Post on 18-Jan-2018
description
Mean Field Effect on J/psi Production in Heavy Ion Collisions
Baoyi Chen Physics Department Tsinghua University
Cooperators: Kai Zhou Yunpeng Liu Pengfei Zhuang (Professor)
Tsinghua University WeiHai July 23 2012
Outline
1. Motivation
2. Transport Model & Hydrodynamics
3. Mean Field Effect on J/psi Mass
4. Numerical Results and Analysics
5. Summery
Tsinghua University WeiHai July 23 2012
In order to understand the properties of the QGP, we consider interactions between Jpsi and the medium -----> collisions( inelastic , elastic)
Tsinghua University WeiHai July 23 2012
Motivation
Inelastic collisions: nuclear absorption, gloun dissociation and regeneration gJpsicc
Elastic collisions : mean field effect
In order to understand the properties of the QGP, we consider interactions between Jpsi and the medium -----> collisions( inelastic , elastic)
Tsinghua University WeiHai July 23 2012
Motivation
Inelastic collisions: nuclear absorption, gloun dissociation and regeneration gJpsicc
Elastic collisions : mean field effectInelastic collisions affect Jpsi yield, pt-spectrum, v2 largely, will elastic collisions change these too?
Tsinghua University WeiHai July 23 2012
Motivation
Mean field effect changes Jpsi mass
Jpsi mass shiftsecond-order stark effect
QCD sum rules
(PRD 79, 011501)
mass shift reduces shreshold of Jpsi regeneration and makes easy regeneration
-200MeV
Tsinghua University WeiHai July 23 2012
Motivation
( ) xm mF x TE T
The mean field force
Inhomogeneous medium makes space gradients of temperature (calculated by hydrodynamics) none-zero.
The attractive mean field force pulls Jpsi to the center of the fireball. and leads to a shift from high pt to low pt
(PRD 79, 01150)
Transport Model & Hydrodynamics
0
0
N
T
nuN
pguupT
)(
ffFfvf px
1. Evolution of Medium (Energy-momentum Conservation) 2+1 demensional boost invariant
Tsinghua University WeiHai July 23 2012
with
+ EOS
2. J/psi Transport Equation (J/psi are so heavy, hard to be thermalied ) suppression
regeneration
both inelsatic
elastic
Transport Model & Hydrodynamics
without elastic collisionsthe analytic solution is
Tsinghua University WeiHai July 23 2012
1222
0
0111 ),,(
111
),,(
00 ),,(),,(),,(xpdxpd
expdexpfxpf
Two competition mechanism: Initial Production V.S. Regeneration
with glouns 、 c quark are totally thermalized
width J/psi decay (gloun dissociaition) mass shift mean field effect
Mean Field Effect on Jpsi Mass
After considering the mass shift effect of Jpsi, we should also consider Jpsi width.In dynamically evolutive QGP
Tsinghua University WeiHai July 23 2012
1.J/psi width
Tsinghua University WeiHai July 23 2012
Mean Field Effect on J/psi Mass
Qualitatively estimate J/psi width
choose typical medium velocity 5.0QGPv
2 times
Jpsi width increases with T, duo to higher gloun density at higher T
Tsinghua University WeiHai July 23 2012
Mean Field Effect on J/psi Mass
Qualitatively estimate J/psi width
choose typical medium velocity 5.0QGPv
2 times
Jpsi width increases with T, duo to higher gloun density at higher T
(PRD 82, 054008)
Jpsi width
Jpsi width in our model(left) is qualitatively consistent with the right figure
Tsinghua University WeiHai July 23 2012
Mean Field Effect on J/psi Mass
fFffvf px
assuming small elastic cross section for charmonia at hadron level is still true at parton level. It can be solved perturbatively
( ) xm mF x TE T
with (PRD 79, 01150)
reduced threshold of J/psi makes regeneration more easily; the mean field force induced by inhomogeneous property of the medium pulls J/psi to the center of the fireball
Tsinghua University WeiHai July 23 2012
Mean Field Effect on J/psi Mass
fFffvf px
assuming small elastic cross section for charmoniaat hadron level is still true at parton level. It can be solved perturbatively
leaving mean field force first, but keeping the temperature dependence of the mass
The first-order solution
Tsinghua University WeiHai July 23 2012
Mean Field Effect on J/psi Mass
fFffvf px
assuming small elastic cross section for charmoniaat hadron level is still true at parton level. It can be solved perturbatively
leaving mean field force first, but keeping the temperature dependence of the mass
The first-order solution
the second-order solution
effective regeneration
Tsinghua University WeiHai July 23 2012
Mean Field Effect on J/psi Mass
fFffvf px
assuming small elastic cross section for charmoniaat hadron level is still true at parton level. It can be solved perturbatively
leaving mean field force first, but keeping the temperature dependence of the mass
The first-order solution
the second-order solution
effective regeneration
The iteration converges rapidly !
Tsinghua University WeiHai July 23 2012
Numerical Results and Analysics
1. Results below only expands to second-order ,
2. neglecting mass shift effect on excited states of J/psi due to
3. neglecting normal suppression and shadowing effect at RHIC
)2(f
ccd TT ),( '
%3||)1(
)1()2(
AA
AAAA
RRR
Tsinghua University WeiHai July 23 2012
Numerical Results and Analysics
26% !
reduced threshold of J/psi makes regeneration more easily + mean field force
mean field force kicks J/psi to low P_t region
affects regeneration only
Tsinghua University WeiHai July 23 2012
Numerical Results and Analysics
Due to experimental data including B-decay and shadowing effect;calculations here contains these factors too, which are absent in calculations at RHIC energies.
describing exprimental data well at low pt region!
( Black lines are provided by Kai Zhou)
Tsinghua University WeiHai July 23 2012
Numerical Results and Analysics
effective region of mean field on J/psi production is around pt=0.5GeV, which is smaller than averaged pt at RHIC and LHC: 2~3GeV
So, even the mean field effect affects J/psi pt-spectra significantly, it changes total yield slightly.
Tsinghua University WeiHai July 23 2012
Numerical Results and Analysics
1. Global yield of J/psi is slightly enhanced by the mean field effect.
Tsinghua University WeiHai July 23 2012
Numerical Results and Analysics
1. total J/psi production are less affected by the mean field effect.
the averaged pt square are suppressed.
2tp
Tsinghua University WeiHai July 23 2012
Summary
1. We developed a pertubative expansion to study the mean field effect on J/psi production.
2. Though the mean field changes global yield of J/psi slightly, it changes J/psi pt-spectrum significantly.
3. Initial J/psi production, which happens before the formation of QGP is not affected by the mean field effect; but regeneration which happens in the evolution of QGP, is largely enhancement at low transverse momentum.
Tsinghua University WeiHai July 23 2012
Thank you for your attention !
Tsinghua University WeiHai July 23 2012
Numerical Results and Analysics
Deviation exists between calculation and data at low pt, because shadowing effect, which will reduce regeneration, is not considered in this calculation.
Tsinghua University WeiHai July 23 2012
BUCKUP
Tsinghua University WeiHai July 23 2012