Dilepton production in HIC at RHIC Energy

Dilepton production in HIC at RHIC Energy

Haojie Xu(徐浩洁 )In collaboration with H. Chen, X. Dong, Q. Wang

2011-8-9 Hadron2011, WeiHai

Haojie Xu(徐浩洁 ) University of Science and Technology of China

I. Introduction

II. Dileptons emission in Heavy Ion

Collisions

III. Semileptonic decays of charmed hadrons

IV. Summary

Electromagnetic Probes


Hadron2011, WeiHaiIntroduction

Suffer less interaction after their production

Emitted in the whole volume of the fireball

Provide crucial of the medium properties created by HIC

Why Dileptons?

α = 1/137

Dileptons signal in HIC


Hadron2011, WeiHaiIntroduction

SPS NA60, PRL96, 162302 (2006) van Hees and Rapp , PRL97,102301(2006) Broadening spectral VS Dropping mass Baryon density VS Meson gasA strong broadening but essentially no shift in mass of rho meson spectrum is needed to explain this result

STAR

,QM

2011

, Jie

Zha

o

PHEN

IX P

RC 8

1 (2

010)

03

4911

Hydrodynamic


Hadron2011, WeiHai

2+1 dimensional ideal hydrodynamic model

Equation of states

Bjorken assumption

[J. D. Bjorken, Phys. Rev. D 27, 140 (1983)]

5 equations, 6 unknown functions

[https://wiki.bnl.gov/hhic/index.php/Lattice_calculatons_of_Equation_of_State]

Dileptons emission in Heavy Ion Collisions

Equation of states(EOS)


Hadron2011, WeiHai

[S. S. Adler et al. (PHENIX), Phys. Rev. C69, 034910 (2004)]Chemical equilbrium EOS Partial Chemical equilbrium EOS


30

0

40 /0.4128

0dec

i

e GeV fmfm

T MeV

30

0

60 /0.4140

( )dec

i i

e GeV fmfm

T MeVT

For the hadronic phase(Vector Dominance Model)

Thermal Dilepton production


Hadron2011, WeiHaiDileptons emission in Heavy Ion Collisions

In the thermalized medium HG or QGP, the rate for the dilepton production per unit volume is given by

For the partonic phase(Leading order)

q

q

e+

e-

e+

e-

p -

p +

γ*

ρ,ω,φ γ*

Hadronic Many Body Theory



The in-medium vector meson self-energy is related to the forward two-body scattering amplitude of the surrounding thermal mesons(.ie.ρπ->a1)[R. Rapp, Phys. Rev. C63, 054907 (2001)]

and hR pp +

Thermal dilepton spectra


Hadron2011, WeiHai

• Including the in-meidum ρ, ω and φ sources

•Thermal dilepton are dominated by the in- medium

ρ meson in LMR.

•the ω compontent is submerged under the

broadening ρ spectra.

•The partonic phase dominated the dilepton yields

for their invariant mass M>1.1GeV.

•w/(w/o) chemical freezeout process(EOS

difference)

Non-zero chemical potential below Tchem

No chemical freeze out process


Effective parameter and elliptic flow



Effective temperature Elliptic flowJ Deng, Q Wang, N Xu, P ZhuangPhys.Lett.,B701,581.

Teff(slope parameter) in the intermediate mass region shows the collectivity developed in the partonic stage.

The decline near rho mass reveals a phase transition from partonic phase to hadronic phase.

Dilepton at thermal freeze out



The vector meson momentum spectra at thermal freezeout can be expressed by the extended Cooper-Frye formular[van Hees and R. Rapp, Nucl. Phys. A806, 339 (2008)]

The dilepton emission rate from the freezeout vector meson is given by

The imaginary parts of the and propagators can be given by the Breit-Wigner formula

Most of the ρ decay in the medium due to its short lifetime.

Dilepton at thermal freeze out



• The medium effects have been included in the

freeze out contribution, the broadening of ρ is

even more obvious

•Only a much lower peak from the in-medium φ

meson is invisible, indicating clear medium effects

•Substracting these sharp peaks from ω and φ the

broadened spectrum of the in-medium ρ meson

can be seen.

•The partonic contribution dominates over the

hadronic one when M>1.1GeV

PYTHIA generator


Hadron2011, WeiHaiSemileptonic decays of charmed hadrons

PYTHIA 6.416 MSEL=4PARP(91)=1 PARP(31)=3.5MSTP(33)=1 MSTP(32)=4

PHENIX p +p collisions: The dilepton yield in the mass range from 1.1-2.5

PHENIX geometrical acceptance correction

[A. Adare et al. (PHENIX), Phys. Lett. B670, 313 (2009)]

Extrapolated to zero dielectrons mass

Converted to Charmed cross section using known branching ratios of semileptonic decays

4.21e-8

Cross Section: 0.5mb

Nuclear Modification Factor


Hadron2011, WeiHaiSemileptonic decays of charmed hadrons

B. I. Abelev et al. (STAR), Phys. Rev. Lett. 98, 192301 (2007)

ɑ =1.22871,b = -1.51186

Significant impact in accessingmedium physics in both IMR and LMR

Summary


Hadron2011, WeiHaiSummary

•Dilepton signals serve as clean probes to the hot and dense medium

created in HIC

•Dileptons production from partonic phase, hadronic phase and

freeze out vector hadrons in heavy ion collision at RHIC energy are

investigated.

•The medium modification of vector mesons are employ in our

calculations.

•Charmed background is a significant impact in accessing medium

physics in both IMR and LMR.

Thank you for your attention


Hadron2011, WeiHai

Documents

Dilepton production in HIC at RHIC Energy