Search for contact interactions, large extra dimensions and finite quark radius in ep collisions at HERA

University of Freiburg, Freiburg, Baden-Württemberg, Germany
Physics Letters B (Impact Factor: 6.13). 02/2004; 591(1-2):23-41. DOI: 10.1016/j.physletb.2004.03.081


A search for physics beyond the Standard Model has been performed with high-Q2 neutral current deep inelastic scattering events recorded with the ZEUS detector at HERA. Two data sets, e+p→e+X and e−p→e−X, with respective integrated luminosities of 112 pb−1 and 16 pb−1, were analyzed. The data reach Q2 values as high as 40 000 GeV2. No significant deviations from Standard Model predictions were observed. Limits were derived on the effective mass scale in eeqq contact interactions, the ratio of leptoquark mass to the Yukawa coupling for heavy leptoquark models and the mass scale parameter in models with large extra dimensions. The limit on the quark charge radius, in the classical form factor approximation, is 0.85×10−16 cm.

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Available from: Sebastian Gliga, Jun 11, 2014
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    • "Constraints on virtual-graviton signatures in the ADD model of extra dimensions have been obtained at HERA [8] [9], LEP [10] [11] [12] [13] [14] [15], and the Tevatron [16] [17]. At the LHC, limits have been presented based on measurements of diphoton events [18] [19] [20]. "
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    ABSTRACT: Results are presented from a search for large, extra spatial dimensions in events with either two isolated muons or two isolated electrons. The data are from proton-proton interactions at sqrt(s) = 7 TeV collected with the CMS detector at the LHC. The size of the data sample corresponds to an integrated luminosity of approximately 2 inverse femtobarns. The observed dimuon and dielectron mass spectra are found to be consistent with standard-model expectations. Depending on the number of extra dimensions, the 95% confidence level limits from the combined dimuon and dielectron channels range from Ms > 2.4 TeV to Ms > 3.8 TeV, where Ms characterizes the scale for the onset of quantum gravity.
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    • "LQ production or exchange at HERA in the limit of large LQ mass M LQ ≫ √ s and indirect LQ limits from the ZEUS contact interaction analysis [6] are also illustrated in figure 1. "
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    ABSTRACT: Recent results of searches for leptoquarks, lepton flavour violating leptoquarks and excited fermions (electrons, neutrinos and quarks) with the H1 experiment at HERA are presented, which use up to the full ep H1 data set. No evidence for the direct or indirect production of such particles is found. The results are interpreted in terms of limits on the Yukawa coupling of leptoquarks and lepton flavour violating processes and for excited fermions on the ratio of the coupling parameter to the compositeness scale f/Lambda, mainly in the framework of gauge mediated interactions. The derived limits extend the excluded regions to higher masses than those reported in previous results.
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    • "If the LQ mass is higher than the kinematic limit, LQs may show up as contact interactions. For this region, the ZEUS collaboration reports preliminary limits on the ratio of LQ mass to coupling M/λ, using 274 pb −1 of data [6]. For example, the production of˜S L 1/2 LQs is excluded for M/λ < 0.96 TeV. "
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    ABSTRACT: Recent results of searches for new physics at HERA using the complete data sample corresponding to about 0.5/fb per experiment are reviewed. Searches for leptoquarks, isolated leptons (electrons, muons and taus) and a generic search for new physics in many topologies are reported. No evidence for new physics is found. The ep collisions at HERA are ideally suited to search for resonantly produced squarks in SUSY with R-parity violation. It is highlighted how the present results can be interpreted in this way.
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