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A complete next-to-leading-order calculation in αs for the J/ψ and ψ' prompt production at the Tevatron, LHC, and RHIC in nonrelativistic QCD is presented. We argue that the next-to-next-to-leading-order color-singlet contribution may not be so important as to resolve the large discrepancy between theory and experiment in J/ψ large PT production cross sections. Therefore, a complete next-to-leading-order calculation, including both color-singlet and color-octet contribution, is necessary and essential to give a good description for J/ψ and ψ' production. We also study the methods to fit the long-distance matrix elements using either two linear combined matrix elements or three matrix elements, and find these two methods can give consistent results. Compared with the measurements at the LHC and RHIC for prompt J/ψ and ψ' production, our predictions are found to agree with all data. In particular, the recently released large pT data (up to 60-70 GeV) at the LHC are in good agreement with our predictions. Our results imply that the universality of color-octet matrix elements holds approximately in charmonium hadroproduction, when one uses fixed-order perturbative calculation to describe data (the data in small pT region are not included). Our work may provide a new test for the universality of color-octet matrix elements, and the color-octet mechanism in general. [ABSTRACT FROM AUTHOR]

We analytically calculate the cross sections of double charmonium production in e+e- → J/ψ(ψ(2S))χcJ (J = 0, 1, 2) at next-to-leading order (NLO) in αs in nonrelativistic QCD, and confirm factorization of these processes. In contrast to χc0 production, for which the NLO correction is large and positive, the NLO corrections for χc1,2 production can be negative, resulting in decreased K factors of 0.91 and 0.78 for J = 1 and 2, respectively, when μ = 2mc. Consequently, the NLO QCD corrections markedly enlarge the difference between cross sections of χc0 and χc1,2. This may explain why e+e- → J/ψ(ψ(2S))χc0 but not e+e- → J/ψ(ψ(2S))χc1,2 is observed experimentally. Moreover, for J/ψ(ψ(2S))χc1,2, the NLO QCD corrections substantially reduce the μ dependence and lead to predictions with small theoretical uncertainties. [ABSTRACT FROM AUTHOR]

To clarify the outstanding problem in charmonium production that existing theories cannot explain the observed cross sections of χcJ(J=0,1,2) and ratio Rχc=σ c2/σ c1≈0.75 (in contrast to the spin counting value 5/3) at the Tevatron, we study the complete next-to-leading order radiative corrections in nonrelativistic QCD, and find next-to-leading order contributions of 3PJ[1] are more important than leading order at high pT, and 3P1[1] decreases slower than 3P2[1], implying a natural explanation for the Rχc puzzle. By fitting Rχc, the predicted cross sections of χcJ are found to agree with data. The result indicates color-octet contribution is crucially needed, thus providing a unique test for heavy quarkonium production mechanisms. Feed-down contributions of χcJ to prompt J/ψ production are estimated to be substantial, about 30%-40% at pT=20??GeV. Production of χcJ(J=0,1,2) at the LHC is also predicted. [ABSTRACT FROM AUTHOR]

We propose an improved version of the color evaporation model to describe heavy quarkonium production. In contrast to the traditional color evaporation model, we impose the constraint that the invariant mass of the intermediate heavy quark-antiquark pair be larger than the mass of produced quarkonium. We also introduce a momentum shift between the heavy quark-antiquark pair and the quarkonium. Numerical calculations show that our model can describe the charmonium yields as well as the ratio of ψ ′ over J / ψ better than the traditional color evaporation model. [ABSTRACT FROM AUTHOR]