QCD resummation for semi-inclusive hadron production processes

We investigate the resummation of large logarithmic perturbative corrections to hadron production in electron-positron annihilation and semi-inclusive deep-inelastic scattering. We find modest, but significant, enhancements of hadron multiplicities in the kinematic regimes accessible in present high-precision experiments. Our results are therefore relevant for the determination of hadron fragmentation functions from data for these processes.Comment: 14 pages, 11 figure

Threshold resummation for the prompt-photon cross section revisited

We study the resummation of large logarithmic perturbative corrections to the partonic cross sections relevant for the process pp->gamma X at high transverse momentum of the photon.These corrections arise near the threshold for the partonic reaction and are associated with soft-gluon emission. We especially focus on the resummation effects for the contribution to the cross section where the photon is produced in jet fragmentation. Previous calculations in perturbation theory at fixed-order have established that this contribution is a subdominant part of the cross section. We find, however, that it is subject to much larger resummation effects than the direct (non-fragmentation) piece and therefore appears to be a significant contribution in the fixed-target regime, not much suppressed with respect to the direct part. Inclusion of threshold resummation for the fragmentation piece leads to some improvement in comparisons between theoretical calculations and experimental data.Comment: 12 pages, 5 figure

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

Next-to-leading order QCD corrections to single-inclusive hadron production in transversely polarized p-p and pbar-p collisions

We present a calculation of the next-to-leading order QCD corrections to the partonic cross sections contributing to single-inclusive high-p_T hadron production in collisions of transversely polarized hadrons. We use a recently developed projection technique for treating the phase space integrals in the presence of the cos(2Phi) azimuthal-angular dependence associated with transverse polarization. Our phenomenological results show that the double-spin asymmetry A_TT^pi for neutral-pion production is expected to be very small for polarized pp scattering at RHIC and could be much larger for the proposed experiments with an asymmetric pbar-p collider at the GSIComment: 7 pages, 5 figure

Threshold Resummation for the Inclusive-Hadron Cross-Section in pp Collisions

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. These corrections arise near the threshold for the partonic reaction and are associated with soft-gluon emission. We perform the resummation to next-to-leading logarithmic accuracy. We present numerical results for the fixed-target regime and find enhancements over the next-to-leading order cross section, which significantly improve the agreement between theoretical predictions and data. We also apply the resummation for RHIC kinematics and find that subleading terms appear to play a rather important role here.Comment: 20 pages, 6 eps figures include

Transverse Double-Spin Asymmetries for Muon Pair Production in pp-Collisions

We calculate the rapidity dependence of the transverse double-spin asymmetry for the Drell-Yan process to next-to-leading order in the strong coupling. Input transversity distributions are obtained by saturating the Soffer inequality at a low hadronic mass scale. Results for the polarized BNL-RHIC proton-proton collider and the proposed HERA-N fixed-target experiment are presented, and the influence of the limited muon acceptance of the detectors on measurements of the asymmetry is studied in detail.Comment: 7 pages including 5 figures; significantly shortened, to be published in Phys. Rev.

The Future of Quark Matter at RHIC

Projected annual results for heavy particle and high-p_{T} correlation studies at future RHICII luminosities.Comment: 8 pages, 3 figures. Proceedings for Quark Matter 2006, Shanghai, Chin

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

Transversity K Factors for Drell-Yan

The question of the K factor in transversely polarised Drell-Yan (DY) processes is examined. The transverse-spin case is peculiar for the absence of a reference point in deeply inelastic scattering (DIS). Therefore, in order to study more fully the possible effects of higher-order corrections on DY asymmetries, a DIS definition for transversity is devised using a hypothetical scalar (Higgs-like) vertex. The results show that some care may be required in interpreting experimentally extracted partonic transversity, in particular when comparing with model calculations or predictions.Comment: 8 pages, 4 figures (eps and feynmp); uses standard LaTeX/MiKTeX packages [svjour.cls, amsmath, bbm, feynmp, graphicx, maybemath, natbib, psfrag, slashed] some homespun packages (included in the zip file); discussion augmented, 1 figure removed; resubmitted to Eur. Phys. J. section

Threshold resummation for polarized (semi-)inclusive deep inelastic scattering

We explore the effects of the resummation of large logarithmic perturbative corrections to double-longitudinal spin asymmetries for inclusive and semi-inclusive deep inelastic scattering in fixed-target experiments. We find that the asymmetries are overall rather robust with respect to the inclusion of the resummed higher-order terms. Significant effects are observed at fairly high values of x, where resummation tends to decrease the spin asymmetries. This effect turns out to be more pronounced for semi-inclusive scattering. We also investigate the potential impact of resummation on the extraction of polarized valence quark distributions in dedicated high-x experiments.Comment: 8 pages, 6 figure