High-momentum proton removal from 16 O and the (e,e'p) cross section

The cross section for the removal of high-momentum protons from 16O is calculated for high missing energies. The admixture of high-momentum nucleons in the 16O ground state is obtained by calculating the single-hole spectral function directly in the finite nucleus with the inclusion of short-range and tensor correlations induced by a realistic meson-exchange interaction. The presence of high-momentum nucleons in the transition to final states in 15N at 60¿100 MeV missing energy is converted to the coincidence cross section for the (e,e¿p) reaction by including the coupling to the electromagnetic probe and the final state interactions of the outgoing proton in the same way as in the standard analysis of the experimental data. Detectable cross sections for the removal of a single proton at these high missing energies are obtained which are considerably larger at higher missing momentum than the corresponding cross sections for the p-wave quasihole transitions. Cross sections for these quasihole transitions are compared with the most recent experimental data available.

Photoionization of Kr 4s: III. Detailed and extended measurements of the Kr 4s-electron ionization cross section

Absolute Kr 4s-electron photoionization cross sections as a function of the exciting-photon energy were measured by photon-induced fluorescence spectroscopy (PIFS) at improved primary-energy resolution. The cross sections were determined from threshold to 33.5 eV and to 90 eV with primary-photon bandwidths of 25 meV and 50 meV, respectively. The measurements were compared with experimental data and selected theoretical calculations for the direct Kr 4s-electron photoionization cross sections.

Two-photon excitation with pico-second fluorescence lifetime imaging to detect nuclear association of flavanols

Two-photon excitation enabled for the first time the observation and measurement of excited state fluorescence lifetimes from three flavanols in solution, which were ∼1.0 ns for catechin and epicatechin, but <45 ps for epigallocatechin gallate (EGCG). The shorter lifetime for EGCG is in line with a lower fluorescence quantum yield of 0.003 compared to catechin (0.015) and epicatechin (0.018). In vivo experiments with onion cells demonstrated that tryptophan and quercetin, which tend to be major contributors of background fluorescence in plant cells, have sufficiently low cross sections for two-photon excitation at 630 nm and therefore do not interfere with detection of externally added or endogenous flavanols in Allium cepa or Taxus baccata cells. Applying two-photon excitation to flavanols enabled 3-D fluorescence lifetime imaging microscopy and showed that added EGCG penetrated the whole nucleus of onion cells. Interestingly, EGCG and catechin showed different lifetime behaviour when bound to the nucleus: EGCG lifetime increased from <45 to 200 ps, whilst catechin lifetime decreased from 1.0 ns to 500 ps. Semi-quantitative measurements revealed that the relative ratios of EGCG concentrations in nucleoli associated vesicles: nucleus: cytoplasm were ca. 100:10:1. Solution experiments with catechin, epicatechin and histone proteins provided preliminary evidence, via the appearance of a second lifetime (τ2 = 1.9–3.1 ns), that both flavanols may be interacting with histone proteins. We conclude that there is significant nuclear absorption of flavanols. This advanced imaging using two-photon excitation and biophysical techniques described here will prove valuable for probing the intracellular trafficking and functions of flavanols, such as EGCG, which is the major flavanol of green tea.

GLUON SATURATION AND THE TOTAL PROTON-AIR CROSS SECTION

In this work we propose a simple model for the total proton-air cross section, which is an improvement of the minijet model with the inclusion of a window in the p(T)-spectrum associated to the saturation physics. Our approach introduces a natural cutoff for the perturbative calculations which modifies the energy behavior of this component. The saturated component is calculated with a dipole model. The results are compared with experimental cross sections measured in cosmic ray experiments.

