Can Dilepton Suppression Be Seen in Heavy Ion Experiments ?

Effects of finite temperature correction to the dilepton emission rate in ultrarelativistic heavy ion collisions have been looked into. It has been seen that although the ρ-peak in the dilepton spectra from the hadronic sector is suppressed at very high temperatures, almost no effect can be observed in the space time integrated count rate. [email protected] [email protected] [email protected] [email protected] 1 Very energetic collisions of heavy ions has become an intense field of study in recent times. The primary motivation for these investigations is to look for a putative new state of matter Quark Gluon Plasma (QGP). But even more generally, the formation of highly excited hadronic matter at high temperature/density is an interesting issue in its own right. Dileptons and photons emanating from the reaction volume constitute an ideal means for studying the property of such hot matter hadronic or QGP [1, 2, 3]. Recently Lee et.al. [4, 5] have calculated the finite temperature effects on the dilepton spectrum from the hadronic sector. They have used the results of QCD sum rule, at finite temperature, to arrive at the conclusion that the ρ-peak in the dilepton emission rate is suppressed in the hot hadronic matter. They have also claimed that this suppression may be observed in the experiments. Their result however refers to the static rate i.e. number of dileptons coming out from a particular space time point (characterised by a single temperature) of the hadronic part of the plasma. Unfortunately, there is no experimental way to measure this quantity. In experiments, one measures the total number of dileptons coming out of the plasma during the entire evolution time (i.e. starting from the time of formation upto freezeout). In this brief report we will look into the finite temperature effects on the experimental dilepton spectra using the same parameterisation as of Lee et.al. [4]. The most significant channel for the production of dileptons in the QGP sector is by annihilation of quark-antiquark pairs (qq̄ → μμ) and by decays and binary reactions in the hadronic sector [2, 3, 6, 7, 8, 9]. As the emission rates from only the hadronic sector are modified by the temperature dependence of the form factors, we will consider only this sector in this work, as in [4]. Also, we confine our attention to the pion channel alone so as to compare our results with those of ref. [4]. The elementary crosssection for pion annihilation (ππ → μμ), assuming vector dominance, is given by [2] σπ(M) = Fπ (M) [