Engineering topics
Ask, S.
Publications and source records attributed to Ask, S..
Search for lepton flavour violation in the eμ continuum with the ATLAS detector in $\sqrt{s} = 7~\mbox{TeV}$ pp collisions at the LHC
This paper presents a search for the t-channel exchange of an R-parity violating scalar top quark ($\sim\atop{t}$) 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 (m$_t^-$). 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 m$_t^-$ = 95 GeV to 30 fb for m$_t^-$ = 1000 GeV.
Measurement of multi-jet cross sections in proton–proton collisions at a 7 TeV center-of-mass energy
Inclusive multi-jet production is studied in proton–proton collisions at a center-of-mass energy of 7 TeV, using the ATLAS detector. The data sample corresponds to an integrated luminosity of 2.4 pb -1 . Results on multi-jet cross sections are presented and compared to both leading-order plus parton-shower Monte Carlo predictions and to next-to-leading-order QCD calculations.
Inclusive search for same-sign dilepton signatures in pp collisions at $ \sqrt {s} = 7 $ TeV with the ATLAS detector
An inclusive search is presented for new physics in events with two isolated leptons (e or μ) having the same electric charge. The data are selected from events collected from pp collisions at √s = 7 TeV by the ATLAS detector and correspond to an integrated luminosity of 34 pb –1 . The spectra in dilepton invariant mass, missing transverse momentum and jet multiplicity are presented and compared to Standard Model predictions. In this event sample, no evidence is found for contributions beyond those of the Standard Model. Limits are set on the cross-section in a fiducial region for new sources of same-sign high-mass dilepton events in the ee, eμ and μμ channels. Four models predicting same-sign dilepton signals are constrained: two descriptions of Majorana neutrinos, a cascade topology similar to supersymmetry or universal extra dimensions, and fourth generation d-type quarks. Assuming a new physics scale of 1 TeV, Majorana neutrinos produced by an effective operator V with masses below 460 GeV are excluded at 95% confidence level. In conclusion, a lower limit of 290 GeV is set at 95% confidence level on the mass of fourth generation d-type quarks.
Limits on the production of the standard model Higgs boson in pp collisions at $\sqrt{s} = 7$ TeV with the ATLAS detector
A search for the Standard Model Higgs boson at the Large Hadron Collider (LHC) running at a centre-of-mass energy of 7 TeV is reported, based on a total integrated luminosity of up to 40 pb -1 collected by the ATLAS detector in 2010. Several Higgs boson decay channels: H→γγ, H→ZZ (*) →ℓℓℓℓ, H→ZZ→ℓℓνν, H→ZZ→ℓℓqq, H→WW (*) →ℓνℓν and H→WW→ℓνqq (ℓ is e, μ) are combined in a mass range from 110 GeV to 600 GeV. The highest sensitivity is achieved in the mass range between 160 GeV and 170 GeV, where the expected 95% CL exclusion sensitivity is at Higgs boson production cross sections 2.3 times the Standard Model prediction. Upper limits on the cross section for its production are determined. Models with a fourth generation of heavy leptons and quarks with Standard Model-like couplings to the Higgs boson are also investigated and are excluded at 95% CL for a Higgs boson mass in the range from 140 GeV to 185 GeV.
Measurement of the W⁺W⁻ Cross Section in √s=7 TeV pp Collisions with ATLAS
This Letter presents a measurement of the W⁺W⁻ production cross section in √s=7 TeV pp collisions by the ATLAS experiment, using 34 pb⁻¹ of integrated luminosity produced by the Large Hadron Collider at CERN. Selecting events with two isolated leptons, each either an electron or a muon, 8 candidate events are observed with an expected background of 1.7±0.6 events. The measured cross section is 41 +20 -16 (stat)±5(syst)±1(lumi) pb, which is consistent with the standard model prediction of 44±3 pb calculated at next-to-leading order in QCD.
Search for an excess of events with an identical flavour lepton pair and significant missing transverse momentum in $\sqrt{s}=7$ TeV proton–proton collisions with the ATLAS detector
Results are presented of a search for supersymmetric particles decaying into final states with significant missing transverse momentum and exactly two identical flavour leptons (e, μ) of opposite charge in √s = 7 TeV collisions at the Large Hadron Collider. This channel is particularly sensitive to supersymmetric particle cascade decays producing flavour correlated lepton pairs. Flavour uncorrelated backgrounds are subtracted using a sample of opposite flavour lepton pair events. Observation of an excess beyond Standard Model expectations following this subtraction procedure would offer one of the best routes to measuring the masses of supersymmetric particles. In a data sample corresponding to an integrated luminosity of 35 pb⁻¹ no such excess is observed. Model-independent limits are set on the contribution to these final states from new physics and are used to exclude regions of a phenomenological supersymmetric parameter space.
Search for supersymmetric particles in events with lepton pairs and large missing transverse momentum in $\sqrt{s}=7~\mbox{TeV}$ proton–proton collisions with the ATLAS experiment
Results are presented of searches for the production of supersymmetric particles decaying into final states with missing transverse momentum and exactly two isolated leptons in √s = 7 TeV proton-proton collisions at the Large Hadron Collider. Search strategies requiring lepton pairs with identical-sign or opposite-sign electric charges are described. In a data sample corresponding to an integrated luminosity of 35 pb -1 collected with the ATLAS detector, no significant excesses are observed. Based on specific benchmark models, limits are placed on the squark mass between 450 and 690 GeV for squarks approximately degenerate in mass with gluinos, depending on the supersymmetric mass hierarchy considered.
Search for squarks and gluinos using final states with jets and missing transverse momentum with the ATLAS detector in s = 7 TeV proton–proton collisions
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Search for contact interactions in dimuon events from pp collisions at √s=7 TeV with the ATLAS detector
A search for contact interactions has been performed using dimuon events recorded with the ATLAS detector in proton-proton collisions at √s=7 TeV. The data sample corresponds to an integrated luminosity of 42 pb⁻¹. No significant deviation from the standard model is observed in the dimuon mass spectrum, allowing the following 95% C.L. limits to be set on the energy scale of contact interactions: Λ>4.9 TeV (4.5 TeV) for constructive (destructive) interference in the left-left isoscalar compositeness model. These limits are the most stringent to date for μμqq contact interactions.
Search for pair production of first or second generation leptoquarks in proton-proton collisions at √s=7 TeV using the ATLAS detector at the LHC
This paper describes searches for the pair production of first or second generation scalar leptoquarks using 35 pb⁻¹ of proton-proton collision data recorded by the ATLAS detector at s√=7 TeV. Leptoquarks are searched in events with two oppositely-charged muons or electrons and at least two jets, and in events with one muon or electron, missing transverse momentum and at least two jets. After event selection, the observed yields are consistent with the predicted backgrounds. Leptoquark production is excluded at the 95% CL for masses M LQ <376 (319) GeV and M LQ <422 (362) GeV for first and second generation scalar leptoquarks, respectively, when assuming the branching fraction of a leptoquark to a charged lepton is equal to 1.0 (0.5).
Search for high mass dilepton resonances in pp collisions at s = 7 TeV with the ATLAS experiment
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Measurement of the W charge asymmetry in the W → μ ν decay mode in pp collisions at s = 7 TeV with the ATLAS detector
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