| 11. |
- Aktas, A., et al.
(författare)
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Search for a narrow baryonic resonance decaying to K(s)(0)p or K-s(0)(p)over-bar in deep inelastic scattering at HERA
- 2006
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 639:3-4, s. 202-209
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Tidskriftsartikel (refereegranskat)abstract
- A search for a narrow baryonic resonance decaying to K(s)(0)p or K-s(0)(p) over bar is carried out in deep inelastic ep scattering with the H1 detector at HERA. ss Such a resonance could be a strange pentaquark Theta(+), evidence for which has been reported by several experiments. The K(s)(0)p and K-s(0)(p) over bar invariant ss mass distributions presented here do not show any significant peak in the mass range from threshold up to 1.7 GeV. Mass dependent upper limits on sigma(ep -> e Theta X+) x BR(Theta(+) -> K(0)p) are obtained at the 95% confidence level.
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| 12. |
- Aktas, A., et al.
(författare)
-
Search for doubly-charged Higgs boson production at HERA
- 2006
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 638:5-6, s. 432-440
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Tidskriftsartikel (refereegranskat)abstract
- A search for the single production of doubly-charged Higgs bosons H-+/-+/- in ep collisions is presented. The signal is searched for via the Higgs decays into a high mass pair of same charge leptons, one of them being an electron. The analysis uses up to 118 pb(-1) of ep data collected by the H1 experiment at HERA. No evidence for doubly-charged Higgs production is observed and mass dependent upper limits are derived on the Yukawa couplings h(el) of the Higgs boson to an electron-lepton pair. Assuming that the doubly-charged Higgs only decays into an electron and a muon via a coupling of electromagnetic strength h(e mu) = root 4 pi alpha(em) similar or equal to 0.3, a lower limit of 141 GeV on the H-+/-+/- mass is obtained at the 95% confidence level. For a doubly-charged Higgs decaying only into an electron and a tau and a coupling h(e tau) similar or equal to 0.3, masses below 112 GeV are ruled out.
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| 13. |
- Aaron, F. D., et al.
(författare)
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A search for excited neutrinos in e(-) p collisions at HERA
- 2008
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 663:5, s. 382-389
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Tidskriftsartikel (refereegranskat)abstract
- A search for first generation excited neutrinos is performed using the full e(-) p data sample collected by the HI experiment at HERA at a centre-of-mass energy of 319 GeV, corresponding to a total luminosity of 184 pb(-1). The electroweak decays of excited neutrinos nu* -> nu gamma, v* -> nu Z and nu* -> eW with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for excited neutrino production is found. Mass dependent exclusion limits on nu* production cross sections and on the ratio of the coupling to the compositeness scale f/boolean AND are derived within gauge mediated models. A limit on f/boolean AND A, independent of the relative couplings to the SU(2) and U(1) gauge bosons, is also determined. These limits extend the excluded region to higher masses than has been possible in previous excited neutrino searches. (c) 2008 Elsevier B.V. All rights reserved.
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| 14. |
- Aaron, F. D., et al.
(författare)
-
Measurement of isolated photon production in deep-inelastic scattering at HERA
- 2008
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 54:3, s. 371-387
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Tidskriftsartikel (refereegranskat)abstract
- The production of isolated photons in deep-inelastic scattering ep -> e gamma X is measured with the H1 detector at HERA. The measurement is performed in the kinematic range of negative four-momentum transfer squared 4 < Q(2)< 150 GeV2 and a mass of the hadronic system W-X > 50 GeV. The analysis is based on a total integrated luminosity of 227 pb(-1). The production cross section of isolated photons with a transverse energy in the range 3 < E-T(gamma)< 10 GeV and pseudorapidity range -1.2
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| 15. |
- Aaron, F. D., et al.
(författare)
-
Three- and four-jet production at low x at HERA
- 2008
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 54:3, s. 389-409
-
Tidskriftsartikel (refereegranskat)abstract
- Three- and four-jet production is measured in deep-inelastic ep scattering at low x and Q(2) with the H1 detector using an integrated luminosity of 44.2 pb(-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(alpha(2)(s)) and O(alpha(3)(s)) and with Monte Carlo simulation programs where higher order effects are approximated by parton showers. A good overall description is provided by the O(alpha(3)(s)) calculation. Too few events are predicted at the lowest x similar to 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.
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| 16. |
- Aktas, A., et al.
