A search for new phenomena in tt¯ events with large missing transverse momentum in proton-proton collisions at a center-of-mass energy of 7 TeV is presented. The measurement is based on 1.04 fb−1 of data collect...
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A search for new phenomena in tt¯ events with large missing transverse momentum in proton-proton collisions at a center-of-mass energy of 7 TeV is presented. The measurement is based on 1.04 fb−1 of data collected with the ATLAS detector at the LHC. Contributions to this final state may arise from a number of standard model extensions. The results are interpreted in terms of a model where new top-quark partners are pair produced and each decay to an on-shell top (or antitop) quark and a long-lived undetected neutral particle. The data are found to be consistent with standard model expectations. A limit at 95% confidence level is set excluding a cross section times branching ratio of 1.1 pb for a top-partner mass of 420 GeV and a neutral particle mass less than 10 GeV. In a model of exotic fourth generation quarks, top-partner masses are excluded up to 420 GeV and neutral particle masses up to 140 GeV.
A process, continuous wrapping tantalum barrier, has been developed and investigated in order to reduce the manufacturing cost. By avoiding inserting expensive tantalum tube, a long sheet barrier was directly used to ...
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Measurements of b hadron production ratios in proton-proton collisions at a center-of-mass energy of 7 TeV with an integrated luminosity of 3 pb−1 are presented. We study the ratios of strange B meson to light B meso...
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Measurements of b hadron production ratios in proton-proton collisions at a center-of-mass energy of 7 TeV with an integrated luminosity of 3 pb−1 are presented. We study the ratios of strange B meson to light B meson production fs/(fu+fd) and Λb0 baryon to light B meson production fΛb/(fu+fd) as a function of the charmed hadron-muon pair transverse momentum pT and the b hadron pseudorapidity η, for pT between 0 and 14 GeV and η between 2 and 5. We find that fs/(fu+fd) is consistent with being independent of pT and η, and we determine fs/(fu+fd)=0.134±0.004−0.010+0.011, where the first error is statistical and the second systematic. The corresponding ratio fΛb/(fu+fd) is found to be dependent upon the transverse momentum of the charmed hadron-muon pair, fΛb/(fu+fd)=(0.404±0.017(stat)±0.027(syst)±0.105(Br))×[1−(0.031±0.004(stat)±0.003(syst))×pT(GeV)], where Br reflects an absolute scale uncertainty due to the poorly known branching fraction B(Λc+→pK−π+). We extract the ratio of strange B meson to light neutral B meson production fs/fd by averaging the result reported here with two previous measurements derived from the relative abundances of B¯s0→Ds+π− to B¯0→D+K− and B¯0→D+π−. We obtain fs/fd=0.267−0.020+0.021.
We introduced a novel negative multiple pulse poling (NMP) method for uniform device fabrication of quasi-phase matching using an in-situ visualization system. Diffraction pattern analysis showed the duty ratio of 0.4...
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This work presents a new inclusive search for supersymmetry (SUSY) by the ATLAS experiment at the LHC in proton-proton collisions at a center-of-mass energy s=7 TeV in final states with jets, missing transverse momen...
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This work presents a new inclusive search for supersymmetry (SUSY) by the ATLAS experiment at the LHC in proton-proton collisions at a center-of-mass energy s=7 TeV in final states with jets, missing transverse momentum and one or more isolated electrons and/or muons. The search is based on data from the full 2011 data-taking period, corresponding to an integrated luminosity of 4.7 fb−1. Single-lepton and multilepton channels are treated together in one analysis. An increase in sensitivity is obtained by simultaneously fitting the number of events in statistically independent signal regions, and the shapes of distributions within those regions. A dedicated signal region is introduced to be sensitive to decay cascades of SUSY particles with small mass differences (“compressed SUSY”). Background uncertainties are constrained by fitting to the jet-multiplicity distribution in background control regions. Observations are consistent with Standard Model expectations, and limits are set or extended on a number of SUSY models.
A combined search for the Standard Model Higgs boson with the ATLAS detector at the LHC is presented. The data sets used correspond to integrated luminosities from 4.6 fb−1 to 4.9 fb−1 of proton-proton collisions co...
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A combined search for the Standard Model Higgs boson with the ATLAS detector at the LHC is presented. The data sets used correspond to integrated luminosities from 4.6 fb−1 to 4.9 fb−1 of proton-proton collisions collected at s=7 TeV in 2011. The Higgs boson mass ranges of 111.4 GeV to 116.6 GeV, 119.4 GeV to 122.1 GeV, and 129.2 GeV to 541 GeV are excluded at the 95% confidence level, while the range 120 GeV to 560 GeV is expected to be excluded in the absence of a signal. An excess of events is observed at Higgs boson mass hypotheses around 126 GeV with a local significance of 2.9 standard deviations (σ). The global probability for the background to produce an excess at least as significant anywhere in the entire explored Higgs boson mass range of 110–600 GeV is estimated to be ∼15%, corresponding to a significance of approximately 1σ.
Measurements are presented of the properties of high transverse momentum jets, produced in proton-proton collisions at a center-of-mass energy of s=7 TeV. The data correspond to an integrated luminosity of 35 pb−1 a...
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Measurements are presented of the properties of high transverse momentum jets, produced in proton-proton collisions at a center-of-mass energy of s=7 TeV. The data correspond to an integrated luminosity of 35 pb−1 and were collected with the ATLAS detector in 2010. Jet mass, width, eccentricity, planar flow and angularity are measured for jets reconstructed using the anti-kt algorithm with distance parameters R=0.6 and 1.0, with transverse momentum pT>300 GeV and pseudorapidity |η|<2. The measurements are compared to the expectations of Monte Carlo generators that match leading-logarithmic parton showers to leading-order, or next-to-leading-order, matrix elements. The generators describe the general features of the jets, although discrepancies are observed in some distributions.
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 ...
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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.
Distributions sensitive to the underlying event are studied in events containing one or more charged-particle jets produced in pp collisions at s=7 TeV with the ATLAS detector at the Large Hadron Collider (LHC). Thes...
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Distributions sensitive to the underlying event are studied in events containing one or more charged-particle jets produced in pp collisions at s=7 TeV with the ATLAS detector at the Large Hadron Collider (LHC). These measurements reflect 800 μb−1 of data taken during 2010. Jets are reconstructed using the anti-kt algorithm with radius parameter R varying between 0.2 and 1.0. Distributions of the charged-particle multiplicity, the scalar sum of the transverse momentum of charged particles, and the average charged-particle pT are measured as functions of pTjet in regions transverse to and opposite the leading jet for 4 GeV
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