Azimuthal Dependence of the Heavy Quark Initiated Contributions to DIS

Abstract

We analyze the azimuthal dependence of the heavy-quark-initiated contributions to the lepton-nucleon deep inelastic scattering (DIS). First we derive the relations between the parton level semi-inclusive structure functions and the helicity ${\gamma }^{\ast }Q$ cross sections in the case of arbitrary values of the heavy quark mass. Then the azimuth-dependent $\mathcal{O}({\alpha }_s)$ lepton-quark DIS is calculated in the helicity basis. Finally, we investigate numerically the properties of the $\cos \varphi$ and $\cos 2\varphi$ distributions caused by the photon-quark scattering (QS) contribution. It turns out that, contrary to the basic photon-gluon fusion (GF) component, the QS mechanism is practically $\cos 2\varphi$-independent. This fact implies that measurements of the azimuthal distributions in charm leptoproduction could directly probe the charm density in the proton.

Comments: 11 pages, 4 figures, revtex4, published version