Abstract
We report on the analysis of charmonia in pp, pPb and PbPb collisions with the CMS experiment with various observables. The cross section for coherent J/ψ photoproduction is measured in ultra-peripheral PbPb collisions at 2.76 TeV. The ratio of prompt J/ψ yields at forward (proton-going direction) and backward (Pb-going direction) is studied as a function of pT, rapidity, and the event activity in pPb collisions at 5.02 TeV. The nuclear modification factor of prompt J/ψ in PbPb collisions at 2.76 TeV is presented as a function of centrality, pT, and rapidity. Finally, the production yields of ψ(2S) and J/ψ in pp and PbPb collisions have been compared.
Highlights
In the early stage of high-energy heavy ion collisions, the transition from a hadronic phase into a deconfined system of quarks and gluons, the Quark-Gluon Plasma (QGP), is predicted
We report on the analysis of charmonia in pp, pPb and PbPb collisions with the CMS experiment with various observables
The nuclear modification factor of prompt J/ψ in PbPb collisions at 2.76 TeV is presented as a function of centrality, pT, and rapidity
Summary
In the early stage of high-energy heavy ion collisions, the transition from a hadronic phase into a deconfined system of quarks and gluons, the Quark-Gluon Plasma (QGP), is predicted. Given the abundance of charm quarks at LHC energies, charmonia can be produced at the hadronization stage by the recombination of initially uncorrelated charm and anticharm quarks [2] This type of process has as result an enhancement of charmonium yields in lead-lead (PbPb) collisions relative to those in proton-proton (pp) collisions. Aside from the formation of QGP, the charmonium production can be affected by the so-called ”cold nuclear matter (CNM) effects”, including modifications of the nuclear parton distribution functions (nPDFs), initial or final state parton energy loss, and nuclear absorption [3] Such effects are best probed in proton-lead (pPb) collisions and ultra-peripheral collisions (UPC). In order to separate the coherent signal contribution from background (incoherent J/ψ and γγ → μ+μ− interactions), a maximum likelihood fit is performed simultaneously to the dimuon invariant mass and pT distributions determined from STARLIGHT simulation
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