The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by the Minimal Supersymmetric Standard Model (MSSM). The data of the four collaborations are statistically combined and examined for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number of "benchmark" models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large exclusions in the MSSM parameter space. Absolute limits are set on the parameter tan β and, in some scenarios, on the masses of neutral Higgs bosons.

Abstract.Muons from cosmic-ray interactions in the atmosphere provide a high-statistics source of particles that can be used to study the performance and calibration of the ATLAS detector. Cosmic-ray muons can penetrate to the cavern and deposit energy in all detector subsystems. Such events have played an important role in the commissioning of the detector since the start of the installation phase in 2005 and were particularly important for understanding the detector performance in the time prior to the arrival of the first LHC beams. Global cosmic-ray runs were undertaken in both 2008 and 2009 and these data have been used through to the early phases of collision data-taking as a tool for calibration, alignment and detector monitoring. These large datasets have also been used for detector performance studies, including investigations that rely on the combined performance of different subsystems. This paper presents the results of performance studies related to combined tracking, lepton identification and the reconstruction of jets and missing transverse energy. Results are compared to expectations based on a cosmic-ray event generator and a full simulation of the detector response.

A search is presented for new particles decaying to large numbers (7 or more) of jets, with missing transverse momentum and no isolated electrons or muons. This analysis uses 20.3 fb −1 of pp collision data at √ s = 8 TeV collected by the ATLAS experiment at the Large Hadron Collider. The sensitivity of the search is enhanced by considering the number of b-tagged jets and the scalar sum of masses of large-radius jets in an event. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of various simplified supersymmetry-inspired models where gluinos are pair produced, as well as an mSUGRA/CMSSM model. The ATLAS collaboration 34 IntroductionMany extensions of the Standard Model of particle physics predict the presence of TeVscale strongly interacting particles that decay to weakly interacting descendants. In the context of R-parity-conserving supersymmetry (SUSY) [1][2][3][4][5], the strongly interacting parent particles are the partners of the quarks (squarks,q) and gluons (gluinos,g), and are produced in pairs. The lightest supersymmetric particle (LSP) is stable, providing a candidate that can contribute to the relic dark-matter density in the universe [6,7]. If they are kinematically accessible, the squarks and gluinos could be produced in the proton-proton interactions at the Large Hadron Collider (LHC) [8].-1 - JHEP10(2013)130Such particles are expected to decay in cascades, the nature of which depends on the mass hierarchy within the model. The events would be characterised by significant missing transverse momentum from the unobserved weakly interacting descendants, and by a large number of jets from emissions of quarks and/or gluons. Individual cascade decays may include gluino decays to a top squark (stop,t) and an anti-top quark, g →t +t (1.1a)followed by the top-squark decay to a top quark and a neutralino LSP,χ 0 1 , t → t +χ 0 1.(1.1b)Alternatively, if the top squark is heavier than the gluino, the three-body decay, g → t +t +χ 0 1 (1.2) may result. Other possibilities include decays involving intermediate charginos, neutralinos, and/or squarks including bottom squarks. A pair of cascade decays produces a large number of Standard Model particles, together with a pair of LSPs, one from the end of each cascade. The LSPs are assumed to be stable and only weakly interacting, and so escape undetected, resulting in missing transverse momentum. In this paper we consider final states with large numbers of jets together with significant missing transverse momentum in the absence of isolated electrons or muons, using the pp collision data recorded by the ATLAS experiment [9] during 2012 at a centre-of-mass energy of √ s = 8 TeV. The corresponding integrated luminosity is 20.3 fb −1 . Searches for new phenomena in final states with large jet multiplicities -requiring from at least six to at least nine jets -and missing transverse momentum have previously been reported by the ATLAS Collaboration using LHC pp collision data corresponding to 1.34 fb −1 [10]...

Jet cross sections have been measured for the first time in proton-proton collisions at a centre-of-mass energy of 7 TeV using the ATLAS detector. The measurement uses an integrated luminosity of 17 nb −1 recorded at the Large Hadron Collider. The anti-k t algorithm is used to identify jets, with two jet resolution parameters, R = 0.4 and 0.6. The dominant uncertainty comes from the jet energy scale, which is determined to within 7% for central jets above 60 GeV transverse momentum. Inclusive single-jet differential cross sections are presented as functions of jet transverse momentum and rapidity. Dijet cross sections are presented as functions of dijet mass and the angular variable χ. The results are compared to expectations based on next-toleading-order QCD, which agree with the data, providing a validation of the theory in a new kinematic regime.

This paper describes the AC-coupled, single-sided, p-in-n silicon microstrip sensors used in the SemiConductor Tracker (SCT) of the ATLAS experiment at the CERN Large Hadron Collider (LHC). The sensor requirements, specifications and designs are discussed, together with the qualification and quality assurance procedures adopted for their production. The measured sensor performance is presented, both initially and after irradiation to the fluence anticipated after 10 years of LHC operation. The sensors are now successfully assembled within the detecting modules of the SCT, and the SCT tracker is completed and integrated within the ATLAS Inner Detector. Hamamatsu Photonics Ltd supplied 92.2% of the 15,392 installed sensors, with the remainder supplied by CiS.