Charged pion production in intermediate

energy heavy-ion collision

M. Sako1, T. Murakami1, Y. Ichikawa1, S. Imajo1, R. Sameshima1, Y. Nakai2, S. Nishimura2, K. Ieki3, M. Matsushita3, J. Murata3, and E.Takatda4

1Kyoto Univ., 2RIKEN, 3Rikkyo Univ., 4NIRS

Introduction

Experiments and Analysis

Discussion

Summary

Contents

Introduction

Symmetric part Asymmetric part

negligible

pn

)/()( pnpn

pn,

δ：isospin asymmetric parameter

density :

: neutron, proton density

Experimental Constraints

Isospin diffusion, GMR, etc

L.W

. Ch

en

, C.M

. Ko

an

d B

.A. L

i,

Ph

ys. R

ev. C

72

(20

05

), 06

43

09

.

charged pion ratio p-/p+

Heavy-ion reaction at intermediate energy

density of overlap region ~ 2 ρ0

Pions are created in the overlap region

Nearby Pion threthold

decay of ⊿ particle

⊿ resonance model

222- )5/()5(/

ZN

NZZNZN

pp

B.A. Li, G.C. Yong, W. Zuo, Phys. Rev. C 71 (2005) 014608.

Our Experiment

HIMAC :

Heavy Ion Medical Accelerator in Chiba

Beam energy dependence using Si beam

400, 600, 800 MeV/nucleon

Mass asymmetric reaction : Si + In

• We can get the information of the rapidity of

pion source.

Xe+In at 400 MeV/nucleon

N/Z dependence

Experiment and Analysis

Experimental Setup

50cm θlab

Beam

Target

Pion Range Counter

Multiplicity

Array Ion

Chamber

Target

Multiplicity Array

Vacuum

Air

Vacuum

• Target : In ~ 390 mg/cm2

• Typical Intensity : ~ 107 ppp

• Range Counter : 14 layers (+2) of Sci.

• measured angle (θlab)

: 30, 45, 60, 75, 90, 120 degree

• solid angle : 10 msr

Beam 28Si 132Xe

Energy(AMeV) 400, 600, 800 400

Identification principles of π+ (and π-)

＜In flight＞ dE/dx is identical for both π+ and π-

＜After STOP＞

・π+ decay to μ+

π+ → μ+ + νμ

・μ+

Energy ~ 4 MeV

Range ~ 1 ㎜

π+ : Double Hits in one counter

p+

・ create a pionic atom

and captured by a nucleus

・ decay to various particles

Unable to use the same

identification method as π+

p-

＜p identification step＞

① p + ID using Double Hit Condition

② p ±ID using

⊿E conditions of well defined π+

③ p - = p ± - p +

π-,π+ by Simulation (Geant4)

E (

MeV

)

⊿E (MeV)

Red : π+

Blue : π-

Histogram of

Range Counter

E7 (MeV)

E8

(M

eV

)

counter #8 stop events

#0~8 Hit #9~13 No Hit

STOP 0 1 2 3 4 counter # 5

6 7 8 9 ・・・ 12

STOP

CONDITION

P

D

T

π

Example counter : #8

Double Hit

π+ and μ+

⊿E signals

We can select π+

We can select p± using

these delta E signals of p+

p m

Definition of π-/π+ ratio

π± : STOP + ⊿E cut + background cut

π+ ： STOP + ⊿E cut + background cut

+ Double Hit

p

pppp ratio/-

Charged pion ratio

Discussion

Invariant cross section of pi+ in the mid rapidity frame

Erapπ (MeV) Erapπ (MeV)

Erapπ (MeV)

□ 30deg

● 45deg

■ 60deg

▲ 75deg

▼ 90deg

○ 120deg

400 MeV 600 MeV

800 MeV

• The distributions are different

by angles,

especially in backward angles.

• There are some pion source

2

Si+In Si+In

Si+In Erapπ: pion kinematic energy

in the mid rapidity frame

p+/ p– ratio : Si + In lo

g s

cale

π

- /π

+

Erapπ (MeV)

400 MeV 600 MeV

800 MeV ● 45deg

■ 60deg

▼ 90deg

○ 120deg

Slopes depend on Beam Energy

Fitting : C*X-a

slope α:

• 400 : (4.5±0.5)×10-1

• 600 : (3.2±0.5)×10-1

• 800 : (2.0±0.5)×10-1

log s

cale

π

- /π

+

log s

cale

π

- /π

+

N/Z dependence : Si and Xe beam

slope α

Si + In : (4.5±0.5)×10-1

Xe+In :(11.0±0.8)×10-1

□ 30deg

● 45deg

■ 60deg

▲ 75deg

Xe + In 400 MeV Si + In 400 MeV

Erapπ (MeV) Erapπ (MeV)

log s

cale

π

- /π

+

log s

cale

π

- /π

+

Fitting : C*X-a ● 45deg

■ 60deg

▼ 90deg

○ 120deg

Average <N/Z>

Si + In : 1.14

Xe+In : 1.39

(N/Z)2

(N/Z)2

Rough Estimation

: integrated-pion ratio

dEd

dE

dEd

ddEdd

dEd

ddEd

i

i

i

ii

p

sin2

sin

p

p

dEd

dE i

i

i

ii

p sin2

Sum the data point

like this formula Z

hig

ang X

iao e

t al.

Phys

. Rev. L

ett. 1

02(2

009)0

62502

Si+In

Xe+In

Summary and Next Step

＜Summary＞

Pion ratio from Si+In of 400, 600, and 800 MeV/nucleon and

Xe+In of 400 MeV/nucleon

We show pion ratio as universal function.

Pion production process is simple

Pion ratio has beam energy and N/Z dependence and is

qualitatively consistent with Theoretical asumption.

<Next Step>

We are planning next experiments

N/Z dependence using Xe isotope beam

129,132,136Xe + CsI

Thank you