Search for leptoquarks with the ZEUS detector

Single production of leptoquarks at the Fermilab Tevatron

“…We showed that in the absence of any excess of events CDF and DØ individually should be able to probe e ± u (e ± d) leptoquark masses up to 265 (245) GeV for Yukawa couplings of the electromagnetic strength and β = 1. In the case β = 0.5 these limits reduce to 250 (235) represent an improvement over the present bounds obtained at the Tevatron [5], however, the bounds are similar to the ones obtained by the HERA collaborations [7].…”

“…The combined CDF and DØ limit on the leptoquark mass is M lq > 242 GeV [6] for scalar leptoquarks decaying exclusively into e ± -jet pairs. At HERA, first generation leptoquarks are produced in the s-channel through their Yukawa couplings, and the HERA experiments [7] placed limits on their masses and couplings, establishing that M lq > ∼ 215 − 275 GeV depending on the leptoquark type.…”

Color evaporation induced rapidity gaps

“…The ZEUS collaboration [1] has measured the formation of rapidity gaps between jets produced in ep collisions with 0.2 < y < 0.85 and photon virtuality Q 2 < 4 GeV 2 . Jets were defined by a cone radius of 1.0 in the (η, φ) plane, where η is the pseudorapidity and φ is the azimuthal angle.…”

“…Background gaps are formed when the region of rapidity between the jets is devoid of hadrons because of statistical fluctuation of ordinary soft particle production. Their rate should fall exponentially as the rapidity separation ∆η between the jets increases [1]. We parametrize the background gap probability as…”

“…The probability to form a rapidity gap is then determined by the color multiplicity of the final states formed by the dynamical partons, and nothing else. All data obtained by ZEUS [1], H1 [2], DØ [3], and CDF [4] collaborations are reproduced when this color structure of the interactions is superimposed on the usual perturbative QCD calculation for the production of the hard jets.…”