Explore the vast range of titles available.

A measurement of b-hadron pair production is presented, based on a data set corresponding to an integrated luminosity of 11.4 fb-1 of proton-proton collisions recorded at √s = 8 TeV with the ATLAS detector at the LHC. Events are selected in which a bhadron is reconstructed in a decay channel containing J/ψ → µµ, and a second b-hadron is reconstructed in a decay channel containing a muon. Results are presented in a fiducial volume defined by kinematic requirements on three muons based on those used in the analysis. The fiducial cross section is measured to be 17.7 ± 0.1(stat.) ± 2.0(syst.) nb. A number of normalised differential cross sections are also measured, and compared to predictions from the Pythia8, Herwig++, MadGraph5 aMC@NLO+Pythia8 and Sherpa event generators, providing new constraints on heavy flavour production.

This paper presents the performance of the ATLAS muon reconstruction during the LHC run with p p collisions at s = 7 –8 TeV in 2011–2012, focusing mainly on data collected in 2012. Measurements of the reconstruction efficiency and of the momentum scale and resolution, based on large reference samples of J / ψ → μ μ , Z → μ μ and Υ → μ μ decays, are presented and compared to Monte Carlo simulations. Corrections to the simulation, to be used in physics analysis, are provided. Over most of the covered phase space (muon | η | < 2.7 and 5 ≲ p T ≲ 100  GeV) the efficiency is above 99 % and is measured with per-mille precision. The momentum resolution ranges from 1.7 % at central rapidity and for transverse momentum p T ≃ 10  GeV, to 4 % at large rapidity and p T ≃ 100  GeV. The momentum scale is known with an uncertainty of 0.05 % to 0.2 % depending on rapidity. A method for the recovery of final state radiation from the muons is also presented.

A bstract Various differential cross-sections are measured in top-quark pair t t ¯ events produced in proton-proton collisions at a centre-of-mass energy of s = 7 TeV at the LHC with the ATLAS detector. These differential cross-sections are presented in a data set corresponding to an integrated luminosity of 4 . 6 fb −1 . The differential cross-sections are presented in terms of kinematic variables, such as momentum, rapidity and invariant mass, of a top-quark proxy referred to as the pseudo-top-quark as well as the pseudo-top-quark pair system. The dependence of the measurement on theoretical models is minimal. The measurements are performed on t t ¯ events in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of them tagged as originating from a b -quark. The hadronic and leptonic pseudo-top-quarks are defined via the leptonic or hadronic decay mode of the W boson produced by the top-quark decay in events with a single charged lepton. Differential cross-section measurements of the pseudo-top-quark variables are compared with several Monte Carlo models that implement next-to-leading order or leading-order multi-leg matrix-element calculations.

The SHiP experiment is proposed to search for very weakly interacting particles beyond the Standard Model which are produced in a 400 GeV/c proton beam dump at the CERN SPS. About 10 11 muons per spill will be produced in the dump. To design the experiment such that the muon-induced background is minimized, a precise knowledge of the muon spectrum is required. To validate the muon flux generated by our Pythia and GEANT4 based Monte Carlo simulation (FairShip), we have measured the muon flux emanating from a SHiP-like target at the SPS. This target, consisting of 13 interaction lengths of slabs of molybdenum and tungsten, followed by a 2.4 m iron hadron absorber was placed in the H4 400 GeV/c proton beam line. To identify muons and to measure the momentum spectrum, a spectrometer instrumented with drift tubes and a muon tagger were used. During a 3-week period a dataset for analysis corresponding to ( 3.27 ± 0.07 ) × 10 11 protons on target was recorded. This amounts to approximatively 1% of a SHiP spill.