Search for contact interactions and large extra dimensions in dilepton events from pp collisions at root s=7 TeV with the ATLAS detector
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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Silicon Detector Results from the First Five-Tower Run of CDMSII
Silicon Detector Results from the First Five-Tower Run of CDMSII
Agnese, R.↗
Search for a Higgs boson in diphoton final states with the D0 detector in9.6 fb-1ofpp¯collisions ats=1.96 TeV
.We present a search for a Higgs boson decaying into a pair of photons based on 9.6 fb- 1 of $p\bar{p}$ collisions at $\sqrt{s}$ = 1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. The search employs multivariate techniques to discriminate signal from the nonresonant background and is separately optimized for a standard model and a fermiophobic Higgs boson. No significant excess of data above the background prediction is observed and upper limits on the product of the cross section and branching fraction are derived at the 95% confidence level as a function of Higgs boson mass. For a standard model Higgs boson with mass of 125 GeV, the observed (expected) upper limits are a factor of 12.8 (8.7) above the standard model prediction. The existence of a fermiophobic Higgs boson with mass in the 100–113 GeV range is excluded at the 95% confidence level.
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Search for microscopic black holes in a like-sign dimuon final state using large track multiplicity with the ATLAS detector
A search is presented for microscopic black holes in a like-sign dimuon final state in proton-proton collisions at $ \sqrt{s}$=8 TeV. The data were collected with the ATLAS detector at the Large Hadron Collider in 2012 and correspond to an integrated luminosity of 20.3 fb -1 . Using a high track multiplicity requirement, 0.6±0.2 background events from Standard Model processes are predicted and none observed. This result is interpreted in the context of low-scale gravity models and 95% C.L. lower limits on microscopic black hole masses are set for different model assumptions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for charginos nearly mass degenerate with the lightest neutralino based on a disappearing-track signature in pp collisions at root(s)=8 TeV with the ATLAS detector
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of the inclusive isolated prompt photons cross section in p p collisions at s = 7 TeV with the ATLAS detector using 4.6 fb - 1
A measurement of the cross section for the production of isolated prompt photons in pp collisions at a center-of-mass energy $ \sqrt{s}$ =7 TeV is presented. The results are based on an integrated luminosity of 4.6 fb -1 collected with the ATLAS detector at the LHC. The cross section is measured as a function of photon pseudorapidity ηγ and transverse energy E γ T in the kinematic range 100 ≤ E γ T < 1000 GeV and in the regions |η γ | < 1.37 and 1.52 ≤ |η γ | < 2.37. The results are compared to leading-order parton-shower Monte Carlo models and next-to-leading-order perturbative QCD calculations. Next-to-leading-order perturbative QCD calculations agree well with the measured cross sections as a function of E γ T and η γ .
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Study of heavy-flavor quarks produced in association with top-quark pairs at s = 7 TeV using the ATLAS detector
Using a sample of dilepton top-quark pair (t$\bar{t}$) candidate events, a study is performed of the production of top-quark pairs together with heavy-flavor (HF) quarks, the sum of t$\bar{t}$+b+X and t$\bar{t}$+c+X, collectively referred to as t$\bar{t}$+HF. The data set used corresponds to an integrated luminosity of 4.7 fb -1 of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. The presence of additional HF (b or c) quarks in the t$\bar{t}$ sample is inferred by looking for events with at least three b-tagged jets, where two are attributed to the b quarks from the t$\bar{t}$decays and the third to additional HF production. The dominant background to t$\bar{t}$+HF in this sample is t$\bar{t}$+jet events in which a light-flavor jet is misidentified as a heavy-flavor jet. To determine the heavy- and light-flavor content of the additional b -tagged jets, a fit to the vertex mass distribution of b -tagged jets in the sample is performed. The result of the fit shows that 79±14(stat)±22(syst) of the 105 selected extra b -tagged jets originate from HF quarks, 3 standard deviations away from the hypothesis of zero t$\bar{t}$+HF production. The result for extra HF production is quoted as a ratio (R HF ) of the cross section for t$\bar{t}$+HF production to the cross section for t$\bar{t}$ production with at least one additional jet. Both cross sections are measured in a fiducial kinematic region within the ATLAS acceptance. R HF is measured to be [6.2±1.1(stat)±1.8(syst)]% for jets with p T >25GeV and |η|<2.5, in agreement with the expectations from Monte Carlo generators.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for dark matter in events with a Z boson and missing transverse momentum in p p collisions at s = 8 TeV with the ATLAS detector
A search is presented for production of dark-matter particles recoiling against a leptonically decaying Z boson in 20.3 fb -1 of pp collisions at $ \sqrt{s} $=8 TeV with the ATLAS detector at the Large Hadron Collider. Events with large missing transverse momentum and two oppositely charged electrons or muons consistent with the decay of a Z boson are analyzed. No excess above the Standard Model prediction is observed. Limits are set on the mass scale of the contact interaction as a function of the dark-matter particle mass using an effective field theory description of the interaction of dark matter with quarks or with Z bosons. Limits are also set on the coupling and mediator mass of a model in which the interaction is mediated by a scalar particle.
