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Register a new userLHC and DIS experimental data in the CT18(Z) global QCD analysis
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We discuss implementation of the LHC experimental data sets in the new CT18 global analysis of quantum chromodynamics (QCD) at the next-to-next-leading order of the QCD coupling strength. New methodological developments in the fitting methodology are discussed. Behavior of the CT18 NNLO PDFs for the conventional and saturation-inspired factorization scales in deep-inelastic scattering is reviewed. Four new families of (N)NLO CTEQ-TEA PDFs are presented: CT18, A, X, and Z.
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Building upon the most recent CT18 global fit, we present a new calculation of the photon content of the proton based on an application of the LUX formalism. In this work, we explore two principal variations of the LUX ansatz. In one approach, which we designate CT18lux, the photon PDF is calculated directly using the LUX formula for all scales, $mu$. In an alternative realization, CT18qed, we instead initialize the photon PDF in terms of the LUX formulation at a lower scale, $mu! sim! mu_0$, and evolve to higher scales with a combined QED+QCD kernel at $mathcal{O}(alpha),~mathcal{O}(alphaalpha_s)$ and $mathcal{O}(alpha^2)$. While we find these two approaches generally agree, especially at intermediate $x$ ($10^{-3}lesssim xlesssim0.3$), we discuss some moderate discrepancies that can occur toward the end-point regions at very high or low $x$. We also study effects that follow from variations of the inputs to the LUX calculation originating outside the pure deeply-inelastic scattering (DIS) region, including from elastic form factors and other contributions to the photon PDF. Finally, we investigate the phenomenological implications of these photon PDFs for the LHC, including high-mass Drell-Yan, vector-boson pair, top-quark pair, and Higgs associated with vector-boson production.
Recently, two photon PDF sets based on implementations of the LUX ansatz into the CT18 global analysis were released. In CT18lux, the photon PDF is calculated directly using the LUX master formula for all scales, $mu$. In an alternative realization, CT18qed, the photon PDF is initialized at the starting scale, $mu_0$, using the LUX formulation and evolved to higher scales $mu(>mu_0)$ with a combined QED+QCD kernel at $mathcal{O}(alpha),~mathcal{O}(alphaalpha_s)$ and $mathcal{O}(alpha^2)$. In the small-$x$ region, the photon PDF uncertainty is mainly induced by the quark and gluon PDFs, through the perturbative DIS structure functions. In comparison, the large-$x$ photon uncertainty comes from various low-energy, nonperturbative contributions, including variations of the inelastic structure functions in the resonance and continuum regions, higher-twist and target-mass corrections, and elastic electromagnetic form factors of the proton. We take the production of doubly-charged Higgs pairs, $(H^{++}H^{--})$, as an example of scenarios beyond the Standard Model to illustrate the phenomenological implications of these photon PDFs at the LHC.
This talk covers three contributions from H1: Measurement of the inclusive e^pm p scattering cross section at high inelasticity y and of the structure function F_L, Determination of the integrated luminosity at HERA using elastic QED Compton events and Inclusive deep inelastic scattering at high Q2 with longitudinally polarized lepton beams at HERA. These are new measurements mainly based on the full HREA-II data but include also those from HERA-I in the combination whenever it is relevant. The main results of these measurements are briefly summarized here.
The neutrino deep inelastic scattering (DIS) data is very interesting for global analyses of proton and nuclear parton distribution functions (PDFs) since they provide crucial information on the strange quark distribution in the proton and allow for a better flavor decompositon of the PDFs. In order to use neutrino DIS data in a global analysis of proton PDFs nuclear effects need to be understood. We study these effects with the help of nuclear PDFs extracted from global analyses of charged-lepton DIS, Drell-Yan and neutrino DIS data at next-to-leading order in QCD.
We consider forward neutron production in DIS within fracture functions formalism. By performing a QCD analysis of available data we extract proton-to-neutron fracture functions exploiting a method which is in close relation with the factorisation theorem for this class of processes.
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