Center∗3 Department of Physics, Korea Universtiy∗2 National Superconducting Cyclotron Laboratory and De-

partment of Physics and Astronomy, Michigan State Uni-

versity∗4 Department of Physics, Kyoto University∗6 Department of Physics,Tsinghua University∗5 Institute of Nuclear Physics, PAN∗7 Institute for Basic Science, Korea

tral collision events.The reaction vertex was extrapolated from tracks

event by event and the Z-vertex of 84% events wasfound around the target within 5mm in sigma for highmultiplicity events. The event ratio originating fromthe target depended on the trigger conditions.

The first commissioning of SπRIT-TPC was success-fully performed outside of the SAMURAI magnet. Thehigh multiplicity track events were reconstructed andthe reaction vertex was found around the target. Thegating-grid driver worked with the fast trigger pro-vided by three trigger arrays. Modification of readoutelectronics and optimization of trigger system is underinvestigation for coming physics run.

Fig. 1. A typical high multiplicity track event produced

with 79Se on Sn (nat.) target. The target was located

8.9 mm upstream from the field cage window.

Fig. 2. The total multiplicity in the TPC gated on the mul-

tiplicity in the ancillary detectors KATANA and Mul-

tiplicity Trigger Array

References1) R. Shane at al.: Nucl. Instr. Meth. A 784 (2015) 513.2) M.B. Tsang et al; Phys. Rev. Lett. bf 102 (2009) 122701.3) T. Isobe et al,; in this report.4) M. Kaneko et al,; in this report.5) G. Jhang et al,; in this report.

Spectroscopy of unbound oxygen isotopes II

Y. Kondo,∗1,∗2 T. Nakamura,∗1,∗2 N. L. Achouri,∗3 L. Atar,∗4 T. Aumann,∗4 H. Baba,∗2 K. Boretzky,∗5,∗2

C. Caesar,∗5,∗2 D. Calvet,∗6,∗2 H. Chae,∗7 N. Chiga,∗2 A. Corsi,∗6,∗2 H. L. Crawford,∗8 F. Delaunay,∗3

A. Delbart,∗6,∗2 Q. Deshayes,∗3 Zs. Dombradi,∗9,∗2 C. Douma,∗10 Z. Elekes,∗9,∗2 P. Fallon,∗8 H. Al. Falou,∗11

I. Gasparic,∗12,∗2 J. -M. Gheller,∗6,∗2 J. Gibelin,∗3 A. Gillibert,∗6,∗2 M. N. Harakeh,∗10 A. Hirayama,∗1,∗2

C. R. Hoffman,∗13 M. Holl,∗4,∗2 A. Horvat,∗4 A. Horvath,∗14 J. W. Hwang,∗7 T. Isobe,∗2 J. Kahlbow,∗4,∗2

N. Kalantar-Nayestanaki,∗10 S. Kawase,∗15 S. Kim,∗7 K. Kisamori,∗2 T. Kobayashi,∗16,∗2 D. Korper,∗5,∗2

S. Koyama,∗17,∗2 I. Kuti,∗9,∗2 V. Lapoux,∗6,∗2 S. Lindberg,∗18,∗2 F. M. Marques,∗3 S. Masuoka,∗19 J. Mayer,∗20,∗2

K. Miki,∗21,∗2 T. Murakami,∗22,∗2 M. A. Najafi,∗10 K. Nakano,∗15,∗2 N. Nakatsuka,∗22,∗2 T. Nilsson,∗18

A. Obertelli,∗6,∗2 F. de Oliveira Santos,∗23 N. A. Orr,∗3 H. Otsu,∗2 T. Ozaki,∗1,∗2 V. Panin,∗2 S. Paschalis,∗4

A. Revel,∗23 D. Rossi,∗4 A. T. Saito,∗1,∗2 T. Saito,∗17,∗2 M. Sasano,∗2 H. Sato,∗2 Y. Satou,∗24 H. Scheit,∗4

F. Schindler,∗4 P. Schrock,∗19 M. Shikata,∗1,∗2 Y. Shimizu,∗2 H. Simon,∗5,∗2 D. Sohler,∗9,∗2 O. Sorlin,∗23

L. Stuhl,∗2 S. Takeuchi,∗1,∗2 M. Tanaka,∗25,∗2 M. Thoennessen,∗21 H. Tornqvist,∗4,∗2 Y. Togano,∗1,∗2

T. Tomai,∗1,∗2 J. Tscheuschner,∗4 J. Tsubota,∗1,∗2 T. Uesaka,∗2 H. Wang,∗2 Z. Yang,∗2 and K. Yoneda∗2

The NP1312-SAMURAI21 experiment, entitled“Spectroscopy of unbound oxygen isotopes II”, wascarried out in November-December 2015, aiming atidentifying resonance states of the extremely neutron-rich oxygen isotopes 27O and 28O, following theNP1106-SAMURAI02 experiment for 25O and 26O1)

