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Dielectron measurements by PHENIX using the HBD
Presented by Dr. Ermias ATOMSSA on 15 Aug 2012 from 08:50 to 09:10
Type: Oral Presentation
Track: Electroweak probes
Measurements of lepton pair spectra are a crucial tool to map out the evolution of the hot dense matter created in ultra-relativistic heavy ion collisions. At low pair mass, direct photons and low mass vector mesons are the main center of interest. Interpretation of lepton pair production rates in excess of expectations from hadronic decays observed by PHENIX and how the data constrains theoretical models on thermalization and chiral symmetry restoration is a hotly debated topic. At intermediate and high mass, the di-electron spectrum has been used by PHENIX to measure cross sections of open charm and open bottom, as well as Quarkonium suppression with implications for color screening and recombination. Due to the small signal to background ratio, measurement of the dielectron spectrum, especially at low mass, is very challenging. In PHENIX, the background results mainly from random combinations of electron positron pairs from uncorrelated sources, mostly $\pi^0$ Dalitz decays and photon conversions. The Hadron Blind Detector (HBD) was developed to address this issue. The HBD accomplishes this by tagging and rejecting tracks from conversions and $\pi^0$ Dalitz decays. It was successfully operated in RHIC run years 2009 to 2010, where Au+Au and reference p+p data sets were taken. We will present the dielectron results from the analysis of these data sets.