D* Production in Deep Inelastic Scattering at HERA

This paper presents measurements of D^{*\pm} production in deep inelastic scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The data have been taken with the ZEUS detector at HERA. The decay channel $D^{*+}\to (D^0 \to K^- \pi^+) \pi^+$ (+ c.c.) has been used in the study. The $e^+p$ cross section for inclusive D^{*\pm} production with $5<Q^2<100 GeV^2$ and $y<0.7$ is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region {$1.3<p_T(D^{*\pm})<9.0$ GeV and $| \eta(D^{*\pm}) |<1.5$}. Differential cross sections as functions of p_T(D^{*\pm}), $\eta(D^{*\pm}), W$ and $Q^2$ are compared with next-to-leading order QCD calculations based on the photon-gluon fusion production mechanism. After an extrapolation of the cross section to the full kinematic region in p_T(D^{*\pm}) and $\eta$(D^{*\pm}), the charm contribution $F_2^{c\bar{c}}(x,Q^2)$ to the proton structure function is determined for Bjorken $x$ between 2 $\cdot$ 10$^{-4}$ and 5 $\cdot$ 10$^{-3}$.Comment: 17 pages including 4 figure

Diminuição do teor de óxido de crômio (III) usado como marcador externo Reduction in chromium (III) oxide level as an external marker

A sensibilidade do método espectrofotométrico da s-difenilcarbazida de determinação do crômio permite que esse metal possa ser determinado em teores e em massas de amostras tão pequenas que as concentrações atualmente usadas de óxido de crômio (III) como marcador externo em ensaios biológicos poderiam ser drasticamente diminuídas. Utilizando-se do piauçu (Leporinus macrocephalus) para um estudo sobre o coeficiente de digestibilidade aparente (CDA) da fração protéica, seis níveis de óxido de crômio (III) - 0,01% - 0,02% - 0,03% - 0,05% - 0,1% e 0,2% - foram incorporados em dietas isoprotéica e isoenergética, objetivando-se verificar se o cálculo do CDA seria afetado pela variação do teor do marcador. Os seis tratamentos foram dispostos em um delineamento em blocos inteiramente casualisados, sendo as fezes coletadas durante 16 dias. Verificou-se que os resultados do coeficiente de digestibilidade aparente da fração protéica não apresentaram diferenças estatísticas significativas devidas aos teores incorporados do marcador à ração e aos dias de coleta. Conseqüentemente, e em experimentos dessa natureza, nada impede que seja reduzido o teor de óxido de crômio (III) ao menos até 0,01%: além da economia relativa ao consumo do mesmo e da facilidade na manipulação de menor quantidade de amostras de fezes, o método espectrofotométrico da s-difenilcarbazida permite dosar esse nível (e até menor do que 0,01%) de modo simples e rápido, com precisão e exatidão.<br>The objective of this study was to reduce the level of the biological marker Cr2O3 in animal diets, due to the sensibility of the sdiphenylcarbazide spectrophotometric method for chromium determination in feces, recently developed. Six levels of marker, chromium (III) oxide (0.01% - 0.02% - 0.03% - 0.05% - 0.1% and 0.2%), were incorporated into isoproteic and isoenergetic diets, for the apparent digestibility assay of the "piauçu" (Leporinus macrocephalus), in a design of entirely randomized groups. Feces were collected during sixteen days. The statistical analysis did not show significant differences in the apparent digestibility of the proteinic fraction due to the concentration levels of the marker incorporated into the diets and the collection days. Consequently, there is nothing to stop us from reducing Cr2O3 rate to at least 0.01% in these digestibility assays: spectrophotometry of sdiphenilcarbazide allows us to determine this level or even smaller levels in an accurate, simple, and quick manner

Observation of isolated high E(t) photons in photoproduction at HERA

Events containing an isolated prompt photon with high transverse energy, together with a balancing jet, have been observed for the first time in photoproduction at HERA.The data were taken with the ZEUS detector, in a $\gamma p$ centre of mass energy range 120--250 GeV. The fraction of the incoming photon energy participating in the production of the prompt photon and the jet, $x_\gamma$, shows a strong peak near unity, consistent with LO QCD Monte Carlo predictions. In the transverse energy and pseudorapidity range 5\le \eTg < 10 GeV, $-0.7 \le \eta^\gamma < 0.8$, \eTj\ge 5 GeV, and $-1.5\le \eta^{jet}\le 1.8$, with \xgO > 0.8, the measured cross section is $15.3 \pm 3.8 \pm 1.8 pb$, in good agreement with a recent NLO calculation.Comment: 22 pages including 8 figure

Differential cross-sections of D*+- photoproduction in e p collisions at HERA

Inclusive photoproduction of D*+- in ep collisions at HERA has been measured with the ZEUS detector for photon-proton centre of mass energies in the range 115 < W < 280 GeV and photon virtuality Q**2 < 4 GeV**2. The cross section sigma(ep --> D*X) integrated over the kinematic region pt(D*) > 3 GeV and -1.5 < eta(D*) < 1.0 is (10.6+-1.7(stat.)+1.6(syst.)-1.3(syst.)) nb. Differential cross sections as functions of pt(D*), eta(D*) and W are given. The data are compared with two next-to-leading order perturbative QCD predictions. For a calculation using a massive charm scheme the predicted cross sections are smaller than the measured ones. A recent calculation using a massless charm scheme is in agreement with the data.Comment: 18 pages including 4 figure

Measurement of elastic J/#psi# photoproduction at HERA

The reaction #gamma# p #-&gt;# J/#psi#p has been studied in ep interactions using the ZEUS detector at HERA. The cross section for elastic J/#psi# photoproduction has been measured as a function of the photon-proton centre of mass energy W in the range 40 &lt; W &lt; 140 GeV at a median photon virtuality Q&quot;2 of 5 x 10&quot;-&quot;5 GeV&quot;2. The photoproduction cross section, #sigma#_#gamma#_p_#-&gt;#_J_/_#psi#_p, is observed to rise steeply with W. A fit to the data presented in this paper to determine the parameter #delta# in the form #sigma#_#gamma#_p_#-&gt;#_J_/_#psi#_p #propor to# W&quot;#delta# yields the value #delta# = 0.92 #+-# 0.14 #+-# 0.10. The differential cross section d#sigma#/d vertical stroke t vertical stroke is presented over the range vertical stroke t vertical stroke &lt; 1.0 GeV&quot;2 where t is the square of the four-momentum exchanged at the proton vertex. d#sigma#/d vertical stroke t vertical stroke falls exponentially with a slope parameter of 4.6 #+-# 0.4&quot;+&quot;0&quot;.&quot;4_-_0_._6 GeV&quot;-&quot;2. The measured decay angular distributions are consistent with s-channel helicity conservation. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman