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