This paper presents the performance of the ATLAS muon reconstruction during the LHC run with collisions at –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 , and 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 and  GeV) the efficiency is above and is measured with per-mille precision. The momentum resolution ranges from at central rapidity and for transverse momentum  GeV, to at large rapidity and  GeV. The momentum scale is known with an uncertainty of to depending on rapidity. A method for the recovery of final state radiation from the muons is also presented.

This paper presents cross sections for the production of a boson in association with jets, measured in proton–proton collisions at with the ATLAS experiment at the large hadron collider. With an integrated luminosity of , this data set allows for an exploration of a large kinematic range, including jet production up to a transverse momentum of and multiplicities up to seven associated jets. The production cross sections for bosons are measured in both the electron and muon decay channels. Differential cross sections for many observables are also presented including measurements of the jet observables such as the rapidities and the transverse momenta as well as measurements of event observables such as the scalar sums of the transverse momenta of the jets. The measurements are compared to numerous QCD predictions including next-to-leading-order perturbative calculations, resummation calculations and Monte Carlo generators.

We report on the high statistics two-pion correlation functions from pp collisions at ffiffi ffi s p ¼ 0:9 TeV and ffiffi ffi s p ¼ 7 TeV, measured by the ALICE experiment at the Large Hadron Collider. The correlation functions as well as the extracted source radii scale with event multiplicity and pair momentum. When analyzed in the same multiplicity and pair transverse momentum range, the correlation is similar at the two collision energies. A three-dimensional femtoscopic analysis shows an increase of the emission zone with increasing event multiplicity as well as decreasing homogeneity lengths with increasing transverse momentum. The latter trend gets more pronounced as multiplicity increases. This suggests the development of space-momentum correlations, at least for collisions producing a high multiplicity of particles. We consider these trends in the context of previous femtoscopic studies in high-energy hadron and heavyion collisions and discuss possible underlying physics mechanisms. Detailed analysis of the correlation reveals an exponential shape in the outward and longitudinal directions, while the sideward remains a Gaussian. This is interpreted as a result of a significant contribution of strongly decaying resonances to the emission region shape. Significant nonfemtoscopic correlations are observed, and are argued to be the consequence of ''mini-jet''-like structures extending to low p t . They are well reproduced by the MonteCarlo generators and seen also in þ À correlations.

Search for new phenomena in events with same-charge leptons and b-jets in p p collisions at √ s = 13 TeV with the ATLAS detectorThe ATLAS Collaboration A search for new phenomena in events with two same-charge leptons or three leptons and jets identified as originating from b-quarks in a data sample of 36.1 fb −1 of pp collisions at √ s = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider is reported. No significant excess is found and limits are set on vector-like quark, four-top-quark, and samesign top-quark pair production. The observed (expected) 95% CL mass limits for a vector-like Tand B-quark singlet are m T > 0.98 (0.99) TeV and m B > 1.00 (1.01) TeV respectively. Limits on the production of the vector-like T 5/3 -quark are also derived considering both pair and single production; in the former case the lower limit on the mass of the T 5/3 -quark is (expected to be) 1.19 (1.21) TeV. The Standard Model four-top-quark production cross-section upper limit is (expected to be) 69 (29) fb. Constraints are also set on exotic four-top-quark production models. Finally, limits are set on same-sign top-quark pair production. The upper limit on uu → tt production is (expected to be) 89 (59) fb for a mediator mass of 1 TeV, and a dark-matter interpretation is also derived, excluding a mediator of 3 TeV with a dark-sector coupling of 1.0 and a coupling to ordinary matter above 0.31. Signals considered 2.1 Vector-like T , B, and T 5/3 quarksVector-like quarks are fractionally charged, coloured fermions whose right-and left-handed components transform identically under weak isospin. Their existence is predicted in many BSM models that address the Higgs boson mass fine-tuning problem [7][8][9][10][11][12][13][14][15][16]. VLQ may come in several varieties, including the ATLAS detectorThe ATLAS detector [29] at the LHC covers nearly the entire solid angle around the collision point.3 It consists of an inner tracking detector surrounded by a thin superconducting solenoid, electromagnetic and hadronic calorimeters, and a muon spectrometer incorporating three large superconducting toroidal magnets. The inner-detector system is immersed in a 2 T axial magnetic field and provides charged-particle tracking in the range |η| < 2.5.A high-granularity silicon pixel detector covers the vertex region and typically provides four threedimensional measurements per track, the innermost being in the insertable B-layer [30]. It is followed by a silicon microstrip tracker, which provides four two-dimensional measurement points per track. These silicon detectors are complemented by a transition radiation tracker, which enables radially extended track reconstruction up to |η| = 2.0. The transition radiation tracker also provides electron identification information based on the fraction of hits (typically 30 in total) above a higher energy-deposit threshold corresponding to transition radiation.The calorimeter system covers the pseudorapidity range |η| < 4.9. Within the region |η| < 3.2, electromagnetic calorimetry is provided ...

Scalar partners of quarks and leptons, predicted in supersymmetric models, are searched for in e+e− collisions at centre-of-mass energies between 192 and 209 GeV at LEP. No evidence for any such particle is found in a data sample of 450 pb−1. Upper limits on their production cross sections are set and lower limits on their masses are derived in the framework of the Minimal Supersymmetric Standard Model