Azimuthal Asymmetries in Heavy Quark Leptoproduction as a Test of pQCD

Abstract

We analyze the perturbative and parametric stability of the QCD predictions for the azimuthal asymmetries in heavy quark leptoproduction. At leading order, the $\cos \phi$ asymmetry vanishes whereas the $\cos 2\phi$ one is of leading twist and predicted to be about 15% at energies sufficiently above the production threshold. We calculate the NLO soft-gluon corrections to $\phi$-dependent leptoproduction to the next-to-leading logarithmic accuracy. The soft-gluon approximation provides a good description of the available exact NLO results at $Q^{2}\lesssim m^{2}$. Our analysis shows that, contrary to the production cross sections, the $\cos 2\phi$ asymmetry is practically insensitive to soft radiation for $Q^{2}\lesssim m^{2}$ at energies of the fixed target experiments. We conclude that the $\cos 2\phi$ asymmetry is well defined in pQCD: it is stable both perturbatively and parametrically, and insensitive (in the case of bottom production) to nonperturbative contributions. Measurements of the azimuthal asymmetries would provide an excellent test of pQCD applicability to heavy flavor production.