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The 56th HENPIC Seminar: Recent $J/\\psi$ measurments from STAR experiment

Thursday, Jan. 5th, 2017, 10:30 AM (Beijing time)  seminar

The 56th HENPIC Seminar: Recent $J/\\psi$ measurments from STAR experiment

Speaker:  Wangmei Zha,USTC

Date:Thursday, Jan. 5th, 2017, 10:30 AM (Beijing time)



The Relativistic Heavy Ion Collider (RHIC) is built to search for the quark-gluon plasma (QGP) and to study its properties in laboratory through high energy heavy-ion collisions. $J/\\psi$ suppression in heavy-ion collisions due to color screening of quark and antiquark potential in the deconfined medium has been proposed as a signature of QGP formation. Other mechanisms, such as the cold nuclear matter effect and charm quark recombination, are likely to contribute to the observed modification of $J/\\psi$ production in heavy-ion collisions.  Interpretation of $J/\\psi$ modification requires good understandings of its production mechanism in elementary collisions. Despite decades of efforts, the quarkonium production mechanism still remains an open question to date. New measurements of $J/\\psi$ in p+p collisions are necessary to constrain different models. On the other hand, measurements of $J/\\psi$ invariant yields in different collision energies, collision system, and centralities can shed new light on understanding the interplay of these mechanisms for $J/\\psi$ production and medium properties.

Recently, an significant excess of $J/\\psi$ yield at very low $p_{T}$ ($<$ 0.3 GeV/c) in peripheral hadronic Pb+Pb collisions at $\\sqrt{s_{NN}}$= 2.76 TeV at forward-rapidity has been observed by ALICE collaboration, which can not be explained within the scenarios mentioned above. The excess observed may originate from the coherent photoproduction of $J/\\psi$, which would be very challenging for the existing coherent photoproduction models. Measurements and calculations 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 on the measurements of $J/\\psi$ invariant yields as a function of transverse momentum at midrapidity ($|y| < 1.0$) in p+p collisions at $\\sqrt{s}  =$ 500 GeV and Au$+$Au collisions at $\\sqrt{s_{NN}}  =$ 39 GeV, 62.4 GeV and 200 GeV from STAR. Measurements of $J/\\psi$ production at very low $p_{T}$ in hadronic Au+Au collisions at $\\sqrt{s_{NN}}$ = 200 GeV and U+U collisions at $\\sqrt{s_{NN}}$ = 193 GeV at mid-rapidity will also be presented. The calculations of $J/\\psi$ coherent photon-production for different scenarios will be discussed and compared to data.

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