60 research outputs found

    Search for bosonic stop decays in R-parity violating supersymmetry in e^+p collisions at HERA.

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    A search for scalar top quarks in R-parity violating supersymmetry is performed in e+p collisions at HERA using the H1 detector. The data, taken at and 301 GeV, correspond to an integrated luminosity of . The resonant production of scalar top quarks in positron quark fusion via an R-parity violating Yukawa coupling λ′ is considered with the subsequent bosonic stop decay . The R-parity violating decay of the sbottom quark and leptonic and hadronic W decays are considered. No evidence for stop production is found in the search for bosonic stop decays nor in a search for the direct R-parity violating decay . Mass dependent limits on λ′ are obtained in the framework of the minimal supersymmetric Standard Model. Stop quarks with masses up to can be excluded at the 95% confidence level for a Yukawa coupling of electromagnetic strength

    Search for squark production in R-parity violating supersyymety at HERA.

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    A search for squarks in R-parity violating supersymmetry is performed in 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 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 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 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

    Search for light gravitinos in events with photons and missing transverse momentum at HERA

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    A search for gravitinos produced in e±p collisions is performed using the H1 detector at HERA. 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. If R-parity is not conserved, the t-channel exchange of a selectron can produce a neutralino, which, in models where the gravitino is the lightest supersymmetric particle, subsequently decays into a photon and a light gravitino. The resulting event signature, which involves an isolated photon, a jet and missing transverse energy, is analysed for the first time at HERA. No deviation from the Standard Model is found. Exclusion limits on the cross section and on R-parity-violating Yukawa couplings are derived in a Gauge Mediated Supersymmetry Breaking scenario. The results are independent of the squark sector. Neutralinos and supersymmetric partners of the left-handed electron with masses up to 112 GeV and 164 GeV, respectively, can be ruled out at the 95% confidence level for R-parity-violating couplings λ′ equal to 1, in some parts of the parameter space of the considered model

    Measurement of the cross-section asymmetry of deuteron photodisintegration process by linearly polarized photons in the energy range E

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    The first measurements of the cross-section asymmetry Σ for the deuteron photodisintegration process at a cm angle of 90° up to 1.6GeV were performed at Yerevan Electron Synchrotron. These results are in reasonable agreement with previous measurements at lower energy. Our data show agreement with the asymptotic meson exchange model predictions in the energy range 0.8–1.6GeV

    Search for Excited Electrons in ep Collisions at HERA

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    A search for excited electrons is performed using the full e ± p data sample collected by the H1 experiment at HERA, corresponding to a total luminosity of 475 pb -1. The electroweak decays of excited electrons e * → e γ, e * → e Z and e * → ν W with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for excited electron production is found. Mass dependent exclusion limits on e * production cross sections and on the ratio f / Λ of the coupling to the compositeness scale are derived within gauge mediated models. These limits extend the excluded region compared to previous excited electron searches. The e * production via contact interactions is also addressed for the first time in ep collisions. © 2008 Elsevier B.V. All rights reserved.0DESY-08-052 / arxiv:0805.4530SCOPUS: ar.jinfo:eu-repo/semantics/publishe

    Measurement of inclusive jet production in deep-inelastic scattering at high Q(2) and determination of the strong coupling [Elektronisk resurs]

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    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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