Heavy Quark Photoproduction Research Articles

Probing a nucleon spin structure at TESLA by the real polarized gamma beam

The recent proposals concerning the usage of the real polarized gamma beam, obtained by Compton backscattering of the laser photons off the electron beams from either the linear or circular accelerators were considered. The heavy quark photoproduction process, which gives a unique opportunity to measure the polarized gluon distribution, was investigated.

Photoproduction of heavy quarks in next-to-leading order QCD with longitudinally polarized initial states

We present all relevant details of our calculation of the complete next-to-leading order O( α S 2 α) QCD corrections to heavy flavor photoproduction with longitudinally polarized point-like photons and hadrons. In particular we provide analytical results for the virtual plus soft gluon cross section. We carefully address the relevance of remaining theoretical uncertainties by varying, for instance, the factorization and renormalization scales independently. Such studies are of importance for a meaningful first direct determination of the polarized gluon density Δg from the total charm production spin asymmetry by the upcoming COMPASS experiment. It is shown that the scale uncertainty is considerably reduced in next-to-leading order, but the dependence on the charm quark mass is sizable at fixed target energies. Finally, we study several differential single-inclusive heavy quark distributions and, for the polarized HERA option, the total bottom spin asymmetry.

Photoproduction of heavy quarks at HERA

Present status and prospects of heavy-quark photoproduction studies at HERA are reviewed.

Probing a nucleon spin structure at TESLA by the real polarized gamma beam

The recent proposals concerning the usage of the real polarized gamma beam, obtained by the Compton backscattering of the laser photons off the electron beams from either the linear or circular accelerators were considered. The heavy quark photoproduction process giving a unique opportunity to measure polarized gluon distribution was investigated.

Polarization asymmetry zero in heavy quark photoproduction and leptoproduction

We demonstrate two novel features of the sea-quark contributions to the polarized structure functions and photoproduction cross sections, a zero sum rule and a zero crossing point of the polarization asymmetry, which can be traced directly to the dynamics of the perturbative tree-graph gluon-splitting contributions. In particular, we show that the Born contribution of massive quarks arising from photon-gluon fusion gives zero contribution to the logarithmic integral over the polarization asymmetry $\int {d\nu \over \nu}\Delta \sigma(\nu,Q^2)$ for any photon virtuality. The vanishing of this integral in the Bjorken scaling limit then implies a zero gluon-splitting Born contribution to the Gourdin-Ellis-Jaffe sum rule for polarized structure functions from massive sea quarks. The vanishing of the polarization asymmetry at or near the canonical position predicted by perturbative QCD provides an important tool for verifying the dominance of the photon-gluon fusion contribution to charm photoproduction and for validating the effectiveness of this process as a measure of the gluon polarization $\Delta G(x,Q^2)$ in the nucleon. The displacement of the asymmetry zero from its canonical position is sensitive to the virtuality of the gluon in the photon-gluon fusion subprocess, and it can provide a measure of intrinsic and higher-order sea quark contributions.

HEAVY QUARK PHOTOPRODUCTION IN THE SEMIHARD APPROACH AT HERA AND BEYOND

Processes of heavy quark photoproduction at HERA energies and beyond are investigated using the semihard (k⊥ factorization) approach. Virtuality and longitudinal polarization of gluons in the photon-gluon subprocess as well as the saturation effects in the gluon distribution function at small x have been taken into account. The total cross-sections, rapidity and p⊥ distributions of the charm and beauty quark photoproduction have been calculated. The results are compared with ZEUS experimental data for charm photoproduction cross-section.

Measuring the longitudinally polarized proton gluon distribution using photoproduction processes.

Little information is known about the polarization of gluons inside a longitudinally polarized proton. We investigate the sensitivity of photoproduction experiments with both beam and target longitudinally polarized to the polarization of the gluon distribution in the proton. We study the photoproduction of jets and heavy quarks and conclude that they are both sensitive to the gluon polarization.

Heavy-quark correlations in photon-hadron collisions

We describe a next-to-leading-order calculation of the fully exclusive parton cross section at next-to-leading order for the photoproduction of heavy quarks. We use our result to compute quantities of interest for current fixed-target experiments. We discuss heavy-quark total cross sections, distributions, and correlations.

On the determination of the gluon density of the proton from heavy-flavour production at HERA

Using a recent next-to-leading-order calculation of the photoproduction double differential cross section for heavy quarks, we study the possibility of extracting the gluon density of the proton from heavy-quark photoproduction data. We discuss the theoretical uncertainties connected with this method, and we conclude that they are well under control in a wide x domain.

QCD radiative corrections to the photoproduction of heavy quarks

We present the results of a full calculation of the QCD O( α S 2 α em) radiative corrections to the heavy-quark photoproduction cross section. Explicit formulae are given for the total cross section for the photoproduction of a heavy-quark pair due to photon-parton fusion. Using our results we present estimates of the differential and total cross-section for the photoproduction of charm. Within the large theoretical uncertainties the calculated charm photoproduction cross section is in reasonable agreement with present data. We show that the cross section for the photoproduction of bottom is reliably calculable.

Production of heavy quarks: A nonperturbative approach

We identify a way of producing heavy quarks overlooked by perturbative QCD. It successfully accommodates the data on photoproduction and hadroproduction of heavy quarks. Rates at higher energies are expected to be significantly in excess of those predicted by perturbative QCD.