in 2012. The motivation for this series of experimentsis exploring the shell evolution towards the possiblydoubly magic nucleus 28O (Z=8 and N=20), which isessential to understand the mechanism of the suddenchange of the neutron drip line from oxygen to fluo-rine (Z=9), called “oxygen anomaly.”2) The invariantmass method is applied to reconstruct the decay ener-gies of 27O and 28O, produced by two- and one-protonremoval reactions from 29Ne and 29F, respectively.The experiment was performed using the SAMURAI

facility3) at RIBF. The secondary beams of 29Ne and29F were produced by the projectile fragmentation of

∗1 Tokyo Institute of Technology∗2 RIKEN Nishina Center∗3 LPC-Caen∗4 Technical University Darmstadt∗5 GSI Helmholtzzentrum fur Schwerionenforschung, Darm-

stadt∗6 CEA Saclay∗7 Seoul National University∗8 Lawrence Berkeley National Laboratory∗9 ATOMKI∗10 KVI-CART∗11 Lebanese-French University of Technology and Applied Sci-

ence∗12 Ruer Boskovic Institute, Zagreb∗13 Argonne National Laboratory∗14 Eotvos Lorand University∗15 Kyushu University∗16 Tohoku University∗17 University of Tokyo∗18 Chalmers University of Technology∗19 Center for Nuclear Studies (CNS), University of Tokyo∗20 University of Cologne, Koln∗21 NSCL, Michigan State University∗22 Kyoto University∗23 GANIL∗24 Institure for Basic Science∗25 Osaka University

a 48Ca primary beam at 345 MeV/nucleon on a 15-mm thick beryllium target, and they were purified byBigRIPS. In addition to a 15-mm thick aluminum de-grader at the first momentum dispersive focal plane(F1) of BigRIPS, a 7-mm thick aluminum degraderwas installed at the second dispersive focal plane F5to reduce the large amounts of light-ion background inthe secondary beam. Plastic scintillators with a thick-ness of 3 mm were installed at the focal planes F3, F5,and F7 for particle identification.

A 15-cm length MINOS4) target cell filled with liq-uid hydrogen was installed 4.4 m upstream from thecenter of the SAMURAI magnet, surrounded by theMINOS TPC and the DALI2 γ-ray detector array.5)

The incident beam was detected by two 1-mm thickplastic scintillators (SBTs) and two drift chambers(BDC1 and BDC2) placed before the MINOS tar-get. The outgoing charged particle and neutrons wereseparated by the SAMURAI dipole magnet with a2.9 Tesla field at the center. Standard drift chambers(FDC1 and FDC2) and a plastic scintillator hodoscope(HODF24) were used for the detection of charged frag-ments. HODF24 was expanded from the existing ho-doscope (HODF) by adding eight new paddles, to coverthe whole effective area of FDC2. For neutron detec-tion, NeuLAND6) (new Large Area Neutron Detectorfor R3B at FAIR) was combined with NEBULA to in-crease the efficiency for multiple neutron detection.

Data analysis is now in progress.

References1) Y. Kondo et al., RIKEN Accel. Prog. Rep. 46, 6 (2013).2) T. Otsuka et al., Phys. Rev. Lett. 105, 032501 (2010).3) T. Kobayashi et al., Nucl. Instrum. and Methods in

Phys. Res. Sect. B317, 294 (2013).4) A. Obertelli et al., Eur. Phys. J. A 50, 8 (2014).5) S. Takeuchi et al., Nucl. Instrum. and Methods in Phys.

Res. Sect. A763, 596 (2014).6) NeuLAND Technical Design Report, http://www.fair-

center.de/fileadmin/fair/experiments/NUSTAR/Pdf/TDRs/NeuLAND-TDR-Web.pdf