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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., Ferrer, A., et al. (2015). Search for production of WW/WZ resonances decaying to a lepton, neutrino and jets in pp collisions at root s=8 TeV with the ATLAS detector. Eur. Phys. J. C, 75(5), 209–20pp.
Abstract: A search is presented for narrow diboson resonances decaying to WW or WZ in the final state where one W boson decays leptonically (to an electron or a muon plus a neutrino) and the other W/Z boson decays hadronically. The analysis is performed using an integrated luminosity of 20.3 fb(-1) of pp collisions at root s = 8 TeV collected by the ATLAS detector at the large hadron collider. No evidence for resonant diboson production is observed, and resonance masses below 700 and 1490 GeV are excluded at 95 % confidence level for the spin-2 Randall-Sundrum bulk graviton G* with coupling constant of 1.0 and the extended gauge model W' boson respectively.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2015). Search for the Standard Model Higgs boson produced in association with top quarks and decaying into in collisions at with the ATLAS detector. Eur. Phys. J. C, 75(7), 349–50pp.
Abstract: A search for the Standard Model Higgs boson produced in association with a top-quark pair, , is presented. The analysis uses 20.3 fb(-1) of pp collision data at , collected with the ATLAS detector at the Large Hadron Collider during 2012. The search is designed for the decay mode and uses events containing one or two electrons or muons. In order to improve the sensitivity of the search, events are categorised according to their jet and b-tagged jet multiplicities. A neural network is used to discriminate between signal and background events, the latter being dominated by +jets production. In the single-lepton channel, variables calculated using a matrix element method are included as inputs to the neural network to improve discrimination of the irreducible background. No significant excess of events above the background expectation is found and an observed (expected) limit of 3.4 (2.2) times the Standard Model cross section is obtained at 95 % confidence level. The ratio of the measured signal cross section to the Standard Model expectation is found to be assuming a Higgs boson mass of 125 Gev.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2015). Measurement of the top quark mass in the t(t)over-bar -> lepton plus jets and t(t)over-bar -> dilepton channels using root s=7 TeV ATLAS data. Eur. Phys. J. C, 75(7), 330–36pp.
Abstract: The top quark mass was measured in the channels t (t) over bar -> lepton+jets and t (t) over bar -> dilepton (lepton = e, mu) based on ATLAS data recorded in 2011. The data were taken at the LHC with a proton-proton centre-of-mass energy of root s = 7 TeV and correspond to an integrated luminosity of 4.6 fb(-1). The t (t) over bar -> lepton+jets analysis uses a three-dimensional template technique which determines the top quark mass together with a global jet energy scale factor (JSF), and a relative b-to-light-jet energy scale factor (bJSF), where the terms b-jets and light-jets refer to jets originating from b-quarks and u,d,c, s-quarks or gluons, respectively. The analysis of the t (t) over bar -> dilepton channel exploits a one-dimensional template method using the m(lb) observable, defined as the average invariant mass of the two lepton+b-jet pairs in each event. The top quark mass is measured to be 172.33 +/- 0.75(stat + JSF + bJSF) +/- 1.02(syst) GeV, and 173.79 +/- 0.54(stat) +/- 1.30(syst) GeV in the t (t) over bar -> lepton+jets and t (t) over bar -> dilepton channels, respectively. The combination of the two results yields m(top) = 172.99 +/- 0.48(stat) +/- 0.78(syst) GeV, with a total uncertainty of 0.91 GeV.
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XENON Collaboration(Aprile, E. et al), & Orrigo, S. E. A. (2015). Lowering the radioactivity of the photomultiplier tubes for the XENON1T dark matter experiment. Eur. Phys. J. C, 75(11), 546–10pp.
Abstract: The low-background, VUV-sensitive 3-inch diameter photomultiplier tube R11410 has been developed by Hamamatsu for dark matter direct detection experiments using liquid xenon as the target material. We present the results from the joint effort between the XENON collaboration and the Hamamatsu company to produce a highly radio-pure photosensor (version R11410-21) for the XENON1T dark matter experiment. After introducing the photosensor and its components, we show the methods and results of the radioactive contamination measurements of the individual materials employed in the photomultiplier production. We then discuss the adopted strategies to reduce the radioactivity of the various PMT versions. Finally, we detail the results from screening 286 tubes with ultra-low background germanium detectors, as well as their implications for the expected electronic and nuclear recoil background of the XENON1T experiment.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2015). Search for a new resonance decaying to a W or Z boson and a Higgs boson in the ll/lv/vv plus b(b)over-bar final states with the ATLAS detectorv. Eur. Phys. J. C, 75(6), 263–21pp.
Abstract: A search for a new resonance decaying to a W or Z boson and a Higgs boson in the ll/lv/vv + b (b) over bar final states is performed using 20.3 fb(-1) of pp collision data recorded at root s = 8 TeV with the ATLAS detector at the Large Hadron Collider. The search is conducted by examining the WH/ZH invariant mass distribution for a localized excess. No significant deviation from the Standard Model background prediction is observed. The results are interpreted in terms of constraints on the Minimal Walking Technicolor model and on a simplified approach based on a phenomenological Lagrangian of Heavy Vector Triplets.
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