Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 50 (2017)

Measurement of p
–6 He elastic scattering at 200 A MeV
S. Sakaguchi, ∗1,∗2 S. Chebotaryov, ∗2,∗3 T. Uesaka, ∗2 T. Akieda, ∗4 Y. Ando, ∗3 M. Assie, ∗5 D. Beaumel, ∗2,∗5N. Chiga, ∗2 M. Dozono, ∗6 A. Galindo-Uribarri, ∗7 B. Heﬀron, ∗7 A. Hirayama, ∗8 T. Isobe, ∗2 S. Kawase, ∗1W. Kim, ∗3 T. Kobayashi, ∗4 H. Kon, ∗4 Y. Kondo, ∗8 Y. Kubota, ∗2 S. Leblond, ∗9 H. Lee, ∗9 T. Lokotko, ∗9Y. Maeda, 10 Y. Matsuda, 11 K. Miki, ∗4 E. Milman, ∗2,∗3 T. Motobayashi, ∗2 T. Mukai, ∗4 S. Nakai, ∗4T. Nakamura, ∗8 A. Ni, ∗3 T. Noro, ∗1 S. Ota, ∗6 H. Otsu, ∗2 T. Ozaki, ∗8 V. Panin, ∗2 S. Park, ∗3 A. Saito, ∗8H. Sakaguchi, ∗12 H. Sakai, ∗2 M. Sasano, ∗2 H. Sato, ∗2 K. Sekiguchi, ∗2,∗4 Y. Shimizu, ∗2 I. Stefan, ∗5L. Stuhl, ∗6 M. Takaki, ∗6 K. Taniue, ∗10 K. Tateishi, ∗2 S. Terashima, ∗13 Y. Togano, ∗8 T. Tomai, ∗8Y. Wada, ∗4 T. Wakasa, ∗1 T. Wakui, ∗2,∗14 A. Watanabe, ∗4 H. Yamada, ∗8 Z. Yang, ∗2 M. Yasuda, ∗8J. Yasuda, ∗1 K. Yoneda ∗2 and J. Zenihiro ∗2We measured the vector analyzing power for p–6 Heelastic scattering at 200 A MeV using a spin-polarized
solid proton target and the SAMURAI spectrometerwith the aim of investigating spin-orbit interaction
between proton and 6 He (SAMURAI13 experiment).
The experimental setup is described in this article.
A 6 He beam was produced from an 18 O beam with
230 A MeV using a 15 mmt Be target and an 8 mmt
F1 degrader. Triton contamination was suppressed to25% of the total beam intensity with an F2 collimatorand was further reduced to 6% by closing the F2 slit
to 2 × 2 mm2 . The experimental setup around thetarget is schematically shown in Fig. 1. Special care
was taken to reduce the size of the beam spot at F13.
STQ25 was moved 1 m closer to the target for betterfocusing. A veto scintillator (SBV) with an φ18 mm
hole was installed in front of the target. The beam
intensity was kept at approximately 0.6 MHz. The
typical transmission ratio of the beam through SBV
was 78%. The beam-spot size on the target was 5 mmin sigma. The polarized proton target was placed 4 mfrom the SAMURAI magnet center. The target material was naphthalene (C10 H8 ) with a size of φ24 mm ×2.5 mmt (285 mg/cm2 ). Two lasers with wavelengthsof 556 nm and 545 nm and average powers of 3 W
and 0.75 W, respectively, were installed near STQ25.
Pulsed laser light with a repetition rate of 3 kHz wasdelivered to the target. Recoil protons were detectedat both the left and right sides of the beamline withESPRI-RPS1) . Each system consists of a drift chamber, an energy absorber, one plastic scintillator andseven NaI(Tl) scintillators. For the detection of scattered particles, FDC0 was placed 400 mm away fromthe target. It is expected to have good high-rate tolerance because of its small cell size of 5 mm. FDC0
was operated with a position resolution of 130 μm insigma and a tracking eﬃciency of >98% even for a1 MHz beam. Two S1-MWDCs from SHARAQ Gr.
were placed behind FDC0. Scattered particles wereanalyzed using the SAMURAI spectrometer with amagnetic ﬁeld of 2.0 T. The eﬀect of the stray ﬁeld on
the performance of PMTs, polarized target and oxygen
monitors was not observed. 95% of the volume of thegap chamber was replaced with helium gas to maximize
the acceptance of SAMURAI without severely degrading the Bρ resolution. The FDC1 chamber was slightly
over-pressurized (+0.35 kPa) compared to the pressurein the gap chamber to avoid reverse force on its windowﬁlm. The obtained Bρ resolution was about 1/300,
which is one third of the typical value. This is primarily because of the multiple scattering in helium gas andsecondarily because of a low magnetic ﬁeld of 2.0 T.
2.9 T is ideal for 6 He at 200 A MeV. The beam propagating through SAMURAI was stopped by a lead blockwith a size of 10×10×40 cm3 for protecting FDC2.
FDC2 and HODF24 were placed parallel to SAMURAI
to cover both 6 He and 4 He trajectories. Measurementsof p–6 He (physics run) and p–4 He scattering (polarization calibration) were performed for 3 days and 1 day,respectively. The polarization axis was reversed oncein each run. The carbon target and empty target data
were also taken. The current status of the data analysis is described in another article2) .
He gasNEBULApp

er

ESPRI-RPS

FDC0 &S1-MWDC

24am
Be

HO

FD

BDC

DF

SBT SBV

Polarized
proton target

2nsto

Department of Physics, Kyushu University
RIKEN Nishina Center∗3 Department of Physics, Kyungpook National University∗4 Department of Physics, Tohoku University∗5 IPN Orsay∗6 CNS University of Tokyo∗7 Oak Ridge National Laboratory∗8 Department of Physics, Tokyo Institute of Technology∗9 Department of Physics, University of Hong Kong
∗10 Department of Physics, Miyazaki University∗11 CYRIC Tohoku University∗12 RCNP Osaka University∗13 Department of Physics, Beihang University∗14 National
Institute of Radiological Sciences
NIRS
∗2C2

∗1SAMURAI(2.0T)

64HeHeFig. 1. Setup for SAMURAI13 experiment.

References
1) Y. Matsuda et al., Phys. Rev. C 87, 034614 (2013).
2) S. Chebotaryov et al., in this report.

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