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Search for high-mass dilepton resonances in p p collisions at s = 8 TeV with the ATLAS detector
Here, the ATLAS detector at the Large Hadron Collider is used to search for high-mass resonances decaying to dielectron or dimuon final states. Results are presented from an analysis of proton-proton (pp) collisions at a center-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3 fb –1 in the dimuon channel. A narrow resonance with Standard Model Z couplings to fermions is excluded at 95% confidence level for masses less than 2.79 TeV in the dielectron channel, 2.53 TeV in the dimuon channel, and 2.90 TeV in the two channels combined. Limits on other model interpretations are also presented, including a grand-unification model based on the E 6 gauge group, Z* bosons, minimal Z' models, a spin-2 graviton excitation from Randall-Sundrum models, quantum black holes, and a minimal walking technicolor model with a composite Higgs boson.
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Simultaneous measurements of the t t ¯ , W + W – , and Z / γ * → τ τ production cross-sections in p p collisions at s = 7 TeV with the ATLAS detector
Simultaneous measurements of the tt¯, W⁺W⁻, and Z/γ ∗ → ττ production cross-sections using an integrated luminosity of 4.6 fb⁻¹ of pp collisions at √s = 7 TeV collected by the ATLAS detector at the LHC are presented. Events are selected with two high transverse momentum leptons consisting of an oppositely charged electron and muon pair. The three processes are separated using the distributions of the missing transverse momentum of events with zero and greater than zero jet multiplicities. Measurements of the fiducial cross-section are presented along with results that quantify for the first time the underlying correlations in the predicted and measured cross-sections due to proton parton distribution functions. These results indicate that the correlated next-to-leading-order predictions for tt¯ and Z/γ ∗ → ττ underestimate the data, while those at next-to-next-to-leading-order generally describe the data well. The full cross-sections are measured to be σ(tt¯) = 181.2 ± 2.8⁺⁹̣˙⁷₋₉̣₅ ± 3.3 ± 3.3 pb, σ(W⁺W⁻) = 53.3 ± 2.7⁺⁷˙³₋₈̣₀ ± 1.0 ± 0.5 pb, and σ(Z/γ ∗ → ττ) = 1174 ± 24⁺⁷²₋₈₇ ± 21 ± 9 pb, where the cited uncertainties are due to statistics, systematic effects, luminosity and the LHC beam energy measurement, respectively. The W⁺W⁻ measurement includes the small contribution from Higgs boson decays, H → W⁺W⁻.
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Search for photonic signatures of gauge-mediated supersymmetry in 8 TeV p p collisions with the ATLAS detector
A search is presented for photonic signatures motivated by generalized models of gauge-mediated supersymmetry breaking. This search makes use of 20.3 fb -1 of proton-proton collision data at √s=8 TeV recorded by the ATLAS detector at the LHC, and explores models dominated by both strong and electroweak production of supersymmetric partner states. Four experimental signatures incorporating an isolated photon and significant missing transverse momentum are explored. These signatures include events with an additional photon, lepton, b-quark jet, or jet activity not associated with any specific underlying quark flavor. No significant excess of events is observed above the Standard Model prediction and model-dependent 95% confidence-level exclusion limits are set.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for pair production of a new heavy quark that decays into a W boson and a light quark in p p collisions at s = 8 TeV with the ATLAS detector
We present a search for pair production of a new heavy quark ( Q ) that decays into a W boson and a light quark (q) in the final state where one W boson decays leptonically (to an electron or muon plus a neutrino) and the other W boson decays hadronically. The analysis is performed using an integrated luminosity of 20.3 fb -1 of pp collisions at $\sqrt{s}$ = 8 TeV collected by the ATLAS detector at the LHC. No evidence of $Q\overline{Q}$ production is observed. New chiral quarks with masses below 690 GeV are excluded at 95% confidence level, assuming BR ( Q → W q ) = 1 . Results are also interpreted in the context of vectorlike quark models, resulting in the limits on the mass of a vectorlike quark in the two-dimensional plane of BR ( Q → W q ) versus BR ( Q → H q ) .
