Speaker
Description
In ultra-peripheral collisions (UPCs), coherent J/$\psi$ photoproduction has been recognized as one of the most sensitive probes of the nuclear gluon distribution. Recently, STAR published differential measurements of photoproduced J/$\psi$ in Au+Au UPCs. These results provide important constraints on gluon distribution functions and sub-nucleonic shape fluctuations in heavy nuclei. Compared to Au+Au collisions, the isobaric collisions ($^{96}_{44}Ru$ + $^{96}_{44}Ru$ and $^{96}_{40}Zr$ + $^{96}_{40}Zr$) feature much smaller nuclear sizes and different gluon distributions. Measurements in these collision systems therefore offer an excellent opportunity to investigate the system-size dependence of the nuclear gluon structure.
In this talk, we present the first measurement of coherent J/$\psi$ photoproduction in isobaric ($Ru+Ru$/$Zr+Zr$) UPCs at $\sqrt{\mathrm{s_{NN}}}$ = 200 GeV with the STAR experiment. The differential cross sections are reported as functions of rapidity and forward neutron multiplicity. Photon-flux-corrected cross sections at a photon–nucleon center-of-mass energy of 25 GeV are compared with Au+Au results and shown as a function of the nuclear mass number. The implications of these results are discussed in the context of theoretical model calculations based on the Impulse Approximation as well as models that account for nuclear shadowing and gluon saturation effects.
| 请选择分会 | 高能重离子物理 |
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