# Hard Probe 2016

22-27 September 2016
East Lake International Conference Center
Asia/Chongqing timezone
<a href="http://hp2016.ccnu.edu.cn">http://hp2016.ccnu.edu.cn</a>

## 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

25 Sep 2016, 11:40
20m
Jing-Zhou Hall (East Lake International Conference Center)

### Jing-Zhou Hall

#### East Lake International Conference Center

Donghu Road 142, Wuchang District, Wuhan, Hubei, China

### 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 centralities 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. Physics perspectives with Zr+Zr and Ru+Ru collisions scheduled for RHIC 2018 run will be discussed.

Presentation type Oral

### Primary author

Wangmei Zha (USTC/BNL)