References - Bogoliubov Laboratory of Theoretical Physics - JINR

2 �p+ 8 He analyzing power measurement
The experiment was carried out at the RIKEN Nishina Center Accelerator Research
Facility (RARF) using the RIKEN Projectile-fragment Separator (RIPS). The 8 He beam
was produced by a fragmentation reaction of an 18 O beam with an energy of 100 MeV/A
bombardedontoa13mm 2 Be target. The energy and the intensity of a 8 He beam were
71 MeV/A and 1.5 ×10 5 pps, respectively. The purity of the beam was 77 %.
As a secondary target, we used the polarized proton solid target (Fig. 1). The material
of the secondary target was a single crystal of naphthalene with a thickness of 4.3×10 21
protons/cm 2 . Protons in the crystal were polarized under a low magnetic field of 0.09 T
at 100 K by the optical excitation of electrons and the cross-polarization method.
The target polarization was 11.0±2.5%
on average. Recoil protons were detected
using multiwire drift chambers and CsI
(Tl) scintillators placed on the left and
right sides of the beam line. Each MWDC
was located 180 mm away from the target
and covered a scattering angle of 50 ◦ − 70 ◦
in the laboratory system. A CsI scintillator
with a sensitive area of 135 mm H
× 60 mm V was placed just behind the
MWDC. Leading particles 6,8 He were detected
using another MWDC and ΔE − E
plastic scintillator hodoscopes with thicknesses
of 5 and 100 mm.
The measured differential cross sections
and analyzing powers are shown in Fig. 2
by closed circles. They are consistent with
the previous data of the differential cross
section [3] plotted by open circles.
3 Optical model analysis
3.1 Phenomenological optical potential
Figure 1: Schematic view of the experimental
setup.
In order to extract the global nature of �p− 6,8 He interactions, the data were phenomenologically
analyzed with an optical model potential. For the central and spin-orbit terms,
we assumed Woods-Saxon and Thomas type functions, respectively. We searched a parameter
set that reproduces the data using a fitting code ECIS79. As an initial potential,
a parameter set for �p+ 6 Li elastic scattering at 72 MeV/A [4] was used. The dashed lines
in Fig. 2 show the calculation with initial parameters. Results of the best-fit parameters
are presented by solid curves. Both differential cross section and analyzing power data
are well reproduced except for the scattering at backward angles.
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