Pion productions in mass asymmetric 28 Si+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

Tsang et al. Phys. Rev. C 86, (2012) RIBF HI Collisions Sn 82 MeV Sn 74 High-density (participant region) Why  - /  + ratio ?  /  0 ~(  +1) 300 MeV/nucleon

The symmetry pressure in high density region of neutron- rich system expels neutrons and attracts protons. 2015/6/29 3 Bao-An Li et al., Phys. Rev. C 71, (2005) Suppress Y(n)/Y(p), Y(  - )/Y(  + ), etc. Prediction of transport theory

2015/6/29 4 NN Inelastic Scattering Most dominant channel for pion production Threshold energy ~ 290 MeV in laboratory pp  - /  + =(5 Ｎ 2 +NZ)/(5Z 2 +NZ)~(N/Z) 2 (  dominance model) Cycle of pion recreation NN→NN NN→N  N  →NN  →N  N  →    Total     production ratio as a function of asymmetric parameter 

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) G. Ferini et al., PRL 97 (2006) Z.Q.Feng and G.-M. Jin, PLB 683 (2010) 140 J.Hong, P. Danielewicz, PRC 90 (2014) /6/29 5 Need more information on various observables

Japanese sub-group started pion experiments using HIMAC from RI-beam >> require large acceptance Usual beam >> small acceptance may be usable 2015/6/29 6

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 2015/6/29 7

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50cm θ lab Beam Target Range Counter Multiplicity Array Ion Chamber Target Multiplicity Array deg. Air Vacuum Target : In ~ 390 mg/cm 2 Typical Intensity : ~ 10 7 ppp Range Counter : 14 layers (+2) of Sci. measured angle (θlab) : 30, 45, 60, 75, 90, 120 degree solid angle : 10 msr Target : In ~ 390 mg/cm 2 Typical Intensity : ~ 10 7 ppp Range Counter : 14 layers (+2) of Sci. measured angle (θlab) : 30, 45, 60, 75, 90, 120 degree solid angle : 10 msr Beam 28 Si 132 Xe Energy(AMeV)400, 600, /6/29 9

#0~7Hit#8~13 No Hit STOP counter # ・・・ 12 STOP CONDITION  + →  + + μ ・ π + decay to μ + ・ μ + : Energy ~ 4 MeV : Range ~ 1 ㎜ Double pulse in one layer 10 ～ 400MeV/u Pion’s are rare less than 1/100 of protons 2015/6/29

Counter #8 STOP Condition + #8 Double Hit ＜ π+ events ＞ 2 nd Hit – 1 st Hit time (nsec) Fit the Histogram “2 nd Hit Time -1 st Hit Time” by Cexp(- t /τ) ⇒ τ = 26.0±0.6 nsec ch7 ch8 Successfully select  + 2 nd Hit Time – 1 st Hit Time of ch8 stop events Fit curve : C*exp(- t /τ) 2015/6/29 11

2015/6/29 12 Using other functional form one couldn’t fit data so well so far……..

E bea m (MeV/nucleon)  mov (c) E 0 (MeV)N-N- N+N+ P (0.05)37.0(4.3)13.7(2.1)0.19(0.05)0.91(0.07) (0.04)44.1(5.0)22.6(2.9)0.63(0.13)0.75(0.05) (0.04)51.8(5.1)26.8(2.6)1.44(0.12)0.59(0.04) 2015/6/29 13 E bea m (MeV/nucleon)  exp (  + )  exp (   )  JQMD (  + )  JQMD (   )

2015/6/29 14 At 400MeV/nucleon

2015/6/ 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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2015/6/ MeV/nucleon800 MeV/nucleon

2015/6/29 19 Semi-analytic formula.

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Normalization constant: 2.02, 1.68, and /6/29 21

2015/6/29 22  + associated multiplicity High multiplicity event/total event

2015/6/29 23 E bea m (MeV/nucleon)  exp (  + )  exp (   )  JQMD (  + )  JQMD (   ) E bea m (MeV/nucleon)  mov (c)  JQMD (c)  CM (c)  part (c)  mid (c) (0.05)0.31(0.02) (0.04)0.34(0.04) (0.04)0.35(0.06)

Measured doubly differential cross sections of  + and  - for the 28 Si + 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. 2015/6/29 24

25 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, Collaborator 1.Kyoto University 2.Riken 3.Rikkyo University 4.NIRS

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