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Search for pair production of heavy top-like quarks decaying to a high-pTW boson and a b quark in the lepton plus jets final state at s=7TeV with the ATLAS detector

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 718:4-5 (2013) 1284-1302

Authors:

G Aad, T Abajyan, B Abbott, J Abdallah, S Abdel Khalek, AA Abdelalim, O Abdinov, R Aben, B Abi, M Abolins, OS AbouZeid, H Abramowicz, H Abreu, BS Acharya, L Adamczyk, DL Adams, TN Addy, J Adelman, S Adomeit, P Adragna, T Adye, S Aefsky, JA Aguilar-Saavedra, M Agustoni, M Aharrouche, SP Ahlen, F Ahles, A Ahmad, M Ahsan, G Aielli, TPA A kesson, G Akimoto, AV Akimov, MS Alam, MA Alam, J Albert, S Albrand, M Aleksa, IN Aleksandrov, F Alessandria, C Alexa, G Alexander, G Alexandre, T Alexopoulos, M Alhroob, M Aliev, G Alimonti, J Alison, BMM Allbrooke, PP Allport, SE Allwood-Spiers, J Almond, A Aloisio, R Alon, A Alonso, F Alonso, A Altheimer, B Alvarez Gonzalez, MG Alviggi, K Amako, C Amelung, VV Ammosov, SP Amor Dos Santos, A Amorim, N Amram, C Anastopoulos, LS Ancu, N Andari, T Andeen, CF Anders, G Anders, KJ Anderson, A Andreazza, V Andrei, ML Andrieux, XS Anduaga, S Angelidakis, P Anger, A Angerami, F Anghinolfi, A Anisenkov, N Anjos, A Annovi, A Antonaki, M Antonelli, A Antonov, J Antos, F Anulli, M Aoki, S Aoun, L Aperio Bella, R Apolle

Abstract:

A search is presented for production of a heavy up-type quark (t ' ) together with its antiparticle, assuming a significant branching ratio for subsequent decay into a W boson and a b quark. The search is based on 4.7 fb -1 of pp collisions at s=7TeV recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. Data are analyzed in the lepton+jets final state, characterized by a high-transverse-momentum isolated electron or muon, large missing transverse momentum and at least three jets. The analysis strategy relies on the substantial boost of the W bosons in the t't¯' signal when mt'?400GeV. No significant excess of events above the Standard Model expectation is observed and the result of the search is interpreted in the context of fourth-generation and vector-like quark models. Under the assumption of a branching ratio BR(t ' ?Wb)=1, a fourth-generation t ' quark with mass lower than 656GeV is excluded at 95% confidence level. In addition, in light of the recent discovery of a new boson of mass ~126GeV at the LHC, upper limits are derived in the two-dimensional plane of BR(t ' ?Wb) versus BR(t ' ?Ht), where H is the Standard Model Higgs boson, for vector-like quarks of various masses. © 2012 CERN.
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Observational constraints on the powering mechanism of transient relativistic jets

(2013)

Authors:

DM Russell, E Gallo, RP Fender
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Synchronous x-ray and radio mode switches: a rapid global transformation of the pulsar magnetosphere.

Science 339:6118 (2013) 436-439

Authors:

W Hermsen, JWT Hessels, L Kuiper, J van Leeuwen, D Mitra, J de Plaa, JM Rankin, BW Stappers, GAE Wright, R Basu, A Alexov, T Coenen, J-M Grießmeier, TE Hassall, A Karastergiou, E Keane, VI Kondratiev, M Kramer, M Kuniyoshi, A Noutsos, M Serylak, M Pilia, C Sobey, P Weltevrede, K Zagkouris, A Asgekar, IM Avruch, F Batejat, ME Bell, MR Bell, MJ Bentum, G Bernardi, P Best, L Bîrzan, A Bonafede, F Breitling, J Broderick, M Brüggen, HR Butcher, B Ciardi, S Duscha, J Eislöffel, H Falcke, R Fender, C Ferrari, W Frieswijk, MA Garrett, F de Gasperin, E de Geus, AW Gunst, G Heald, M Hoeft, A Horneffer, M Iacobelli, G Kuper, P Maat, G Macario, S Markoff, JP McKean, M Mevius, JCA Miller-Jones, R Morganti, H Munk, E Orrú, H Paas, M Pandey-Pommier, VN Pandey, R Pizzo, AG Polatidis, S Rawlings, W Reich, H Röttgering, AMM Scaife, A Schoenmakers, A Shulevski, J Sluman, M Steinmetz, M Tagger, Y Tang, C Tasse, S ter Veen, R Vermeulen, RH van de Brink, RJ van Weeren, RAMJ Wijers, MW Wise, O Wucknitz, S Yatawatta, P Zarka

Abstract:

Pulsars emit from low-frequency radio waves up to high-energy gamma-rays, generated anywhere from the stellar surface out to the edge of the magnetosphere. Detecting correlated mode changes across the electromagnetic spectrum is therefore key to understanding the physical relationship among the emission sites. Through simultaneous observations, we detected synchronous switching in the radio and x-ray emission properties of PSR B0943+10. When the pulsar is in a sustained radio-"bright" mode, the x-rays show only an unpulsed, nonthermal component. Conversely, when the pulsar is in a radio-"quiet" mode, the x-ray luminosity more than doubles and a 100% pulsed thermal component is observed along with the nonthermal component. This indicates rapid, global changes to the conditions in the magnetosphere, which challenge all proposed pulsar emission theories.
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Measurement of the azimuthal anisotropy of neutral pions in Pb-Pb collisions at √sNN=2.76 TeV

