MEASUREMENT OF TOTAL AND PARTIAL PHOTON PROTON CROSS-SECTIONS AT 180 GEV CENTER-OF-MASS ENERGY RID C-1693-2008 RID B-9165-2008 RID C-5889-2009 RID A-4818-2008

Photon proton cross sections for elastic light vector meson production, sigma(el)gammap, inelastic diffractive production, sigma(d)gammap, non-diffractive production, sigma(nd)gammap, as well as the total cross section, sigma(tot)gammap, have been measured at an average gammap center of mass energy of 180 GeV with the ZEUS detector at HERA. The resulting values are sigma(el)gammap = 18 +/- 7 mub, sigma(d)gammap = 33 +/- 8 mub, sigma(nd)gammap = 91 +/- 11 mub, and sigma(tot)gammap = 143 +/- 17 mub, where the errors include statistical and systematic errors added in quadrature

Search for excited electrons using the ZEUS detector

This paper reports a search for excited electrons at the HERA electron-proton collider. In a sample corresponding to an integrated luminosity of 26 nb<sup>−</sup>, no evidence was found for any resonant state decaying into e<sup>−</sup>γ, νW<sup>−</sup> or e<sup>−</sup>Z0. Limits on the coupling strength of an excited electron have been determined for masses between 45 and 225 GeV. This study also reports the observation of the wide-angle eγ Compton scattering process

Observation of two jet production in deep inelastic scattering at HERA

A sample of events with two distinct jets, in addition to the proton remnant, has been identified in deep inelastic, neutral current ep interactions recorded at HERA by the ZEUS experiment. For these events, the mass of the hadronic system ranges from 40 to 260 GeV. The salient features of the observed jet production agree with the predictions of higher order QCD

A measurement of σtot(γp) at √s = 210 GeV

The total photoproduction cross section is determined from a measurement of electroproduction with the ZEUS detector at HERA. The Q2 values of the virtual photons are in the range 10-7 < Q2 < 2 × 10-2 GeV2. The γp total cross section in the γp centre of mass energy range 186-233 GeV is 154 ± 16 (stat.) ± 32 (syst.) μb

Search for leptoquarks with the ZEUS detector

A search for any resonant state coupled to an electron and a proton constituent has been performed using collisions of electron and proton beams at HERA. In a sample with integrated luminosity of 26 nb<sup>−1</sup>, no evidence has been found for production of leptoquarks with decays to e<sup>−</sup> + jet or ν + je to electron and quark have been determined for masses above 25 GeV. For example, scalar isosinglet leptoquarks (S0) with electroweak coupling strength to (e<sup>−</sup>u) states are ruled out at the 95% confidence level for masses below 168 GeV for left-handed couplings and below 176 GeV for right-handed couplings