C. Alexa

Publications (334)409.5 Total impact

• Article: Measurement of the top quark pair production cross-section with ATLAS in the single lepton channel

  G. ATLAS Collaboration Aad, B. Abbott, J. Abdallah, A. A. Abdelalim, A. Abdesselam, O. Abdinov, B. Abi, M. Abolins, H. Abramowicz, H. Abreu, [......], R. Zitoun, L. Živković, V. V. Zmouchko, G. Zobernig, A. Zoccoli, Y. Zolnierowski, A. Zsenei, M. zur Nedden, V. Zutshi, L. Zwalinski
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  ABSTRACT: A measurement of the production cross-section for top quark pairs (tt¯) in pp collisions at s=7 TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in the single lepton topology by requiring an electron or muon, large missing transverse momentum and at least three jets. With a data sample of 35 pb-1, two different multivariate methods, one of which uses b-quark jet identification while the other does not, use kinematic variables to obtain cross-section measurements of σ=187±11(stat.)-17+18(syst.)±6(lumi.) pb and σ=173±17(stat.)-16+18(syst.)±6(lumi.) pb respectively. The two measurements are in agreement with each other and with QCD calculations. The first measurement has a better a priori sensitivity and constitutes the main result of this Letter.
  Physics Letters B 04/2012; 711:244-263. · 3.95 Impact Factor
• Article: Measurement of Wγ and Zγ production in proton-proton collisions at TeV with the ATLAS detector

  The ATLAS collaboration, G. Aad, B. Abbott, J. Abdallah, A. A. Abdelalim, A. Abdesselam, O. Abdinov, B. Abi, M. Abolins, H. Abramowicz, [......], R. Zitoun, L. Živković, V. V. Zmouchko, G. Zobernig, A. Zoccoli, Y. Zolnierowski, A. Zsenei, M. zur Nedden, V. Zutshi, L. Zwalinski
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  ABSTRACT: We present studies of W and Z bosons with associated high energy photons produced in pp collisions at Ös = 7 \sqrt {s} = 7 TeV. The analysis uses 35 pb−1 of data collected by the ATLAS experiment in 2010. The event selection requires W and Z bosons decaying into high p T leptons (electrons or muons) and a photon with E T > 15GeV separated from the lepton(s) by a distance ∆R(l, γ) > 0.7 in η-ϕ space. A total of 95 (97) pp → e ± νγ + X(pp → μ ± νγ + X) and 25 (23) pp → e + e − γ + X(pp → μ + μ − γ + X) event candidates are selected. The kinematic distributions of the leptons and photons and the production cross sections are measured. The data are found to agree with Standard Model predictions that include next-to-leading-order O(αα s ) contributions. KeywordsHadron-Hadron Scattering
  Journal of High Energy Physics 04/2012; 2011(9):1-42. · 5.83 Impact Factor
• Source

  Available from: Andreas Werner Jung

  Article: Search for squarks in R-parity violating supersymmetry in ep collisions at HERA

  The Collaboration, F. D. Aaron, C. Alexa, V. Andreev, S. Backovic, A. Baghdasaryan, S. Baghdasaryan, E. Barrelet, W. Bartel, K. Begzsuren, [......], Y. Vazdik, M. von den Driesch, D. Wegener, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, H. Zohrabyan, F. Zomer
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  ABSTRACT: A search for squarks in R-parity violating supersymmetry is performed in e ± p collisions at HERA using the H1 detector. The full data sample taken at a centre-of-mass energy Ös=319\sqrt{s}=319GeV is used for the analysis, corresponding to an integrated luminosity of 255pb−1 of e + p and 183pb−1 of e − p collision data. The resonant production of squarks via a Yukawa coupling λ′ is considered, taking into account direct and indirect R-parity violating decay modes. Final states with jets and leptons are investigated. No evidence for squark production is found and mass dependent limits on λ′ are obtained in the framework of the Minimal Supersymmetric Standard Model and in the Minimal Supergravity Model. In the considered part of the parameter space, for a Yukawa coupling of electromagnetic strength λ′=0.3, squarks of all flavours are excluded up to masses of 275GeV at 95% confidence level, with down-type squarks further excluded up to masses of 290GeV.
  European Physical Journal C 04/2012; 71(3):1-16. · 3.63 Impact Factor
• Article: Measurement of the inclusive e±p scattering cross section at high inelasticity y and of the structure function FL

