A lattice calculation of thermal dilepton rates

F. Karsch,S. Stickan,P. Petreczky,E. Laermann,I. Wetzorke

doi:10.1016/s0370-2693(02)01326-6

Abstract

Using clover improved Wilson fermions we calculate thermal vector meson correlation functions above the deconfinement phase transition of quenched QCD. At temperatures 1.5 Tc and 3Tc they are found to differ by less than 15% from that of a freely propagating quark anti-quark pair. This puts severe constraints on the dilepton production rate and in particular rules out a strong divergence of the dilepton rate at low energies. The vector spectral function, which has been reconstructed using the Maximum Entropy Method, yields an enhancement of the dilepton rate over the Born rate of at most a factor two in the energy interval 4 < E/T < 8 and suggests that the spectrum is cut-off at low energies by a thermal mass threshold of about (2-3)T.

Highlights

The dilepton spectrum is one of the key observables in the study of thermal properties of the hot and dense medium created in heavy ion collisions [1, 2, 3]
Perturbative 2-loop [5] calculations as well as calculations based on hard thermal loop (HTL) resummed perturbation theory [6] lead to an enhancement of the spectrum at low energies, which dominates over the suppression arising from massive quasi-particle poles [1, 6] or non-perturbative gluon condensates [7]
The thermal dilepton rate describing the production of lepton pairs with energy ω and total momentum p is related to the Euclidean correlation function of the vector current, JVμ(τ, x) = ψ(τ, x)γμψ(τ, x), which can be calculated numerically in the framework of lattice regularized QCD

Summary

Introduction

The dilepton spectrum is one of the key observables in the study of thermal properties of the hot and dense medium created in heavy ion collisions [1, 2, 3]. The thermal dilepton rate describing the production of lepton pairs with energy ω and total momentum p is related to the Euclidean correlation function of the vector current, JVμ(τ, x) = ψ(τ, x)γμψ(τ, x), which can be calculated numerically in the framework of lattice regularized QCD. This relation is established through the vector spectral function, σV (ω, p, T ), which directly gives the differential dilepton rate in two-flavor QCD, dW dωd3p.

Thermal correlation functions

Reconstructed spectral functions

Findings

Conclusions