Di-lepton Production Measurements In P+P And Au+Au Collisions At RHIC

The Relativistic Heavy Ion Collider at Brookhaven National laboratory （BNL） wasbuilt to create strongly interacting matter in a laboratory setting to reach extreme con-dition of the early universe where a few tens of microseconds following the Big Bang.A strongly coupled Quark Gluon Plasma （sQGP）, is believed that has been created inheavy ion collisions at RHIC. The study of unobserved behaviors and properties of QGPbecomes one of the most interesting physics topics. Electro-magnetic probes, i.e. leptonpairs, can penetrate the hot dense matter created in heavy ion collisions with minimalfinal state interaction, bring the whole evolution information of the heavy ion collisions.They are considered as the crucial probes for the sQGP.The analysis is carried out at the Solenoidal Tracker at RHIC （STAR） experiment.The newly installed Time-of-Flight （TOF） enables the di-electron study at STAR. Inthis thesis, we present measurement of di-electron pairs production from p+p collisionsat√s = 200 GeV in year 2009 RHIC run and Au+Au collisions at√sNN=200 GeVduring year 2010 RHIC run with the STAR detector. The di-electron mass spectrumin p+p is consistent with the simulations of di-electrons from light meson decays andheavy -avor decays （charmonium and open charm correlation）. The extractedωâ†'e⁺e^-invariant yields in p+p are consistent with the previous publication. The invariant yieldsofωin Au+Au are measured and consistent with the Tsallis-Blast-Wave model fit. Theextracted dN/dy ofφand J/ψin p+p, through their di-electron channels are consistentwith the previous measurements ofφâ†'K⁺K^- and J/ψâ†'e⁺e^-. The new upper limitof the branching ratio of theηâ†'e⁺e^- is 4.3×10^-6,a factor of six below the worldlimit. The charm cross section extracted from the simultaneously fit of di-electron massspectrum, previous published D, and non-photonic electron spectra is 0.96±0.10（stat.）±0.27（syst.） mb.The di-electron continuum measured in p+p provides a reference for the study inAu+Au. We observed an enhanced factor of 1.53±0.07（stat.）±0.41（syst.） of di-electron yields in Low Mass Region （LMR） in minimum bias Au+Au collisions compared to thecocktail simulation. Comparison between STAR data and PHENIX results will be dis-cussed.