Abstract
We compute the J/ψ polarization observables λθ, λϕ, λθϕ in a Color Glass Condensate (CGC) + nonrelativistic QCQ (NRQCD) formalism that includes contributions from both color singlet and color octet intermediate states. Our results are compared to low pT data on J/ψ polarization from the LHCb and ALICE experiments on proton-proton collisions at center-of-mass energies of sqrt{s}=7 TeV and 8 TeV. Our CGC+NRQCD computation provides a better description of data for pT ≤ 15 GeV relative to extant next-to-leading (NLO) calculations within the collinear factorization framework. These results suggest that higher order computations in the CGC+NRQCD framework have the potential to greatly improve the accuracy of extracted values of the NRQCD universal long distance matrix elements.
Highlights
ALICE experiments on protonproton collisions at center-of-mass energies of s = 7 TeV and 8 TeV
Computation provides a better description of data for pT ≤ 15 GeV relative to extant nextto-leading (NLO) calculations within the collinear factorization framework. These results suggest that higher order computations in the Color Glass Condensate (CGC)+NRQCD framework have the potential to greatly improve the accuracy of extracted values of the NRQCD universal long distance matrix elements
For the J/ψ, the long distance matrix elements (LDMEs) of the color singlet channel is dominant in the power counting of the matrix elements, with significant contributions arising from several color octet channels [2,3,4]
Summary
We will explicitly compute the expressions in eqs. (3.3) and (3.4) and use these to determine the angular distribution coefficients specifying J/ψ polarization. (3.3) and (3.4) and use these to determine the angular distribution coefficients specifying J/ψ polarization. The solution of the rcBK equation employs the code of Albacete et al [62] with MV initial conditions and the initial input parameters γ = 1, Q2s0,proton = 0.2 GeV2, αfr = 0.5 and C = 1; these were determined from fits to the HERA DIS data [62]. We have checked that our results for the angular coefficients, being ratios of cross-sections, are insensitive to the values of these parameters. The theoretical errors we quote are for the angular coefficients (collectively denoted as λ) and are obtained by varying the LDME values by their statistical uncertainties and by taking the minimal/maximal value of the obtained set
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