ATLAS

Abstract:

We provide an assessment of the state of the art in various issues related to experimental measurements, phenomenological methods and theoretical results relevant for the determination of parton distribution functions (PDFs) and their uncertainties, with the specific aim of providing benchmarks of different existing approaches and results in view of their application to physics at the LHC. We discuss higher order corrections, we review and compare different approaches to small x resummation, and we assess the possible relevance of parton saturation in the determination of PDFS at HERA and its possible study in LHC processes. We provide various benchmarks of PDF fits, with the specific aim of studying issues of error propagation, non-gaussian uncertainties, choice of functional forms of PDFs, and combination of data from different experiments and different processes. We study the impact of combined HERA (ZEUS-H1) structure function data, their impact on PDF uncertainties, and their implications for the computation of standard candle processes, and we review the recent F L determination at HERA. Finally, we compare and assess methods for luminosity measurements at the LHC and the impact of PDFs on them.

Abstract:

When particle physic started, cosmic ray were used as source of new particles. Nowadays particle physic is a fundamental key to understand the nature of the very high energy cosmic rays. Above 1014 eV, primary cosmic rays are detected via air showers whose development strongly rely on the physic of the forward region of hadronic interactions as tested in the HERA and LHC experiments. After an introduction on air shower phenomenology, we will review how HERA and LHC can constrain the physic used both in hadronic interaction model, or for photon or neutrino primaries.

Abstract:

Recent ZEUS measurements of inclusive-jet and dijet cross sections in neutral current deep inelastic ep scattering at HERA are presented. The data correspond to more than a two-fold increase in statistics compared to previous studies. The cross sections are measured in the Breit frame, for boson virtualities of Q2 > 125 GeV2, as functions of various kinematic and jet observables. The data are found to be well described by NLO QCD and have the potential to constrain the gluon density in the proton. Two new extractions of the strong coupling, αs, are also presented: the first is determined from the inclusive-jet neutral current DIS measurement presented here, while the second is from a re-analysis of previously published data on inclusive jet photoproduction. Both measurements are of competitive precision and in agreement with the world average.