Showing papers by "Mara Senghi Soares published in 2007"
TL;DR: In this paper, the authors used the helicity analysis of the decay-matrix elements of the rho^0 to study the ratio of the gamma^* p cross section for longitudinal and transverse photon as a function of Q^2 and W.
Abstract: Exclusive rho^0 electroproduction at HERA has been studied with the ZEUS detector using 120 pb^{-1} of integrated luminosity collected during 1996-2000. The analysis was carried out in the kinematic range of photon virtuality 2 rho^0 p cross section and the distribution of the squared-four-momentum transfer to the proton. The helicity analysis of the decay-matrix elements of the rho^0 was used to study the ratio of the gamma^* p cross section for longitudinal and transverse photon as a function of Q^2 and W. Finally, an effective Pomeron trajectory was extracted. The results are compared to various theoretical predictions.
85 citations
TL;DR: In this article, the production of dijets in diffractive deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 61-pb-1.
Abstract: The production of dijets in diffractive deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 61 pb-1. The dijet cross section has been measured for virtualities of the exchanged virtual photon, 5 < Q2 < 100 GeV2, and γ*p centre-of-mass energies, 100 < W < 250 GeV. The jets, identified using the inclusive kT algorithm in the γ*p frame, were required to have a transverse energy E*
T,jet > 4 GeV and the jet with the highest transverse energy was required to have E*
T,jet > 5 GeV. All jets were required to be in the pseudorapidity range -3.5<η*
jet<0. The differential cross sections are compared to leading-order predictions and next-to-leading-order QCD calculations based on recent diffractive parton densities extracted from inclusive diffractive deep inelastic scattering data.
45 citations
TL;DR: In this article, the authors measured different jet radii in neutral current deep inelastic ep scattering for boson virtualities Q 2 > 125 GeV 2 with the ZEUS detector at HERA using an integrated luminosity of 81.7 pb−1.
44 citations
TL;DR: The first observation of d(d) in ep collisions in the DIS regime at HERA is presented in this paper, where the production rate is smaller than that for p(p) by three orders of magnitude, in broad agreement with other experiments.
22 citations
TL;DR: In this article, diffractive photoproduction of D*±(2010) mesons was measured with the ZEUS detector at the ep collider HERA, using an integrated luminosity of 78.6 pb-1.6, using the decay D*+→D0π+s followed by D0→K-π+c.
Abstract: Diffractive photoproduction of D*±(2010) mesons was measured with the ZEUS detector at the ep collider HERA, using an integrated luminosity of 78.6 pb-1. The D* mesons were reconstructed in the kinematic range: transverse momentum pT(D*) > 1.9 GeV and pseudorapidity |η(D*)|<1.6, using the decay D*+→D0π+s followed by D0→K-π+(+c.c.). Diffractive events were identified by a large gap in pseudorapidity between the produced hadronic state and the outgoing proton. Cross sections are reported for photon–proton centre-of-mass energies in the range 130 < W < 300 GeV and for photon virtualities Q2 < 1 GeV2, in two ranges of the Pomeron fractional momentum xIP<0.035 and xIP<0.01. The relative contribution of diffractive events to the inclusive D*±(2010) photoproduction cross section is about 6%. The data are in agreement with perturbative QCD calculations based on various parameterisations of diffractive parton distribution functions. The results are consistent with diffractive QCD factorisation.
22 citations
TL;DR: In this paper, the neutral hadrons K0S, Λ and Λ have been measured in ep collisions at HERA using the ZEUS detector, and cross sections, baryon-to-meson ratios, relative yields of strange and charged light hadrons, asymmetry and polarization were measured in three kinematic regions: Q2 > 25 GeV2; 5 < Q2 < 25 geV2, and in photoproduction (Q2≃0).
Abstract: The production of the neutral strange hadrons K0S, Λ and Λ has been measured in ep collisions at HERA using the ZEUS detector. Cross sections, baryon-to-meson ratios, relative yields of strange and charged light hadrons, Λ (Λ) asymmetry and polarization have been measured in three kinematic regions: Q2 > 25 GeV2; 5 < Q2 < 25 GeV2; and in photoproduction (Q2≃0). In photoproduction the presence of two hadronic jets, each with at least 5 GeV transverse energy, was required. The measurements agree in general with Monte Carlo models and are consistent with measurements made at e+e- colliders, except for an enhancement of baryon relative to meson production in photoproduction.
16 citations
15 citations