Person: Kagan, M
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Publication Search for Heavy Neutrinos and Right-Handed W Bosons in Events With Two Leptons and Jets in pp Collisions at √s =7 TeV With the ATLAS Detector(Springer Nature, 2012) Franklin, Melissa; Huth, John; Jeanty, L; Kagan, M; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Zevi Della Porta, GThis letter reports on a search for hypothetical heavy neutrinos, N, and right-handed gauge bosons, WR, in events with high transverse momentum objects which include two reconstructed leptons and at least one hadronic jet. The results were obtained from data corresponding to an integrated luminosity of 2.1 fb⁻¹ collected in proton–proton collisions at √s = 7 TeV with the ATLAS detector at the CERN Large Hadron Collider. No excess above the Standard Model background expectation is observed. Excluded mass regions forMajorana and Dirac neutrinos are presented using two approaches for interactions that violate lepton and lepton-flavor numbers. One approach uses an effective operator framework, the other approach is guided by the Left– Right Symmetric Model. The results described in this letter represent the most stringent limits to date on the masses of heavy neutrinos and WR bosons obtained in direct searches.Publication Search for Lepton Flavour Violation in the eμ Continuum With the ATLAS Detector in √s=7 TeV Pp Collisions at the LHC(Springer Nature, 2012) Franklin, Melissa; Huth, John; Jeanty, L; Kagan, M; Mercurio, Kevin; Morii, Masahiro; Zevi Della Porta, GThis paper presents a search for the t-channel exchange of an R-parity violating scalar top quark ( t~ ) in the e ± μ ∓ continuum using 2.1 fb−1 of data collected by the ATLAS detector in s√=7 TeV pp collisions at the Large Hadron Collider. Data are found to be consistent with the expectation from the Standard Model backgrounds. Limits on R-parity-violating couplings at 95 % C.L. are calculated as a function of the scalar top mass ( mt~ ). The upper limits on the production cross section for pp→eμX, through the t-channel exchange of a scalar top quark, ranges from 170 fb for mt~=95 GeV to 30 fb for mt~=1000 GeV .Publication Jet Energy Resolution in Proton-Proton Collisions at √s= 7 TeV Recorded in 2010 With the ATLAS Detector(Springer Nature, 2013) Huth, John; Jeanty, L; Kagan, M; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Zevi Della Porta, GThe measurement of the jet energy resolution is presented using data recorded with the ATLAS detector in proton-proton collisions at √s=7 TeV . The sample corresponds to an integrated luminosity of 35 pb−1. Jets are reconstructed from energy deposits measured by the calorimeters and calibrated using different jet calibration schemes. The jet energy resolution is measured with two different in situ methods which are found to be in agreement within uncertainties. The total uncertainties on these measurements range from 20 % to 10 % for jets within |y|<2.8 and with transverse momenta increasing from 30 GeV to 500 GeV. Overall, the Monte Carlo simulation of the jet energy resolution agrees with the data within 10 %.Publication Multi-Channel Search for Squarks and Gluinos in √s=7 TeV pp Collisions With the ATLAS Detector(Springer Nature, 2013) Franklin, Melissa; Huth, John; Jeanty, L; Kagan, M; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Yen, Andy; Zevi Della Porta, GA search for supersymmetric particles in final states with zero, one, and two leptons, with and without jets identified as originating from b-quarks, in 4.7 fb-1 of √s=7 TeV pp collisions produced by the Large Hadron Collider and recorded by the ATLAS detector is presented. The search uses a set of variables carrying information on the event kinematics transverse and parallel to the beam line that are sensitive to several topologies expected in supersymmetry. Mutually exclusive final states are defined, allowing a combination of all channels to increase the search sensitivity. No deviation from the Standard Model expectation is observed. Upper limits at 95% confidence level on fiducial cross-sections for the production of new particles are extracted. Results are interpreted in the context of the constrained minimal supersymmetric extension to the Standard Model and in supersymmetry-inspired models with diverse, high-multiplicity final states.Publication A Search for tt¯ Resonances With the ATLAS Detector in 2.05 Fb−1 of Proton-Proton Collisions at √s=7 TeV(Springer Nature, 2012) Huth, John; Jeanty, L; Kagan, M; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Zevi Della Porta, GA search for top quark pair resonances in final states containing at least one electron or muon has been performed with the ATLAS experiment at the CERN Large Hadron Collider. The search uses a data sample corresponding to an integrated luminosity of 2.05 fb−1, which was recorded in 2011 at a proton-proton centre-of-mass energy of 7 TeV. No evidence for a resonance is found and limits are set on the production cross-section times branching ratio to tt¯ for narrow and wide resonances. For narrow Z′ bosons, the observed 95 % Bayesian credibility level limits range from 9.3 pb to 0.95 pb for masses in the range of m Z′=500 GeV to m Z′=1300 GeV. The corresponding excluded mass region