494 research outputs found
Measurement of the production cross section of jets in association with a Z boson in pp collisions at √s=7 TeV with the ATLAS detector
No full textMeasurements of the production of jets of particles in association with a Z boson in pp collisions at s√=7 TeV are presented, using data corresponding to an integrated luminosity of 4.6 fb−1 collected by the ATLAS experiment at the Large Hadron Collider. Inclusive and differential jet cross sections in Z events, with Z decaying into electron or muon pairs, are measured for jets with transverse momentum p T > 30 GeV and rapidity |y| < 4.4. The results are compared to next-to-leading-order perturbative QCD calculations, and to predictions from different Monte Carlo generators based on leading-order and next-to-leading-order matrix elements supplemented by parton showers
The SU(3)-invariant sector of new maximal supergravity
No full textWe investigate the SU(3)-invariant sector of the one-parameter family of SO(8) gauged maximal supergravities that has been recently discovered. To this end, we construct the N = 2 truncation of this theory and analyse its full vacuum structure. The number of critical point is doubled and includes new N = 0 and N = 1 branches. We numerically exhibit the parameter dependence of the location and cosmological constant of all extrema. Moreover, we provide their analytic expressions for cases of special interest. Finally, while the mass spectra are found to be parameter independent in most cases, we show that the novel non-supersymmetric branch with SU(3) invariance provides the first counterexample to this.
Measurement of the top quark mass with the template method in the t<span style="text-decoration: overline">t</span> →lepton+jets channel using ATLAS data
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103516.pdf (Publisher’s version ) (Open Access
Prospects for Observing an Invisibly Decaying Higgs Boson in Production at the LHC
No full textIn this thesis we study the prospects for observing the invisibly decaying Higgs boson in the associated production at the LHC. The results of the Monte Carlo simulations of signal and background processes show that there is a possibility of observing the statistically significant number of signal events required for the discovery. Moreover, the analysis can be further improved to reduce the number of false reconstructions of the boson. The analysis of the production is independent of the model in which the Higgs boson decays into the invisible channel. There are several possibilities for models where can be of interest. For this thesis, we have studied the simplest supersymmetric model, called mSUGRA. The results of the scans of the mSUGRA model parameter space show that the regions, where the branching ratio of the lightest neutral Higgs boson to the lightest neutralino pair is high, are excluded by current experimental constraints. The channel dominates, and the possibility for discovery in this c hannel will not be suppressed by the invisible decays. This result does not disqualify invisible channel as possible signature in other models. Chapter 4 of this thesis is based on the published paper: B.P. Kersevan, M. Malawski, E. Richter-Was: Prospects for observing an invisibly decaying Higgs boson in the production at the LHC, In: Eur. Phys. J. C, 29(2003) pp. 541-54
Searches for supersymmetry with the ATLAS detector using final states with two leptons and missing transverse momentum in √s=7 TeV proton–proton collisions
No full textResults of three searches are presented for the production of supersymmetric particles decaying into final states with missing transverse momentum and exactly two isolated leptons, e or µ. The analysis uses a data sample collected during the first half of 2011 that corresponds to a total integrated luminosity of 1 fb<sup>−1</sup> of √s=7 TeV proton–proton collisions recorded with the ATLAS detector at the Large Hadron Collider. Opposite-sign and same-sign dilepton events are separately studied, with no deviations from the Standard Model expectation observed. Additionally, in opposite-sign events, a search is made for an excess of same-flavour over different-flavour lepton pairs. Effective production cross sections in excess of 9.9 fb for opposite-sign events containing supersymmetric particles with missing transverse momentum greater than 250 GeV are excluded at 95% CL. For same-sign events containing supersymmetric particles with missing transverse momentum greater than 100 GeV, effective production cross sections in excess of 14.8 fb are excluded at 95% CL. The latter limit is interpreted in a simplified electroweak gaugino production model excluding chargino masses up to 200 GeV, under the assumption that slepton decay is dominant
Search for light scalar top-quark pair production in final states with two leptons with the ATLAS detector in √s =7 TeV proton–proton collisions
No full textA search is presented for the pair production of light scalar top quarks in s√=7 TeV proton–proton collisions recorded with the ATLAS detector at the Large Hadron Collider. This analysis uses the full data sample collected during 2011 running that corresponds to a total integrated luminosity of 4.7 fb−1. Light scalar top quarks are searched for in events with two opposite-sign leptons (e, μ), large missing transverse momentum and at least one jet in the final state. No excess over Standard Model expectations is found, and the results are interpreted under the assumption that the light scalar top decays to a b-quark in addition to an on-shell chargino whose decay occurs through a virtual W boson. If the chargino mass is 106 GeV, light scalar top-quark masses up to 130 GeV are excluded for neutralino masses below 70 GeV
Measurement of the tt production cross section in the tau + jets channel using the ATLAS detector
No full textA 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 fb−1. The cross section is measured to be σtt¯=194±18 (stat.)±46 (syst.) pb and is in agreement with other measurements and with the Standard Model prediction
Measurement of the t\bar{t} production cross section in the tau + jets channel using the ATLAS detector
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111185.pdf (Publisher’s version ) (Open Access
Search for a light charged Higgs boson in the decay channel H+→cs¯ in tt¯ events using pp collisions at s√=7 TeV with the ATLAS detector
No full textA search for a charged Higgs boson (H +) in tt¯ decays is presented, where one of the top quarks decays via t→H + b, followed by H +→ two jets ( cs¯ ). The other top quark decays to Wb, where the W boson then decays into a lepton (e/μ) and a neutrino. The data were recorded in pp collisions at s√=7 TeV by the ATLAS detector at the LHC in 2011, and correspond to an integrated luminosity of 4.7 fb−1. With no observation of a signal, 95 % confidence level (CL) upper limits are set on the decay branching ratio of top quarks to charged Higgs bosons varying between 5 % and 1 % for H + masses between 90 GeV and 150 GeV, assuming B(H+→cs¯)=100 %
Search for charged Higgs bosons through the violation of lepton universality in t\overline{t} events using pp collision data at \sqrt{s}=7 TeV with the ATLAS experiment
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111227.pdf (Publisher’s version ) (Open Access
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