Fragmentation mechanism andenhanced mid-rapidity emission for

neutron-rich LCPsYingxun Zhang( 张英逊 )中国原子能科学研究院

Colloborator: Chengshuang Zhou 周承双 (CIAE,GXNU), Jixian Chen 陈佶贤 (CIAE,GXNU), Ning Wang 王宁 (GXNU), Zhuxia Li 李祝霞 (CIAE)

第十四届全国核结构大会， 2012 年 4 月 14 日 浙江 湖州

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• Features of Intermediate energy HICs• Multifragmentation <15 intermediate mass fragments (IMFs)

1 ， Mechanism (two scenario)

Thermal process Dynamical process

1, Y(A) ~ A-t

2, E_kin independent of frag. size

1, Y(A) ~ A-t

2, E_kin independent of frag. size

3, bimodality3, bimodality (???)

Data support Dynamical process, but not finished!!

2， related to the Liquid-Gas Phase transition and asy-EoS

H.Jaqaman et al. PRC27(1983)2782

Heavy Ion Collisions large regions of r, T, d ,

measure the N/Z ratios of the emitted particles (n/p ratios, isospin diffusion, t/He3, N/Z ratios of IMFs, flow, pi-/pi+, ……)

compare with the prediction from the transport model, in which the different symmetry potential can be used.

the symmetry energy information can be extracted. Indirectly! (depends on models)

• Constraints on symmetry energy at subsaturatoin density

S0 ： the values of S(r) energy at r0

L ： the slope of S(r) energy at r0

Ksym: the curvature of S(r) energy at r0

LWChen, BALi, et al,(Skin, Ri)

Danielewicz, et.al

PDR(Pb), A.Klimkiewicz

Tsang,Zhang, et al.,PRL102(2009)

ImQMD (DR, Ri, R7) 50MeV/A, 35MeV/A,

Problem: Although overlap, but different in detail!

S0~31 ± 4 (MeV)L~60 ± 23 (MeV)

How to further understand the fragmentation mechanism and constrain the asy-EOS with HICs?

More DATA and observable !!

Z Kohley, PRC83,044601 (2011) Ni,Zn+Ni,Zn @ 35AMeV

QT

QP

LCP,

Significant difference !!

?? Statistical decay of QP ?? (Kohley ， 2011)

LCPbeam

Dynamical points: binary and ternary fragmentation dominate the reaction process

1, Why diff. ??2, Equilibrium??3, Symmetry energy??

Aims:

Analyze with ImQMD05

>1, enhanced mid-rapidity emission

pd

t

He3

He4 He6

• ImQMD05 (Improved QMD model developed at CIAE)

the mean fields acting on nucleon wavepackets are derived from Skyrme potential energy density functional

potential energy density functional:

EOSH=T+U+U_coul

Surface symmetry energy term

Detail of code: Zhang, et alPR C71 (05) 024604, PR C74 (06) 014602, PRC75,034615(07)., PL B664 (08) 145, PRC85(2012)024602

Isospin dependent nucleon-nucleon cross sections are adopted, the medium corrections are

freenp

mednp rr )/1( 0

freeppnn

medppnn ,0, )/1( rr

ddfreeppnnnp /,)(,

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), DR(n/p), Ri (at 50AMeV, 35AMeV), Ri(y), et.al.,

64Ni+64NI, 35AMeV, b=4fm

1, LCP mainly came from neck region

2, Yield of LCP depend on the density dependence of symmetry energy

3, Calculation with soft symmetry energy case predict larger yield for d, t,He3, He4, He6

4, t,He3, He4, He6, Dynamical emission. Better to probe the symmetry energy.

Properties of LCP emission g_i=0.5 or 2.0

Fragmentation mechanism

QT

QP

beam

1, binary, ternary fragmentation events are ~50%; and mult-fragmentation events are ~50%. more transparency.

2, binary, ternary fragmentation events; increase the yield at middle rapidity

3, 50% multi-fragmentation events; decrease the yield at proj/targ region

Zhang/Zhou/Chen, et.al, Submitted

Binary: M(Z>3)=2,Ternary: M(Z>3)=3,Multi: M(Z>3) >=4

Rapidity distribution for LCP

1, Calculations with stiff symmetry energy case well reproduce rapidity distribution for LCPs.

2, Width of rapidity distribution for LCP decrease with mass increasing

Zhang/Zhou/Chen, et.al, Submitted

3, Difference at backward. The decreased efficiency for detection of LCPs at backward region.

1, reproduce the R^mid_yield for 64Zn reaction system2, LCP data definitely rule out gamma_i<0.5, it improve the previous constraints g_i=[0.45,0.95].3, Underestimate the R^mid_yield for neutron-rich reaction system, should be further understand.

Zhang/Zhou/Chen, et.al, Submitted

Enhanced emission of LCPs and constraints on S(r)

Conclusion• Dynamical process is the main reason on well describing the

rapidity distribution for LCP. Our results suggest that reaction system is more transparency than that predicted by SMF approaches. Binary and ternary events, 50%; multi-fragmentation events: 50%.

• Binary and ternary fragmentation events tends to produce LCPs at middle rapidity, but multi-fragmentation events tends to produce at forward and backward region.

• The data of rapidity distribution for LCP and their ratio R^mid_yield definitely rule out the g_i=0.5, and it improve the previous constraints on symmetry energy g_i=(0.45,0.95).

Thanks for your attention!!