Pion productions in mass asymmetric 28Si+In
reactions at 400, 600, 800 MeV/nucleon
Tetsuya MURAKAMI
Department of Physics
Kyoto University
Based on Mr. Sako-kun’s upcoming PhD thesis Work
2015/6/29
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124 Sn
50
74
r/r0~(g+1)
2.3 @ 300 MeV/nucleon
132 Sn
50
82
(n-rich)
@200~300 MeV
High-density
(participant region)
RIBF HI Collisions
Why p-/p+ ratio ?
Tsang et al. Phys. Rev. C
86, 015803 (2012)
The symmetry pressure in high density region of neutronrich system expels neutrons and attracts protons.
Prediction of
transport theory
Suppress Y(n)/Y(p),
Y(p-)/Y(p+), etc.
Bao-An Li et al., Phys. Rev. C 71, 014608 (2005)
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NN Inelastic Scattering
D
p
•Most dominant channel for pion
production
•Threshold energy ~ 290 MeV in
laboratory pp
•p-/p+=(5Ｎ2+NZ)/(5Z2+NZ)~(N/Z)2
(D dominance model)
•Cycle of pion recreation
NN→NN NN→ND
ND→NN
D→Np
Np→D
Total p--p+ production ratio as a function of asymmetric parameter d
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Need more information on various observables
Au+Au
Z. Xiao et al., PRL 102 (2009) 625
J. Xie et al., PLB 718 (2013) 1510
J. Xu et al., PRC 87 (2013) 067601
G. Ferini et al., PRL 97 (2006) 202301
Z.Q.Feng and G.-M. Jin, PLB 683 (2010) 140
J.Hong, P. Danielewicz, PRC 90 (2014) 024605
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 Japanese sub-group started pion experiments using
HIMAC from 2007.
RI-beam >> require large acceptance
Usual beam >> small acceptance may be usable
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 Using mass-symmetric collisions so far
(N/Z)participant≈(N/Z)proj ≈(N/Z)targ
 Over-simplified the situation
Impossible to distinguish different moving source
frames, like
NN cm, participant cm, nucleus-nucleus cm etc.
Better study mass-asymmetric collisions
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Multiplicity Array
27-58 deg.
Multiplicity Array
Ion
Chamber
Target
Beam
Vacuum
θlab
Air
Target
50cm
Beam
28Si
Energy(AMeV)
Range Counter
400, 600, 800
132Xe
400
• 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
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counter
#
0
1
2
3 4
5 6 7 8 9 ・・・
12
STOP
・
π+ decay to μ+
p+ → m+ + nμ
STOP CONDITION
・μ+ : Energy ~ 4 MeV
: Range ~ 1 ㎜
#0~7Hit
#8~13 No Hit
Double pulse in one layer
 ～400MeV/u
Pion’s are rare
less than 1/100 of protons
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ch8
＜π+ events＞
Counter #8 STOP Condition
+
#8 Double Hit
ch7
2nd Hit Time – 1st Hit
Time
of ch8 stop events
Fit the Histogram
“2nd Hit Time -1st Hit
Time”
by Cexp(- t /τ)
Fit curve :
C*exp(- t /τ)
⇒ τ = 26.0±0.6 nsec
Successfully select p+
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2nd Hit – 1st Hit time (nsec)
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Using other functional form one couldn’t fit data so well so far……..
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Ebeam(MeV/nucleon)
bmov(c)
E0(MeV)
400
0.20(0.05)
37.0(4.3)
600
0.19(0.04)
800
0.22(0.04)
N-
N+
P
13.7(2.1)
0.19(0.05)
0.91(0.07)
44.1(5.0)
22.6(2.9)
0.63(0.13)
0.75(0.05)
51.8(5.1)
26.8(2.6)
1.44(0.12)
0.59(0.04)
Ebeam(MeV/nucleon)
sexp(p+)
sexp(p-)
sJQMD(p+)
sJQMD(p-)
400
0.33
0.63
0.28
0.38
600
0.87
1.37
0.90
1.12
800
1.41
2.10
1.68
2.01
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At 400MeV/nucleon
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400 MeV/nucleon
600 MeV/nucleon
800 MeV/nucleon
Simple Coulomb effect?
Ratio alone can be fitted by functional form of
Maheswari et al. (NP A628 (1998) 669), but
differential cross sections seem to be
imposible.
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400 MeV/nucleon
800 MeV/nucleon
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Semi-analytic formula
NT  AT F (n , b ( 0 ) ),
n
RT
,
R p + RT
b (0) 
b
R p + RT
(0)
3
1
1 - b (0) 3
1/ 2 1 - b
2
1/ 2
F (n , b )  (1 -n ) (
) - [3(1 -n ) - 1](
)
4
n
8
n
Apart  Atot F (1 / 2,b ( 0) )
(0)
.
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Normalization
constant: 2.02,
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1.68,
and 1.43
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p+ associated multiplicity
High multiplicity event/total event
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Ebeam(MeV/nucleon)
sexp(p+)
sexp(p-)
sJQMD(p+)
sJQMD(p-)
400
0.33
0.63
0.28
0.38
600
0.87
1.37
0.90
1.12
800
1.41
2.10
1.68
2.01
Ebeam(MeV/nucleon)
bmov(c)
bJQMD(c)
bCM(c)
bpart(c)
bmid(c)
400
0.20(0.05)
0.31(0.02)
0.18
0.34
0.42
600
0.19(0.04)
0.34(0.04)
0.22
0.41
0.49
800
0.22(0.04)
0.35(0.06)
0.26
0.46
0.55
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 Measured doubly differential cross sections of p+ and p- for
the 28Si + In reactions at 400, 600 and 800 MeV/nucleons.
 They are emitted isotropically from the single moving
source, whose velocity is quite slower than the mid rapidity.
 The differential pion ratios represented in such moving
frames overlap each other at each incident energy.
 PHITS fails to reproduce the observed absolute cross
section, the angular dependence of the cross sections and
the charged pion ratio.
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Collaborator
M, Sako1;2,
T, Murakami1;2,
Y, Nakai2,
Y. Ichikawa1,
K. Ieki3,
S. Imajo1,
T. Isobe2,
M. Matsushita3,
J. Murata3,
S. Nishimura2,
H. Sakurai2,
R.D. Sameshima1,
E. Takada4,
1. Kyoto University
2. Riken
3. Rikkyo University
4. NIRS
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