Dilepton production in HIC at RHIC Energy

1. I. Introduction II. Dileptons emission in Heavy Ion Collisions III. Semileptonic decays of charmed hadrons IV. Summary Dilepton production in HIC at RHIC Energy HaojieXu(徐浩洁) In collaboration with H. Chen, X. Dong, Q. Wang 2011-8-9 Hadron2011, WeiHai HaojieXu(徐浩洁)University of Science and Technology of China

2. Introduction Hadron2011, WeiHai α = 1/137 Electromagnetic Probes Why Dileptons? Suffer less interaction after their production Emitted in the whole volume of the fireball Provide crucial of the medium properties created by HIC HaojieXu(徐浩洁)University of Science and Technology of China

3. Introduction Hadron2011, WeiHai SPS NA60, PRL96, 162302 (2006) van Hees and Rapp , PRL97,102301(2006) Broadening spectral VS Dropping mass Baryon density VS Meson gas A strong broadening but essentially no shift in mass of rho meson spectrum is needed to explain this result Dileptons signal in HIC STAR,QM2011, Jie Zhao PHENIX PRC 81 (2010) 034911 HaojieXu(徐浩洁)University of Science and Technology of China

4. Dileptons emission in Heavy Ion Collisions Hadron2011, WeiHai 2+1 dimensional ideal hydrodynamic model Hydrodynamic Bjorken assumption [J. D. Bjorken, Phys. Rev. D 27, 140 (1983)] 5 equations, 6 unknown functions Equation of states [https://wiki.bnl.gov/hhic/index.php/Lattice_calculatons_of_Equation_of_State] HaojieXu(徐浩洁)University of Science and Technology of China

5. Dileptons emission in Heavy Ion Collisions Hadron2011, WeiHai Equation of states(EOS) [S. S. Adler et al. (PHENIX), Phys. Rev. C69, 034910 (2004)] Chemical equilbrium EOS Partial Chemical equilbrium EOS HaojieXu(徐浩洁)University of Science and Technology of China

6. Dileptons emission in Heavy Ion Collisions Hadron2011, WeiHai In the thermalized medium HG or QGP, the rate for the dilepton production per unit volume is given by Thermal Dilepton production q q e+ e- γ* For the partonic phase (Leading order) e+ e- p- p+ For the hadronic phase (Vector Dominance Model) ρ,ω,φ γ* HaojieXu(徐浩洁)University of Science and Technology of China

7. Dileptons emission in Heavy Ion Collisions Hadron2011, WeiHai 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)] Hadronic Many Body Theory and HaojieXu(徐浩洁)University of Science and Technology of China

8. Dileptons emission in Heavy Ion Collisions Hadron2011, WeiHai Non-zero chemical potential below Tchem • Including the in-meidumρ, ω and φ sources • Thermal dilepton are dominated by the in- medium ρ meson in LMR. • the ωcompontent 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) Thermal dilepton spectra No chemical freeze out process HaojieXu(徐浩洁)University of Science and Technology of China

9. Dileptons emission in Heavy Ion Collisions Hadron2011, WeiHai Effective parameter and elliptic flow J Deng, Q Wang, N Xu, P Zhuang Phys.Lett.,B701,581. Effective temperature Elliptic flow 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. HaojieXu(徐浩洁)University of Science and Technology of China

10. Dileptons emission in Heavy Ion Collisions Hadron2011, WeiHai 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)] Dilepton at thermal freeze out 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. HaojieXu(徐浩洁)University of Science and Technology of China

11. Dileptons emission in Heavy Ion Collisions Hadron2011, WeiHai • 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 Dilepton at thermal freeze out HaojieXu(徐浩洁)University of Science and Technology of China

12. Semileptonic decays of charmed hadrons Hadron2011, WeiHai PHENIX p +p collisions: The dilepton yield in the mass range from 1.1-2.5 PYTHIA generator 4.21e-8 PHENIX geometrical acceptance correction Extrapolated to zero dielectrons mass [A. Adare et al. (PHENIX), Phys. Lett. B670, 313 (2009)] Converted to Charmed cross section using known branching ratios of semileptonic decays PYTHIA 6.416 MSEL=4 PARP(91)=1 PARP(31)=3.5 MSTP(33)=1 MSTP(32)=4 Cross Section: 0.5mb HaojieXu(徐浩洁)University of Science and Technology of China

13. Semileptonic decays of charmed hadrons Hadron2011, WeiHai Nuclear Modification Factor B. I. Abelev et al. (STAR), Phys. Rev. Lett. 98, 192301 (2007) Significant impact in accessing medium physics in both IMR and LMR ɑ =1.22871,b = -1.51186 HaojieXu(徐浩洁)University of Science and Technology of China

14. Summary Hadron2011, WeiHai • Dilepton signals serve as clean probes to the hot and dense medium created in HIC • Dileptons production frompartonic 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. Summary HaojieXu(徐浩洁)University of Science and Technology of China

15. Hadron2011, WeiHai Thank you for your attention HaojieXu(徐浩洁)University of Science and Technology of China