Next-to-leading order QCD corrections to the polarized photoproduction of heavy flavors

Abstract

We present a calculation of the next-to-leading order (O(α 2 s α)) QCD corrections to heavy flavor photoproduction with longitudinally polarized beams. We apply our results to study the longitudinal spin asymmetry for the total charm quark production cross section which will be utilized by the forthcoming COMPASS experiment at CERN to obtain first direct information on the polarized gluon density ∆g. We also briefly discuss the main theoretical uncertainties inherent in this calculation. In particular we demonstrate that the factorization scale dependence is considerably reduced in next-to-leading order.

Longitudinally polarized photoproduction of heavy flavors at next-to-leading order of QCD

“…Our results complement and significantly extend previously existing spin-dependent NLO calculations of single-inclusive heavy quark yields based on largely analytical methods [16,17], where the resolved contribution was neglected, any information on the partonic recoil system was lost, and most experimental cuts could not be implemented. The results presented here will be also useful for future studies of spin-dependent charm photoproduction at an EIC [10].…”

“…If the virtuality Q of the photon is of O(1 GeV) or higher, resolved processes are sufficiently suppressed but the additional momentum scale Q greatly complicates the calculations of phase-space and loop integrals. Not surprisingly, only very few calculations at NLO of QCD are available in case of polarized beams and targets [16,17,18], none of which for large virtualities Q. As a consequence, the available data sets on hadron and open charm production [12,13,14,15] have not been included in global QCD analyses of helicity parton densities so far.…”

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

“…Unless otherwise stated we use here the GRV [43] and GRSV [8] "standard" set of unpolarized and longitudinally polarized parton distributions, respectively, in our calculations. The strong dependence of the results on the chosen, experimentally poorly constrained polarized gluon distribution ∆g (and to a lesser extent also on the unpolarized gluon g) has been already demonstrated in [20] for the case of the total charm production cross section and the corresponding spin asymmetry. Of course this sensitivity in turn implies that such a measurement is particularly suited to pin down ∆g more precisely.…”

“…Unfortunately we have no data so far, but in the near future COMPASS [13] is going to measure the total charm spin asymmetry A c γp with sufficient accuracy [13,20]. Therefore we mainly focus on the kinematical range accessible by COMPASS in our analyses below, i.e., √ S = S γp = 10 GeV.…”

“…In [20] we only highlighted some of the most important phenomenological aspects, but we skipped most calculational details. In addition, we now present, again for the first time, NLO studies of differential single-inclusive heavy quark distributions.…”