Spectroscopic features of erbium-doped CaM2O6 (M = Nb, Ta) single crystal fibers grown by the laser-heated pedestal growth technique

Erbium-doped single crystal fibers, with low phonon energy and fairly high absorption and emission cross sections are interesting laser active media, for compact, near-infrared and/or upconversion lasers. In this work, high optical quality Er3+-doped CaNb2O6 and CaTa2O6 single crystal fibers were successfully grown by the versatile laser-heated pedestal growth technique, and characterized from the structural and spectroscopic points of view. The results indicate that these crystal fiber compositions, which had not been explored so far, offer potential applications, not only as laser active media, but also in other optical devices. (c) 2007 Elsevier B.V. All rights reserved.

eta ->gamma gamma decay width via the Primakoff cross section

Incoherent eta photoproduction in nuclei is evaluated at forward angles within 4 to 9 GeV using a multiple scattering Monte Carlo cascade calculation with full eta-nucleus final-state interactions. The Primakoff, nuclear coherent and nuclear incoherent components of the cross sections fit remarkably well previous measurements for Be and Cu from Cornell, suggesting a destructive interference between the Coulomb and nuclear coherent amplitudes for Cu. The inelastic background of the data is consistently attributed to the nuclear incoherent part, which is clearly not isotropic as previously considered in Cornell's analysis. The respective Primakoff cross sections from Be and Cu give Gamma(eta ->gamma gamma)=0.476(62) keV, where the quoted error is only statistical. This result is consistent with the Particle Data Group average of 0.510(26) keV and in sharp contrast (similar to 50%) with the value of 0.324(46) keV obtained at Cornell.

Charmonium-pion cross section from QCD sum rules

The J/psipi --> (D) over barD*, D (D) over bar*, (D) over bar *D* and (D) over barD cross sections as a function of roots are evaluated in a QCD sum rule calculation. We study the Borel sum rule for the four point function involving pseudoscalar and vector meson currents, up to dimension four in the operator product expansion. We find that our results are smaller than the J/psipi --> charmed mesons cross sections obtained with models based on meson exchange, but are close to those obtained with quark exchange models. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Ultra peripheral heavy ion collisions and the energy dependence of the nuclear radius

To estimate realistic cross sections in ultra peripheral heavy ion collisions we must remove effects of strong absorption. One method to eliminate these effects make use of a Glauber model calculation, where the nucleon-nucleon energy dependent cross sections at small impact parameter are suppressed. In another method we impose a geometrical cut on the minimal impact parameter of the nuclear collision ((b)min > R-1 + R-2, where R-i is the radius of ion 'i'). In this last case the effect of a possible nuclear radius dependence with the energy has not been considered in detail up to now. Here we introduce this effect showing that for final states with small invariant mass the effect is negligible. However when the final state has a relatively large invariant mass, e.g., an intermediate mass Higgs boson, the cross section can decrease up to 50%. (C) 2003 Published by Elsevier B.V.

Measurement of the t-channel single top quark production cross section

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Measurement of the differential cross section for the production of an isolated photon with associated jet in p(p)over-bar collisions at root s=1.96 TeV

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Dependence of the t(t)over-bar production cross section on the transverse momentum of the top quark

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Combination of t(t)over-bar cross section measurements and constraints on the mass of the top quark and its decays into charged Higgs bosons

We combine measurements of the top quark pair production cross section in p (p) over bar collisions in the l + jets, ll, and tau l final states ( where l is an electron or muon) at a center of mass energy of root s = 1.96 TeV in 1 fb(-1) of data collected with the D0 detector. For a top quark mass of 170 GeV/c(2), we obtain sigma(t (t) over bar) = 8.18(-0.87)(+0.98) pb in agreement with the theoretical prediction. Based on predictions from higher order quantum chromodynamics, we extract a mass for the top quark from the combined t (t) over bar cross section, consistent with the world average of the top quark mass. In addition, the ratios of t (t) over bar cross sections in different final states are used to set upper limits on the branching fractions B(t -> H(+)b -> tau(+) vb) and B(t -> H(+)b -> c (s) over barb) as a function of the charged Higgs boson mass.

Measurement of the B+ Production Cross Section in pp Collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Upsilon production cross section in pp collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of the B-0 Production Cross Section in pp Collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)