  The Collaboration, F. D. Aaron, C. Alexa, V. Andreev, S. Backovic, A. Baghdasaryan, S. Baghdasaryan, E. Barrelet, W. Bartel, O. Behrend, [......], Y. Vazdik, M. von den Driesch, D. Wegener, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, H. Zohrabyan, F. Zomer
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  ABSTRACT: A measurement is presented of the inclusive neutral current e ± p scattering cross section using data collected by the H1 experiment at HERA during the years 2003 to 2007 with proton beam energies E p of 920, 575, and 460GeV. The kinematic range of the measurement covers low absolute four-momentum transfers squared, 1.5GeV2<Q 2<120GeV2, small values of Bjorken x, 2.9⋅10−5<x<0.01, and extends to high inelasticity up to y=0.85. The structure function F L is measured by combining the new results with previously published H1 data at E p =920GeV and E p =820GeV. The new measurements are used to test several phenomenological and QCD models applicable in this low Q 2 and low x kinematic domain.
  European Physical Journal C 04/2012; 71(3):1-50. · 3.63 Impact Factor
• Article: Search for supersymmetric particles in events with lepton pairs and large missing transverse momentum in proton–proton collisions with the ATLAS experiment

  The ATLAS Collaboration, G. Aad, B. Abbott, J. Abdallah, A. A. Abdelalim, A. Abdesselam, O. Abdinov, B. Abi, M. Abolins, H. Abramowicz, [......], R. Zitoun, L. Živković, V. V. Zmouchko, G. Zobernig, A. Zoccoli, Y. Zolnierowski, A. Zsenei, M. zur Nedden, V. Zutshi, L. Zwalinski
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  ABSTRACT: Results are presented of searches for the production of supersymmetric particles decaying into final states with missing transverse momentum and exactly two isolated leptons in Ös=7TeV\sqrt {s}=7~\mbox{TeV} proton–proton collisions at the Large Hadron Collider. Search strategies requiring lepton pairs with identical-sign or opposite-sign electric charges are described. In a data sample corresponding to an integrated luminosity of 35pb−1 collected with the ATLAS detector, no significant excesses are observed. Based on specific benchmark models, limits are placed on the squark mass between 450 and 690GeV for squarks approximately degenerate in mass with gluinos, depending on the supersymmetric mass hierarchy considered.
  European Physical Journal C 04/2012; 71(7):1-19. · 3.63 Impact Factor
• Source

  Available from: Andreas Werner Jung

  Article: Measurement of leading neutron production in deep-inelastic scattering at HERA

  The Collaboration, F. D. Aaron, C. Alexa, V. Andreev, B. Antunovic, S. Backovic, A. Baghdasaryan, E. Barrelet, W. Bartel, K. Begzsuren, [......], D. Wegener, C. Wissing, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, T. Zimmermann, H. Zohrabyan, F. Zomer
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  ABSTRACT: The production of leading neutrons, where the neutron carries a large fraction x L of the incoming proton’s longitudinal momentum, is studied in deep-inelastic positron-proton scattering at HERA. The data were taken with the H1 detector in the years 2006 and 2007 and correspond to an integrated luminosity of 122pb−1. The semi-inclusive cross section is measured in the phase space defined by the photon virtuality 6<Q 2<100GeV2, Bjorken scaling variable 1.5⋅10−4<x<3⋅10−2, longitudinal momentum fraction 0.32<x L <0.95 and neutron transverse momentum p T <0.2GeV. The leading neutron structure function, F2LN(3)(Q2,x,xL)F_{2}^{LN(3)}(Q^{2},x,x_{L}), and the fraction of deep-inelastic scattering events containing a leading neutron are studied as a function of Q 2, x and x L . Assuming that the pion exchange mechanism dominates leading neutron production, the data provide constraints on the shape of the pion structure function.
  European Physical Journal C 04/2012; 68(3):381-399. · 3.63 Impact Factor
• Article: Study of deconfinement in NA50

