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Benitez, V. et al, Bernabeu, J., Garcia, C., Lacasta, C., Marco, R., Rodriguez, D., et al. (2016). Sensors for the End-cap prototype of the Inner Tracker in the ATLAS Detector Upgrade. Nucl. Instrum. Methods Phys. Res. A, 833, 226–232.
Abstract: The new silicon microstrip sensors of the End-cap part of the HL-LHC ATLAS Inner Tracker (ITk) present a number of challenges due to their complex design features such as the multiple different sensor shapes, the varying strip pitch, or the built-In stereo angle. In order to investigate these specific problems, the “petalet” prototype was defined as a small End-cap prototype. The sensors for the petalet prototype include several new layout and technological solutions to investigate the issues, they have been tested in detail by the collaboration. The sensor description and detailed test results are presented in this paper. New software tools have been developed for the automatic layout generation of the complex designs. The sensors have been fabricated, characterized and delivered to the institutes in the collaboration for their assembly on petalet prototypes. This paper describes the lessons learnt from the design and tests of the new solutions implemented on these sensors, which are being used for the full petal sensor development. This has resulted in the ITIc strip, community acquiring the necessary expertise to develop the full End-cap structure, the petal.
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Han, X. F., Wang, L., & Yang, J. M. (2016). Higgs pair signal enhanced in the 2HDM with two degenerate 125 GeV Higgs bosons. Mod. Phys. Lett. A, 31(31), 1650178–14pp.
Abstract: We discuss a scenario of the type-II two-Higgs- doublet model (2HDM) in which the b (b) over bar gamma gamma rate of the Higgs pair production is enhanced due to the two nearly degenerate 125 GeV Higgs bosons ( h, H). Considering various theoretical and experimental constraints, we figure out the allowed ranges of the trilinear couplings of these two Higgs bosons and calculate the signal rate of b (b) over bar gamma gamma from the productions of Higgs pairs (hh, hH, HH) at the large hadron collider (LHC). We find that in the allowed parameter space some trilinear Higgs couplings can be larger than the Standard Model (SM) value by an order and the production rate of b _ b.. can be greatly enhanced. We also consider a “decoupling” benchmark point where the light CP-even Higgs has a SM-like cubic self-coupling while other trilinear couplings are very small. With a detailed simulation on the b (b) over bar gamma gamma signal and backgrounds, we find that in such a “decoupling” scenario the hh and hH channels can jointly enhance the statistical significance to 5 sigma at 14 TeV LHC with an integrated luminosity of 3000 fb(-1).
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Pich, A., & Rodriguez-Sanchez, A. (2016). Updated determination of alpha(s)(m(tau)(2)) from tau decays. Mod. Phys. Lett. A, 31(30), 1630032–15pp.
Abstract: Using the most recent release of the ALEPH tau decay data, we present a very detailed phenomenological update of the alpha(s)(m(tau)(2)) determination. We have exploited the sensitivity to the strong coupling in many different ways, exploring several complementary methodologies. All determinations turn out to be in excellent agreement, allowing us to extract a very reliable value of the strong coupling. We find alpha((nf =3))(s)(m(tau)(2)) = 0.328 +/- 0.012 which implies alpha((nf=5))(s)(M-Z(2)) = 0.1197 +/- 0.0014. We critically revise previous work, and point out the problems flawing some recent analyses which claim slightly smaller values.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., Costa, M. J., et al. (2016). Measurement of total and differential W plus w- production cross sections in proton-proton collisions at root s=8 TeV with the ATLAS detector and limits on anomalous triple-gauge-boson couplings. J. High Energy Phys., 09(9), 029–81pp.
Abstract: The production of W boson pairs in proton-proton collisions at root s = 8TeV is studied using data corresponding to 20.3 fb(-1) of integrated luminosity collected by the ATLAS detector during 2012 at the CERN Large Hadron Collider. The W bosons are reconstructed using their leptonic decays into electrons or muons and neutrinos. Events with reconstructed jets are not included in the candidate event sample. A total of 6636 W W candidate events are observed. Measurements are performed in fiducial regions closely approximating the detector acceptance. The integrated measurement is corrected for all acceptance effects and for the W branching fractions to leptons in order to obtain the total W W production cross section, which is found to be 71.1 +/- 1.1( stat) + (5.7) (5.0) (syst) +/- 1 : 4( lumi) pb. This agrees with the next-to-next-to-leading-order Standard Model prediction of 63.2(+1.6) (-1.4) (scale) +/- 1.2(PDF) pb. Fiducial differential cross sections are measured as a function of each of six kinematic variables. The distribution of the transverse momentum of the leading lepton is used to set limits on anomalous triple-gauge-boson couplings.
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Lami, A., & Roig, P. (2016). H -> ll ' in the simplest little Higgs model. Phys. Rev. D, 94(5), 056001–7pp.
Abstract: Little Higgs models are promising constructs to solve the hierarchy problem affecting the Higgs boson mass for generic new physics. However, their preservation of lepton universality forbids them to account for the H -> tau μCMS hint and at the same time respect (as they do) the severe limits on H -> μe inherited from the nonobservation of μ-> e gamma We compute the predictions of the simplest little Higgs model for the H -> ll' decays and conclude that the measurement of any of these decays at LHC (even with a much smaller rate than currently hinted) would, under reasonable assumptions, disfavor this model. This result is consistent with our earlier observation of very suppressed lepton flavor violating semileptonic tau decays within this model.
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