SciPost Phys. Proc. 3, 020 (2020)

Measurement of 3 He analyzing power for p−3 He scattering
using the polarized 3 He target
Atomu Watanabe1? , Shinnosuke Nakai1 , Kimiko Sekiguchi1 , Tomomi Akieda1 , Daijiro
Etoh1 , Minami Inoue1 , Yoshinori Inoue1 , Kenta Kawahara1 , Hiroshi Kon1 , Kenjiro Miki1 ,Tomoyuki Mukai1 , Daisuke Sakai1 , Shun Shibuya1 , Yuta Shiokawa1 , Takahiro Taguchi1 ,Hiroo Umetsu1 , Yuta Utsuki1 , Yasunori Wada1 , Morihiro Watanabe1 , Masatoshi Itoh2 ,Takashi Ino3 , Takashi Wakui4 , Kichiji Hatanaka5 , Hiroki Kanda5 , Hooi Jin Ong5 , Dinh
Trong Tran5 , Shuhei Goto6 , Yuma Hirai6 , Daiki Inomoto6 , Hina Kasahara6 , Shinji
Mitsumoto6 , Hisanori Oshiro6 , Tomotsugu Wakasa6 , Yukie Maeda7 , Kotaro Nonaka7 ,Hideyuki Sakai8 and Tomohiro Uesaka8
1 Department of Physics, Tohoku University, Sendai, Miyagi 980–8578, Japan
2 Cyclotron and Radioisotope Center (CYRIC),
Tohoku University, Sendai, Miyagi 980–8578, Japan
3 High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305–0801, Japan
4 National Institute of Radiological Science, Chiba 263–8555, Japan
5 Research Center for Nuclear Physics (RCNP),
Osaka University, Ibaraki, Osaka 567–0047, Japan
6 Department of Physics, Kyushu University, Fukuoka 812–8581, Japan
7 Faculty of Engineering, University of Miyazaki, Miyazaki 889–2192, Japan
8 RIKEN Nishina Center, Wako, Saitama 351–0198, Japan? watanabe@lambda.phys.tohoku.ac.jp
Proceedings for the 24th edition of European Few Body Conference,
Surrey, UK, 2-6 September 2019
doi:10.21468/SciPostPhysProc.3

Abstract
Proton–3 He scattering is one of the good probes to study the T = 3/2 channel of three–nucleon forces. We have measured 3 He analyzing powers for p−3 He elastic scatteringwith the polarized 3 He target at 70 and 100 MeV. In the conference the data were compared with the theoretical predictions based on the modern nucleon–nucleon potentials.
Large discrepancies were found between the data and the calculations at the angles
where the 3 He analyzing power takes the minimum and maximum values.
Copyright A. Watanabe et al.
This work is licensed under the Creative Commons
Attribution 4.0 International License.
Published by the SciPost Foundation.

1

Received 05-11-2019
Accepted 03-01-2020
Check forupdatesPublished 25-02-2020
doi:10.21468/SciPostPhysProc.3.020

Introduction

Understanding nuclear properties based on bare nuclear forces is one of the main interests innuclear physics. Three–nucleon forces (3NFs) are essentially important to clarify various nu020.1

SciPost Phys. Proc. 3, 020 (2020)

clear phenomena such as few–nucleon scattering [1], binding energies of light mass nuclei [2]and equation of state of nuclear matter [3]. To investigate dynamical aspects (momentum,
spin and isospin dependence) of 3NFs, the few-nucleon scattering is a good probe. One canperform direct comparison between the rigorous numerical calculations and precise experimental data, and extract the information of 3NFs. With the aim of studying 3NFs, we have
performed the experimental studies of nucleon–deuteron scattering at intermediate energies(65−300 MeV/nucleon) [4,5]. In the case of the cross section for the elastic deuteron–proton
scattering at 135 MeV/nucleon, large discrepancies between the experimental data and therigorous numerical calculations based on the modern nucleon–nucleon (N N ) potentials (suchas AV18 [6], CD–Bonn [7] and Nijmegen I, II, 93 [8]) are found. The theoretical calculations
with the Tucson-Melbourne’99 [9] or Urbana IX [10] 3NF reproduce well the cross section
data. This is taken as the first signature of 3NF effects in three-nucleon scattering.
Recently, the importance of the isospin dependence of 3NFs has been suggested for understanding of asymmetric nuclear matter (e.g., neutron-rich nuclei and neutron matter properties) [2, 3]. However, the total isospin of N d scattering system is limited to T = 1/2. In order
to explore the properties of the 3NFs in A ≥ 3 nuclear systems and to approach the isospin
dependence of 3NFs, we have performed the measurement of p–3 He elastic scattering at intermediate energies. In this contribution we report the measurement of 3 He analyzing powers
for p–3 He elastic scattering at CYRIC, Tohoku University and RCNP, Osaka University using thepolarized 3 He target.
In this paper, we present the measurement of 3 He analyzing powers at 70 and 100 MeV
using the polarized 3 He target. Section 2 deals with the details of the polarized 3 He target
system developed for p−3 He scattering experiment. In Sec. 3 we describe the measurementof 3 He analyzing powers, and Section 4 presents comparison between the obtained data andthe theoretical predictions. We summarize and conclude in Sec. 5.

