Charmonium Dissociation and Recombination: Cold Effects
Thirty years ago, Matsui and Satz proposed the $J/\psi$ destruction as a signal of a Quark Gluon Plasma (QGP) formation, due to the Debye screening between the pair c-cbar. At the light of the recent experimental data, I review the different effects on $J/\psi$ production, from SPS to LHC energies, distinguishing between Cold Nuclear Matter (CNM) and QGP effects. Different possibilities and explanations for the available experimental data are discussed. Model predictions for the arriving LHC data are also presented.
Hyperboloidal foliations and scri-fixing
A useful choice of gauge when including null infinity in the computational domain is scri-fixing, that is, fixing the spatial coordinate location of null infinity. This choice allows us to avoid the introduction of artificial timelike outer boundaries in numerical calculations. We construct manifestly stationary scri-fixing coordinates explicitly on Minkowski, Schwarzschild and Kerr spacetimes.
Cold Nuclear Matter Effects on J/Psi as Constrained by Deuteron-Gold Measurements at sqrt(s_NN) = 200 GeV
We present a new analysis of J/psi production yields in deuteron-gold collisions at sqrt(s_NN) = 200 GeV using data taken by the PHENIX experiment in 2003 and previously published in [S.S. Adler et al., Phys. Rev. Lett 96, 012304 (2006)]. The high statistics proton-proton J/psi data taken in 2005 is used to improve the baseline measurement and thus construct updated cold nuclear matter modification factors R_dAu. A suppression of J/psi in cold nuclear matter is observed as one goes forward in rapidity (in the deuteron-going direction), corresponding to a region more sensitive to initial state low-x gluons in the gold nucleus. The measured nuclear modification factors are compared to theoretical calculations of nuclear shadowing to which a J/psi (or precursor) break-up cross-section is added. Breakup cross sections of sigma_breakup = 2.8^[+1.7_-1.4] (2.2^[+1.6_-1.5]) mb are obtained by fitting these calculations to the data using two different models of nuclear shadowing. These breakup cross section values are consistent within large uncertainties with the 4.2 +/- 0.5 mb determined at lower collision energies. Projecting this range of cold nuclear matter effects to copper-copper and gold-gold collisions reveals that the current constraints are not sufficient to firmly quantify the additional hot nuclear matter effect.