  Paula bordalo, M. C. Abreu, B. Alessandro, C. Alexa, R. Arnaldi, M. Atayan, C. Baglin, A. Baldit, M. Bedjidian, S. Beolé, [......], F. Sigaudo, S. Silva, M. Sitta, P. Sonderegger, X. Tarrago, N. S. Topilskaya, G. L. Usai, E. Vercellin, L. Villatte, N. Willis
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  ABSTRACT: TheJ/Ψ production in 158 A GeV Pb-Pb interactions is studied, in the dimuon decay channel, as a function of centrality, as measured with the electromagnetic or, alternatively, with the very forward hadronic calorimeters. After a first sharp variation at mid-centrality, both patterns continue to fall down and exhibit a curvature change at high centrality values. This trend excludes any conventional hadronic model and finds a natural explanation in a deconfined quark-gluon phase scenario.
  Pramana 04/2012; 60(4):817-828. · 0.57 Impact Factor
• Article: Three- and four-jet production at low x at HERA

  F.D. Aaron, A. Aktas, C. Alexa, V. Andreev, B. Antunovic, S. Aplin, A. Asmone, A. Astvatsatourov, S. Backovic, A. Baghdasaryan, [......], J. Žáček, J. Zálešák, Z. Zhang, A. Zhelezov, A. Zhokin, Y.C. Zhu, T. Zimmermann, H. Zohrabyan, F. Zomer, The Collaboration
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  ABSTRACT: Three- and four-jet production is measured in deep-inelastic ep scattering at low x and Q2 with the H1 detector using an integrated luminosity of 44.2pb-1. Several phase space regions are selected for the three-jet analysis in order to study the underlying parton dynamics from global topologies to the more restrictive regions of forward jets close to the proton direction. The measurements of cross sections for events with at least three jets are compared to fixed order QCD predictions of O(a\texts2){\mathcal{O}}(\alpha_{{\text{s}}}^2) and O(a\texts3){\mathcal{O}}(\alpha_{{\text{s}}}^3) and with Monte Carlo simulation programs where higher order effects are approximated by parton showers. A good overall description is provided by the O(a\texts3){\mathcal{O}}(\alpha_{{\text{s}}}^3) calculation. Too few events are predicted at the lowest x∼10-4, especially for topologies with two forward jets. This hints to large contributions at low x from initial state radiation of gluons close to the proton direction and unordered in transverse momentum. The Monte Carlo program in which gluon radiation is generated by the colour dipole model gives a good description of both the three- and the four-jet data in absolute normalisation and shape.
  European Physical Journal C 04/2012; 54(3):389-409. · 3.63 Impact Factor
• Article: Measurement of charm and beauty jets in deep inelastic scattering at HERA

