4He(p,2p) reactions for studing in-medium NN interactions

S. Asaji Department of Physics, Kyushu University

CollaboratorsT. Noro, K. Fujita1, Y. Hagihara, K. Hatanaka1,

T. Ishida, M. Ito1 , S. Kishi2, Y. Nagasue, M. Nakamura2, K. Sagara, H. Sakaguchi2, Y. Sakemi1, Y. Shimizu1,

H. Takeda3, Y. Tameshige1,S.Terashima2, M. Uchida2, T. Wakasa, Y. Yasuda2, H. P.Yoshida1, M.Yosoi2,

and T. Yonemura

Department of Physics, Kyushu University Research Center for Nuclear Physics, Osaka University1

Department of Physics, Kyoto University2

RIKEN3

Introduction

Our interest is to study the NN interaction in the nuclear field.

A direct way is by examining the difference between the NN interactions in free space and in nuclear medium.

(p,2p) is a NN scattering which takes place in nuclear medium.

NN scattering in free space

NN scattering in nuclear medium

Purpose of 4He(p,2p) measurement (1) Analyzing Power (Ay)

Ay reduced monotonically depending on effective mean density, and also on Q-value.

Determine the key parameter of Ay reduction by measuring Ay of 4He nucleus.

4He(1s1/2)

Kinematics:θlab=25.5°Precoil=0MeV/c

4He(1s1/2)

Distorted Wave Impulse Approximation (DWIA)

χi(r): distorted waves of incident particles (i=0) outgoing particles (i=1,2)

φ: bound wave function t : t-matrix for NN scatteringσ: cross section

rrrrr dtTDWIA

pp)()()()(

0

*

2

*

1)2,( χχχ φ

2||Tσ

A (p,2p) reaction is effective to study nuclear structure.

There are difficulties specific to studies of light nuclei such as recoil effect.

To examine how accurately we can deduce the momentum distribution of protons in the light nucleus.

At Riken, study of unstable nuclei by (p,2p) reaction in inverse kinematics is schemed.

Purpose of 4He(p,2p) measurement (2)Cross Section

Experiment

Facility RCNP

Beam 392MeV polarized

proton beam Two-armed

spectrometer

Cooled Gas Target System

Cooled Gas Target System

Cooled down target to increase target density and to reduce background.

Target Monitor

proton

4HeAramid Foil Target

CryogenicRefrigerator

4He GasReservoir

Target Cell

Heater

Pressure Gauge& Transducer

Cooled 4He Gas

Window Foil :Aramid 12.5μm

Aluminum Cover

Bearing

Beamp+α 　 elastic scattering

Add drive unit

Energy Spectrum

Yield increased about 30 times higher than at room temperature by cooling the target.

log scale log scale

Separation Energy

Pr=0MeV/c Pr=250MeV/c

10

4He(p,2p)3H

p+4He→p+p+n+d

103

102

10

Separation Energy

Background from Aramid FoilBackground from Aramid Foil

Result of Ay

Ay is plotted as a function of the effective mean density and as a function of the Q-value.

Ay is better aligned with the Q-value.

Additional Measurement on Other Light Nuclei

In order to examine systematics,

we also measured Ay for many light

nuclei.

2D,3He,4He‥Gas　6Li,7Li, 9Be,10B,11B,16O,19F‥Solid

Ay of other nuclei

The ratios of observed Ay to DWIA calculations are plotted as a function of effective mean density and as a function of the Q-value.

The ratios are better aligned with the Q-value.

( ) ( )

srecoilfi 2EEm

AEE

off-energy-shell effect

Non relativistic Ay calculations of p-p scattering including off-energy-shell effect.

The calculations show that off-energy-shell effect is smaller than a few percent.

Calculated by H. Kamada (Kyushu Institute of technology), private communication

Cross section Measurement

In order to determine the reliability of DWIA calculations, measurements have been performed for various kinds of kinematics.

Kinematics

Result of Cross Section

The data for all kinds of kinematical conditions are consistent within 10% in FWHM.

1. θ1=const.

3. θ1,θ2=const.

2. P0 // Pr

Result of Ay

3. θ1,θ2=const.1. 2.

3.

1. θ1=const. 2. P0 // Pr

Summary and Conclusion Measurement

We measured cross section and Ay for the 4He(p,2p) reaction with various kinematics.

Cooled down target to increase target density and to reduce background. As a result, yield increased about 30 times higher than at room temperature.

Ay

Ay was reduced by 30% compared with DWIA calculations. (⇔ 　 50% reduction is expected from density dependence.)

Additional measurement for ten target nuclei The ratio, Ay(exp)/Ay(DWIA), are better aligned with the Q-value.

It implies that the Ay-reduction is caused by off-energy effect.

but the non-relativistic off-energy-shell amplitude gives no reduction.

Cross section The momentum width of bound wave function can be deduced within 10%

accuracy by comparing with simple DWIA calculations. Theoretical improvement is required for further study.

Cross Section with various kinds of wave function

The data is also consistent within 10% in FWHM with various kinds of wave functions made in previous experimental and theoretical studies.