520 research outputs found
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
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