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Register a new userSearch for excited fermions and leptoquarks at HERA
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Ulrich F. Katz
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Recent results on searches for new particles at the electron-proton collider HERA are reported. Based on roughly 40pb-1 of e^+p data taken in the years 1994-1997, the H1 and ZEUS collaborations have derived new exclusion limits for the direct production of excited fermion states and of leptoquarks in different decay channels, including lepton-flavor violating decays. The results of searches for contact interactions further constrain the parameter space for such particles and their couplings in the high-mass regime, where direct production is kinematically prohibited. Also preliminary analyses of the e^-p data taken in 1998 and 1999 do not find signals of new physics.
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Recent results on searches for new particles at the electron-proton collider HERA are reported. Based on roughly 100pb-1 of e^+p data and 16pb-1 of e^-p data per experiment, taken in the years 1994-2000, the H1 and ZEUS collaborations have derived new exclusion limits for the direct production of excited fermion states and leptoquarks. The latter are searched for in different decay channels, including lepton-flavor violating decays. The production of R_P-violating squarks followed by leptoquark-like decays to lepton and quark is studied, as are cascade decays yielding multi-jet plus lepton signatures. New limits from indirect searches are also reported. Several of the searches obtain sensitivities of the same order or exceeding those of other experiments, indicating the substantial discovery potential of future HERA running.
We present the result of direct leptoquark searches based on 110 pb-1 of integrated luminosity collected by the Collider Detector at Fermilab during the 1992-93 and 1994-95 Tevatron runs at sqrt{s}=1.8 TeV. We present upper limits on the production cross sections as a function of the leptoquark mass. Using the NLO calculation of the leptoquark-pair production cross sections we extract lower-mass limits for first, second and third generation leptoquarks. We also present the result of an indirect search for Pati-Salam leptoquarks via exclusive e-mu decay modes of B^{0}_{s} and B^{0}_{d}.
In this paper searches are presented for the pair production of first and second generation scalar leptoquarks and limits are given on the quark-lepton compositeness scale from proton-antiproton collision data at a center-of-mass energy 1.96 TeV, collected with Run II D0 Detector in 2002-2004. No evidence for a leptoquark signal has been observed. From the upper bounds on the product of cross section times branching ratio beta=Br(LQ to lj), a lower mass limits of M(LQ1) > 241 GeV and M(LQ2) > 247 GeV for the first and second LQ generation are set for beta=1. These results, combined with those obtained by D0 in Run I at a center-of-mass energy of 1.8 TeV, allow to exclude scalar LQ masses up to 256 GeV and 251 GeV (for beta=1) for the first and second generation, respectively. The dilepton mass spectra in pp -> l+l-+X interactions are studied using dielectron (dimuon) data samples, corresponding to an integrated luminosity of 271 pb-1 (406 pb-1). The mass spectra being a probe for new physics are examined for new interactions of quarks and leptons from a common composite structure. No excess of events is found over the expectation from Standard Model processes. The current experimental lower limits on the compositeness scale vary, for different chirality channels, from 3.6 to 9.1 TeV for the (eeqq) and from 4.2 to 9.8 TeV for the (mumuqq) contact interaction.
Recent results on the searches for new physics in ep collisions at HERA using the ZEUS and H1 detectors are presented. No evidence for excited fermions or supersymmetric particles within the context of the Minimal Supersymmetric Standard Model nor R-parity violation has been found using an integrated luminosity of up to 20 inv pb. New limits have therefore been established.
We present a search for excited neutrinos and electrons using all data collected by the H1 experiment at HERA at a center-of-mass energy of 320 GeV with an integrated luminosity of up to 435 pb$^{-1}$. No evidence for excited neutrino or electron production is found. Mass dependent exclusion limits are determined for the ratio of the coupling to the compositeness scale, $f/{Lambda}$. These limits greatly extend the excluded region to higher masses than has been possible in previous searches.
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