Physical Review Letters 110:4 (2013)

Authors:

S Chatrchyan, V Khachatryan, AM Sirunyan, A Tumasyan, W Adam, E Aguilo, T Bergauer, M Dragicevic, J Erö, C Fabjan, M Friedl, R Frühwirth, VM Ghete, J Hammer, N Hörmann, J Hrubec, M Jeitler, W Kiesenhofer, V Knünz, M Krammer, I Krätschmer, D Liko, I Mikulec, M Pernicka, B Rahbaran, C Rohringer, H Rohringer, R Schöfbeck, J Strauss, A Taurok, W Waltenberger, G Walzel, E Widl, CE Wulz, V Mossolov, N Shumeiko, J Suarez Gonzalez, S Bansal, T Cornelis, EA De Wolf, X Janssen, S Luyckx, L Mucibello, S Ochesanu, B Roland, R Rougny, M Selvaggi, Z Staykova, H Van Haevermaet, P Van Mechelen, N Van Remortel, A Van Spilbeeck, F Blekman, S Blyweert, J D'Hondt, R Gonzalez Suarez, A Kalogeropoulos, M Maes, A Olbrechts, W Van Doninck, P Van Mulders, GP Van Onsem, I Villella, B Clerbaux, G De Lentdecker, V Dero, APR Gay, T Hreus, A Léonard, PE Marage, T Reis, L Thomas, G Vander Marcken, C Vander Velde, P Vanlaer, J Wang, V Adler, K Beernaert, A Cimmino, S Costantini, G Garcia, M Grunewald, B Klein, J Lellouch, A Marinov, J McCartin, AA Ocampo Rios, D Ryckbosch, N Strobbe, F Thyssen, M Tytgat, P Verwilligen, S Walsh, E Yazgan, N Zaganidis, S Basegmez, G Bruno, R Castello, L Ceard, C Delaere

Abstract:

First measurements of the azimuthal anisotropy of neutral pions produced in Pb-Pb collisions at a center-of-mass energy of √sNN=2.76 TeV are presented. The amplitudes of the second Fourier component (v2) of the π0 azimuthal distributions are extracted using an event-plane technique. The values of v2 are studied as a function of the neutral pion transverse momentum (pT) for different classes of collision centrality in the kinematic range 1.6
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Search for squarks and gluinos with the ATLAS detector in final states with jets and missing transverse momentum using 4.7 fb-1 of √s=7 TeV proton-proton collision data

Physical Review D - Particles, Fields, Gravitation and Cosmology 87:1 (2013)

Authors:

G Aad, T Abajyan, B Abbott, J Abdallah, S Abdel Khalek, AA Abdelalim, O Abdinov, R Aben, B Abi, M Abolins, OS Abouzeid, H Abramowicz, H Abreu, E Acerbi, BS Acharya, L Adamczyk, DL Adams, TN Addy, J Adelman, S Adomeit, P Adragna, T Adye, S Aefsky, JA Aguilar-Saavedra, M Agustoni, M Aharrouche, SP Ahlen, F Ahles, A Ahmad, M Ahsan, G Aielli, T Akdogan, TPA Åkesson, G Akimoto, AV Akimov, MS Alam, MA Alam, J Albert, S Albrand, M Aleksa, IN Aleksandrov, F Alessandria, C Alexa, G Alexander, G Alexandre, T Alexopoulos, M Alhroob, M Aliev, G Alimonti, J Alison, BMM Allbrooke, PP Allport, SE Allwood-Spiers, J Almond, A Aloisio, R Alon, A Alonso, F Alonso, B Alvarez Gonzalez, MG Alviggi, K Amako, C Amelung, VV Ammosov, A Amorim, N Amram, C Anastopoulos, LS Ancu, N Andari, T Andeen, CF Anders, G Anders, KJ Anderson, A Andreazza, V Andrei, XS Anduaga, P Anger, A Angerami, F Anghinolfi, A Anisenkov, N Anjos, A Annovi, A Antonaki, M Antonelli, A Antonov, J Antos, F Anulli, M Aoki, S Aoun, L Aperio Bella, R Apolle, G Arabidze, I Aracena, Y Arai, ATH Arce, S Arfaoui, JF Arguin, E Arik, M Arik, AJ Armbruster, O Arnaez

Abstract:

A search for squarks and gluinos in final states containing jets, missing transverse momentum and no high-pT electrons or muons is presented. The data represent the complete sample recorded in 2011 by the ATLAS experiment in 7 TeV proton-proton collisions at the Large Hadron Collider, with a total integrated luminosity of 4.7 fb-1. No excess above the Standard Model background expectation is observed. Gluino masses below 860 GeV and squark masses below 1320 GeV are excluded at the 95% confidence level in simplified models containing only squarks of the first two generations, a gluino octet and a massless neutralino, for squark or gluino masses below 2 TeV, respectively. Squarks and gluinos with equal masses below 1410 GeV are excluded. In minimal supergravity/constrained minimal supersymmetric Standard Model models with tanâ-¡β=10, A0=0 and μ>0, squarks and gluinos of equal mass are excluded for masses below 1360 GeV. Constraints are also placed on the parameter space of supersymmetric models with compressed spectra. These limits considerably extend the region of supersymmetric parameter space excluded by previous measurements with the ATLAS detector.
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