Dilepton measurements with CERES

TL;DR

This study presents dilepton measurements in high-energy Pb-Au collisions, revealing spectral broadening of the rho meson, excluding mass dropping scenarios, and providing new insights into phi meson decay channels with implications for understanding hot dense nuclear matter.

Contribution

First simultaneous measurement of phi meson in both dilepton and hadronic channels in high-energy heavy-ion collisions, confirming spectral broadening of the rho meson.

Findings

Observed enhancement in dilepton mass spectrum consistent with rho broadening

Ruled out phi yield enhancement factor greater than 1.6 in leptonic channel

Results agree with NA49 measurements and exclude dropping mass scenario

Abstract

We report on dilepton measurements for central Pb on Au collisions at the top CERN SPS energy with the upgraded CERES experiment. The dilepton mass spectrum of 2000 data with improved mass resolution shows an enhancement over the expectation from hadron decays that is well described by a model including a strong broadening of the $\rho$ spectral function. The measured excess yield excludes the dropping mass scenario. We also report on the $\phi$ meson measured simultaneously both in the $K^+K^-$ and in the dilepton decay channel for the first time in high energy heavy-ion collisions. An excellent agreement is found between the rapidity densities and the shape of the measured tranverse momentum spectrum. The data rule out a possible enhancement of the $\phi$ yield in the leptonic over hadronic channel by a factor larger than 1.6 at 95% CL. CERES results are in agreement with NA49 results.