Dielectrons and Direct Virutal Photons at RHIC-STAR

Chi Yang,I Vitev,I Sarcevic,S Mioduszewski,C Ratti,M Schlegel,C Da Silva

doi:10.1051/epjconf/202023502002

Abstract

Electromagnetic probes are unique probes of the hot and dense medium cre- ated in relativistic heavy-ion collisions due to their minimal interactions with the partonic and hadronic medium. They can be produced at all stages of a collision, thus they provide unique ways to study the medium properties of the whole collision evolution. We present the dielectron invariant mass spectrum at √sNN = 27, 39, 39, and 62.4 GeV. Comparing to hadronic cocktail simulation, significant excesses of dielectron invariant mass spectrum at low mass are observed. The direct virtual photon invariant yields derived from the low-mass e+e− continuum in Au+Au collisions at √sNN = 200 GeV is presented and the excesses from thermal photons in low transverse momentum (pT) have been observed. Model calculations can simultaneously describe both dielectron low mass excesses and direct virtual photon low pT excesses.

Highlights

Electromagnetic probes such as dielectrons and direct virutal photons are unique probes in the study of the fundamental properties of the hot and dense medium created in ultra-relativistic heavy-ion collisions [1]
√trasNnsNp=ort2m00odGeelVca[n4,w5e]l.l describe published STAR The Relativistic Heavy dilepton mass spectraIon Collider (RHIC) Beam Energy measurements of the Scan (BES) program excess yield [6] provides a unique opportunity to systematically test these calculations as a function of the initial collisions energies
The back solid curves represent the hadronic cocktail without the vacuum ρ−meson which contribution is expected√to be strongly modified in the medium

Summary

Introduction

Electromagnetic probes such as dielectrons and direct virutal photons are unique probes in the study of the fundamental properties of the hot and dense medium created in ultra-relativistic heavy-ion collisions [1]. Both dielectrons and direct virtual photons are produced in the whole evolution of the system and escape with minimum interaction with the strongly interacting medium. They provide information about the various stages of the system during the evolution. √trasNnsNp=ort2m00odGeelVca[n4,w5e]l.l describe published STAR The RHIC Beam Energy measurements of the Scan (BES) program excess yield [6] provides a unique opportunity to systematically test these calculations as a function of the initial collisions energies

39 GeV 10

Dielectron Results from STAR BES Program

Summary