Transcript Slide 1
Dilepton Spectra from Open Charm Decays in Heavy-Ion Collisions Jia Shen Saint Mary’s College of California Dr. Ralf Rapp Cyclotron Institute at Texas A&M University Quark-Gluon Plasma and Heavy-Ion Collisions • A quark-gluon plasma is believed to exist during the first 10 microseconds after the universe is created from the Big Bang. • In the heavy-ion collision, a quark-gluon plasma is believed to exist for a very short time. rhic.physics.wayne.edu/~sean/collision_a.gif Particles produced in a Heavy-Ion Collision as seen by the STAR Detector http://en.wikipedia.org/wiki/Quark-gluon_plasma This project • How to detect the Quark-Gluon Plasma? • Idea: - Light quarks and gluons thermalize quickly and lose imprinted information - charm quarks are much heavier and do not easily thermalize => more sensitive probe of interactions in QGP - use di-electron decay spectra from charm quarks to probe Quark-Gluon Plasma Dilepton Spectra from PHENIX Collaboration (2007) • Dileptons from charm dominant in the M=1-3GeV mass region! Step-1: Angular Correlation between charm and anticharm quark • Back-to-Back (no interaction) • Random angle (thermalization) Step-2: Input charm transverse-momentum spectra dN/dPt =c Pt e^(-Et/Teff) • key parameter: Teff => slope of the charm spectrum Step-3: Procedure to calculate e+e- spectrum • Decay c-quark into positron in its rest system • boost positron into lab system • repeat for anticharm -> electron • Calculate invariant mass of electronpositron pair: M^2=(E_+E+)^2-(P_+P+)^2 • study dependence of invariant mass distribution on charm-quark input (slope and angular correlation) Result-1: Sensitivity to charm-anticharm relative angle • random angle gives softer spectrum than “back-to-back “(180deg) Result-2: Sensitivity to slope of charm spectrum Back-to-back Random Angle • softer charm pt-spectrum reflects itself in softer dilepton invariant-mass spectrum for both angular scenarios Conclusions • Sensitivity of dilepton spectra to singlecharm and charm-anticharm correlations confirmed and quantified • Experimental acceptance cuts implemented Future Directions: More realistic charm-anticharm input spectra: • Check against single electron spectra in p-p collisions • Use a model for charm-quark Interactions in the QGP (consistent with single-electron spectra in Au-Au Collisions) to obtain charm and dilepton spectra in Au-Au collisions