85 research outputs found
Real next-to-next-to-leading-order QCD corrections to J/ψ and ϒ hadroproduction in association with a photon
AbstractWe update the study of the QCD corrections to direct J/ψ and ϒ hadroproduction in association with a photon in the QCD-based approach of the Colour-Singlet (CS) Model. After comparison with the recent full next-to-leading-order (NLO) computation for this process, we provide an independent confirmation to the inclusive case that NLO QCD corrections to quarkonium-production processes whose LO exhibits a non-leading PT behaviour can be reliably computed at mid and large PT by considering only the real emission contributions accompanied with a kinematical cut. In turn, we evaluate the leading part of the αS4α contributions, namely those coming from (J/ψ,ϒ)+γ associated with two light partons. We find that they are dominant at mid and large PT. This confirms our expectations from the leading PT scaling of the new topologies appearing at NNLO. We obtain that the yield from the CS becomes one order of magnitude larger than the upper value of the potential colour-octet yield. The polarisation of the S13 quarkonia produced in association with a photon is confirmed to be longitudinal at mid and large PT
Generalized Parton Distributions of the Pion
Off-forward structure functions of the pion are investigated in twist-two and
twist-three approximation. A simple model is used for the pion, which allows to
introduce finite size effects, while preserving gauge invariance. Results for
the imaginary parts of the gamma^* pi -> gamma^* pi off-forward amplitude and
of the structure functions are presented. Generalized Callan-Gross relations
are obtained.Comment: 4 pages, 5 figures, LaTeX, uses espcrc2.sty (included), presented at
QCD03 Conference, Montpellier, France, July 200
Upsilon production in pp and pA collisions: from RHIC to the LHC
I discuss Upsilon production in pp collisions at RHIC, Tevatron and LHC
energies, in particular the behaviour of the differential cross section in
rapidity and the impact of QCD corrections on the P_T differential cross
section. I also emphasise the very good agreement between the parameter-free
predictions of the Colour-Singlet Model (CSM) and the first LHC data,
especially in the region of low transverse momenta, which is the most relevant
one for heavy-ion studies. I also show that the CSM predicts Upsilon
cross-section ratios in agreement with the most recent LHC data. I then briefly
discuss the nuclear-matter effects on Upsilon production at RHIC and the LHC in
p(d)A collisions and, by extension, in AA collisions. I argue that a) the
Upsilon break-up probability can be neglected, at RHIC and the LHC, b) gluon
shadowing --although non-negligible-- is not strong enough to describe forward
RHIC data, c) backward RHIC data hints at a gluon EMC effect, possibly stronger
than the quark one. Outlooks for the LHC pPb run are also presented.Comment: Contribution to the 5th International Conference On Hard And
Electromagnetic Probes Of High-Energy Nuclear Collisions (HP2012), 27 May - 1
June 2012, Cagliari, Italy. 4 pages, 5 figures, LaTeX, uses ecrc.sty
(included). v2: version to appear in Nucl. Phys. A (A few typos corrected, 2
refs. added and fig. 1(a) updated with the new STAR point
Single-Transverse-Spin-Asymmetry studies with a fixed-target experiment using the LHC beams (AFTER@LHC)
We discuss the potential of AFTER@LHC to measure single-transverse-spin asymmetries in open-charm and bottomonium production. With a HERMES-like hydrogen polarised target, such measurements over a year can reach precisions close to the per cent level. This is particularly remarkable since these analyses can probably not be carried out anywhere elsePeer Reviewe
Cold nuclear matter effects on J/psi production: intrinsic and extrinsic transverse momentum effects
Cold nuclear matter effects on J/psi production in proton-nucleus and
nucleus-nucleus collisions are evaluated taking into account the specific J/psi
production kinematics at the partonic level, the shadowing of the initial
parton distributions and the absorption in the nuclear matter. We consider two
different parton processes for the c-cbar pair production: one with collinear
gluons and a recoiling gluon in the final state and the other with initial
gluons carrying intrinsic transverse momentum. Our results are compared to RHIC
observables. The smaller values of the nuclear modification factor R_AA in the
forward rapidity region (with respect to the mid rapidity region) are partially
explained, therefore potentially reducing the need for recombination effects.Comment: 7 pages, 11 figures, LaTeX, uses elsarticle.cls (included).v2:
version (with minor text revisions and Fig 2 and 4a modified) to appear in
Phys.Lett.
Centrality, rapidity, and transverse-momentum dependence of gluon shadowing and antishadowing on production in Au collisions at =200 GeV
We have carried out a wide study of shadowing and antishadowing effects on
\jpsi\ production in \dAu\ collisions at GeV. We have
studied the effects of three different gluon nPDF sets, using the exact
kinematics for a process, namely as expected from LO
pQCD. We have computed the rapidity dependence of \RCP\ and for
the different centrality classes of the PHENIX data. For mid rapidities, we
have also computed the transverse-momentum dependence of the nuclear
modification factor, which cannot be predicted with the usual
simplified kinematics. All these observables have been compared to the PHENIX
data in \dAu\ collisions.Comment: 10 pages, 11 figures, talk given by N. Matagne at the conference
"thirty years of hadronic physics", Spa, Belgium, April 6-8, 2011, to appear
in Few Body System
New contributions to heavy-quarkonium production
We reconsider quarkonium production in a field-theoretical setting and we
show that the lowest-order mechanism for heavy-quarkonium production receives
in general contributions from two different cuts. The first one corresponds to
the usual colour-singlet mechanism. The second one has not been considered so
far. We treat it in a gauge-invariant manner, and introduce new 4-point
vertices, suggestive of the colour-octet mechanism. These new objects enable us
to go beyond the static approximation. We show that the contribution of the new
cut can be as large as the usual colour-singlet mechanism at high transverse
momentum for J/psi. In the psi' case, theoretical uncertainties are shown to be
large and agreement with data is possible.Comment: 16 pages, 12 figures, LaTeX. References updated, typo fixed,
discussion of the scale dependence, minor corrections to the tex
Quarkonium as a tool: cold nuclear matter effects
We discuss the quarkonium production as a tool for the study of the Quark
Gluon Plasma. In particular, we concentrate on the Cold Nuclear Matter effetcs.
We show that quarkonium production is also useful for the study of Quantum
Chromodynamics first principles and the nuclear Parton Distribution Functions.Comment: Contribution to the proceedings of QUARKONIUM 2010: Three Days Of
Quarkonium Production in pp and pA Collisions, 29-31 July 2010, Palaiseau,
France. 4 pages, 4 figure
On the mechanisms of heavy-quarkonium hadroproduction
We discuss the various mechanisms potentially at work in hadroproduction of
heavy quarkonia in the light of computations of higher-order QCD corrections
both in the Colour-Singlet (CS) and Colour-Octet (CO) channels and the
inclusion of the contribution arising from the s-channel cut in the CS channel.
We also discuss new observables meant to better discriminate between these
different mechanisms.Comment: Invited review talk at 3rd International Conference On Hard And
Electromagnetic Probes Of High-Energy Nuclear Collisions (HP2008), 8-14 June
2008, Illa da Toxa, Galicia, Spain. 11 pages, 21 figures, LaTeX, uses
svjour.cls and svepj.clo (included
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