| 41. |
- Aktas, A, et al.
(författare)
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Muon pair production in ep collisions at HERA
- 2004
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 583:1-2, s. 28-40
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Tidskriftsartikel (refereegranskat)abstract
- Cross sections for the production of two isolated muons up to high di-muon masses are measured in ep collisions at HERA with the H1 detector in a data sample corresponding to an integrated luminosity of 71 pb(-1) at a centre of mass energy of roots = 319 GeV. The results are in good agreement with Standard Model predictions, the dominant process being photon-photon interactions. Additional muons or electrons are searched for in events with two high transverse momentum muons using the full data sample corresponding to 114 pb(-1), where data at roots = 301 GeV and roots = 319 GeV are combined. Both the di-lepton sample and the tri-lepton sample agree Well with the predictions. (C) 2004 Published by Elsevier B.V.
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| 42. |
- Aktas, A, et al.
(författare)
-
Search for squark production in R-parity violating supersymmetry at HERA
- 2004
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 36:4, s. 425-440
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Tidskriftsartikel (refereegranskat)abstract
- A search for squarks in R-parity violating supersymmetry is performed in e(+/-)p collisions at HERA using the H1 detector. The data were taken at a centre-of-mass energy of 319 GeV and correspond to an integrated luminosity of 64.3 pb(-1) for e (+) p collisions and 13.5 pb(-1) for e(-)p collisions. The resonant production of squarks via a Yukawa coupling lambda' is considered, taking into account direct and indirect R-parity violating decay modes. No evidence for squark production is found in the multi-lepton and multi-jet final state topologies investigated. Mass dependent limits on lambda' are obtained in the framework of the Minimal Supersymmetric Standard Model. In addition, the results are interpreted in terms of constraints on the parameters of the minimal Supergravity model. At the 95% confidence level squarks of all flavours with masses up to 275 GeV are excluded in a large part of the parameter space for a Yukawa coupling of electromagnetic strength. For a coupling strength 100 times smaller, masses up to 220 GeV can be ruled out.
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| 43. |
- Andreev, V, et al.
(författare)
-
Isolated electrons and muons in events with missing transverse momentum at HERA
- 2003
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 561:3-4, s. 241-257
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Tidskriftsartikel (refereegranskat)abstract
- A search for events with a high-energy isolated electron or muon and missing transverse momentum has been performed at the electron-proton collider HERA using an integrated luminosity of 13.6 pb(-1) in e(-) p scattering and 104.7 pb(-1) in e(+) p scattering. Within the Standard Model such events are expected to be mainly due to W boson production with subsequent leptonic decay. In e(-) p interactions one event is observed in the electron channel and none in the muon channel, consistent with the expectation of the Standard Model. In the e(+) p data a total of 18 events are seen in the electron and muon channels compared to an expectation of 12.4 +/- 1.7 dominated by W production (9.4 +/- 1.6). Whilst the overall observed number of events is broadly in agreement with the number predicted by the Standard Model, there is-an excess of events with transverse momentum of the hadronic system greater than 25 GeV with 10 events found compared to 2.9 +/- 0.5 expected. The results are used to determine the cross-section for events with an isolated electron or muon and missing transverse momentum. (C) 2003 Published by Elsevier Science B.V.
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| 44. |
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| 45. |
- Adloff, C, et al.
(författare)
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Measurement of inclusive jet cross-sections in deep-inelastic ep scattering at HERA
- 2002
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 542:3-4, s. 193-206
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Tidskriftsartikel (refereegranskat)abstract
- A measurement of inclusive jet cross-sections in deep-inelastic ep scattering at HERA is presented based on data with an integrated luminosity of 21.1 pb(-1). The measurement is performed for photon virtualities Q(2) between 5 and 100 GeV2, differentially in Q(2), in the jet transverse energy E-T, in E-T(2)/Q(2) and in the pseudorapidity eta(lab). With the renormalization scale mu(R) = E-T, perturbative QCD calculations in next-to-leading order (NLO) give a good description of the data in most of the phase space. Significant discrepancies are observed only for jets in the proton beam direction with ET below 20 GeV and Q2 below 20 GeV2. This corresponds to the region in which NLO corrections are largest and further improvement of the calculations is thus of particular interest.
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| 46. |
- Adloff, C, et al.
