An inclusive search for anomalous production of two prompt, isolated muons with the same electric charge is presented. The search is performed in a data sample corresponding to 1.6 fb−1 of integrated luminosity colle...
An inclusive search for anomalous production of two prompt, isolated muons with the same electric charge is presented. The search is performed in a data sample corresponding to 1.6 fb−1 of integrated luminosity collected in 2011 at s=7 TeV with the ATLAS detector at the LHC. Muon pairs are selected by requiring two isolated muons of the same electric charge with pT>20 GeV and |η|<2.5. Minimal requirements are placed on the rest of the event activity. The distribution of the invariant mass of the muon pair m(μμ) is found to agree well with the background expectation. Upper limits on the cross section for anomalous production of two muons with the same electric charge are placed as a function of m(μμ) within a fiducial region defined by the event selection. The fiducial cross-section limit constrains the like-sign top-quark pair-production cross section to be below 3.7 pb at 95% confidence level. The data are also analyzed to search for a narrow like-sign dimuon resonance as predicted for e.g. doubly charged Higgs bosons (H±±). Assuming pair production of H±± bosons and a branching ratio to muons of 100% (33%), this analysis excludes masses below 355 (244) GeV and 251 (209) GeV for H±± bosons coupling to left-handed and right-handed fermions, respectively.
We report a study of final states containing a W boson and hadronic jets, produced in proton-proton collisions at a center-of-mass energy of 7 TeV. The data were collected with the ATLAS detector at the CERN LHC and c...
We report a study of final states containing a W boson and hadronic jets, produced in proton-proton collisions at a center-of-mass energy of 7 TeV. The data were collected with the ATLAS detector at the CERN LHC and comprise the full 2010 data sample of 36 pb−1. Cross sections are determined using both the electron and muon decay modes of the W boson and are presented as a function of inclusive jet multiplicity, Njet, for up to five jets. At each multiplicity, cross sections are presented as a function of jet transverse momentum, the scalar sum of the transverse momenta of the charged lepton, missing transverse momentum, and all jets, the invariant mass spectra of jets, and the rapidity distributions of various combinations of leptons and final-state jets. The results, corrected for all detector effects and for all backgrounds such as diboson and top quark pair production, are compared with particle-level predictions from perturbative QCD. Leading-order multiparton event generators, normalized to the next-to-next-to-leading-order total cross section for inclusive W-boson production, describe the data reasonably well for all measured inclusive jet multiplicities. Next-to-leading-order calculations from MCFM, studied here for Njet≤2, and BlackHat-Sherpa, studied here for Njet≤4, are found to be mostly in good agreement with the data.
A generic search is presented for a heavy particle decaying to WZ→ℓνℓ′ℓ′ (ℓ, ℓ′=e, μ) final states. The data were recorded by the ATLAS detector in s=7 TeV pp collisions at the Large Hadron Collider and corresp...
A generic search is presented for a heavy particle decaying to WZ→ℓνℓ′ℓ′ (ℓ, ℓ′=e, μ) final states. The data were recorded by the ATLAS detector in s=7 TeV pp collisions at the Large Hadron Collider and correspond to an integrated luminosity of 1.02 fb−1. The transverse mass distribution of the selected WZ candidates is found to be consistent with the standard model expectation. Upper limits on the production cross section times branching ratio are derived using two benchmark models predicting a heavy particle decaying to a WZ pair.
This paper presents a study of the possible ordering of charged hadrons in the azimuthal angle relative to the beam axis in high-energy proton-proton collisions at the Large Hadron Collider (LHC). A spectral analysis ...
This paper presents a study of the possible ordering of charged hadrons in the azimuthal angle relative to the beam axis in high-energy proton-proton collisions at the Large Hadron Collider (LHC). A spectral analysis of correlations between longitudinal and transverse components of the momentum of the charged hadrons, driven by the search for phenomena related to the structure of the QCD field, is performed. Data were recorded with the ATLAS detector at center-of-mass energies of s=900 GeV and s=7 TeV. The correlations measured in a kinematic region dominated by low-pT particles are not well described by conventional models of hadron production. The measured spectra show features consistent with the fragmentation of a QCD string represented by a helixlike ordered gluon chain.
The ATLAS detector is used to search for excited leptons in the electromagnetic radiative decay channel ℓ*→ℓγ. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresp...
The ATLAS detector is used to search for excited leptons in the electromagnetic radiative decay channel ℓ*→ℓγ. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 2.05 fb−1. No evidence for excited leptons is found, and limits are set on the compositeness scale Λ as a function of the excited lepton mass mℓ*. In the special case where Λ=mℓ*, excited electron and muon masses below 1.87 TeV and 1.75 TeV are excluded at 95% C.L., respectively.
Inclusive jet and dijet cross sections have been measured in proton-proton collisions at a center-of-mass energy of 7 TeV using the ATLAS detector at the Large Hadron Collider. The cross sections were measured using j...
