ausblenden:
Schlagwörter:
STAR
Zusammenfassung:
We report on the first measurements of J/\psi production at very low transverse momentum (p_{T} < 0.2 GeV/c) in hadronic Au+Au collisions at \sqrt{s_{\rm{NN}}} = 200 GeV and U+U collisions at \sqrt{s_{\rm{NN}}} = 193 GeV. Remarkably, the inferred nuclear modification factor of J/\psi at mid-rapidity in Au+Au (U+U) collisions reaches about 24 (52) for p_{T} < 0.05 GeV/c in the 60-80$\% collision centrality class. This noteworthy enhancement cannot be explained by hadronic production accompanied by cold and hot medium effects. In addition, the dN/dt distribution of J/\psi for the very low p_{T} range is presented for the first time. The distribution is consistent with that expected from the Au nucleus and shows a hint of interference. Comparison of the measurements to theoretical calculations of coherent production shows that the excess yield can be described reasonably well and reveals a partial disruption of coherent production in semi-central collisions, perhaps due to the violent hadronic interactions. Incorporating theoretical calculations, the results strongly suggest that the dramatic enhancement of J/$\psi$ yield observed at extremely low p_{T} originates from coherent photon-nucleus interactions. In particular, coherently produced J/\psi's in violent hadronic collisions may provide a novel probe of the quark-gluon-plasma.
