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1. chinaXiv:201609.01016 [pdf]

Next-to-Leading Order Differential Cross Sections for J/ψ,ψ(2S), and Υ Production in Proton-Proton Collisions at a Fixed-Target Experiment Using the LHC Beams (AFTER@LHC)

Yu Feng; Jian-Xiong Wang
Subjects: Physics >> Nuclear Physics

Using nonrelativistic QCD (NRQCD) factorization, we calculate the yields for?J/ψ,?ψ(2S)?and?Υ(1S)hadroproduction at?s√=?72 GeV and 115 GeV including the next-to-leading order QCD corrections. Both these center-of-mass energies correspond to those obtained with 7~TeV and 2.76~TeV nucleon beam impinging a fixed target. We study the cross section integrated in?pt?as a function of the rapidity as well as the?pt?differential cross section in the central rapidity region. Using different NLO fit results of the NRQCD long-distance matrix elements, we evaluate a theoretical uncertainty which is certainly much larger than the projected experimental uncertainties with the expected 20 fb?1?to be collected per year with AFTER@LHC.

submitted time 2016-09-14 Hits504Downloads293 Comment 0

2. chinaXiv:201609.00900 [pdf]

Energy dependence of direct-quarkonium production in $pp$ collisions from fixed-target to LHC energies: complete one-loop analysis

Yu Feng; Jean-Philippe Lansberg; Jian-XiongWang
Subjects: Physics >> Nuclear Physics

We compute the energy dependence of the P_T-integrated cross section of directly produced quarkonia in pp collisions at next-to-leading order (NLO), namely up to alpha_s^3, within nonrelativistic QCD (NRQCD). Our analysis is based on the idea that the P_T-integrated and the P_T-differential cross sections can be treated as two different observables. The colour-octet NRQCD parameters needed to predict the P_T-integrated yield can thus be extracted from the fits of the P_T-differential cross sections at mid and large P_T. For the first time, the total cross section is evaluated in NRQCD at full NLO accuracy using the recent NLO fits of the P_T-differential yields at RHIC, the Tevatron and the LHC. Both the normalisation and the energy dependence of the J/psi, psi' and Upsilon(1S), we obtained, are in disagreement with the data irrespective of the fit method. The same is true if one uses CEM-like colour-octet NRQCD parameters. If, on the contrary, one disregards the colour-octet contribution, the existing data in the TeV range are well described by the alpha_s^3 contribution in the colour-singlet model --which, at alpha_s^4, however shows an unphysical energy dependence. A similar observation is made for eta(c,b). This calls for a full NNLO or for a resummation of the initial-state radiation in this channel. In any case, past claims that colour-octet transitions are dominantly responsible for low-P_T quarkonium production are not supported by our results. This may impact the interpretation of quarkonium suppression in high-energy proton-nucleus and nucleus-nucleus collisions.

submitted time 2016-09-13 Hits520Downloads274 Comment 0

3. chinaXiv:201609.00899 [pdf]

An updated study of $\Upsilon$ production and polarization at the Tevatron and LHC

Yu Feng; Bin Gong; Lu-Ping Wan; Jian-Xiong Wang
Subjects: Physics >> Nuclear Physics

Following the nonrelativistic QCD factorization scheme, by taking latest available measurement on?χb(3P)?into consideration, we present an updated study on the yield and polarization of?Υ(1S,2S,3S)?hadroproduction, and the fractions of?χb(mP)?feed-down in?Υ(nS)?production at QCD next-to-leading order. In the fitting, three schemes are applied with different choice of?χb(mP)?feed-down ratios and NRQCD factorization scale. The results can explain the measurements on yield very well as in our previous work. The polarization puzzle to?Υ(3S)?is now solved by considering the?χb(3P)?feed-down contributions. The ratio of?σ[χb2(1P)]/σ[χb1(1P)]?measurements from CMS can also be reproduced in our prediction. Among the different schemes, the results show little difference, but there are sizeable difference for the fitted long-distance color-octet matrix elements. It may bring large uncertainty when the values are applied in other experiments such as in?ee,?ep?colliders.

submitted time 2016-09-13 Hits534Downloads322 Comment 0

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