Mean Field Effect on J/psi Production in Heavy Ion Collisions Baoyi Chen Physics Department Tsinghua...

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


In order to understand the properties of the QGP, we consider interactions between Jpsi and the medium -----> collisions( inelastic , elastic)


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)


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?


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


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


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


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


1.J/psi width


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



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



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



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



fFffvf px




the second-order solution

effective regeneration



fFffvf px




the second-order solution

effective regeneration

The iteration converges rapidly !


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



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



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)



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.



1. Global yield of J/psi is slightly enhanced by the mean field effect.



1. total J/psi production are less affected by the mean field effect.

the averaged pt square are suppressed.

2tp


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.


Thank you for your attention !



Deviation exists between calculation and data at low pt, because shadowing effect, which will reduce regeneration, is not considered in this calculation.


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Mean Field Effect on J/psi Production in Heavy Ion Collisions Baoyi Chen Physics Department Tsinghua...

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