Jia ShenSaint Mary’s College of California
Dr. Ralf RappCyclotron Institute at Texas A&M University
Dilepton Spectra from Open Charm Dilepton Spectra from Open Charm Decays in Heavy-Ion CollisionsDecays in Heavy-Ion Collisions
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
http://en.wikipedia.org/wiki/Quark-gluon_plasma
Particles produced in a Heavy-Ion Collisionas seen by the STAR Detector
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 electron-
positron 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 single-charm 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