  The Collaboration, F. D. Aaron, C. Alexa, V. Andreev, S. Backovic, A. Baghdasaryan, E. Barrelet, W. Bartel, K. Begzsuren, A. Belousov, [......], Y. Vazdik, M. von den Driesch, D. Wegener, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, H. Zohrabyan, F. Zomer
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  ABSTRACT: Measurements of cross sections for events with charm and beauty jets in deep inelastic scattering at HERA are presented. Events with jets of transverse energy $E_{T}^{\mathrm{jet}}>6$E_{T}^{\mathrm{jet}}>6GeV and pseudorapidity −1.0<η jet<1.5 in the laboratory frame are selected in the kinematic region of photon virtuality Q 2>6GeV2 and inelasticity variable 0.07<y<0.625. Measurements are also made requiring a jet in the Breit frame with $E_{T}^{*{\mathrm{jet}}}>6$E_{T}^{*{\mathrm{jet}}}>6GeV. The data were collected with the H1 detector in the years 2006 and 2007 corresponding to an integrated luminosity of 189pb−1. The numbers of charm and beauty jets are determined using variables reconstructed using the H1 vertex detector with which the impact parameters of the tracks to the primary vertex and the position of secondary vertices are measured. The measurements are compared with QCD predictions and with previous measurements where heavy flavours are identified using muons.
  European Physical Journal C 04/2012; 71(1):1-21. · 3.63 Impact Factor
• Article: Jet production in ep collisions at high Q2 and determination of αs

  The Collaboration, F. D. Aaron, C. Alexa, K. Alimujiang, V. Andreev, B. Antunovic, A. Asmone, S. Backovic, A. Baghdasaryan, E. Barrelet, [......], Ch. Wissing, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, T. Zimmermann, H. Zohrabyan, F. Zomer, R. Zus
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  ABSTRACT: The production of jets is studied in deep-inelastic e ± p scattering at large negative four momentum transfer squared 150<Q 2<15000GeV2 using HERA data taken in 1999–2007, corresponding to an integrated luminosity of 395pb−1. Inclusive jet, 2-jet and 3-jet cross sections, normalised to the neutral current deep-inelastic scattering cross sections, are measured as functions of Q 2, jet transverse momentum and proton momentum fraction. The measurements are well described by perturbative QCD calculations at next-to-leading order corrected for hadronisation effects. The strong coupling as determined from these measurements is as(MZ)=0.1168±0.0007(exp.)+0.0046-0.0030(th.)±0.0016\alpha_{s}(M_{Z})=0.1168\pm0.0007\,\mathrm{(exp.)}{}^{+0.0046}_{-0.0030}\,\mathrm{(th.)}\pm 0.0016 (PDF).
  European Physical Journal C 04/2012; 65(3):363-383. · 3.63 Impact Factor
• Article: Diffractive electroproduction of ρ and ϕ mesons at HERA

  The Collaboration, F. D. Aaron, M. Aldaya Martin, C. Alexa, V. Andreev, B. Antunovic, A. Asmone, S. Backovic, A. Baghdasaryan, E. Barrelet, [......], Ch. Wissing, E. Wünsch, J. Žáček, J. Záleák, Z. Zhang, A. Zhokin, T. Zimmermann, H. Zohrabyan, F. Zomer, R. Zus
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  ABSTRACT: Diffractive electroproduction of ρ and ϕ mesons is measured at HERA with the H1 detector in the elastic and proton dissociative channels. The data correspond to an integrated luminosity of 51 pb−1. About 10500 ρ and 2000 φ events are analysed in the kinematic range of squared photon virtuality 2.5 ≤ Q 2 ≤ 60 GeV2, photon-proton centre of mass energy 35 ≤ W ≤ 180 GeV and squared four-momentum transfer to the proton |t| ≤ 3 GeV2. The total, longitudinal and transverse cross sections are measured as a function of Q 2, W and |t|. The measurements show a transition to a dominantly “hard” behaviour, typical of high gluon densities and small q[`(q)] q\overline q dipoles, for Q 2 larger than 10 to 20 GeV2. They support flavour independence of the diffractive exchange, expressed in terms of the scaling variable (Q 2+M 2 V )/4, and proton vertex factorisation. The spin density matrix elements are measured as a function of kinematic variables. The ratio of the longitudinal to transverse cross sections, the ratio of the helicity amplitudes and their relative phases are extracted. Several of these measurements have not been performed before and bring new information on the dynamics of diffraction in a QCD framework. The measurements are discussed in the context of models using generalised parton distributions or universal dipole cross sections. KeywordsLepton-Nucleon Scattering
  Journal of High Energy Physics 04/2012; 2010(5):1-111. · 5.83 Impact Factor
• Article: Strangeness production at low Q2 in deep-inelastic ep scattering at HERA

