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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