In recent papers [1, 2], two new ways have been proposed to probe the linear polarization of gluons in unpolarized proton: using the azimuthal asymmetries and Callan-Gross ratio in heavy-quark pair leptoproduction, lN → l′QQ̅X. In this talk, we discuss in details the sensitivity of the QCD predictions for the azimuthal cos φ and cos 2φ asymmetries to the contribution of linearly polarized gluons inside unpolarized proton, where the azimuth φ is the angle between the lepton scattering plane (l, l′) and the heavy quark production plane (N, Q). Our analysis shows that the azimuthal distributions under consideration vary from 0 to 1 depending on the value of the gluonic counterpart of the Boer- Mulders function, $h_{1}^{ \bot g}$. We conclude that the cos φ and cos 2φ asymmetries in heavy-quark pair production in DIS processes are predicted to be large in wide kinematic ranges and sensitive to the contribution of linearly polarized gluons.
Heavy quarkonium fragmentation functions from a heavy quark pair. I.Swave