(författare)
-
Search for new physics in e +/- q contact interactions at HERA
- 2003
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 568:1-2, s. 35-47
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Tidskriftsartikel (refereegranskat)abstract
- Deep-inelastic e(+/-) p scattering at high squared momentum transfer Q(2) up to 30 000 GeV2 is used to search for eq contact interactions associated to scales far beyond the HERA centre of mass energy. The neutral current cross section measurements dsigma / dQ(2), corresponding to integrated luminosities of 16.4 pb(-1) of e(-) p data and 100.8 pb(-1) of e(+) p data, are well described by the Standard Model and are analysed to set constraints on new phenomena. For conventional contact interactions lower limits are set on compositeness scales A ranging between 1.6-5.5 TeV. Couplings and masses of leptoquarks and squarks in R-parity violating supersymmetry are constrained to M / lambda > 0.3-1.4 TeV. A search for low scale quantum gravity effects in models with large extra dimensions provides limits on the effective Planck scale of MS > 0.8 TeV. A form factor analysis yields a bound on the radius of light quarks of R-q < 1.0 10(-18) m. (C) 2003 Published by Elsevier B.V.
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| 47. |
- Aktas, A, et al.
(författare)
-
Measurement of beauty production at HERA using events with muons and jets
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 41:4, s. 453-467
-
Tidskriftsartikel (refereegranskat)abstract
- A measurement of the beauty production cross section in ep collisions at a centre-of-mass energy of 319 GeV is presented. The data were collected with the H1 detector at the HERA collider in the years 1999-2000. Events are selected by requiring the presence of jets and muons in the final state. Both the long lifetime and the large mass of b-flavoured hadrons are exploited to identify events containing beauty quarks. Differential cross sections are measured in photoproduction, with photon virtualities Q(2) < 1 GeV2, and in deep inelastic scattering, where 2 < Q(2) < 100 GeV2. The results are compared with perturbative QCD calculations to leading and next-to-leading order. The predictions are found to be somewhat lower than the data.
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| 48. |
- Aktas, A, et al.
(författare)
-
Measurement of deeply virtual Compton scattering at HERA
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 44:1, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- A measurement is presented of elastic deeply virtual Compton scattering gamma* p -> gamma p made using e(+) p collision data corresponding to a luminosity of 46.5 pb(-1), taken with the H1 detector at HERA. The cross section is measured as a function of the photon virtuality, Q(2), the invariant mass of the gamma* p system, W, and for the first time, differentially in the squared momentum transfer at the proton vertex, t, in the kinematic range 2 < Q(2) < 80 GeV2, 30 < W < 140 GeV and vertical bar t vertical bar < 1 GeV2. QCD based calculations at next-to-leading order using generalized parton distributions can describe the data, as can colour dipole model predictions.
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| 49. |
- Aktas, A, et al.
(författare)
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Measurement of dijet cross sections in ep interactions with a leading neutron at HERA
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 41:3, s. 273-286
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Tidskriftsartikel (refereegranskat)abstract
- Measurements are reported of the production of dijet events with a leading neutron in ep interactions at HERA. Differential cross sections for photoproduction and deep inelastic scattering are presented as a function of several kinematic variables. Leading order QCD simulation programs are compared with the measurements. Models in which the real or virtual photon interacts with a parton of an exchanged pion are able to describe the data. Next-to-leading order perturbative QCD calculations based on pion exchange are found to be in good agreement with the measured cross sections. The fraction of leading neutron dijet events with respect to all dijet events is also determined. The dijet events with a leading neutron have a lower fraction of resolved photon processes than do the inclusive dijet data.
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| 50. |
- Aktas, A, et al.
(författare)
-
Search for leptoquark bosons in ep collisions at HERA
- 2005
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 629:1, s. 9-19
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Tidskriftsartikel (refereegranskat)abstract
- A search for scalar and vector leptoquarks coupling to first generation fermions is performed using the e(+) p and e(-) p scattering data collected by the H1 experiment between 1994 and 2000. The data correspond to a total integrated luminosity of 117 pb(-1). No evidence for the direct or indirect production of such particles is found in data samples with a large transverse momentum final state electron or with large missing transverse momentum. Constraints on leptoquark models are established. For leptoquark couplings of electromagnetic strength, leptoquarks with masses up to 275-325 GeV are ruled out at 95% confidence level. These limits improve and supercede earlier H1 limits based on subsamples of the data used here.
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