A Search for Selectrons and Squarks at HERA

Data from electron-proton collisions at a center-of-mass energy of 300 GeV are used for a search for selectrons and squarks within the framework of the minimal supersymmetric model. The decays of selectrons and squarks into the lightest supersymmetric particle lead to final states with an electron and hadrons accompanied by large missing energy and transverse momentum. No signal is found and new bounds on the existence of these particles are derived. At 95% confidence level the excluded region extends to 65 GeV for selectron and squark masses, and to 40 GeV for the mass of the lightest supersymmetric particle.Comment: 13 pages, latex, 6 Figure

Energy Flow in the Hadronic Final State of Diffractive and Non-Diffractive Deep-Inelastic Scattering at HERA

An investigation of the hadronic final state in diffractive and non--diffractive deep--inelastic electron--proton scattering at HERA is presented, where diffractive data are selected experimentally by demanding a large gap in pseudo --rapidity around the proton remnant direction. The transverse energy flow in the hadronic final state is evaluated using a set of estimators which quantify topological properties. Using available Monte Carlo QCD calculations, it is demonstrated that the final state in diffractive DIS exhibits the features expected if the interaction is interpreted as the scattering of an electron off a current quark with associated effects of perturbative QCD. A model in which deep--inelastic diffraction is taken to be the exchange of a pomeron with partonic structure is found to reproduce the measurements well. Models for deep--inelastic $ep$ scattering, in which a sizeable diffractive contribution is present because of non--perturbative effects in the production of the hadronic final state, reproduce the general tendencies of the data but in all give a worse description.Comment: 22 pages, latex, 6 Figures appended as uuencoded fil

Aplicação materna de glicocorticoide nos parâmetros vitais de cordeiros nascidos a termo e prematuros

O objetivo deste trabalho foi avaliar a influência do glicocorticoide sobre parâmetros vitais de cordeiros nascidos a termo e prematuros, do nascimento às 48 horas de vida. Foram constituídos quatros grupos: PN (cordeiros nascidos de parto normal, n=15, média de 146 dias); PNDEX (cordeiros nascidos de parto normal, cujas mães receberam 16mg de dexametasona aos 141 dias de gestação, n=8, média de 143 dias); PRE (cordeiros prematuros nascidos de cesarianas aos 138 dias de gestação, n=10); e PREDEX (cordeiros prematuros nascidos de cesarianas aos 138 dias de gestação, cujas mães receberam 16mg de dexametasona dois dias antes, n=9). As frequências cardíaca e respiratória variaram ao longo do período, com os maiores valores nos grupos de partos normais. A temperatura retal diminuiu em todos os grupos nos primeiros 60 minutos de vida, sendo os menores valores observados nos cordeiros prematuros, e o escore Apgar foi mais alto nos animais nascidos em tempo gestacional normal. Os cordeiros prematuros apresentaram menor vitalidade e menor taxa de sobrevivência, entretanto, menor taxa de mortalidade foi observada nos prematuros sob influência da dexametasona

Photoproduction of D*+- mesons in electron - proton collisions at HERA

At the electron-proton collider HERA the inclusive $D^{*\pm}$ meson photoproduction cross section has been measured with the H1 detector in two different, but partly overlapping, kinematical regions. For the first, where $\approx 200$ GeV and Q^2 < 0.01 \gev^2, the result is \sigma(\gamma p \to c \bar{c} X) = (13.2 \pm 2.2 ^{+2.1}_{-1.7} ^{+9.9}_{-4.8}) \mu b. The second measurement for Q^2 < 4 \gev^2 yields \sigma(\gamma p \to c \bar{c} X) = (9.3 \pm 2.1 ^{+1.9}_{-1.8} ^{+6.9}_ {-3.2}) \mu b at $\approx 142$ GeV and \sigma(\gamma p \to c \bar{c} X) = (20.6 \pm 5.5 ^ {+4.3}_{-3.9} ^{+15.4}_{-7.2}) \mu b at $\approx 230$ GeV, respectively. The third error accounts for an additional uncertainty due to the proton and photon parton density parametrizations. Differential cross sections are presented as a function of the $D^{*\pm}$ transverse momentum and rapidity. The results compare reasonably well with next-to-leading order QCD calculations. Evidence for diffractive photoproduction of charm quark is presented.Comment: 18 pages, latex, 5 Figure