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Measurement of the correlation between the polar angles of leptons from top quark decays in the helicity basis at $\sqrt{s}$ = 7 TeV using the ATLAS detector
A measurement of the correlations between the polar angles of leptons from the decay of pair-produced t and $\bar{t}$ quarks in the helicity basis is reported, using proton-proton collision data collected by the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 4.6 fb$^{-1}$ at a center-of-mass energy of $\sqrt{s}$ = 7 TeV collected during 2011. Candidate events are selected in the dilepton topology with large missing transverse momentum and at least two jets. The angles θ$_1$ and θ$_2$ between the charged leptons and the direction of motion of the parent quarks in the $t\bar{t}$ rest frame are sensitive to the spin information, and the distribution of cosθ$_1$ ∙ cosθ$_2$ is sensitive to the spin correlation between the t and $\bar{t}$ quarks. The distribution is unfolded to parton level and compared to the next-to-leading order prediction. A good agreement is observed.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of the differential cross-section of highly boosted top quarks as a function of their transverse momentum in s = 8 TeV proton-proton collisions using the ATLAS detector
The differential cross-section for pair production of top quarks with high transverse momentum is measured in 20.3 fb -1 of proton-proton collisions at a center-of-mass energy of 8 TeV. The measurement is performed for t$\bar{t}$t events in the lepton + jets channel. The cross-section is reported as a function of the hadronically decaying top quark transverse momentum for values above 300 GeV. The hadronically decaying top quark is reconstructed as an anti- k t jet with radius parameter R = 1.0 and identified with jet substructure techniques. The observed yield is corrected for detector effects to obtain a cross-section at particle level in a fiducial region close to the event selection. A parton-level cross-section extrapolated to the full phase space is also reported for top quarks with transverse momentum above 300 GeV. The predictions of a majority of next-to-leading-order and leading-order matrix-element Monte Carlo generators are found to agree with the measured cross-sections.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurements of W ± Z production cross sections in p p collisions at s = 8 TeV with the ATLAS detector and limits on anomalous gauge boson self-couplings
This paper presents measurements of W ± Z production in p p collisions at a center-of-mass energy of 8 TeV. The gauge bosons are reconstructed using their leptonic decay modes into electrons and muons. The data were collected in 2012 by the ATLAS experiment at the Large Hadron Collider and correspond to an integrated luminosity of 20.3 fb - 1 . The measured inclusive cross section in the detector fiducial region is σ W ± Z → ℓ ' ν ℓ ℓ = 35.1 ± 0.9 ( stat ) ± 0.8 ( sys ) ± 0.8 ( lumi ) fb , for one leptonic decay channel. In comparison, the next-to-leading-order Standard Model expectation is 30.0 ± 2.1 fb . Cross sections for W + Z and W - Z production and their ratio are presented as well as differential cross sections for several kinematic observables. Limits on anomalous triple gauge boson couplings are derived from the transverse mass spectrum of the W ± Z system. From the analysis of events with a W and a Z boson associated with two or more forward jets an upper limit at 95% confidence level on the W ± Z scattering cross section of 0.63 fb, for each leptonic decay channel, is established, while the Standard Model prediction at next-to-leading order is 0.13 ± 0.01 fb . Limits on anomalous quartic gauge boson couplings are also extracted.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurements of Z γ and Z γ γ production in p p collisions at s = 8 TeV with the ATLAS detector
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for pair production of gluinos decaying via stop and sbottom in events with b -jets and large missing transverse momentum in p p collisions at s = 13 TeV with the ATLAS detector
A search for supersymmetry involving the pair production of gluinos decaying via third-generation squarks to the lightest neutralino ( χ$~0\atop{1}$ ) is reported. It uses an LHC proton-proton data set at a center-of-mass energy √ s = 13 TeV with an integrated luminosity of 3.2 fb -1 collected with the ATLAS detector in 2015. The signal is searched for in events containing several energetic jets, of which at least three must be identified as b jets, large missing transverse momentum, and, potentially, isolated electrons or muons. Large-radius jets with a high mass are also used to identify highly boosted top quarks. No excess is found above the predicted background. For χ$~0\atop{1}$ masses below approximately 700 GeV, gluino masses of less than 1.78 TeV and 1.76 TeV are excluded at the 95% C.L. in simplified models of the pair production of gluinos decaying via sbottom and stop, respectively. These results significantly extend the exclusion limits obtained with the √ s = 8 TeV data set.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for new phenomena in final states with an energetic jet and large missing transverse momentum in p p collisions at s = 13 TeV using the ATLAS detector
We report results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum. The search uses proton-proton collision data corresponding to an integrated luminosity of 3.2 fb $-$1 at $\sqrt{s}$ = 13 TeV collected in 2015 with the ATLAS detector at the Large Hadron Collider. Events are required to have at least one jet with a transverse momentum above 250 GeV and no leptons. Several signal regions are considered with increasing missing-transverse-momentum requirements between E$miss\atop{T}$ > 250 GeV and E$miss\atop{T}$ > 700 GeV . Good agreement is observed between the number of events in data and Standard Model predictions. The results are translated into exclusion limits in models with large extra spatial dimensions, pair production of weakly interacting dark-matter candidates, and the production of supersymmetric particles in several compressed scenarios.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