Two of the most pressing questions in current research in Particle Physics are the characterisation of the newly discovered Higgs-like boson at the LHC and the search for New Phenomena beyond the ...Standard Model of Particle Physics. Physicists at LPSC in Grenoble are leading the search for one type of New Phenomena in ATLAS. Given the rich multitude of physics studies proceeding in parallel in ATLAS, one limiting factor in the timely analysis of data is the availability of computing resources. Another LPSC team suffers from the same limitation. This team is leading the ultimate precision measurement of the W boson mass with DØ data, which yields an indirect constraint on the Higgs boson mass which can be compared with the direct measurements of the mass of the newly discovered boson at LHC. In this paper, we describe the synergy between CIMENT, a regional multidisciplinary HPC centre, and the HEP community in Grenoble in the context of the analysis of data recorded by the ATLAS experiment at the LHC collider and the D0 experiment at the Tevatron collider. CIMENT is a federation of twelve HPC clusters, of about 90 TFlop/s, one of the most powerful HPC tier-2 centres in France. The sharing of resources between different scientific fields, like the ones discussed in this article, constitutes a great asset because the spikes in need of computing resources are uncorrelated in time between different fields.
Recent results from the CDF and DØ Collaborations on searches for squarks and gluinos at the Run II of the Fermilab Tevatron collider are presented. This review covers searches for final states ...involving specific mass hierarchies. The analysed datasets correspond to an integrated luminosity of 300-1000 pb-1 collected from proton anti-proton collisions at a center-of-mass energy of 1.96 TeV. No significant deviations from the Standard Model expectations are observed and limits on parameters of supersymmetry are set in generic MSSM and in specific mSUGRA scenarios.
We report on a search for the pair production of second generation scalar leptoquarks (LQ) in pp¯ collisions at the center of mass energy s=1.96 TeV using a data set corresponding to an integrated ...luminosity of 1.0 fb−1 collected with the DØ experiment at the Fermilab Tevatron Collider. Topologies arising from the LQLQ¯→μqνq and LQLQ¯→μqμq decay modes are investigated. No excess of data over the standard model prediction is observed and upper limits on the leptoquark pair production cross section are derived at the 95% C.L. as a function of the leptoquark mass and the branching fraction β for the decay LQ→μq. These are interpreted as lower limits on the leptoquark mass as a function of β. For β=1(0.5), scalar second generation leptoquarks with masses up to 316 GeV (270 GeV) are excluded.
A fully instrumented slice of the ATLAS detector was exposed to test beams from the SPS (Super Proton Synchrotron) at CERN in 2004. In this paper, the results of the measurements of the response of ...the barrel calorimeter to hadrons with energies in the range 20–350
GeV and beam impact points and angles corresponding to pseudo-rapidity values in the range 0.2–0.65 are reported. The results are compared to the predictions of a simulation program using the Geant 4 toolkit.
A search is presented for production of a heavy up-type quark (t') together with its antiparticle, assuming a significant branching ratio for subsequent decay into a W boson and a b quark. The search ...is based on 4.7 fb^-1 of pp collisions at sqrt(s)=7 TeV recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. Data are analyzed in the lepton+jets final state, characterized by a high-transverse-momentum isolated electron or muon, large missing transverse momentum and at least three jets. The analysis strategy relies on the substantial boost of the W bosons in the t't'bar signal when mt'>=400 GeV. No significant excess of events above the Standard Model expectation is observed and the result of the search is interpreted in the context of fourth-generation and vector-like quark models. Under the assumption of a branching ratio BR(t'->Wb)=1, a fourth-generation t' quark with mass lower than 656 GeV is excluded at 95% confidence level. In addition, in light of the recent discovery of a new boson of mass ~126 GeV at the LHC, upper limits are derived in the two-dimensional plane of BR(t'->Wb) versus BR(t'->Ht), where H is the Standard Model Higgs boson, for vector-like quarks of various masses.
In several extensions of the Standard Model, the top quark can decay into a bottom quark and a light charged Higgs boson H+, t to bH+, in addition to the Standard Model decay t to bW. Since W bosons ...decay to the three lepton generations equally, while H+ may predominantly decay into tau+nu, charged Higgs bosons can be searched for using the violation of lepton universality in top quark decays. The analysis in this paper is based on 4.6/fb of proton-proton collision data at sqrt(s) = 7 TeV collected by the ATLAS experiment at the Large Hadron Collider. Signatures containing leptons (e or mu) and/or a hadronically decaying tau (tau_had) are used. Event yield ratios between e+tau_had and e+mu, as well as between mu+tau_had and mu+e, final states are measured in the data and compared to predictions from simulations. This ratio-based method reduces the impact of systematic uncertainties in the analysis. No significant deviation from the Standard Model predictions is observed. With the assumption that the branching fraction B(H+ to tau+nu) is 100%, upper limits in the range 3.2%-4.4% can be placed on the branching fraction B(t to bH+) for charged Higgs boson masses m(H+) in the range 90-140 GeV. After combination with results from a search for charged Higgs bosons in ttbar decays using the tau_had+jets final state, upper limits on B(t to bH+) can be set in the range 0.8%-3.4%, for m(H+) in the range 90-160 GeV.
A measurement of the top quark pair production cross section in the final state with a hadronically decaying tau lepton and jets is presented. The analysis is based on proton-proton collision data ...recorded by the ATLAS experiment at the LHC, with a centre-of-mass energy of 7 TeV. The data sample corresponds to an integrated luminosity of 1.67 inverse femtobarns. The cross section is measured to be 194 +/- 18 (stat.) +/- 46 (syst.) pb and is in agreement with other measurements and with the Standard Model prediction.
A measurement of splitting scales, as defined by the kT clustering algorithm, is presented for final states containing a W boson produced in proton--proton collisions at a centre-of-mass energy of 7 ...TeV. The measurement is based on the full 2010 data sample corresponding to an integrated luminosity of 36 pb-1 which was collected using the ATLAS detector at the CERN Large Hadron Collider. Cluster splitting scales are measured in events containing W bosons decaying to electrons or muons. The measurement comprises the four hardest splitting scales in a kT cluster sequence of the hadronic activity accompanying the W boson, and ratios of these splitting scales. Backgrounds such as multi-jet and top-quark-pair production are subtracted and the results are corrected for detector effects. Predictions from various Monte Carlo event generators at particle level are compared to the data. Overall, reasonable agreement is found with all generators, but larger deviations between the predictions and the data are evident in the soft regions of the splitting scales.
The production of W bosons in association with two jets in proton-proton collisions at a centre-of-mass energy of sqrt(s)=7 TeV has been analysed for the presence of double-parton interactions using ...data corresponding to an integrated luminosity of 36/pb, collected with the ATLAS detector at the LHC. The fraction of events arising from double-parton interactions, fDP(D) has been measured through the momentum balance between the two jets and amounts to fDP(D) = 0.08 +- 0.01 (stat.) +- 0.02 (sys) for jets with transverse momentum PT > 20 GeV and rapidity |y|<2.8. This corresponds to a measurement of the effective area parameter for hard double-parton interactions of \sigma_eff = 15 +- 3 (stat.) +5 -3 (sys.) mb.
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