Detailed Next-to-Leading Order Analysis of Deep Inelastic Neutrino Induced Charm Production off Strange Sea Partons

Neutrino induced deep inelastic charm production off strange sea partons in the nucleon is studied in the framework of the MS fixed flavor factorization scheme. The momentum (z) distributions of the produced D mesons as calculated in the next–to–leading order QCD analysis are presented and compared to their leading order counterparts. Perturbative stability within this formalism is demonstrated and the compatibility of recent next-to-leading order (NLO) strange quark distributions with available dimuon data is investigated. Our NLO (MS) results provide, for the first time, the tools required for a consistent and complete NLO (MS) analysis of charged current dimuon data in order to extract the strange sea density in NLO. It is furthermore shown that the absolute predictions of radiatively (dynamically) generated strange sea densities are in agreement with all present measurements. Recent attempts [1, 2] to determine the strange sea content of the nucleon , s(x,Q), from a next-to-leading order (NLO) QCD analysis of neutrino induced charm production (opposite-sign dimuon events) were undertaken in the framework of the NLO formalism of [3]. In this formalism one considers, in addition to the leading order (LO) process Ws → c, etc., the Wg → cs̄ gluon fusion contribution with ms 6= 0, i.e. one employs a finite mass regularization and subtracts from it that (collinear) part which is already contained in the renormalized, Q–dependent s(x,Q). In a previous publication [4] we have started a study of NLO QCD effects based on the conventional MS factorization scheme where the mass of the strange quark is neglected (ms = 0) and the corresponding mass singularities are dimensionally regularized [5]. Such an analysis is imperative in connection with all those NLO parton distributions and cross sections given in this, most frequently utilized, massless MS factorization scheme. The analysis in [4] was incomplete, however, in the sense of not addressing the detailed momentum distributions of the produced c–quark (D–meson) utilized in [1, 2]. The present paper is devoted to this issue and the relevant expressions are now calculated in their full differential form, by extending the original inclusive analysis in [5]. The formulae and notations of [4] will be strictly taken over everywhere, being extended merely by the introduction of the fractional charm momentum variable ζ ≡ pc · pN/q · pN , i.e. H i (ξ , μ, λ) in [4] will be replaced by H i (ξ , ζ, μ, λ) where the fermionic and gluonic NLO coefficient functions H i=1,2,3 and H g i for heavy quark (charm) production derive from the subprocess Ws → cg (together with the virtual vertex correction to Ws → c) and Wg → cs̄, respectively. Furthermore, dσ/dxdy in [4] will be replaced by dσ/dxdydz with the relevant semi–inclusive structure functions, describing the momentum distributions of the produced D–mesons, being obtained from a convolution with the charm fragmentation function Dc(z), 1 Instead of z ≡ pD · pN/q · pN , it is customary to use [1, 2, 7] zp ≡ pD/p D which differs only marginally from z in the relevant experimental region (z ∼ > 0.05).