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Maxim Titov
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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.
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We report on D0 searches for leptoquarks (LQ) predicted in extended gauge theories and composite models to explain the symmetry between quarks and leptons. Data samples obtained with the D0 detector from proton-antiproton collisions at a center-of-mass energy of 1.96 TeV corresponding to intergrated luminosities of 1--4 inverse-fb were analyzed. No evidence for the production of such particles were observed and lower limits on leptoquark masses are set.
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}.
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.
We make a Monte Carlo study on compositeness of first generation quarks and leptons using the Drell-Yan distribution in the high dielectron mass region at the Tevatron and LHC energies. The current experimental lower limits on the compositeness scale, Lambda, vary from 2.5 to 6.1 TeV. In the present analysis, we assume that there will be no deviation of the dielectron mass spectrum from Standard Model prediction at center of mass energy 2 TeV (Tevatron) and 14 TeV (LHC). We then find that in the LL, RR, RL and LR chirality channels of the quark-electron currents, it is possible to extend the lower limits on Lambda (at 95% {CL}) to a range of 6 to 10 TeV for 2 fb^{-1} and 9 to 19 TeV for 30 fb^{-1} of integrated luminosity at Tevatron. At LHC, the corresponding limits extend to a range of 16 to 25 TeV for 10 fb^{-1} and 20 to 36 TeV for 100 fb^{-1} of integrated luminosity.
We present a review of global searches at the Tevatron with D0 detector. The strategy involves splitting the data from the Tevatron into many final states and looking for signs of new physics in the high $p_T$ tails of various distributions using SLEUTH algorithm. We analyzed 117 D0 final states and 5543 D0 distributions. No evidence of new physics is found. The two discrepant final states arise from detector modeling issues.
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