Inclusive J/$\psi$ production at mid-rapidity in pp andPb–Pb collisions with ALICE

Abstract

The measurement of J/ψ production in heavy-ion collisions is seen as a keymeasurement in the hunt for the Quark-Gluon Plasma. At high collision energiesas reached at the LHC it was predicted that a significant fraction of the J/ψyield is formed by (re)combination of deconfined charm and anticharm quarks inthe medium or at the phase boundary. This mechanism is expected to be mostimportant at very low transverse momentum.In this thesis the production of J/ψ mesons is studied at mid-rapidity (|y| < 0.9) in pp and Pb–Pb collisions at a collision energy of √s_NN = 5.02 TeV with ALICE.The J/ψ mesons are reconstructed in the e+e− decay channel down to vanishingtransverse momentum (pT = 0). The electrons and positrons are identified usingthe specific energy loss dE/dx in the TPC. The J/ψ spectrum and the nuclearmodification factor R_AA in most central collisions are consistent with modelswhich include (re)combination as a dominant source of J/ψ production. Themeasurement of the first two moments of the pT distribution as a function ofcentrality shows that this mechanism becomes more important for more centralcollisions.