Mass shift of charmonium states in $\bar p A$ collision

TL;DR

This paper investigates the downward mass shifts of low-lying charmonium states in antiproton-nucleus collisions using a transport model, proposing dilepton spectra as a probe for gluon condensate changes in nuclear matter.

Contribution

It introduces a study of in-medium charmonium mass shifts via a BUU transport model and suggests experimental detection through dilepton spectra at PANDA/FAIR.

Findings

Mass shifts are observable in dilepton spectra.

Dilepton decay channels can reveal gluon condensate modifications.

The study provides a method to measure in-medium effects at FAIR.

Abstract

The masses of the low lying charmonium states, namely, the $J/\Psi$, $\Psi(3686)$, and $\Psi(3770)$ are shifted downwards due to the second order Stark effect. In $\bar p + \text{Au}$ collisions at $6-10$ GeV we study their in\,-\,medium propagation. The time evolution of the spectral functions of these charmonium states is studied with a Boltzmann\,-\,Uehling\,-\,Uhlenbeck (BUU) type transport model. We show that their in\,-\,medium mass shift can be observed in the dilepton spectrum. Therefore, by observing the dileptonic decay channel of these low lying charmonium states, especially for $\Psi(3686)$, we can gain information about the magnitude of the gluon condensate in nuclear matter. This measurement could be performed at the upcoming PANDA experiment at FAIR.