Today at 11am CET in the CERN Council chamber, Evgeny Kryshen will present the lastest results on lead-lead and proton-lead collisions on behalf of the ALICE collaboration.
The strong electromagnetic fields surrounding the Pb-ions accelerated at the LHC allow two-photon, photon-proton and photon-lead interactions to be studied in a new kinematic regime. These interactions can be studied in ultra-peripheral collisions,where the impact parameters are larger than the sum of the nuclear radii and hadronic interactions are suppressed. During the lead-lead runs at the LHC in 2010 and 2011, and during the proton-lead run in 2013, the ALICE experiment implemented dedicated triggers to select ultra-peripheral collisions. Based on signals from the Muon spectrometer, the Time-of-Flight detector, the Silicon Pixel detector, and the VZERO scintillator array. The cross section for photoproduction of J/Psi mesons at mid- and forward-rapidities in Pb-Pb collisions will be presented.
The results will be compared to model calculations and their implications for the study of nuclear gluon shadowing will be discussed. First results on J/Psi photoproduction in p-Pb collisions will also be discussed and compared with previous measurements and QCD based models.