Simulation study of the determination of temperature of QGP produced in the CBM experiment using thermal dileptons

Abstract

Nuclear matter is expected to exist in various phases and it’s phase transitions are mapped on a phase diagram that has been created using Quantum Chromodynamics which is the leading theory governing the interaction of quarks and gluons that make up the nuclear matter. One of the predicted phases of the nuclear matter is the quark gluon plasma in which the system evolves from a hadronic to partonic degrees of freedom. QGP is a hot thermal medium and Boltzmann statistics is reasonably applicable for all thermodynamic quantities. Hence, the invariant mass distribution of the thermally equilibrated matter will follow an exponential decay and the inverse of the slope of the exponential decay will provide the average temperature of the QGP. The most important condition that a possible probe must satisfy for the measurement of the temperature of the QGP is that they must have mean free path longer than the total size of the QGP medium. A large mean free path indicates a small interaction cross section as mean free path is inversely proportional to the interaction cross section. That means that hadrons are not good probes for measuring the temperature of QGP medium as they have significant interaction cross section as they interact through the strong force and hence their initial invariant mass distribution is modified before reaching any detector in heavy ion experiments. An ideal probe therefore should interact electromagnetically and not via strong force. Leptons and photons satisfy such criteria. Hence thermal dileptons produced from the annihilation of quark and antiquark in the QGP medium could be used to extract the temperature of the QGP.In this simulation work, we have taken 200k thermal Dimuons which is generated using the PLUTO event generator and analyzed various attributes of the Dimuon spectra. Next, We have analyzed the invariant mass distribution of these thermal dimuons without passing them through any detector setup. The CBM experiment is a future project that is designed to probe nuclear matter at high baryon density. So, Next we have passed these 200k dimuons through the entire CBM detector simulation setup and obtained the invariant mass distribution at the MUCH detector of the CBM experiment. Next we have created the background particles in a heavy ion collision using UrQMD event generator and passed both signal dimuons and background particles through the entire CBM setup and obtained the invariant mass distribution. Next we have only used background from UrQMD and passed them through the CBM setup and obtained the invariant mass distribution of the background particles at the MUCH detector. And finally we have subtracted the background from the entire realistic event created using both PLUTO and UrQMD and obtained the subtracted invariant mass spectra at the MUCH detector to get an estimate of temperature measurement capabilities of the CBM experiment.