A Lattice Calculation of Thermal Dilepton Rates

TL;DR

This study uses lattice QCD with improved Wilson fermions to compute thermal vector meson correlators above the deconfinement transition, revealing constraints on dilepton production rates and indicating a spectral cutoff at low energies.

Contribution

It provides the first lattice calculation of thermal vector meson correlators above Tc using clover improved Wilson fermions, constraining dilepton production rates in quenched QCD.

Findings

Dilepton rates differ less than 15% from free quark-antiquark pairs at 1.5Tc and 3Tc.

No strong divergence of dilepton rate at low energies is observed.

Spectral function suggests a thermal mass threshold around 2-3 times T.

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.