The ratio image in DIS as a probe of the charm content of the proton Original Research Article

We analyze the Callan–Gross ratio image in heavy-quark leptoproduction as a probe of the charm content of the proton. To estimate the charm-initiated contributions, we use the ACOT(χ) variable-flavor-number scheme. Our analysis shows that charm densities of the recent CTEQ sets of parton distributions have sizeable impact on the Callan–Gross ratio in a wide region of x and image. In particular, the ACOT(χ) predictions for the quantity image are about half as large as the corresponding expectations of the photon–gluon fusion mechanism for image and image. This is because the structure functions image and image have different dependences on the mass logarithms of the type image. On the other hand, our recent studies indicate that, contrary to the production cross sections, the Callan–Gross ratio is sufficiently stable under radiative corrections to the photon–gluon fusion component for image. We conclude that the quantity image in heavy-quark leptoproduction is perturbatively stable but sensitive to resummation of the mass logarithms. For this reason, in contrast to the structure functions, the ratio image could be good probe of the charm density in the proton.