Charm of small $x$ neutrino DIS.pdf

a r X i v : 0 8 0 3 .4 4 9 2 v 2 [ h e p - p h ] 1 5 M a y 2 0 0 8 Charm of small x neutrino DIS. R. Fiore1? and V.R. Zoller2? 1Dipartimento di Fisica, Universita? della Calabria and Istituto Nazionale di Fisica Nucleare, Gruppo collegato di Cosenza, I-87036 Rende, Cosenza, Italy 2ITEP, Moscow 117218, Russia Abstract Due to the weak current non-conservation the diffractive excitation of charm and strangeness dominates the longitudinal structure function FL(x,Q 2) of neutrino DIS at small Bjorken x. Based on the color dipole BFKL approach we report quantitative predictions for this effect in the kinematical range of the CCFR/NuTeV experiment. We comment on the relevance of our findings to experimental tests of PCAC. ?email address: fiore@cs.infn.it ?email address: zoller@itep.ru 1 1. Introduction. The neutrino deep inelastic scattering (DIS) at small values of the Bjorken variable xBj = Q 2/2mNν provides a useful tool for studies of fundamental proper- ties of electro-weak (EW) interactions. In particular, the analysis of neutrino-nucleon cross sections at vanishing four-momentum transfer squared, Q2, can be used to test the hypoth- esis of partial conservation of the axial current (PCAC) in the kinematical region of high leptonic energy transfer, ν, [1, 2] (for theoretical introduction see [3]). The partial conserva- tion hypothesis [4] connects via Adler’s theorem [5] the longitudinal structure function (LSF) at Q2 → 0 induced by the light-quark axial-vector current (ud-current) with the on-shell pion-nucleon total cross section, F udL (x,Q 2 → 0) = f 2 π π σπ(ν), (1) where fπ ? 130 MeV is the pion decay constant (see [6] for more discussion on the origin of Eq.(1)). To test the Eq.(1) the structure function F2 = FL + FT measured experimentally is extrapolated down to Q2 → 0 making use of the fact that the transverse structure function FT for ud-current vanishes at Q 2 → 0. It is assumed that the contribution of the charmed- strange (cs) current can be negl