  Collaboration, F. D. Aaron, C. Alexa, V. Andreev, B. Antunovic, S. Aplin, A. Asmone, A. Astvatsatourov, A. Bacchetta, S. Backovic, [......], V. Yeganov, J. Žáček, J. Zálešák, Z. Zhang, A. Zhelezov, A. Zhokin, Y. C. Zhu, T. Zimmermann, H. Zohrabyan, F. Zomer
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  ABSTRACT: The production of neutral strange hadrons is investigated using deep-inelastic scattering events measured with the H1 detector at HERA. The measurements are made in the phase space defined by the negative four-momentum transfer squared of the photon 2<Q 2<100 GeV2 and the inelasticity 0.1<y<0.6. The K s 0 and \varLambda([`\varLambda])\varLambda(\bar{\varLambda}) production cross sections and their ratios are determined. K s 0 production is compared to the production of charged particles in the same region of phase space. The Λ– [`\varLambda]\bar{\varLambda} asymmetry is also measured and found to be consistent with zero. Predictions of leading order Monte Carlo programs are compared to the data.
  European Physical Journal C 04/2012; 61(2):185-205. · 3.63 Impact Factor
• Article: Prompt photons in photoproduction at HERA

  The Collaboration, F. D. Aaron, M. Aldaya Martin, C. Alexa, V. Andreev, B. Antunovic, S. Backovic, A. Baghdasaryan, E. Barrelet, W. Bartel, [......], Ch. Wissing, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, T. Zimmermann, H. Zohrabyan, F. Zomer, R. Zus
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  ABSTRACT: The production of prompt photons is measured in the photoproduction regime of electron–proton scattering at HERA. The analysis is based on a data sample corresponding to a total integrated luminosity of 340pb−1 collected by the H1 experiment. Cross sections are measured for photons with transverse momentum and pseudorapidity in the range 6 < ETg < 156
  European Physical Journal C 04/2012; 66(1):17-33. · 3.63 Impact Factor
• Article: Measurement of the charm and beauty structure functions using the H1 vertex detector at HERA

  The Collaboration, F. D. Aaron, M. Aldaya Martin, C. Alexa, K. Alimujiang, V. Andreev, B. Antunovic, A. Asmone, S. Backovic, A. Baghdasaryan, [......], C. Wissing, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, T. Zimmermann, H. Zohrabyan, F. Zomer, R. Zus
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  ABSTRACT: Inclusive charm and beauty cross sections are measured in e − p and e + p neutral current collisions at HERA in the kinematic region of photon virtuality 5≤Q 2≤2000GeV2 and Bjorken scaling variable 0.0002≤x≤0.05. The data were collected with the H1 detector in the years 2006 and 2007 corresponding to an integrated luminosity of 189pb−1. The numbers of charm and beauty events are determined using variables reconstructed by the H1 vertex detector including the impact parameter of tracks to the primary vertex and the position of the secondary vertex. The measurements are combined with previous data and compared to QCD predictions.
  European Physical Journal C 04/2012; 65(1):89-109. · 3.63 Impact Factor
• Article: Search for baryonic resonances decaying to Ξπ in deep-inelastic scattering at HERA

