Effect of isospin-dependent cluster recognition on the observables in heavy ion collisions Yingxun Zhang ( 张英逊 ) 2012 年 8 月 10 日， 兰州 合作者： Zhuxia Li, (CIAE) Chengshuang Zhou, (CIAE, GXNU) M.B.Tsang (MSU) China Institute of Atomic Energy

Transport model is one of the powerful methods for understanding the mechanism of SHE synthesis and the properties of nuclear matter General view of transport models Three parts in the transport models 1, Initial condition 2, Motion of equation Cluster recognition methods 3, Observables 1), Nucleonic potential 2), In medium XS 1), proj., targ., 2), density profile 3), BE, rms 4), Ebeam, b 5), stability

A, BUU type: f(r,p,t) one body phase space density Two-body collision: occurs between test part. Mean field Solved with test particle methods EOS, symmetry energy B, QMD type: solve N-body equation of motion nucleon Two body collision: occurs between nucleons Rearrange whole nucleon-> large flucturation EOS, symmetry energy Motion of Equation

also play very important roles on the final observables as well as on EOS and in-medium XS! Cluster recognition methods in the QMD and BUU models: 1.MST, Aichelin, et.al., PR202(1991) 2.ECRA, C. O. Dorso and J. Randrup, Phys. Lett. B 301, 328 (1993). 3.SACA, R. K. Puri and J. Aichelin, J. Comput. Phys. 162, 245 (2000). 4.MSTB, P. B. Gossiaux, R. K. Puri, C. Hartnack, and J. Aichelin, Nucl. Phys. A 619, 379 (1997). 5. Cluster Correlation, Danielewicz et al., NPA533 (1991) 712, A.Ono, Coalescence model, LWChen, et.al., NPA 2004 Cluster recognition methods

Problems in current QMD models simualtions: 1 Z=1 largely overestimated, Z=2, underestimated, A. Ono K. Zbiri, A Le Fever, J. Aichelin, et.al, PRC75, 2007

2, Enhancements of the productions of neutron-rich isotopes observed in isoscaling, Y 2 / Y 1 Not well predicted by the transport models TXLiu, et.al., Phys.Rev.C 69, (2004) The predicted final isotope distributions are narrower than the experimental data, ……

3, Strong enhancement of heavy fragments in neutron-rich reaction system, 124Sn+64Ni 112Sn+58Ni P.Rustto, et.al., PRC81 The result shows that the dynamical process is about twice as probable in the neutron-rich system as in the neutron-poor one. This unexpected and significant difference …. ~ 2 times

4, Predict more transparency than that observed experimentally in central collisions at intermediate energy Insufficient production of fragments in the mid-rapidity region R.Nebauer, J.Aichelin, NPA658(1999)

All the problems are not fixed by only changing the EOS or in-medium XS in previous studies! It naturally require an improvements on the cluster recognition methods in the transport models !

R nn 0= R np 0= R pp 0= R 0 ∼ 3.5 fm In Regular MST, nucleons with relative distance of coordinate and momentum of |r i − r j |<R 0 and |p i − p j |<P 0 belong to a fragment. roughly be in the range of nucleon-nucleon interaction, and is determined by fitting the global experimental data, such as the IMF multiplicities. However, previous algorithms do not address the lack of isospin dependence in cluster recognition, which is the main focus of this work. Failed in details, such as problem 2) and 3)

Isospin dependent MST Rnn0= Rnp0~6.0 fm Rpp0~3.0fm Physical point of view: 1.properties of neutron-rich nuclei, such as neutron skin or neutron halo effect 2. long-range repulsive Coulomb force between protons in the cluster 3. hints from neutron-rich heavy ion collisions 11Be Isospin dependent cluster recognition methods (iso-MST)

Effect of iso-MST on observables 112,124Sn+112,124Sn, b=2fm, E_beam=50AMeV Reaction systems: Transport models: ImQMD05

Improved Quantum Molecular Dynamics model (ImQMD05)  the mean fields acting on nucleon wavepackets are derived from Skyrme potential energy density functional potential energy density functional: EOS H=T+U+U_coul Surface symmetry energy term Detail of code: Zhang, et alPR C71 (05) , PR C74 (06) , PRC75,034615(07)., PL B664 (08) 145, PRC85(2012)024602

 Isospin dependent nucleon-nucleon cross sections are adopted, the medium corrections are Cugnon, et al., Nucl.Instr.Meth.Phys. B111, 215(1996) h depend on the beam energy Well reproduce the data of charge distribution, direct flow, elliptical flow and stopping power (30-400AMeV)

Effect of iso-MST on observables YXZhang, Zhuxia Li, Chengshuang Zhou, MBTsang, PRC85,051602(2012)(R) 1, Charge distribution 1, obviously reduce the yield of Z=1 part. 2, enhance the yield of fragments with Z>=2. 3, strongly enhance the yield of heavy fragments. (Z>=12) Sn+Sn, Ebeam=50AMeV

Rapidity distribution for n,p 2, n, p, t, He3 production 1, reduce the yield of both neutron and protons, 2, enhancement of the n/p, t/He3 ratios appears at mid-rapidity and lower kinetic energy

n/p, DR(n/p), t/He3, DR(t/He3) 3, enhancement of the DR(n/p), DR(t/He3) ratios appears at mid- rapidity and lower kinetic energy Zhang, et.al., PLB2008

3,isotope distribution and isoscaling isoscaling YXZhang, Zhuxia Li, Chengshuang Zhou, MBTsang, PRC85,051602(2012)(R) 1, enhance the production of the neutron-rich isotope, especially for neutron-rich reaction system 2, predict larger values of isoscaling parameter, alpha

4, Effect of iso-MST on equilibrium MST: Vartl=0.58 Iso-MST: Vartl=0.62 YXZhang, Zhuxia Li, Chengshuang Zhou, MBTsang, PRC85,051602(2012)(R) the equilibrium or stopping power of the system also depends on the detailed description of cluster formation implemented in the transport models as well as on the mean field and the in-medium NN cross section.

Conclusion 1.we introduce a phenomenological isospin dependence in the description of cluster formation in transport models by adopting different R0 values for pp, nn, and np, Rpp0= 3 fm and Rnn0= Rnp0= 6 fm. 2.The isospin-dependent minimum spanning tree method show suppression of Z = 1 particles and enhancement of fragments, especially for heavier fragments with Z >=12. 3.Furthermore, we find enhanced production of neutron-rich isotopes at mid- rapidity. Consequently, isospin-sensitive observables, such as the double ratios, DR(t/3He), and isoscaling parameter α increase to larger values. 4.The widths of the longitudinal and transverse rapidity distributions of Z = 1–6 particles also change, the degree of equilibrium become higher. 5.The isospin dependence of the cluster recognition can be easily implemented and should be included in nuclear transport models.

Thanks