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Register a new userThe Large-x Factorization of the Longitudinal Structure Function
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A leading-twist factorization formula is derived for the longitudinal structure function in the x -->1 limit of deeply inelastic scattering. This is achieved by defining a new jet function which is gauge independent and probes the transverse momentum of the struck parton in the target. In moment space, terms of order (ln^k N)/N, which are the leading ones for F_L, are shown to be resummable through the cusp anomalous dimension gamma_K and the anomalous dimension gamma_{J^prime} of the new jet function. This anomalous dimension is computed to O(alpha_s). The suggested factorization for F_L reproduces the fixed order results known to O(alpha_s^2). The general ideas for resumming the terms of order (ln^k N)/N in moment space may be extended to the other structure functions and to other inclusive processes near the elastic limit.
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We discuss the longitudinal structure function in nuclear DIS at small $x$. We work within the framework of universal parton densities obtained in DGLAP analyses at NLO. We show that the nuclear effects on the longitudinal structure function closely follow those on the gluon distribution. The error analyses available from newest sets of nuclear PDFs also allow to propagate the uncertainties from present data. In this way, we evaluate the minimal sensitivity required in future experiments for this observable to improve the knowledge of the nuclear glue. We further discuss the uncertainties on the extraction of $F_2$ off nuclear targets, introduced by the usual assumption that the ratio $F_L/F_2$ is independent of the nuclear size. We focus on the kinematical regions relevant for future lepton-ion colliders.
We use results for the structure functions $F_L$ for a gluon target having nonzero transverse momentum square at order $alpha_s$, obtained in our previous paper, to compare with recent H1 experimental data for $F_L$ at fixwd W values and with collinear GRV predictions at LO and NLO approximation.
A novel factorization formula is presented for the longitudinal structure function $F_L$ near the elastic region $x to 1$ of deeply inelastic scattering. In moment space this formula can resum all contributions to $F_L$ that are of order $ln^k N/N$. This is achieved by defining a new jet function which probes the transverse momentum of the struck parton in the target at leading twist. The anomalous dimension $gamma_{J^prime}$ of this new jet operator generates in moment space the logarithmic enhancements coming from the fragmentation of the current jet in the final state. It is also shown how the suggested factorization for $F_L$ is related to the corresponding one for $F_2$ in the same kinematic region.
Measurements of charged current neutrino and anti-neutrino nucleon interactions in the CCFR detector are used to extract the structure functions, F_2, xF_3(nu), xF_3(nubar) and R(longitudinal) in the kinematic region 0.01<x<0.6 and 1<Q^2<300 GeV^2. The new measurements of R in the x<0.1 region provide a constraint on the level of the gluon distribution. The x and Q^2 dependence of R is compared with a QCD based fit to previous data. The CKM matrix element |V_cs| is extracted from a combined analysis of xF_3 and dimuon data.
Inclusive electron scattering data are presented for ^2H and Fe targets at an incident electron energy of 4.045 GeV for a range of momentum transfers from Q^2 = 1 to 7 (GeV/c)^2. Data were taken at Jefferson Laboratory for low values of energy loss, corresponding to values of Bjorken x greater than or near 1. The structure functions do not show scaling in x in this range, where inelastic scattering is not expected to dominate the cross section. The data do show scaling, however, in the Nachtmann variable xi. This scaling may be the result of Bloom Gilman duality in the nucleon structure function combined with the Fermi motion of the nucleons in the nucleus. The resulting extension of scaling to larger values of xi opens up the possibility of accessing nuclear structure functions in the high-x region at lower values of Q^2 than previously believed.
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