Inclusive jet and dijet cross sections have been measured in proton-proton collisions at a center-of-mass energy of 7 TeV using the ATLAS detector at the Large Hadron Collider. The cross sections were measured using jets clustered with the anti-kt algorithm with parameters R=0.4 and R=0.6. These measurements are based on the 2010 data sample, consisting of a total integrated luminosity of 37 pb−1. Inclusive jet double-differential cross sections are presented as a function of jet transverse momentum, in bins of jet rapidity. Dijet double-differential cross sections are studied as a function of the dijet invariant mass, in bins of half the rapidity separation of the two leading jets. The measurements are performed in the jet rapidity range |y|<4.4, covering jet transverse momenta from 20 GeV to 1.5 TeV and dijet invariant masses from 70 GeV to 5 TeV. The data are compared to expectations based on next-to-leading-order QCD calculations corrected for nonperturbative effects, as well as to next-to-leading-order Monte Carlo predictions. In addition to a test of the theory in a new kinematic regime, the data also provide sensitivity to parton distribution functions in a region where they are currently not well-constrained.
The results of a search for supersymmetry in events with large missing transverse momentum and heavy-flavor jets using an integrated luminosity corresponding to 2.05 fb−1 of pp collisions at s=7 TeV recorded with th...
The results of a search for supersymmetry in events with large missing transverse momentum and heavy-flavor jets using an integrated luminosity corresponding to 2.05 fb−1 of pp collisions at s=7 TeV recorded with the ATLAS detector at the Large Hadron Collider are reported. No significant excess is observed with respect to the prediction for standard model processes. Results are interpreted in a variety of R-parity conserving models in which scalar bottoms and tops are the only scalar quarks to appear in the gluino decay cascade, and in an SO(10) model framework. Gluino masses up to 600–900 GeV are excluded, depending on the model considered.
A search is presented for heavy-quark pair production (QQ¯) under the decay hypothesis QQ¯→W+qW−q¯ with q=d, s, b for up-type Q or q=u, c for down-type Q. The search is performed with 1.04 fb−1 of int...
A search is presented for heavy-quark pair production (QQ¯) under the decay hypothesis QQ¯→W+qW−q¯ with q=d, s, b for up-type Q or q=u, c for down-type Q. The search is performed with 1.04 fb−1 of integrated luminosity from pp collisions at s=7 TeV collected by the ATLAS detector at the CERN LHC. Dilepton final states are selected, requiring large missing transverse momentum and at least two jets. Mass reconstruction of heavy-quark candidates is performed by assuming that the W boson decay products are nearly collinear. The data are in agreement with standard model expectations; a heavy quark with mass less than 350 GeV is excluded at 95% confidence level.
Differential measurements of charged particle azimuthal anisotropy are presented for lead-lead collisions at sNN=2.76 TeV with the ATLAS detector at the LHC, based on an integrated luminosity of approximately 8 μb−1....
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Differential measurements of charged particle azimuthal anisotropy are presented for lead-lead collisions at sNN=2.76 TeV with the ATLAS detector at the LHC, based on an integrated luminosity of approximately 8 μb−1. This anisotropy is characterized via a Fourier expansion of the distribution of charged particles in azimuthal angle relative to the reaction plane, with the coefficients vn denoting the magnitude of the anisotropy. Significant v2–v6 values are obtained as a function of transverse momentum (0.52) and one particle with pT<3 GeV, the v2,2–v6,6 values are found to factorize as vn,n(pTa,pTb)≈vn(pTa)vn(pTb) in central and midcentral events. Such factorization suggests that these values of v2,2–v6,6 are primarily attributable to the response of the created matter to the fluctuations in the geometry of the initial state. A detailed study shows that the v1,1(pTa,pTb) data are consistent with the combined contributions from a rapidity-even v1 and global momentum conservation. A two-component fit is used to extract the v1 contribution. The extracted v1 is observed to cross zero at pT≈1.0 GeV, reaches a maximum at 4–5 GeV with a value comparable to that for v3, and decreases at higher pT.
This paper reports a measurement of D*± meson production in jets from proton-proton collisions at a center-of-mass energy of s=7 TeV at the CERN Large Hadron Collider. The measurement is based on a data sample r...
This paper reports a measurement of D*± meson production in jets from proton-proton collisions at a center-of-mass energy of s=7 TeV at the CERN Large Hadron Collider. The measurement is based on a data sample recorded with the ATLAS detector with an integrated luminosity of 0.30 pb−1 for jets with transverse momentum between 25 and 70 GeV in the pseudorapidity range |η|<2.5. D*± mesons found in jets are fully reconstructed in the decay chain: D*+→D0π+, D0→K−π+, and its charge conjugate. The production rate is found to be N(D*±)/N(jet)=0.025±0.001(stat.)±0.004(syst.) for D*± mesons that carry a fraction z of the jet momentum in the range 0.3
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