Transcript HBT puzzle, a puzzle approaching a new world

Isospin effects
in neutron and proton flows
by Qingfeng Li @ FIAS,
(AvH fellow, Host: Horst Stöcker)
Thanks: Marcus Bleicher, Sven Soff, Zhuxia Li
Outline
Our purpose -and- many observables
The isospin effect on nucleons
The flows and the differential flows
The importance of precise
measurement on neutrons
 Good future, laborious work.
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08.07.2015
Qingfeng Li for GSI 2006
The purpose
The uncertainty in symmetry term,
especially in the density dependence
of symmetry energy
Obviously, it is closely related to
Astrophysics and neutron-rich
structure and reaction physics (with
large neutron access).
08.07.2015
Qingfeng Li for GSI 2006
Normal Observables
 Particle species: emitted neutrons and
protons, resonances (), Sigmas, light and
heavy fragments, mesons (pions, kaons,etc)
 Single-particle observables: excitation
function of particle multiplicities,
(transverse)momentum-/energy-/rapiditydistribution, momentum quadrupole (Qzz),
radial-/direct-/elliptic- flows,…
 Two-particle correlations: HBT (coordinatemomentum corr.), angular correlation, …
08.07.2015
Qingfeng Li for GSI 2006
“New” observables
 Single-/double- negatively/positively
charged particle (nucleons, pions, kaons,
etc) ratios from Ru/Zr+Zr/Ru (mass
symmetric but isospin asymmetric)
reactions (FOPI), or from Sn-isotope
reactions (Michigan).
 Vartl, (FOPI), or Rt/l=dN/dYx/dN/dYz
 flow difference/differential flow (Fn-p,v2pm)
of negatively-positively charged particles
08.07.2015
Qingfeng Li for GSI 2006
To study the isospin effects
 Nucleons are still one of the most sensitive
candidates, which should be preferentially
considered
 Now, experimentally, it is able to measure
neutrons with much more higher precision.
Hmmm, right? 
 Other particles? Of course important, but
raise more uncertainties. As the first step, I
suggest to measure neutrons and protons.
08.07.2015
Qingfeng Li for GSI 2006
Many efforts
 At quite low densities
(/0=0.01-0.05)
Nucl-ex/0602023
 At subnormal densities
(compared with BUU):
 At supranormal
densities:
08.07.2015
 ~ 0.3
Esym  31.6( / 0 )1.05
Esym  31.6(  / 0 )
?
Qingfeng Li for GSI 2006
+
0.69
 free
+

*
Symmetry energy effects on
nucleons
n/p
48
52
Ca+ Ca, Eb100A MeV, <11%
2.3
2.2
2.1
2.0
1.9
1.8
1.7
45

=0.3
N
30
15
1.5

dN/dt

1.0
0.5
3
2
S-II
umax
S-I
1
u|r|<2 fm
2
1
0
0
2005-PhysRevC_72_034613
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Qingfeng Li for GSI 2006
30
60
90
t (fm/c)
120
150
Flows and
differential transverse flow
 To explore the medium at early stage
when the central density is high.
 The differential transverse flow suggested
by Bao-An:
pn  p p
If
x
x

 The multiplicities of nucleons should be
firstly nicely reproduced by model.
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Qingfeng Li for GSI 2006
Pion elliptic flow difference
At pt~0.2-0.5 GeV/c,
v_2^pm reflects explicitly
the density dependence of
sym.ene. at u>1.
IE @ supranormal densities!


Eb=800A GeV
b=7-9 fm
2006-JPG_32_151
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ZPA352,171(1995): by Bass, Hartnack, etal
(neutron squeeze-out)
PLB 562, 215(2003): by Greco, Baran, etal
(neutron-proton v2 difference)
Qingfeng Li for GSI 2006
Nucleon double ratio from Ru/Zr+Zr/Ru

Advantage: to show simultaneously
the dependence on symmetry energy
and the degree of isospin
equilibrium
The symmetry energy effect
On FD is enhanced when
Eb~400A MeV, b/b0~0.5
Others: Bao-An Li et al.:

(using Sn isotoptes)
Double N/P ratio:
Phys.Lett.B634:378-382,2006
Double pi-/pi+ ratios:
Phys.Rev.C73:034603,2006
Double N-P differential flow :
nucl-th/0606003

2006-PhysRevC_73_051601(R)
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Qingfeng Li for GSI 2006
Isopin dependent medium effects
on N-N elastic cross sections
MF and C come from the same Lagrangian.
They are both isospin dependent
2006-JPG_32_407
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Qingfeng Li for GSI 2006
At Eb~400A MeV
 When comparing with those at Eb< 100A
MeV:
more IMF, excitataion energies of IMF are
also large. They will decay
(statistically/promptly/sequentially?)
afterwards.
The isospin-asymmetric and high-excited
IMF play important role in final results.
 The treatment of isospin effects on the late
stage (in some after-burner program)
should be paid more attention. (When to
terminate the transport computation?)
08.07.2015
Qingfeng Li for GSI 2006
My suggestions
 Experimentally:
1. Multi-systems and Multi-observables.
such as: Zr+Ru/Ru+Zr and Sn132+Sn124/Sn112+Sn112
For nucleons: multiplicities, (hence, the transverse
momdnetum of n/p ratio), transverse and elliptic flows
(hence, the flow diff./diff.flow) are required to measure.
2. Higher precision. (at least, errors should be well <10%)
 Theoretically:
1. A completely self-consistent and relativisitic transport
model (at least, in the N-- system)+ a good afterburner program are indispensable, since the isospin
effects are small.
08.07.2015
Qingfeng Li for GSI 2006
Outlook
 Not easy, (effect is small, many
uncertainties in theory/models)
 but of great value. (neutrons, neutron
flows, flow differentials)
 Optimistic
08.07.2015
Qingfeng Li for GSI 2006