J/psi production at sqrt(s)=1.96 and 7 TeV: Color-Singlet Model, NNLO* and polarisation

We study J/psi production in pp collisions at sqrt(s)=1.96 and 7 TeV using the Colour-Singlet Model (CSM), including next-to-leading order (NLO) corrections and dominant alphaS^5 contributions (NNLO*). We find that the CSM reproduces the existing data if the upper range of the NNLO* is near the actual --but presently unknown-- NNLO. The direct yield polarisation for the NLO and NNLO* is increasingly longitudinal in the helicity frame when P_T gets larger. Contrary to what is sometimes claimed in the literature, the prompt J/psi yield polarisation in the CSM is compatible with the experimental data from the CDF collaboration, when one combines the direct yield with a data-driven range for the polarisation of J/psi from chi(c).Comment: Contributed to the 22nd International Conference On Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2011), Annecy, France, May 23 - 28, 2011. 4 pages, 4 figures, uses iopams.sty, iopart12.clo, iopart.cls (included

Off-shell and non-static contributions to heavy-quarkonium production

We have shown that if one relaxes the constraint that the quarks in a heavy quarkonium are at rest and on-shell, new contributions to the discontinuity of the production amplitude appear. These can be seen as a s-cut in the amplitude and are on the same footage as the classical cut of the Colour-Singlet Model (CSM), where the heavy quarks forming the quarkonium are put on-shell by hypothesis. We treat this cut in a gauge-invariant manner by introducing necessary new 4-point vertices, suggestive of the colour-octet mechanism. We have further shown that this cut contributes at least as much as the LO CSM at large P_T. However, the 4-point vertices cannot be totally constrained and an ambiguity remains to what concerns their actual contribution. Theoretical insights from meson photoproduction are discussed in that context.Comment: Presented at the 7th International Conference on Quark Confinement and Hadron Spectrum (QCHS7), September 2-7 2006, Ponta Delgada, Portugal and at the 4th Meeting of the Quarkonium Working Group, June 27-30 2006, BNL, USA, 4 pages, 3 figures, LaTeX, uses aip-6s.clo, aipproc.cls and aipxfm.sty (included

Total J/psi production cross section at the LHC

We evaluate the production cross section for direct J/psi integrated in P_T for various collision energies of the LHC in the QCD-based Colour-Singlet Model. We consider the LO contribution from gluon fusion as well as the one from a fusion of a gluon and a charm quark from the colliding protons. The rapidity distribution of the yield is evaluated in the central region relevant for the ATLAS and CMS detectors, as well as in the more forward region relevant for the ALICE and LHC-b detectors. The results obtained here are compatible with those of other approaches within the range of the theoretical uncertainties which are admittedly very large. This suggests that the "mere" measurements of the yield at the LHC will not help disentangle between the different possible quarkonium production mechanisms.Comment: Invited talk at 45th Rencontres de Moriond: QCD and High Energy Interactions, La Thuile, Aosta Valley, Italy, 13-20 Mar 2010. 4 pages, 6 figures, uses moriond.sty (included

Associated-quarkonium production

We discuss the growing interest to measure associated-quarkonium production in a number of channels at the LHC. Whereas back-to-back production of quarkonium + isolated photon provides a unique way to extract gluon TMDs, observables such as quarkonium + W/Z can be of great help to better understand the quarkonium production mechanism as well as to shed light on double-parton scatterings. Along these lines, we also argue that quarkonium-pair production is a potentially rich source of information which only has started to be harvested. Finally, we discuss the relevance of studying the production of quarkonium + heavy-quark, as e.g. J/psi + charm and Upsilon + non-prompt J/psi.Comment: 6 pages, 4 figures, 1 table, LaTeX. Proceedings of the XXII. International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS2014), 28 April - 2 May 2014, Warsaw, Polan

Lepton-pair production in ultraperipheral collisions at AFTER@LHC

We investigate the potentialities offered by the study of lepton-pair production in ultraperipheral collisions at a fixed-target experiment using the proton and ion LHC beams. In these collisions, exclusive or semi-exclusive lepton-pair production can be used as luminosity monitor as well as a check of the equivalent-photon approximation, via the measurement of the Bethe-Heitler cross section. It can also serve as a probe of the inner hadron structure via the measurement of the lepton-pair azimuthal asymmetry which is sensitive to the timelike virtual Compton scattering. We also briefly discuss the possibility offered by the study of eta(c) production. Finally, we outline the possibilities for lepton-pair production by Pomeron-Odderon fusion in exclusive pp and pA collisions.Comment: 21 pages, 19 figures, uses jheppub.sty (included

Two-photon decay of pseudoscalar quarkonia

We report on our recent evaluation of the two-photon width of the pseudoscalar quarkonia, eta_c(nS) and eta_b(nS) in an approach based on Heavy-Quark Spin Symmetry (HQSS). To what concerns the 1S state eta_c, our parameter-free computation agrees with experiments, as well as most of other theoretical works. On the other hand, our computation for the 2S-state looks 2S like a confirmation that there may exist an anomaly related to the decay of eta_c(2S), especially in the light of the new preliminary result of the Belle collaboration. We also point out that the essentially model-independent ratio of eta_b two-photon width to the Upsilon leptonic width and the eta_b two-photon width could be used to extract the strong coupling constant alpha_s.Comment: Presented by T.N. Pham at the Joint Meeting Heidelberg-Liege-Paris-Wroclaw (HLPW08), Spa, Belgium, 6-8 March 2008, 9 pages, 2 figures, LaTeX, uses aip-6s.clo, aipproc.cls and aipxfm.sty (included

Exploring backward pion electroproduction in the scaling regime

We use general relations between the Transition Distribution Amplitudes (TDAs), entering the description of the p -> pi0 transition, and the proton Distribution Amplitudes (DAs) in the soft-pion limit to estimate the size of the amplitude for backward electroproduction of pi0 at large Q2.Comment: Presented at the 7th International Conference on Quark Confinement and Hadron Spectrum (QCHS7), September 2-7 2006, Ponta Delgada, Portugal and at Soft-Pions in hard processes, August 3-5 2006, Regensburg, Germany, 4 pages, LaTeX, uses aip-6s.clo, aipproc.cls and aipxfm.sty (included

Hard exclusive electroproduction of a pion in the backward region

We study the scaling regime of pion electroproduction in the backward region, eN->e'N'pi. We compute the leading-twist amplitude in the kinematical region, where it factorises into a short-distance matrix element and long-distance dominated nucleon Distribution Amplitudes and nucleon to pion Transition Distribution Amplitudes. Using the chiral limit of the latter, we obtain a first estimate of the cross section, which may be experimentally studied at JLab or Hermes.Comment: 8 pages, 17 figures, RevTeX; v3: update according to an erratum to be published by Phys Rev D : equations (19), (28) and (29) are modified and Fig. 3 corrected accordingly; Conclusions unchange