  A. Aktas, C. Alexa, V. Andreev, T. Anthonis, B. Antunovic, S. Aplin, A. Asmone, A. Astvatsatourov, S. Backovic, A. Baghdasaryan, [......], J. Žáček, J. Zálešák, Z. Zhang, A. Zhelezov, A. Zhokin, Y.C. Zhu, T. Zimmermann, H. Zohrabyan, F. Zomer, The Collaboration
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  ABSTRACT: A search for narrow baryonic resonances decaying into Ξ-π- or Ξ-π+ and their antiparticles is carried out with the H1 detector using deep inelastic scattering events at HERA in the range of negative photon four-momentum transfer squared 2 < Q2 < 100GeV2. No signal is observed for a new baryonic state in the mass range 1600–2300MeV in either the doubly charged or the neutral decay channels. The known Ξ(1530)0 is observed through its decay mode into Ξ-π+. Upper limits are given on the ratio of the production rates of new baryonic states, such as the hypothetical pentaquark states Ξ– 5q or Ξ0 5q, relative to the Ξ(1530)0 baryon state.
  European Physical Journal C 04/2012; 52(3):507-514. · 3.63 Impact Factor
• Source

  Available from: Ehud Duchovni

  Article: Studies of the performance of the ATLAS detector using cosmic-ray muons

  The ATLAS Collaboration, G. Aad, B. Abbott, J. Abdallah, A. A. Abdelalim, A. Abdesselam, O. Abdinov, B. Abi, M. Abolins, H. Abramowicz, [......], X. Zhuang, V. Zhuravlov, R. Zimmermann, S. Zimmermann, M. Ziolkowski, L. Živković, G. Zobernig, A. Zoccoli, M. zur Nedden, V. Zutshi
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  ABSTRACT: Muons from cosmic-ray interactions in the atmosphere provide a high-statistics source of particles that can be used to study the performance and calibration of the ATLAS detector. Cosmic-ray muons can penetrate to the cavern and deposit energy in all detector subsystems. Such events have played an important role in the commissioning of the detector since the start of the installation phase in 2005 and were particularly important for understanding the detector performance in the time prior to the arrival of the first LHC beams. Global cosmic-ray runs were undertaken in both 2008 and 2009 and these data have been used through to the early phases of collision data-taking as a tool for calibration, alignment and detector monitoring. These large datasets have also been used for detector performance studies, including investigations that rely on the combined performance of different subsystems. This paper presents the results of performance studies related to combined tracking, lepton identification and the reconstruction of jets and missing transverse energy. Results are compared to expectations based on a cosmic-ray event generator and a full simulation of the detector response.
  European Physical Journal C 04/2012; 71(3):1-36. · 3.63 Impact Factor
• Article: Inelastic production of J/ψ mesons in photoproduction and deep inelastic scattering at HERA

  The Collaboration, F. D. Aaron, C. Alexa, V. Andreev, B. Antunovic, S. Backovic, A. Baghdasaryan, E. Barrelet, W. Bartel, K. Begzsuren, [......], D. Wegener, Ch. Wissing, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, T. Zimmermann, H. Zohrabyan, F. Zomer
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  ABSTRACT: A measurement is presented of inelastic photo- and electroproduction of J/ψ mesons in ep scattering at HERA. The data were recorded with the H1 detector in the period from 2004 to 2007. Single and double differential cross sections are determined and the helicity distributions of the J/ψ mesons are analysed. The results are compared to theoretical predictions in the colour singlet model and in the framework of non-relativistic QCD. Calculations in the colour singlet model using ak T factorisation ansatz are able to give a good description of the data, while colour singlet model calculations to next-to-leading order in collinear factorisation underestimate the data.
  European Physical Journal C 04/2012; 68(3):401-420. · 3.63 Impact Factor
• Source

  Available from: Luca Spogli

  Article: Measurement of the W → ℓν and Z/γ* → ℓℓ production cross sections in proton-proton collisions at with the ATLAS detector