for a leptophobic topcolour Z′ boson (Kaluza-Klein gluon excitation in the Randall-Sundrum model) is m Z′<880 GeV ( mgKK<1130 GeV ).Publication Measurement of tt Production With a Veto on Additional Central Jet Activity in Pp Collisions at √s = 7 TeV Using the ATLAS Detector(Springer Nature, 2012) Franklin, Melissa; Huth, John; Jeanty, L; Kagan, M; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Skottowe, Hugh Philip; Zevi Della Porta, GA measurement of the jet activity in tt events produced in proton–proton collisions at a centre-of-mass energy of 7 TeV is presented, using 2.05 fb^(−1) of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. The tt events are selected in the dilepton decay channel with two identified b-jets from the top quark decays. Events are vetoed if they contain an additional jet with transverse momentum above a threshold in a central rapidity interval. The fraction of events surviving the jet veto is presented as a function of this threshold for four different central rapidity interval definitions. An alternate measurement is also performed, in which events are vetoed if the scalar transverse momentum sum of the additional jets in each rapidity interval is above a threshold. In both measurements, the data are corrected for detector effects and compared to the theoretical models implemented in MC@NLO, Powheg, Alpgen and Sherpa. The experimental uncertainties are often smaller than the spread of theoretical predictions, allowing deviations between data and theory to be observed in some regions of phase space.Publication Measurement of K T Splitting Scales in W→ℓν Events at √s=7 TeV With the ATLAS Detector(Springer Nature, 2013) Barreiro Guimarães da Costa, Joao; Catastini, Pierluigi; Franklin, Melissa; Huth, John; Jeanty, L; Kagan, M; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Skottowe, Hugh Philip; Yen, Andy; Zevi Della Porta, GA measurement of splitting scales, as defined by the k T 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 k T 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.Publication Measurement of the Inclusive Jet Cross-Section in pp Collisions at √s=2.76 TeV and Comparison to the Inclusive Jet Cross-Section at √s=7 TeV Using the ATLAS Detector(Springer Nature, 2013) Franklin, Melissa; Huth, John; Jeanty, L; Kagan, M; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Zevi Della Porta, GThe inclusive jet cross-section has been measured in proton–proton collisions at s√=2.76 TeV in a dataset corresponding to an integrated luminosity of 0.20 pb−1 collected with the ATLAS detector at the Large Hadron Collider in 2011. Jets are identified using the anti-k t algorithm with two radius parameters of 0.4 and 0.6. The inclusive jet double-differential cross-section is presented as a function of the jet transverse momentum p T and jet rapidity y, covering a range of 20≤p T<430 GeV and |y|<4.4. The ratio of the cross-section to the inclusive jet cross-section measurement at √s=7 TeV , published by the ATLAS Collaboration, is calculated as a function of both transverse momentum and the dimensionless quantity xT=2pT/s√ , in bins of jet rapidity. The systematic uncertainties on the ratios are significantly reduced due to the cancellation of correlated uncertainties in the two measurements. Results are compared to the prediction from next-to-leading order perturbative QCD calculations corrected for non-perturbative effects, and next-to-leading order Monte Carlo simulation. Furthermore, the ATLAS jet cross-section measurements at √s=2.76 TeV and √s=7 TeV are analysed within a framework of next-to-leading order perturbative QCD calculations to determine parton distribution functions of the proton, taking into account the correlations between the measurements.Publication Search for a Light Charged Higgs Boson in the Decay Channel H+->csbar in Ttbar Events Using pp Collisions at sqrt(s) = 7 TeV With the ATLAS Detector(Springer Nature, 2013) Franklin, Melissa; Huth, John; Kagan, M; Jeanty, L; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Yen, Andy; Zevi Della Porta, GA search for a charged Higgs boson (H+) in ttbar decays is presented, where one of the top quarks decays via t->H+b, followed by H+->two jets (csbar). The other top quark decays to Wb, where the W boson then decays into a lepton (e/mu) and a neutrino. The data were recorded in pp collisions at sqrt(s) = 7TeV 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 Br(H+->csbar)=100%.Publication Improved Luminosity Determination in pp Collisions at √s = 7 TeV Using the ATLAS Detector at the LHC(Springer Nature, 2013) Huth, John; Jeanty, L; Kagan, M; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Skottowe, Hugh Philip; Zevi Della Porta, GThe luminosity calibration for the ATLAS detector at the LHC during pp collisions at √s=7 TeV in 2010 and 2011 is presented. Evaluation of the luminosity scale is performed using several luminosity-sensitive detectors, and comparisons are made of the long-term stability and accuracy of this calibration applied to the pp collisions at √s=7 TeV. A luminosity uncertainty of Delta L/L = +/- 3.5% is obtained for the 47 pb-1 of data delivered to ATLAS in 2010, and an uncertainty of Delta L/L = +/- 1.8% is obtained for the 5.5 fb-1 delivered in 2011.