1. 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

2. Electromagnetic Probes Haojie Xu( 徐浩洁 ) University of Science and Technology of China 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

3. Dileptons signal in HIC Haojie Xu( 徐浩洁 ) University of Science and Technology of China Hadron2011, WeiHaiIntroduction 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 STAR,QM2011, Jie Zhao PHENIX PRC 81 (2010) 034911

4. Hydrodynamic Haojie Xu( 徐浩洁 ) University of Science and Technology of China 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_c alculatons_of_Equation_of_State] Dileptons emission in Heavy Ion Collisions

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

6. For the hadronic phase (Vector Dominance Model) Thermal Dilepton production Haojie Xu( 徐浩洁 ) University of Science and Technology of China 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) qqqq e+ee+e e+e-e+e-  γ*γ* ρ,ω,φρ,ω,φ γ*γ*

7. Hadronic Many Body Theory Haojie Xu( 徐浩洁 ) University of Science and Technology of China Hadron2011, WeiHaiDileptons emission in Heavy Ion Collisions 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

8. Thermal dilepton spectra Haojie Xu( 徐浩洁 ) University of Science and Technology of China 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 Dileptons emission in Heavy Ion Collisions

9. Effective parameter and elliptic flow Haojie Xu( 徐浩洁 ) University of Science and Technology of China Hadron2011, WeiHaiDileptons emission in Heavy Ion Collisions Effective temperatureElliptic flow J Deng, Q Wang, N Xu, P Zhuang Phys.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.

10. Dilepton at thermal freeze out Haojie Xu( 徐浩洁 ) University of Science and Technology of China Hadron2011, WeiHaiDileptons emission in Heavy Ion Collisions 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.

11. Dilepton at thermal freeze out Haojie Xu( 徐浩洁 ) University of Science and Technology of China Hadron2011, WeiHaiDileptons emission in Heavy Ion Collisions 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

12. PYTHIA generator Haojie Xu( 徐浩洁 ) University of Science and Technology of China Hadron2011, WeiHaiSemileptonic decays of charmed hadrons PYTHIA 6.416 MSEL=4 PARP(91)=1 PARP(31)=3.5 MSTP(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

13. Nuclear Modification Factor Haojie Xu( 徐浩洁 ) University of Science and Technology of China 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 accessing medium physics in both IMR and LMR

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

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