2Polarized 3 He Target

We developed the polarized 3 He target system for the measurement of 3 He analyzing power. A
schematic view of the polarized 3 He target system is shown in Fig. 1. The polarized 3 He target
system consisted of main coils which were the Helmholtz type providing a static magnetic
field, and coils for polarimetry, the oven and the laser system.
In order to polarize 3 He nucleus, we adopted the alkali–hybrid spin–exchange opticalpumping (AH–SEOP) method. This method consisted of two step processes. First, Rb vapor
was polarized by optical pumping with circularly polarized light in the presence of a static magnetic field. Then the polarization of Rb atoms was transferred to K atoms via spin–exchange
collisions. Second, the alkali metal polarization was transferred to 3 He nuclei by hyper–fineinteractions. We used a spectrally narrowed laser with the optics to produce circularly polarized light. The output power of the laser was 60 W and the wavelength was 795 nm with
FWHM of 0.2 nm. The target cell consisted of a cylindrical pumping chamber with a length of
45 mm and a cylindrical target chamber with a length of 150 mm. A diameter of the pumping
chamber and the target chamber were 60 mm and 40 mm, respectively. It contained the 3 He
gas with pressure of 3 atm. at room temperature together with a small amount of Rb and K as
well as N2 gas. The target cell was installed at the center of the main coils, and the pumping
chamber was placed in the oven to obtain a sufficient amount of Rb and K vapor by heating
up to ∼ 200 ◦ C.
We measured the target polarization by the adiabatic fast passage–NMR (AFP–NMR)
method in combination with the electron paramagnetic resonance (EPR) method [11]. The
AFP–NMR system consisted of the main coils, drive coils and a pick-up coil. Sweeping a static
020.2

SciPost Phys. Proc. 3, 020 (2020)

Drive Coils

Main Coils
Pick–up Coil

Target CellBeam

EPR Coil
Collimator
EPR Photodiode

B0

Oven

Laser System

Laser Light from
Laser Diode

Figure 1: (Color online) Schematic view of the polarized 3 He target.
magnetic field while applying a RF field by the drive coils under the AFP condition, we flippedthe direction of 3 He spin. The induced NMR signals were detected by the pick–up coil. We haveobtained the absolute values of the 3 He polarization by the EPR method. This method uses the
EPR frequency shift due to the magnetic filed created by polarized 3 He nuclei. The EPR system
consisted of a EPR coil placed inside the oven and a photodiode to detect a EPR signal. The
EPR coil created an RF magnetic filed to induce EPR. However, the EPR measurement gives us
only the 3 He polarization of the pumping chamber because it is needed to the mixture of 3 He
and alkali metal vapor. It is necessary to know the 3 He polarization of the target chamber toextract 3 He analyzing powers from the p−3 He elastic scattering experiment. For this reason,
we have performed the neutron transmission measurement which offers direct measurementof the 3 He polarization in the target chamber. Neutron transmission Tn is described as;
Tn = e−σabs nHe d cosh(PHe σabs nHe d),(1)

where σabs is the neutron absorption cross section of 3 He, nHe is the 3 He number density, d isthe inner length of the target chamber and PHe is the 3 He polarization, respectively. Therefore,
the 3 He polarization is calculated as,


Tn
1
−1
PHe = −cosh,(2)
ln Tn,0Tn,0where Tn,0 is the neutron transmission with the un–polarized 3 He cell. The experiment has
been performed using a neutron source at RIKEN. We obtained the 3 He polarization of thetarget to be about 40 %.

