RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-1. Nuclear Physics

Present status of data analysis of p − 6 He elastic scattering∗1,∗2∗1,∗3∗1∗1∗1,∗5S.S.Chebotaryov,
S.
T.T.
Uesaka,T.T.Akieda,
D.Beaumel,Beaumel,∗1,∗5
Chebotaryov,∗1,∗2S. Sakaguchi,
Sakaguchi,∗3Uesaka,
Akieda,∗4∗4 Y.
Y. Ando,Ando,∗2 M. Assie,∗5∗5D.
∗1∗1
∗6
∗7
∗7
∗6
∗7
∗8∗8
∗1 ∗1
∗3 ∗3
N. N.
Chiga,
A.Hirayama,
Hirayama, T.T.Isobe,
Isobe, S. S.
Kawase,Chiga, M.M.Dozono,
Dozono, A.
A.Galindo-Uribarri,Galindo-Uribarri, B. Heﬀron,Heffron, A.
Kawase,
∗2 ∗2
∗1,∗4
∗9
∗1,∗4H. Kon, ∗4∗9 ∗9 H. Lee,∗9 ∗9W. W.
Kim,
T.T.
Kobayashi,
Y. Kubota,
Kubota,∗1∗1S.S.Leblond,Leblond,T.
Lokotko,
Kim,
Kobayashi,
H. Kon,∗4 Y.
Y. Kondo,Kondo,∗8 Y.
H. Lee,∗9 T.
Lokotko,∗10∗1,∗11
∗1,∗4
∗1,∗2
∗1
∗4
∗10
∗1,∗11
∗1,∗2
∗1
∗4
∗4
Y. Y.
Maeda,
K.
T.Motobayashi,
Motobayashi, T.T.Mukai,
Mukai, S. S.
Nakai, ∗4Maeda, Y.Y.Matsuda,Matsuda,
K.Miki,Miki,E. Milman,
T.
Nakai,
∗8 ∗8
∗2 ∗2
∗3∗3
∗6
∗1
∗8
∗1
∗2
∗6
∗1
∗8
∗1
∗2
∗8 ∗8
T. Nakamura,
Ni,Ni, T.T.
Noro,
T. Ozaki,
Ozaki, V.V.Panin,Panin, S. S.
Park, A. Saito,
A. Saito,
T. Nakamura,A. A.
Noro, S.S.Ota,
Ota, H. Otsu, T.
Park,
∗12
∗1
∗1
∗1
∗4
∗1
∗5
∗12
∗1
∗1
∗1
∗1,∗4
∗1
∗5
∗6 ∗6
H.H.Sakaguchi,
H. Sato,Sato, K.K.Sekiguchi,
Sekiguchi,
Y.
Stefan, L.L.Stuhl,Stuhl,
Sakaguchi, H.
H.Sakai,Sakai, M.
M. Sasano,Sasano, H.
Y. Shimizu,Shimizu, I.I. Stefan,
∗6
∗10
∗1
∗13
∗8∗8
∗6
∗10
∗1
∗13
∗1,∗8
∗1,∗8∗4
M. Takaki,
Takaki, K.
K.Taniue,Taniue, K.K.Tateishi,Tateishi, S. S.
Terashima, Y. Y.
Togano, T.T.Tomai,
Tomai,Y.
M.
Terashima,Togano,
Y. Wada,Wada,∗14∗8 Z. Yang, ∗1T.
A.A.Watanabe,
M. Yasuda,Yasuda,∗8∗8T. Wakasa,Wakasa,∗3 T. Wakui,∗1,∗14Watanabe,∗4∗4H.
H.Yamada,Yamada,∗8Z. Yang, ∗1 M.
∗3 K. Yoneda ∗1J.J.Yasuda,and J.
J. Zenihiro
Zenihiro∗1∗1Yasuda,∗3Yoneda ∗1 andIn the summer of 2016, we conducted an experimentat the RIKEN RI-beam factory (RIBF) on the elastic
scattering of spin-polarized protons from unstable 6 Henuclei at 200A MeV to probe its spin-orbit potential.
The experiment was performed at the BigRIPS beamline using the SAMURAI spectrometer and a spinpolarized proton target system.1) Data obtained fromthis experiment should help us understand how an exotic structure of neutron-rich nuclei aﬀects spin-orbit
coupling owing to its extended neutron density distribution. Details of the experimental setup are presented in another report.2) The current status of thedata analysis will be presented here.
To cleanly select p-6 He elastic scattering events,
mainly two contributions should be discriminated: inelastic channels, where incident 6 He breaks up into 4 He
+ 2n, and quasi-free scattering (QFS) of a proton fromcarbon nuclei contained in the target material (C10 H8 ).
For the ﬁrst part, the SAMURAI spectrometer wasused as it can easily discriminate 4 He and 6 He particles by Bρ analysis. Figure 1(a) shows the distributionof events at a plastic scintillator hodoscope, where 4 He
and 6 He are clearly separated.
Figure 1(b) shows a PID spectrum from proton detectors. The solid line shows the simulated ΔE-E
curve for a proton, which corresponds suitably wellwith the obtained data. On this spectrum, a separate
locus of deuteron particles can also be observed, and it
can be discriminated with ΔE-E cut on proton events.
Figure 1(c) shows the polar-angle correlation of recoil and scattered particles for the cases of polarized
proton (upper panel) and carbon target runs (lowerpanel). In the upper panel, one can ﬁnd a locus along

the solid line that represents the kinematical correlation of elastic scattering. It overlaps with a thinner
locus in the smaller θ6 He region, which corresponds to
QFS from carbon, as can be seen in the lower panel.
Figure 1(d) shows the projection of Fig. 1(c) along thesolid line. The QFS contribution is normalized withthe target thickness. It is found that the QFS contribution is as small as 10% of the elastic scattering andcan be adequately subtracted.
After the event selection and background subtraction, the elastic scattering yield can be obtained witha high S/N ratio. At present, the analysis is ongoing
to deduce p-6 He cross section and analyzing power.

∗1RIKEN Nishina Center
Department of Physics, Kyungpook National University∗3 Department of Physics, Kyushu 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∗2Fig. 1.: Plots showing the PID of (a) scattered and(b) recoil particles. (c) Polar-angle correlations. (d)Carbon background subtraction.

References
1) T. Wakui et al.: Nucl. Instr. Meth. Phys. Res. A 550,521 (2005).
2) S. Sakaguchi et al.: In this report.

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