  The ATLAS Collaboration, G. Aad, B. Abbott, J. Abdallah, A. A. Abdelalim, A. Abdesselam, O. Abdinov, B. Abi, M. Abolins, H. Abramowicz, [......], M. Ziolkowski, R. Zitoun, L. Živković, V. V. Zmouchko, G. Zobernig, A. Zoccoli, Y. Zolnierowski, A. Zsenei, M. zur Nedden, V. Zutshi
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  ABSTRACT: First measurements of the W → ℓν and Z/γ * → ℓℓ (ℓ = e, μ) production cross sections in proton-proton collisions at Ös = 7\textTeV \sqrt {s} = 7\;{\text{TeV}} are presented using data recorded by the ATLAS experiment at the LHC. The results are based on 2250 W → ℓν and 179 Z/γ * → ℓℓ candidate events selected from a data set corresponding to an integrated luminosity of approximately 320 nb. The measured total W and Z/γ ∗-boson production cross sections times the respective leptonic branching ratios for the combined electron and muon channels are sW\texttot \sigma_W^{\text{tot}} . BR(W → ℓν) = 9.96 ± 0.23(stat) ± 0.50(syst) ± 1.10(lumi) nb and sZ / g \texttot \sigma_{{{Z} \left/ {\gamma } \right.}}^{\text{tot}} BR(Z/γ ∗ → ℓℓ) = 0.82 ± 0.06 (stat) ± 0.05 (syst) ± 0.09(lumi) nb (within the invariant mass window 66 < m ℓℓ < 116GeV). The W/Z cross-section ratio is measured to be 11.7 ± 0.9(stat) ± 0.4(syst). In addition, measurements of the W + and W − production cross sections and of the lepton charge asymmetry are reported. Theoretical predictions based on NNLO QCD calculations are found to agree with the measurements. KeywordsHadron-Hadron Scattering
  Journal of High Energy Physics 04/2012; 2010(12):1-65. · 5.83 Impact Factor
• Article: Measurement of the inclusive ep scattering cross section at low Q2 and x at HERA

  The Collaboration, F. D. Aaron, C. Alexa, V. Andreev, B. Antunovic, S. Aplin, A. Asmone, A. Astvatsatourov, S. Backovic, A. Baghdasaryan, [......], D. Wegener, Ch. Wissing, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, T. Zimmermann, H. Zohrabyan, F. Zomer
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  ABSTRACT: A measurement of the inclusive ep scattering cross section is presented in the region of low momentum transfers, 0.2 GeV2 ≤Q 2≤12 GeV2, and low Bjorken x, 5⋅10−6≤x≤0.02. The result is based on two data sets collected in dedicated runs by the H1 Collaboration at HERA at beam energies of 27.6 GeV and 920 GeV for positrons and protons, respectively. A combination with data previously published by H1 leads to a cross section measurement of a few percent accuracy. A kinematic reconstruction method exploiting radiative ep events extends the measurement to lower Q 2 and larger x. The data are compared with theoretical models which apply to the transition region from photoproduction to deep inelastic scattering.
  European Physical Journal C 04/2012; 63(4):625-678. · 3.63 Impact Factor
• Article: Events with isolated leptons and missing transverse momentum and measurement of W production at HERA

  The Collaboration, F. D. Aaron, C. Alexa, V. Andreev, B. Antunovic, S. Aplin, A. Asmone, A. Astvatsatourov, S. Backovic, A. Baghdasaryan, [......], D. Wegener, Ch. Wissing, E. Wünsch, J. Žáček, J. Zálešák, Z. Zhang, A. Zhokin, T. Zimmermann, H. Zohrabyan, F. Zomer
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  ABSTRACT: Events with high energy isolated electrons, muons or tau leptons and missing transverse momentum are studied using the full e ± p data sample collected by the H1experiment at HERA, corresponding to an integrated luminosity of 474pb−1. Within the Standard Model, events with isolated leptons and missing transverse momentum mainly originate from the production of single W bosons. The total single W boson production cross section is measured as 1.14±0.25(stat.)±0.14(sys.)pb, in agreement with the Standard Model expectation. The data are also used to establish limits on the WW γ gauge couplings and for a measurement of the W boson polarisation.
  European Physical Journal C 04/2012; 64(2):251-271. · 3.63 Impact Factor