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第十四届全国核结构大会, 2012 年 4 月 14 日 浙江 湖州. Fragmentation mechanism and enhanced mid-rapidity emission for neutron-rich LCPs. Yingxun 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).

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fragmentation mechanism and enhanced mid rapidity emission for neutron rich lcps

第十四届全国核结构大会, 2012年4月14日 浙江 湖州

Fragmentation mechanism andenhanced mid-rapidity emission for neutron-rich LCPs

Yingxun 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)

slide2

Features of Intermediate energy HICs

  • Multifragmentation
  • <15 intermediate mass fragments (IMFs)

1, Mechanism (two scenario)

2

Thermal process

Dynamical process

1, Y(A) ~ A-t

1, Y(A) ~ A-t

2, E_kin independent of frag. size

2, E_kin independent of frag. size

3, bimodality (???)

3, bimodality

Data support Dynamical process, but not finished!!

slide3

H.Jaqaman et al. PRC27(1983)2782

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

slide4

Constraints on symmetry energy at subsaturatoin density

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

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

Danielewicz, et.al

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

S0~31 ± 4 (MeV)

L~60 ± 23 (MeV)

PDR(Pb), A.Klimkiewicz

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

Problem: Although overlap, but different in detail!

slide5

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

LCP

beam

LCP,

QP

Significant difference !!

Dynamical points:

binary and ternary fragmentation dominate the reaction process

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

slide6

t

He4

He6

>1, enhanced mid-rapidity emission

d

He3

p

Aims:

1, Why diff. ??

2, Equilibrium??

3, Symmetry energy??

Analyze with ImQMD05

imqmd05 improved qmd model developed at ciae
ImQMD05 (Improved QMD model developed at CIAE)

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

  • the mean fields acting on nucleon wavepackets are derived fromSkyrme potential energy density functional

H=T+U+U_coul

EOS

potential energy density functional:

Surface symmetry energy term

slide8

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

slide9

Properties of LCP emission

g_i=0.5 or 2.0

1, LCP mainly came from neck region

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

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

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.

fragmentation mechanism
Fragmentation mechanism

Zhang/Zhou/Chen, et.al, Submitted

QT

beam

QP

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-fragmentationevents; decrease the yield at proj/targ region

Binary: M(Z>3)=2,

Ternary: M(Z>3)=3,

Multi: M(Z>3) >=4

rapidity distribution for lcp
Rapidity distribution for LCP

Zhang/Zhou/Chen, et.al, Submitted

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

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

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

slide12

Enhanced emission of LCPs and constraints on S(r)

Zhang/Zhou/Chen, et.al, Submitted

1, reproduce the R^mid_yield for 64Zn reaction system

2, LCP data definitely rule outgamma_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.

conclusion
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).