| 1. |
- Schael, S, et al.
(författare)
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Precision electroweak measurements on the Z resonance
- 2006
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
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Forskningsöversikt (refereegranskat)abstract
- We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLID experiment using a polarised beam at SLC. The measurements include cross-sections, forward-backward asymmetries and polarised asymmetries. The mass and width of the Z boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the p parameter and the effective electroweak mixing angle for leptons, are precisely measured: m(Z) = 91.1875 +/- 0.0021 GeV, Gamma(Z) = 2.4952 +/- 0.0023 GeV, rho(l) = 1.0050 +/- 0.0010, sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016. The number of light neutrino species is determined to be 2.9840 +/- 0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward-backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) = 80.363 +/- 0.032 GeV. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of m(t) and m(W), the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than 285 GeV at 95% confidence level. (c) 2006 Elsevier B.V. All rights reserved.
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| 2. |
- Aaron, F. D., et al.
(författare)
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Multi-leptons with high transverse momentum at HERA
- 2009
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Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479. ; :10
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Tidskriftsartikel (refereegranskat)abstract
- Events with at least two high transverse momentum leptons (electrons or muons) are studied using the H1 and ZEUS detectors at HERA with an integrated luminosity of 0.94 fb(-1). The observed numbers of events are in general agreement with the Standard Model predictions. Seven di- and tri-lepton events are observed in e(+)p collision data with a scalar sum of the lepton transverse momenta above 100 GeV while 1.94 +/- 0.17 events are expected. Such events are not observed in e(-)p collisions for which 1.19 +/- 0.12 are predicted. Total visible and differential di-electron and di-muon photoproduction cross sections are extracted in a restricted phase space dominated by photon-photon collisions.
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| 3. |
- Aaron, F. D., et al.
(författare)
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A general search for new phenomena at HERA
- 2009
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 674:4-5, s. 257-268
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Tidskriftsartikel (refereegranskat)abstract
- A model-independent search for deviations from the Standard Model prediction is performed using the full e(+/-) p data sample collected by the H1 experiment at HERA. All event topologies involving isolated electrons, photons, muons, neutrinos and jets with transverse momenta above 20 GeV are investigated in a single analysis. Events are assigned to exclusive classes according to their final state. A dedicated algorithm is used to search for deviations from the Standard Model in the distributions of the scalar sum of transverse momenta or the invariant mass of final state particles and to quantify their significance. Variables related to angular distributions and energy sharing between final state particles are also introduced to study the final state topologies. No significant deviation from the Standard Model expectation is observed in the phase space covered by this analysis. (C) 2009 Elsevier B.V. All rights reserved.
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| 4. |
- Aaron, F. D., et al.
(författare)
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Events with isolated leptons and missing transverse momentum and measurement of W production at HERA
- 2009
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 64:2, s. 251-271
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Tidskriftsartikel (refereegranskat)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 H1 experiment at HERA, corresponding to an integrated luminosity of 474 pb(-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 gamma gauge couplings and for a measurement of the W boson polarisation.
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| 5. |
- Aaron, F. D., et al.
(författare)
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Inclusive photoproduction of rho(0), K*(0) and phi mesons at HERA H1 Collaboration
- 2009
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 673:2, s. 119-126
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Tidskriftsartikel (refereegranskat)abstract
- Inclusive non-diffractive photoproduction of rho(770)(0), K*(892)(0) and phi(1020) mesons is investigated with the H1 detector in ep collisions at HERA. The corresponding average gamma p centre-of-mass energy is 210 GeV. The mesons are measured in the transverse momentum range 0.5 < p(T) < 7 GeV and the rapidity range vertical bar y(lab)vertical bar < 1. Differential cross sections are presented as a function of transverse momentum and rapidity, and are compared to the predictions of hadroproduction models. (C) 2009 Elsevier B.V. All rights reserved.
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| 6. |
- Aaron, F. D., et al.
(författare)
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Measurement of the inclusive ep scattering cross section at low Q (2) and x at HERA
- 2009
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 63:4, s. 625-678
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Tidskriftsartikel (refereegranskat)abstract
- A measurement of the inclusive ep scattering cross section is presented in the region of low momentum transfers, 0.2 GeV2 a parts per thousand currency signQ (2)a parts per thousand currency sign12 GeV2, and low Bjorken x, 5a <...10(-6)a parts per thousand currency signxa parts per thousand currency sign0.02. 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.
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| 7. |
- Aaron, F. D., et al.
(författare)
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A precision measurement of the inclusive ep scattering cross section at HERA
- 2009
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 64:4, s. 561-587
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Tidskriftsartikel (refereegranskat)abstract
- A measurement of the inclusive deep inelastic neutral current e(+) p scattering cross section is reported in the region of four-momentum transfer squared, 12GeV(2) <= Q(2) <= 150 GeV2, and Bjorken x, 2 x 10(-4) <= x <= 0.1. The results are based on data collected by the H1 Collaboration at the ep collider HERA at positron and proton beam energies of E-e = 27.6 GeV and E-p = 920 GeV, respectively. The data are combined with previously published data, taken at E-p = 820 GeV. The accuracy of the combined measurement is typically in the range of 1.3-2%. A QCD analysis at next-to-leading order is performed to determine the parton distributions in the proton based on H1 data.
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| 8. |
- Aaron, F. D., et al.
(författare)
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Search for excited quarks in ep collisions at HERA
- 2009
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 678:4, s. 335-343
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Tidskriftsartikel (refereegranskat)abstract
- A search for excited quarks is performed using the full e(+/-)p data sample collected by the HI experiment at HERA, corresponding to a total integrated luminosity of 475 pb(-1). The electroweak decays of excited quarks q* -> q gamma. q* -> qZ and q* - qW with Subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for first generation excited quark production is found. Mass dependent exclusion limits on q* production cross sections and on the ratio f/Lambda of the coupling to the compositeness scale are derived Within gauge mediated models. These limits extend the excluded region compared to previous excited quark searches. (C) 2009 Elsevier B.V. All rights reserved.
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| 9. |
- Aaron, F. D., et al.
(författare)
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Search for single top quark production at HERA
- 2009
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 678:5, s. 450-458
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Tidskriftsartikel (refereegranskat)abstract
- A search for single top quark production is performed in the full e(+/-)p data sample collected by the H1 experiment at HERA, corresponding to an integrated luminosity of 474 pb(-1). Decays of top quarks into a b quark and a W boson with Subsequent leptonic or hadronic decay of the W are investigated. A multivariate analysis is performed to discriminate top quark production from Standard Model background processes. An upper limit on the top quark production cross section via flavour changing neutral current processes sigma(ep -> et X) < 0.25 pb is established at 95% CL. Limits on the anomalous coupling K-tu gamma are derived. (C) 2009 Elsevier B.V. All rights reserved.
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| 10. |
- Aaron, F. D., et al.
(författare)
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Observation of the hadronic final state charge asymmetry in high Q(2) deep-inelastic scattering at HERA
- 2009
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 681:2, s. 125-133
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Tidskriftsartikel (refereegranskat)abstract
- A first measurement is presented of the charge asymmetry in the hadronic final state from the hard interaction in deep-inelastic ep neutral current scattering at HERA. The measurement is performed in the range of negative squared four momentum transfer 100 < Q(2) < 8000 GeV2. The difference between the event normalised distributions of the scaled momentum, x(p), for positively and negatively charged particles, measured in the current region of the Breit frame, is studied together with its evolution as a function of Q. The results are compared to Monte Carlo models at the hadron and parton levels. (C) 2009 Elsevier B.V. All rights reserved.
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