Azimuthal Asymmetries in DIS as a Probe of Intrinsic Charm Content of the Proton
We calculate the azimuthal dependence of the heavy-quark-initiated ${\cal O}(\alpha_{s})$ contributions to the lepton-nucleon deep inelastic scattering (DIS). It is shown that, contrary to the photon-gluon fusion (GF) component, the photon-quark scattering (QS) mechanism is practically $\cos2\phi$-independent. We investigate the possibility to discriminate experimentally between the GF and QS contributions using their strongly different azimuthal distributions. Our analysis shows that the GF and QS predictions for the azimuthal $\cos2\phi$ asymmetry are quantitatively well defined in the fixed flavor number scheme: they are stable, both parametrically and perturbatively. We conclude that measurements of the azimuthal distributions at large Bjorken $x$ could directly probe the intrinsic charm content of the proton. As to the variable flavor number schemes, the charm densities of the recent CTEQ and MRST sets of parton distributions have a dramatic impact on the $\cos2\phi$ asymmetry in the whole region of $x$ and, for this reason, can easily be measured.