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Register a new userNon-linear QCD meets data: A global analysis of lepton-proton scattering with running coupling BK evolution
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We perform a global fit to the structure function F_2 measured in lepton-proton experiments at small values of Bjorken-x, xle 0.01, for all experimentally available values of Q^2, 0.045 GeV^2le Q^2 le 800 GeV^2. We show that the recent improvements resulting from the inclusion of running coupling corrections allow for a description of data in terms of non-linear QCD evolution equations. In this approach F_2 is calculated within the dipole model with all Bjorken-x dependence described by the running coupling Balitsky-Kovchegov equation. Two different initial conditions for the evolution are used, both yielding excellent fits to data with chi^2/d.o.f.<1.1. Data for the proton longitudinal structure function F_L, not included in the fits, are also well described. We provide predictions for F_2 and F_L in the kinematical regions of interest for future colliders and ultra-high energy cosmic rays. Our analysis allows to perform a first principle extrapolation of the proton-dipole scattering amplitude. A numerical implementation of our results down to x=10^{-12} is released as a computer code for public use.
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We present a global fit to the structure function F_2 measured in lepton-proton experiments at small values of Bjorken-x, x< 0.01, for all experimentally available values of Q^2, 0.045< Q^2 < 800 GeV^2, using the Balitsky -Kovchegov equation including running coupling corrections. Using our fits to F_2, we reproduce available data for F_L and perform predictions, parameter-free and completely driven by small-x evolution, to the kinematic range relevant for the LHeC.
The perturbative QCD predicts that the growth of the gluon density at small-$x$ (high energies) should saturate, forming a Color Glass Condensate (CGC), which is described in mean field approximation by the Balitsky-Kovchegov (BK) equation. Recently, the next-to-leading order corrections for the BK equation were derived and a global fit of the inclusive $ep$ HERA data was performed, resulting in a parameterization for the forward scattering amplitude. In this paper we compare this parameterization with the predictions of other phenomenological models and investigate the saturation physics in diffractive deep inelastic electron-proton scattering and in the forward hadron production in $pp$ collisions. Our results demonstrate that the running coupling BK solution is able to describe these observables.
The very precise combined HERA data provides a testing ground in which the relevance of novel QCD regimes, other than the successful linear DGLAP evolution, in small-x inclusive DIS data can be ascertained. We present a study of the dependence of the AAMQS fits, based on the running coupling BK non-linear evolution equations (rcBK), on the fitted dataset. This allows for the identification of the kinematical region where rcBK accurately describes the data, and thus for the determination of its applicability boundary. We compare the rcBK results with NNLO DGLAP fits, obtained with the NNPDF methodology with analogous kinematical cuts. Further, we explore the impact on LHC phenomenology of applying stringent kinematical cuts to the low-x HERA data in a DGLAP fit.
We present the first extraction of the transversity distribution in the framework of collinear factorization based on the global analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets and in proton-proton collisions with one transversely polarized proton. The extraction relies on the knowledge of di-hadron fragmentation functions, which are taken from the analysis of electron-positron annihilation data. For the first time, the chiral-odd transversity is extracted from a global analysis similar to what is usually done for the chiral-even spin-averaged and helicity distributions. The knowledge of transversity is important for, among other things, detecting possible signals of new physics in high-precision low-energy experiments.
A new QCD analysis of Deep Inelastic Scattering (DIS) data is presented. All available neutrino and anti-neutrino cross sections are reanalysed and included in the fit, along with charged-lepton DIS and Drell-Yan data. A massive factorisation scheme is used to describe the charm component of the structure functions. Next-to-leading order parton distribution functions are provided. In particular, the strange sea density is determined with a higher accuracy with respect to other global fits.
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