Charmonium production from the hadron gas formed in ultra-relativistic heavy-ion collisions is studied. Using the J/ψ-hadron absorption cross section determined from the nonperturbative quark-exchange model, which has a peak value similar to that used in the comover model for J/ψ suppression and a thermally averaged value consistent from that extracted from J/ψ data in heavy-ion collisions, we find that J/ψ production from the hadron gas is negligible in heavy-ion collisions at RHIC energies but is important at LHC energies as a result of the large number of charm mesons produced at higher energy collisions. The number of J/ψ produced from these secondary collisions at LHC may be comparable to that of primary J/ψ's, which are expected to be dissociated in the quark-gluon plasma created in the collisions, leading thus to a possible absence of J/ψ suppression. Similar results are obtained for ψ ′ production in ultra-relativistic heavy-ion collisions.
Production rates of large pT jets inpp collisions at RHIC and LHC energies are studied using the next-to-leading order calculation of S.D. Ellis, Z. Kunszt and D. Soper. The computed inclusive one-jet cross sections are compared against the CERN and Fermilab jet data from [Formula: see text] and pp collisions. The dependence of the results on the choice of parton distributions and renormalization/factorization scales is investigated.
Dijet acoplanarity is dominated by vacuum (Sudakov) pQCD radiation even in Pb+Pb collisions, but future higher precision measurements of the tails of the acoplanarity distributions can help to resolve separately the medium opacity, χ = L/λ, and the color screening scale µ 2 from the path averaged BDMS saturation scale Q 2 s [χ, µ] = dLq(E, T (L)) ∝ µ 2 L/λ, that is already well constrained by nuclear modification factor data on R AA (p T ). We compare Gaussian (BDMS) and non-Gaussian (GLV) models of medium broadening of vacuum (Sudakov) induced acoplanarity distributions in A+A. With few percent accuracy on the ratio of A+A to p+p distributions, experiments can easily identify non-Gaussian Landau and Rutherford tails due to multiple collisions. However, we find that sub-percent precision will be required to constrain χ and µ separately from Q s .
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