ATLAS

Abstract:

Differential cross sections for the production of at least four jets have been measured in proton-proton collisions at (Formula presented.) TeV at the Large Hadron Collider using the ATLAS detector. Events are selected if the four anti-ktR = 0.4 jets with the largest transverse momentum (pT) within the rapidity range |y| < 2.8 are well separated (ΔR4j min > 0.65), all have pT > 64 GeV, and include at least one jet with pT > 100 GeV. The dataset corresponds to an integrated luminosity of 20.3 fb−1. The cross sections, corrected for detector effects, are compared to leading-order and next-to-leading-order calculations as a function of the jet momenta, invariant masses, minimum and maximum opening angles and other kinematic variables.

Abstract:

A combination is presented of all inclusive deep inelastic cross sections previously published by the H1 and ZEUS collaborations at HERA for neutral and charged current e±p scattering for zero beam polarisation. The data were taken at proton beam energies of 920, 820, 575 and 460 GeV and an electron beam energy of 27.5 GeV. The data correspond to an integrated luminosity of about 1 fb−1 and span six orders of magnitude in negative four-momentum-transfer squared, Q2, and Bjorken x. The correlations of the systematic uncertainties were evaluated and taken into account for the combination. The combined cross sections were input to QCD analyses at leading order, next-to-leading order and at next-to-next-to-leading order, providing a new set of parton distribution functions, called HERAPDF2.0. In addition to the experimental uncertainties, model and parameterisation uncertainties were assessed for these parton distribution functions. Variants of HERAPDF2.0 with an alternative gluon parameterisation, HERAPDF2.0AG, and using fixed-flavour-number schemes, HERAPDF2.0FF, are presented. The analysis was extended by including HERA data on charm and jet production, resulting in the variant HERAPDF2.0Jets. The inclusion of jet-production cross sections made a simultaneous determination of these parton distributions and the strong coupling constant possible, resulting in αs(MZ)=0.1183±0.0009(exp)±0.0005(model/parameterisation)±0.0012(hadronisation)+0.0037−0.0030(scale). An extraction of xFγZ3 and results on electroweak unification and scaling violations are also presented.