983 research outputs found
Single-Inclusive Hadron Production in Polarized pp Scattering at Next-to-Leading Logarithmic Accuracy
We study the resummation of large logarithmic perturbative corrections to the
partonic cross sections relevant for the process pp-> h X at high transverse
momentum of the hadron h, when the initial protons are longitudinally
polarized. We perform the resummation to next-to-leading logarithmic accuracy.
We present numerical results for center-of-mass energies of 19.4 GeV, relevant
for comparisons to data from the Fermilab E704 experiment, and 62.4 GeV, where
preliminary data from RHIC have recently become available. We find significant
enhancements of the spin-dependent cross sections, but a decrease of the
double-spin asymmetry for the process. This effect is less pronounced at the
higher energy.Comment: 18 pages, 5 figures. Figures 3, 4 and 5 modifie
Production of Neutral Pions and Eta-mesons in pp Collisions Measured with ALICE
Invariant cross sections for neutral pions and eta mesons in pp collisions at
sqrt(s) = 0.9, 2.76, and 7 TeV were measured by the ALICE detector at the Large
Hadron Collider. Next-to-leading order (NLO) perturbative QCD calculations
describe the pi0 and eta spectra at 0.9 TeV, but overestimate the measured
cross sections at 2.76 TeV and 7 TeV. The measured eta/pi0 ratio is consistent
with mT scaling at 2.76 TeV. At 7 TeV indications for a violation of mT scaling
were found.Comment: 4 pages, 2 figures, to appear in the proceedings of the XXII
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions,
Quark Matter 2011, Annec
Q_T Resummation in Transversely Polarized Drell-Yan Process
We calculate QCD corrections to transversely polarized Drell-Yan process at a
measured of the produced lepton pair in the dimensional regularization
scheme. The distribution is discussed resumming soft gluon effects
relevant for small .Comment: 4 pages, 1 figure, contribution to proceedings of International
Conference on QCD and Hadronic Physics, Beijing, June 16-20, 200
Low-mass lepton pair production at large transverse momentum
We study the transverse momentum distribution of low-mass lepton pairs
produced in hadronic scattering, using the perturbative QCD factorization
approach. We argue that the distribution at large transverse momentum, , with the pair's invariant mass as low as , can be systematically factorized into universal
parton-to-lepton pair fragmentation functions, parton distributions, and
perturbatively calculable partonic hard parts evaluated at a short distance
scale . We introduce a model for the input lepton pair
fragmentation functions at a scale GeV, which are then evolved
perturbatively to scales relevant at RHIC. Using the evolved fragmentation
functions, we calculate the transverse momentum distributions in hadron-hadron,
hadron-nucleus, and nucleus-nucleus collisions at RHIC. We also discuss the
sensitivity of the transverse momentum distribution of low-mass lepton pairs to
the gluon distribution.Comment: 16 pages, 11 figures, revised version to appear in Phys. Rev.
Next-to-leading Order Evolution of Transversity Distributions and Soffer's Inequality
We present a calculation of the two-loop splitting functions for the
evolution of the twist-2 `transversity' parton densities of transversely
polarized nucleons. We study the implications of our results for Soffer's
inequality for the case of valence quark densities.Comment: 23 Pages, LaTeX, 2 figures as eps files, final, slightly modified
version, to appear in Phys. Rev.
Next-to-Leading Order Analysis of Inclusive and Semi-inclusive Polarized Data
We present a combined next-to-leading order QCD analysis to data on both
inclusive and semi-inclusive polarized deep inelastic scattering asymmetries.
Performing NLO QCD global fits with different sets of observables, we evaluate
the impact of the very recent semi-inclusive results presented by SMC in the
extraction of NLO polarized parton distributions.Comment: 22 pages, 4 figures include
Direct Photons at RHIC
The PHENIX experiment has measured direct photons in
GeV Au+Au collisions and p+p collisions. The fraction of photons due to direct
production in Au+Au collisions is shown as a function of and centrality.
This measurement is compared with expectation from pQCD calculations. Other
possible sources of direct photons are discussed.Comment: 7 pages, 5 figures, presented at Hot Quarks 2004, Taos, N
Direct Photons in Nuclear Collisions at FAIR Energies
Using the extrapolation of existing data estimations of prompt photon
production at FAIR energies have been made. At the rapidity
density of prompt photons with 1.5 GeV/c per central Au+Au event at 25
AGeV is estimated as . With the planed beam intensity
per second and 1% interaction probability, for 10% of most central events one
can expect the prompt photon rate photons per second.
Direct photons from the hadron scenario of ion collisions generated by the
Hadron-String-Dynamics (HSD) transport approach with implemented meson
scatterings have been analyzed.
Photons from short-living resonances (e.g. )
decaying during the dense phase of the collision should be considered as direct
photons. They contribute significantly in the direct photon spectrum at
GeV/c. At the FAIR energy 25 AGeV in Au+Au central collisions
the HSD generator predicts, as a lower estimate,
0.5% in the region
GeV/c. At GeV/c 2%.
Thermal direct photons have been evaluated with the Bjorken Hydro-Dynamics
(BHD) model. The BHD spectra differ strongly from the HSD predictions. The
direct photon spectrum is very sensitive to the initial temperature parameter
of the model. The 10 MeV increase in the value leads to
2 times higher photon yield.Comment: 9 pages, 5 figures, Talk at the session of Russian Academy of
Sciences, ITEP, Moscow, 26 - 30 November 200
Comparing extractions of Sivers functions
A comparison is given of the various recently published extractions of the
Sivers functions from the HERMES and COMPASS data on single-transverse spin
asymmetries in semi-inclusive deeply inelastic scattering.Comment: Contribution to the proceedings of "The International Workshop on
Transverse Polarisation Phenomena in Hard Processes" (Transversity 2005),
Villa Olmo (Como), 7-10th. September 200
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