The plan for measurement of angular distributionin (n,γ) reaction with polarized neutron beam
KMI 2017@Nagoya University Tomoki Yamamoto (Nagoya University)
H. M. Shimizu, M. Kitaguchi, K. Hirota, A. Okada, K. Nagamoto, F. Goto, I. Ito(Nagoya Univ.), T. Ino(KEK), K. Aasahi(Tokyo Tech), T. Momose(Univ. British Columbia)
T. Iwata(Yamagata Univ. ), K. Sakai(JAEA), M. Hino(Kyoto Univ.), T. Yoshioka, S. Takada, J. Koga(Kyushu Univ.), T. Shima(Osaka Univ.), Y. Yamagata(RIKEN)

Motivation

Estimation

The current universe cannot be understood by CP violation instandard theory.

▫ Optimum thickness

When neutrons are incident on target nuclei, the scattering amplitude
can be described by Eq(1).
D≠0 suggests CP violation via CPT theorem.
Neutron spin(1) k̂ Neutron momentumIˆ Nucleus spin

To measure P violation, polarized neutron and non-polarized target
are needed, and CP violation needs to polarize each other. (Fig.1)
CP violation

P violation

Ikn

kn

Fig.1 Measurement system of P and CP violation

The P violation enhanced by 106 times have been observed incompound nucleus reactions.

If enhancement of P violation occurs in the nucleus, the CPviolation is also enhanced. It is given by the Eq(2).

WT
CP = (J)W

Spin factor(2) WT /W gcp/gp
P violation in nuclei
Pthickness [cm]of lanthanum is 3.0 cm when P violation measured with anaccuracy of 10%. However, when we use a thick lanthanum likethis values, we measure the blurred angular distribution due toscattered neutron in the target. Therefore, it is considered good to
use as thin as possible.
Neutron intensity
Polarization of 3He
Neutron polarization
Neutron transmission
Effective thickness

P

Outline of experiment▫ P violation measurement

232Th

139La

Asymmetry [%]

232Th
131Xe
81Br

232Th
115In

117Sn

107Ag

113Cd
232Th

238U

121Sb

127I

109Ag

113Cd

Neutron Energy[eV]Fig.2 Relationship between neutron
resonance energy and asymmetry

Experiment setup
As shown in Fig.6, first, unpolarized
neutrons are polarized with 3He spin
filter from the beam line upstream. After
that, polarized neutrons are irradiatedthe target. At that time, gamma rays
emitted by (n, γ) reaction are measured
with germanium detectors(Fig.5), andThe neutron transmitted through thetarget is measured with a transmission
detector.

Fig.5 Germanium detectors

γ raydetector
Polarized
Neutron beam

Unpolarized
Neutron beam

▫ Final state dependence of P violation
By further increasing the statistics, it becomes possible to measure
the final state dependence of P violation.
. order to measure this, it is necessary to detect γ rays emitted
Inby (n,γ) reaction.

2613 n/s
45%
20%
65%
17 atm･cm

Table.1 Parameters in the experiment

(J)It is necessary to precisely measure P violation as a
pre-measurement step for CP violation.

We will measure the P violation innuclei with the highest precisionby using high intensity neutron
beam of J-PARC at BL04.
139
La with low neutron resonanceenergy and large asymmetry(Fig.2)
is used for the target nucleus.
Highly polarized neutron andoptimum thickness target arerequired.

required times [hour]

We aim to search for CP violation in compound nuclei.

When we try to measure P violation,
the optimum thickness of the targetis determined by the cross-section
and the polarization ratio of theneutron. Fig.4 shows therelationship between the thicknessof lanthanum and measurement time
139La
Fig.4
Relationshipbetweenwhen P violation is measured withthickness and required times
an accuracy of 10%.
Table.1 shows experimental condition. The optimum thickness

2613 n/s
E=0.75 eV

γ ray

3He spin filter

Target17 atm･cm
P3He=45％

Lanthanum
Thickness=30 mm

Transmission
detector

Fig.6 Experiment setup for P violation measurement

Conclusion
・Final state dependence of P violation has not been measured yet.
・In the case of La, it takes 1.5 hours beam time to measure the asymmetry with an accuracy of 10%.
・The optimum thickness is 3.0 cm. In addition, we need to consider the effect of scattering.

NOP-T