(författare)
-
Measurement of inclusive jet production in deep-inelastic scattering at high Q(2) and determination of the strong coupling
- 2007
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 653:2-4, s. 134-144
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Tidskriftsartikel (refereegranskat)abstract
- Inclusive jet production is studied in neutral current deep-inelastic positron-proton scattering at large four momentum transfer squared Q(2) > 150 GeV2 with the H1 detector at HERA. Single and double differential inclusive jet cross sections are measured as a function of Q(2) and of the transverse energy E-T of the jets in the Breit frame. The measurements are found to be well described by calculations at next-to-leading order in perturbative QCD. The running of the strong coupling is demonstrated and the value of alpha(s)(M-Z) is determined. The ratio of the inclusive jet cross section to the inclusive neutral current cross section is also measured and used to extract a precise value for ces (M-Z) = 0.1193 +/- 0.0014(exp.)(-0.0030)(+0.0047) (th.) +/- 0.0016(pdf). (c) 2007 Elsevier BX All rights reserved.
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| 17. |
- Aktas, A., et al.
(författare)
-
Tau lepton production in ep collisions at HERA
- 2006
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 48:3, s. 699-714
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Tidskriftsartikel (refereegranskat)abstract
- The production of tau leptons in ep collisions is investigated using data recorded by the H1 detector at HERA in the period 1994-2000. Tau leptons are identified by detecting their decay products, using leptonic and hadronic decay modes. The cross section for the production of tau lepton pairs is measured for the first time at HERA. Furthermore, a search for events with an energetic isolated tau lepton and with large missing transverse momentum is performed. The results are found to be in agreement with the Standard Model predictions.
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| 18. |
- Aktas, A., et al.
(författare)
-
Inclusive D*(+/-) meson and associated dijet production in deep-inelastic scattering at HERA
- 2007
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 51:2, s. 271-287
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Tidskriftsartikel (refereegranskat)abstract
- Inclusive D*(+/-) production is measured in deep-inelastic ep scattering at HERA with the H1 detector. In addition, the production of dijets in events with a D*(+/-) meson is investigated. The analysis covers values of photon virtuality 2 <= Q(2) <= 100 GeV2 and of inelasticity 0.05 <= y <= 0.7. Differential cross sections are measured as a function of Q(2) and x and of various D*(+/-) meson and jet observables. Within the experimental and theoretical uncertainties all measured cross sections are found to be adequately described by next-to-leading order (NLO) QCD calculations, based on the photon - gluon fusion process and DGLAP evolution, without the need for an additional resolved component of the photon beyond what is included at NLO. A reasonable description of the data is also achieved by a prediction based on the CCFM evolution of partons involving the kT- unintegrated gluon distribution of the proton.
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| 19. |
- Aktas, A, et al.
(författare)
-
Inclusive production of D+, D-0, D-s(+) and D*(+) mesons in deep inelastic scattering at HERA
- 2005
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 38:4, s. 447-459
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Tidskriftsartikel (refereegranskat)abstract
- Inclusive production cross sections are measured in deep inelastic scattering at HERA for meson states composed of a charm quark and a light antiquark or the charge conjugate. The measurements cover the kinematic region of photon virtuality 2 < Q(2) < 100 GeV2, inelasticity 0.05 < y < 0.7, D meson transverse momenta p(t)( D) greater than or equal to 2.5 GeV and pseudorapidity |eta( D)| less than or equal to 1.5. The identification of the D-meson decays and the reduction of the combinatorial background profit from the reconstruction of displaced secondary vertices by means of the H1 silicon vertex detector. The production of charmed mesons containing the light quarks u, d and s is found to be compatible with a description in which the hard scattering is followed by a factorisable and universal hadronisation process.
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| 20. |
- Aktas, A, et al.
(författare)
-
Measurement of prompt photon cross sections in photoproduction at HERA
- 2005
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 38:4, s. 437-445
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Tidskriftsartikel (refereegranskat)abstract
- Results are presented on the photoproduction of isolated prompt photons, inclusively and associated with jets, in the gammap center of mass energy range 142 < W < 266 GeV. The cross sections are measured for the transverse momentum range of the photons 5 < E. T < 10 GeV and for associated jets with E-T(jet) > 4.5 GeV. They are measured differentially as a function of E-T(gamma), E-T(jet), the pseudorapidities eta(gamma) and eta(jet) and estimators of the momentum fractions x(gamma) and x(p) of the incident photon and proton carried by the constituents participating in the hard process. In order to further investigate the underlying dynamics, the angular correlation between the prompt photon and the jet in the transverse plane is studied. Predictions by perturbative QCD calculations in next to leading order are about 30% below the inclusive prompt photon data after corrections for hadronisation and multiple interactions, but are in reasonable agreement with the results for prompt photons associated with jets. Comparisons with the predictions of the event generators PYTHIA and HERWIG are also presented.
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