Thermal Dilepton Rates and Meson Spectral Functions from Lattice QCD

TL;DR

This paper computes meson spectral functions in lattice QCD across the deconfinement transition, revealing modifications in dilepton production rates at high temperatures using advanced reconstruction techniques.

Contribution

It introduces a method to extract spectral functions from lattice correlators without assuming spectral shape, applied to study mesons above the QCD transition.

Findings

Enhanced dilepton rate at 1.5 and 3 T_c in specific energy ranges.

Spectral functions deviate from free quark behavior above T_c.

Sharp drop in spectral function below 2-3 T at certain energies.

Abstract

Pseudo-scalar and vector meson correlation functions were calculated at temperatures below and above the deconfinement transition using ${\cal O}(a)$ improved Wilson fermions in quenched lattice QCD. The spectral functions were reconstructed from the correlator given only at discrete points in Euclidean time by means of the Maximum Entropy Method without a priori assumptions on the spectral shape. The deviation of the spectral functions from the one of a freely propagating quark anti-quark pair is examined above the critical temperature. At 1.5 and 3 $T_c$ the vector spectral function yields an enhancement of the dilepton rate over the Born rate in the energy interval $4 < \omega/T < 8$ and a sharp drop at energies below 2-3 T.