Raman Spectroscopy Study of Annealing-Induced Effects on Graphene Prepared by Micromechanical Exfoliation

In this note, we report a Raman spectroscopy study of annealing-induced effects on graphene samples prepared by the microexfoliation method. It was shown that randomly located adhesive residues often contaminate nearby graphene sheets during thermal annealing. The contamination on graphene can be as thin as ~1 nm, but gives several new Raman bands of unusually strong intensity. We also find that their intensity is strongly dependent on the excitation wavelength implying that graphene-induced Raman enhancement may be operative. The current study also suggests that graphene can be selectively sensitive towards certain molecular species in binding, which can be exploited for interesting application.Comment: 8 pages, 4 figure

Hot medium effects on J/psi production in p+Pb collisions at sqrt{s_{NN}}=5.02 TeV

Based on a kinetic description of J/psi dissociation and production in an expanding quark-gluon plasma that is described by a 2+1 dimensional ideal hydrodynamics, we have studied the hot medium effects on J/psi production in p+Pb collisions at sqrt{s_{NN}}=5.02 TeV. Including also the cold nuclear matter effects, we are able to reproduce recent experimental results on the nuclear modification factor R_{pPb}(J/psi) measured by the ALICE Collaboration. We have also made predictions for the R_{pPb} of J/psi and the double ratio R_{pPb}^{pro}(psi')/R_{pPb}^{pro}(J/psi) of prompt quarkonia produced in the most central 10% p+Pb collisions. We find that different from the cold nuclear matter effects, the R_{pPb}(J/psi) is slightly smaller than that in the minimum bias collisions, and the double ratio is significantly less than one at backward rapidity.Comment: 8 pages, 6 figure

Quarkonium formation time in quark-gluon plasma

The quarkonium formation time in a quark-gluon plasma (QGP) is determined from the space-time correlator of heavy quark vector currents using the quarkonium in-medium mass and wave function obtained from heavy quark potentials extracted from the lattice QCD. It is found that the formation time of a quarkonium increases with the temperature of the QGP and diverges near its dissociation temperature. Also, the quarkonium formation time is longer if the heavy quark potential is taken to be the free energy from lattice calculations for a heavy quark pair, compared to that based on the more negative internal energy.Comment: 5 pages, 4 figure

Quarkonium formation time in relativistic heavy-ion collisions

We calculate the quarkonium formation time in relativistic heavy-ion collisions from the space-time correlator of heavy quark vector currents in a hydrodynamics background with the initial nonequilibrium stage expanding only in the longitudinal direction. Using in-medium quarkonia properties determined with the heavy quark potential taken to be the free energy from lattice calculations and the fact that quarkonia can only be formed below their dissociation temperatures due to color screening, we find that $\Upsilon$(1S), $\Upsilon$(2S), $\Upsilon$(3S), $J/\psi$ and $\psi^\prime$ are formed, respectively, at 1.2, 6.6, 8.8, 5.8, and 11.0 fm/c after the quark pair are produced in central Au+Au collisions at the top energy of Relativistic Heavy Ion Collider (RHIC), and these times become shorter in semi-central collisions. We further show, as an example, that including the effect of formation time enhances appreciably the survivability of $\Upsilon$(1S) in the produced hot dense matter.Comment: 6 pages, 4 figure