Results are presented from searches for the standard model Higgs boson in proton-proton collisions at root s = 7 and 8 TeV in the Compact Muon Solenoid experiment at the LHC, using data samples corresponding to integrated luminosities of up to 5.1 fb(-1) at 7 TeV and 5.3 fb(-1) at 8 TeV. The search is performed in five decay modes: gamma gamma, ZZ, W+W-, tau(+)tau(-), and b (b) over bar. An excess of events is observed above the expected background, with a local significance of 5.0 standard deviations, at a mass near 125 GeV, signalling the production of a new particle. The expected significance for a standard model Higgs boson of that mass is 5.8 standard deviations. The excess is most significant in the two decay modes with the best mass resolution, gamma gamma and ZZ; a fit to these signals gives a mass of 125.3 +/- 0.4(stat.) +/- 0.5(syst.) GeV. The decay to two photons indicates that the new particle is a boson with spin different from one. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved

A measurement of the Higgs boson mass is presented based on the combined data samples of the ATLAS and CMS experiments at the CERN LHC in the H → γγ and H → ZZ → 4l decay channels. The results are obtained from a simultaneous fit to the reconstructed invariant mass peaks in the two channels and for the two experiments. The measured masses from the individual channels and the two experiments are found to be consistent among themselves. The combined measured mass of the Higgs boson is m H ¼ 125.09 AE 0.21 ðstatÞ AE 0.11 ðsystÞ GeV. DOI: 10.1103/PhysRevLett.114.191803 PACS numbers: 14.80.Bn, 13.85.Qk The study of the mechanism of electroweak symmetry breaking is one of the principal goals of the CERN LHC program. In the standard model (SM), this symmetry breaking is achieved through the introduction of a complex doublet scalar field, leading to the prediction of the Higgs boson H [1-6], whose mass m H is, however, not predicted by the theory. In 2012, the ATLAS and CMS Collaborations at the LHC announced the discovery of a particle with Higgs-boson-like properties and a mass of about 125 GeV [7][8][9]. The discovery was based primarily on mass peaks observed in the γγ and ZZ → l þ l − l 0þ l 0−(denoted H → ZZ → 4l for simplicity) decay channels, where one or both of the Z bosons can be off shell and where l and l 0 denote an electron or muon. With m H known, all properties of the SM Higgs boson, such as its production cross section and partial decay widths, can be predicted. Increasingly precise measurements [10][11][12][13] have established that all observed properties of the new particle, including its spin, parity, and coupling strengths to SM particles are consistent within the uncertainties with those expected for the SM Higgs boson.The ATLAS and CMS Collaborations have independently measured m H using the samples of proton-proton collision data collected in 2011 and 2012, commonly referred to as LHC Run 1. The analyzed samples correspond to approximately 5 fb −1 of integrated luminosity at ffiffi ffi s p ¼ 7 TeV, and 20 fb −1 at ffiffi ffi s p ¼ 8 TeV, for each experiment. Combined results in the context of the separate experiments, as well as those in the individual channels, are presented in Refs. [12,[14][15][16].This Letter describes a combination of the Run 1 data from the two experiments, leading to improved precision for m H . Besides its intrinsic importance as a fundamental parameter, improved knowledge of m H yields more precise predictions for the other Higgs boson properties. Furthermore, the combined mass measurement provides a first step towards combinations of other quantities, such as the couplings. In the SM, m H is related to the values of the masses of the W boson and top quark through loopinduced effects. Taking into account other measured SM quantities, the comparison of the measurements of the Higgs boson, W boson, and top quark masses can be used to directly test the consistency of the SM [17] and thus to search for evidence of physics beyond the SM.The combination is performed usin...

The performance of muon reconstruction, identification, and triggering in CMS has been studied using 40 pb −1 of data collected in pp collisions at √ s = 7 TeV at the LHC in 2010. A few benchmark sets of selection criteria covering a wide range of physics analysis needs have been examined. For all considered selections, the efficiency to reconstruct and identify a muon with a transverse momentum p T larger than a few GeV/c is above 95% over the whole region of pseudorapidity covered by the CMS muon system, |η| < 2.4, while the probability to misidentify a hadron as a muon is well below 1%. The efficiency to trigger on single muons with p T above a few GeV/c is higher than 90% over the full η range, and typically substantially better. The overall momentum scale is measured to a precision of 0.2% with muons from Z decays. The transverse momentum resolution varies from 1% to 6% depending on pseudorapidity for muons with p T below 100 GeV/c and, using cosmic rays, it is shown to be better than 10% in the central region up to p T = 1 TeV/c. Observed distributions of all quantities are well reproduced by the Monte Carlo simulation.

By using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally segmented electromagnetic and hadronic calorimeters. The transverse energies of dijets in opposite hemispheres are observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.

A search for squarks and gluinos in final states containing high-p T jets, missing transverse momentum and no electrons or muons is presented. The data were recorded in 2012 by the ATLAS experiment in √ s = 8 TeV proton-proton collisions at the Large Hadron Collider, with a total integrated luminosity of 20.3 fb −1 . Results are interpreted in a variety of simplified and specific supersymmetry-breaking models assuming that R-parity is conserved and that the lightest neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 1330 GeV for a simplified model incorporating only a gluino and the lightest neutralino. For a simplified model involving the strong production of first-and second-generation squarks, squark masses below 850 GeV (440 GeV) are excluded for a massless lightest neutralino, assuming mass degenerate (single light-flavour) squarks. In mSUGRA/CMSSM models with tan β = 30, A 0 = −2m 0 and µ > 0, squarks and gluinos of equal mass are excluded for masses below 1700 GeV. Additional limits are set for non-universal Higgs mass models with gaugino mediation and for simplified models involving the pair production of gluinos, each decaying to a top squark and a top quark, with the top squark decaying to a charm quark and a neutralino. These limits extend the region of supersymmetric parameter space excluded by previous searches with the ATLAS detector.

