How to measure the charm density in the proton

Abstract

We study two experimental ways to measure the heavy-quark content of the proton: using the Callan-Gross ratio $R(x,Q^2)=F_L/F_T$ and/or the azimuthal $\cos (2\phi )$ asymmetry in DIS. Our approach is based on the following observations. First, the ratio $R(x,Q^2)=F_L/F_T$ and azimuthal $\cos (2\phi )$ asymmetry in heavy-quark leptoproduction are stable, both parametrically and perturbatively, within pQCD. Second, both these quantities are sensitive to resummation of the mass logarithms of the type ${\alpha }_s\ln (Q^2/m^2)$. We conclude that the heavy-quark densities in the nucleon can, in principle, be determined from high-$Q^2$ data on the Callan-Gross ratio and/or the azimuthal asymmetry. In particular, the charm content of the proton can be measured in future studies at the proposed Large Hadron-Electron (LHeC) and Electron-Ion (EIC) Colliders.

6 pages, 3 figures, talk given at the 20th International Symposium on Spin Physics "Spin 2012", JINR, Dubna, Russia, September 17-22, 2012. arXiv admin note: substantial text overlap with arXiv:1010.5424