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SciPost Phys. Proc. 3, 020 (2020)3

Detailed Measurement of 3 He Analyzing Powers

The polarized cross section for p−3 He elastic scattering is expressed as,


dσ
dσ
=
(1 + p y A y ),
dΩ
dΩ 0

(3)

where dσ/dΩ ((dσ/dΩ)0 ) is the polarized (un–polarized) differential cross section, and p ydenotes the polarization of the 3 He target. The polarization axis of the target is normal to thereaction plane in this experiment. The 3 He analyzing power can be extracted by applying thepolarized 3 He target with the upward and downward directions.
We performed the measurement of 3 He analyzing powers for p−3 He elastic scattering at
CYRIC, Tohoku University and RCNP, Osaka University. The experimental conditions are summarized in Table 1.
Table 1: Summary of the experimental conditions.
Facilities
Observables
BeamEnergyBeam intensity
TargetTarget polarization
Detectors
Measured angles
Solid angles

CYRIC
A0 y
proton70 MeV
5 − 10 nA
3
He gas (2 mg/cm2 )max. ∼ 40 %∆E–E detectors
θc.m. = 46◦ − 141◦
0.4 msr

RCNP
A0 yproton100 MeV
30 nA
3
He gas (2 mg/cm2 )max. ∼ 40 %∆E–E detectors
θc.m. = 47◦ − 149◦
0.4 msr

A schematic view of the experimental setup at CYRIC is shown in Fig. 2. The proton beams
were accelerated up to 70 MeV by the AVF cyclotron. Typical beam intensities were 5 – 10 nA.
Charge collection of the beams was performed by using the Faraday cup placed downstreamof the target. We also monitored relative values of the beam intensities by the beam monitor
installed in the vacuum chamber placed upstream of the target. The scattered protons from thepolyethylene film with a thickness of 20 µm were detected by the beam monitor at θlab. = 45◦ .
The beam monitor was ∆E − E detectors which consists of thin and thick plastic scintillators
coupled with photomultiplier tubes (PMTs). The scattered protons from the polarized 3 Hetarget were detected by ∆E − E detectors placed on a left and right side of the target. The ∆E
detectors were plastic scintillators with thickness of 0.2, 0.5 or 1 mm. The E detectors werea NaI(Tl) scintillator with thickness of 50 mm. The measured angles were θc.m. = 46◦ − 141◦in the center of mass system. During the experiment, we measured the 3 He polarization andflipped 3 He nuclear spin direction by using the AFP–NMR method every hour.
We also performed the measurement of 3 He analyzing powers at RCNP, Osaka University.
The proton beams were provided by a ion source and then were accelerated up to 100 MeV
by the AVF cyclotron and the Ring cyclotron. A typical beam intensity was ∼ 30 nA. Chargecollection of the beams was performed by using the Faraday cup placed downstream of thetarget. An experimental setup around the target was the same as that of CYRIC. The measured
angles were θc.m. = 47◦ − 149◦ in the center of mass system.

020.4

SciPost Phys. Proc. 3, 020 (2020)

Scattering Chamber
Main Coils
Target Cell

Polyethylene Filmto F. C.

p beamBeam Monitor
Detectors

Figure 2: (Color online) Schematic view of the experimental setup for p−3 He scattering at CYRIC.

4

Results

Figure 3 shows the experimental data for the 3 He analyzing powers. In the conference theexperimental data were compared with the rigorous numerical calculations based on various
realistic nuclear potentials [12]. The angular distribution of the experimental data had amoderate agreement with the theoretical predictions. However, the large discrepancies were
found at around minimum and maximum angles both at 70 and 100 MeV. Careful analysis isin progress now together with the evaluation of the target 3 He polarization.

5

Summary and Conclusions

We have performed the measurement of 3 He analyzing powers for p−3 He elastic scattering
at 70 and 100 MeV by using the polarized 3 He target in a wide angular range. In the conference the experimental data were compared with the rigorous numerical calculations basedon the modern N N potentials. For both the incident energies large discrepancies were foundbetween the data and the calculations at around the angles where the data takes maximum
and minimum values. For the lower energies 5–35 MeV, the data of 3 He analyzing powers
are reproduced by the theoretical predictions based on the N N potential only [13, 14]. The
obtained results indicate that some other components are missed in the theoretical predictionin p–3 He scattering. In order to perform detailed quantitative discussions of the 3NF effects,
study is in progress both from experiment and theory.

Acknowledgements
We performed the scattering experiments at CYRIC, Tohoku University and RCNP, Osaka University. We also performed the measurement of the target polarization at RANS, RIKEN. We
acknowledge all the accelerator groups for providing high quality beams. This work was supported financially in part by the Grants-in-Aid for Scientific Research No. 25105502, No.

020.5

SciPost Phys. Proc. 3, 020 (2020)

exp. data
stat. error
sys. error

0.5

70 MeV
0

m
i
l
re

y
r
a
n
i

P

−0.5
0

20

40

60

80

100

100 MeV

0.5

m
i
l
re

0

120

140

120

140

y
r
a
n
i

160

180

160

180

P

−0.5
0

20

40

60

80

100

θ c.m. [deg]Figure 3: (Color online) 3 He analyzing powers for p−3 He elastic scattering at 70 and
100 MeV. The theoretical calculations are not shown here.
16H02171, and No. 18H05404 of the Ministry of Education, Culture, Sports, Science, andTechnology of Japan.

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