Searches for the electroweak production of charginos, neutralinos and sleptons in final states characterized by the presence of two leptons (electrons and muons) and missing transverse momentum are performed using 20.3 fb −1 of proton-proton collision data at √ s = 8 TeV recorded with the ATLAS experiment at the Large Hadron Collider.No significant excess beyond Standard Model expectations is observed. Limits are set on the masses of the lightest chargino, next-to-lightest neutralino and sleptons for different lightest-neutralino mass hypotheses in simplified models. Results are also interpreted in various scenarios of the phenomenological Minimal Supersymmetric Standard Model.Keywords: Supersymmetry, Hadron-Hadron Scattering The ATLAS collaboration 33 IntroductionSupersymmetry (SUSY) [1][2][3][4][5][6][7][8][9] is a spacetime symmetry that postulates for each Standard Model (SM) particle the existence of a partner particle whose spin differs by one-half unit. The introduction of these new particles provides a potential solution to the hierarchy problem [10][11][12][13]. If R-parity is conserved [14][15][16][17][18], as is assumed in this paper, SUSY particles are always produced in pairs and the lightest supersymmetric particle (LSP) emerges as a stable dark-matter candidate.-1 - JHEP05(2014)071The charginos and neutralinos are mixtures of the bino, winos and higgsinos that are superpartners of the U(1), SU(2) gauge bosons and the Higgs bosons, respectively. Their mass eigenstates are referred to asχ ± i (i = 1, 2) andχ 0 j (j = 1, 2, 3, 4) in the order of increasing masses. Even though the gluinos and squarks are produced strongly in pp collisions, if the masses of the gluinos and squarks are large, the direct production of charginos, neutralinos and sleptons through electroweak interactions may dominate the production of SUSY particles at the Large Hadron Collider (LHC). Such a scenario is possible in the general framework of the phenomenological minimal supersymmetric SM (pMSSM) [19][20][21]. Naturalness suggests that third-generation sparticles and some of the charginos and neutralinos should have masses of a few hundred GeV [22,23]. Light sleptons are expected in gauge-mediated [24][25][26][27][28][29] and anomaly-mediated [30,31] SUSY breaking scenarios. Light sleptons could also play a role in the co-annihilation of neutralinos, allowing a dark matter relic density consistent with cosmological observations [32,33]. This paper presents searches for electroweak production of charginos, neutralinos and sleptons using 20.3 fb −1 of proton-proton collision data with a centre-of-mass energy √ s = 8 TeV collected at the LHC with the ATLAS detector. The searches target final states with two oppositely-charged leptons (electrons or muons) and missing transverse momentum. Similar searches [34,35] SUSY scenariosSimplified models [42] are considered for optimization of the event selection and interpretation of the results. The LSP is the lightest neutralinoχ 0 1 in all SUSY scenarios considered, except in...

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This paper presents a search for the pair production of top squarks in events with a single isolated electron or muon, jets, large missing transverse momentum, and large transverse mass. The data sample corresponds to an integrated luminosity of 19.5 fb −1 of pp collisions collected in 2012 by the CMS experiment at the LHC at a center-of-mass energy of √ s = 8 TeV. No significant excess in data is observed above the expectation from standard model processes. The results are interpreted in the context of supersymmetric models with pair production of top squarks that decay either to a top quark and a neutralino or to a bottom quark and a chargino. For small mass values of the lightest supersymmetric particle, top-squark mass values up to around 650 GeV are excluded.Published in the European Physical Journal C as doi:10.1140/epjc/s10052-013-2677-2. IntroductionThe standard model (SM) has been extremely successful at describing particle physics phenomena. However, it suffers from such shortcomings as the hierarchy problem, where fine-tuned cancellations of large quantum corrections are required in order for the Higgs boson to have a mass at the electroweak symmetry breaking scale of order 100 GeV [1][2][3][4][5][6]. Supersymmetry (SUSY) is a popular extension of the SM that postulates the existence of a superpartner for every SM particle, with the same quantum numbers but differing by one half-unit of spin. SUSY potentially provides a "natural", i.e., not fine-tuned, solution to the hierarchy problem through the cancellations of the quadratic divergences of the top-quark and top-squark loops. In addition, it provides a connection to cosmology, with the lightest supersymmetric particle (LSP), if neutral and stable, serving as a dark matter candidate in R-parity conserving SUSY models. This paper describes a search for the pair production of top squarks using the full dataset collected at √ s = 8 TeV by the Compact Muon Solenoid (CMS) experiment [7] at the Large Hadron Collider (LHC) during 2012, corresponding to an integrated luminosity of 19.5 fb −1 . This search is motivated by the consideration that relatively light top squarks, with masses below around 1 TeV, are necessary if SUSY is to be the natural solution to the hierarchy problem [8][9][10][11][12]. These constraints are especially relevant given the recent discovery of a particle that closely resembles a Higgs boson, with a mass of ∼125 GeV [13][14][15]. Searches for top-squark pair production have also been performed by the ATLAS Collaboration at the LHC in several final states [16][17][18][19][20], and by the CDF [21] and D0 [22] Collaborations at the Tevatron.The search presented here focuses on two decay modes of the top squark ( t): t → t χ 0 1 and t → b χ + . These modes are expected to have large branching fractions if kinematically allowed. Here t and b are the top and bottom quarks, and the neutralinos ( χ 0 ) and charginos ( χ ± ) are the mass eigenstates formed by the linear combination of the gauginos and higgsinos, which are the fermi...