Scale dependence of open c{bar{c}} and b{bar{b}} production in the low x region

Abstract

The ‘optimal’ factorization scale mu _0 is calculated for open heavy quark production. We find that the optimal value is mu _F=mu _0simeq 0.85sqrt{p^2_T+m_Q^2} ; a choice which allows us to resum the double-logarithmic, (alpha _sln mu ^2_Fln (1/x))^n corrections (enhanced at LHC energies by large values of ln (1/x)) and to move them into the incoming parton distributions, PDF(x,mu _0^2). Besides this result for the single inclusive cross section (corresponding to an observed heavy quark of transverse momentum p_T), we also determined the scale for processes where the acoplanarity can be measured; that is, events where the azimuthal angle between the quark and the antiquark may be determined experimentally. Moreover, we discuss the important role played by the 2rightarrow 2 subprocesses, ggrightarrow Qbar{Q} at NLO and higher orders. In summary, we achieve a better stability of the QCD calculations, so that the data on c{bar{c}} and b{bar{b}} production can be used to further constrain the gluons in the small x, relatively low scale, domain, where the uncertainties of the global analyses are large at present.