# Quark Matter 2017

Feb 5 – 11, 2017
Hyatt Regency Chicago
America/Chicago timezone

## Excess of $J/\psi$ yield at very low $p_{T}$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV measured with STAR experiment

Not scheduled
2h 30m
Hyatt Regency Chicago

#### Hyatt Regency Chicago

151 East Wacker Drive Chicago, Illinois, USA, 60601
Board: H09
Poster

### Speaker

Wangmei Zha (USTC/BNL)

### Description

Suppression of $J/\psi$ production in heavy-ion collisions due to color screening of quark and antiquark potential in the deconfined medium has been proposed as a signature of the QGP formation. Other mechanisms, such as the cold nuclear matter effects and charm quark recombination, can contribute to the observed modification of $J/\psi$ production in heavy-ion collisions. Recently, a significant excess of $J/\psi$ yield at very low $p_{T}$ ($<$ 0.3 GeV/c) was observed by the ALICE collaboration in peripheral Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV at forward-rapidity, which can not be explained by the above-mentioned effects. It has been hypothesized that such $J/\psi$'s are produced from the coherent photoproduction in Pb+Pb collisions at impact parameters smaller than twice the nuclear radius, which would be very challenging for the existing models developed to describe coherent photoproduction in ultra-peripheral collisions. Measurements of $J/\psi$ production at very low $p_{T}$ in different collision energies, collision systems, and collision geometries can shed new light on the origin of the excess.\

In this presentation we report the STAR measurements of $J/\psi$ production at very low $p_{T}$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV at mid-rapidity. Centrality dependence of $J/\psi$ production cross section and nuclear modification factors at very low $p_{T}$ will be presented.

Collaboration STAR Quarkonia

### Primary author

Wangmei Zha (USTC/BNL)