The ratio [formula omitted] in DIS as a probe of the charm content of the proton

Abstract

We analyze the Callan–Gross ratio R ( x , Q 2 ) = F L / F T 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 Q 2 . In particular, the ACOT( χ) predictions for the quantity R ( x , Q 2 ) are about half as large as the corresponding expectations of the photon–gluon fusion mechanism for x ∼ 10 − 2 – 10 − 1 and Q 2 ≫ m 2 . This is because the structure functions F T ( x , Q 2 ) and F L ( x , Q 2 ) have different dependences on the mass logarithms of the type α s ln ( Q 2 / m 2 ) . 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 x ≳ 10 − 4 . We conclude that the quantity R ( x , Q 2 ) 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 R ( x , Q 2 ) = F L / F T could be good probe of the charm density in the proton.