Mass dependence of vector meson photoproduction off protons and nuclei within the energy-dependent hot-spot model

We study the photoproduction of vector mesons off proton and off nuclear targets. We work within the colour dipole model in an approach that includes subnucleon degrees of freedom, so-called hot spots, whose positions in the impact-parameter plane change event-by-event. The key feature of our model is that the number of hot spots depends on the energy of the photon--target interaction. Predictions are presented for exclusive and dissociative production of $\rho^{0}$, $\mathrm{J/}\psi$, and $\Upsilon(1S)$ off protons, as well as for coherent and incoherent photoproduction of $\rho^{0}$ off nuclear targets, where Xe, Au, and Pb nuclei are considered. We find that the mass dependence of dissociative production off protons as a function of the energy of the interaction provides a further handle to search for saturation effects at HERA, the LHC and future colliders. We also find that the coherent photonuclear production of $\rho^{0}$ is sensitive to fluctuations in the subnucleon degrees of freedom at RHIC and LHC energies.Comment: 19 pages, 4 figures. Typo in legend of figs. 1 and 2 correcte

Aspectos fotomorfogenéticos de plantas jovens de erva-mate.

O objetivo deste experimento foi determinar as respostas fotomorfogenéticas de ervamate na fase juvenil em condições controladas, para o estudo de estratégias utilizadas pela espécie na sombra. O crescimento de mudas de erva-mate foi acompanhado na câmara climatizada (fitotron), com período diurno de 12 horas com fluxo de fótons de radiação fotossinteticamente ativa (PPFD) de 510µmol.m-2.-1, razão vermelho: vermelho extremo (V:VE) de 2,35, temperatura de 25°/18°C e umidade relativa de 80%. No fim do dia (tratamento EOD), durante 1 hora e 15 minutos, as plantas foram submetidas à radiação de intensidade reduzida - à sombra, simulando a radiação no nível de sub-bosque de V:VE = 0,31 com PPFD = 13 µmol.m-2s-1 e à sombra do sub-bosque profundo e denso de V:VE = 0,06 com PPFD = 7,2 µmol.m-2s-1. As observações foram realizadas a cada 10 dias. As plantas de erva-mate sob tratamento de sombra no fim de dia com V:VE = 0,31 alongaram o caule mais rápido que as plantas submetidas aos tratamentos V:VE = 0,06 e controle (V:VE = 2,35). As plantas mais sombreadas (EOD V:VE=0,06) mostraram menor emissão de folhas quando comparadas com as plantas controle. Tanto plantas na sombra menos severa (EOD V:VE = 0,31) quanto plantas mais sombreadas (EOD V:VE = 0,06), mostraram o aumento de área foliar total por planta, embora com o número total de folhas menor. Assim, as plantas jovens de erva-mate mostraram respostas de "shade - avoiding" ao gradiente de sombra, com estratégia de aumento de área foliar individual.Seção: Manejo e Extensão. Feira do Agronegócio da Erva-mate, 1., 2003, Chapecó. Integrar para promover o agronegócio da erva-mate

Two-nucleon knockout contributions to the 12^{12}C(e,e′p)(e,e'p) reaction in the dip and {Δ\Delta}(1232) regions

The contributions from $^{12}$C$(e,e'pn)$ and $^{12}$C$(e,e'pp)$ to the semi-exclusive $^{12}$C$(e,e'p)$ cross section have been calculated in an unfactorized model for two-nucleon emission. We assume direct two-nucleon knockout after virtual photon coupling with the two-body pion-exchange currents in the target nucleus. Results are presented at several kinematical conditions in the dip and $\Delta$(1232) regions. The calculated two-nucleon knockout strength is observed to account for a large fraction of the measured $(e,e'p)$ strength above the two-nucleon emission threshold.Comment: 12 Revtex pages, 4 postscript figures (available upon request), University of Gent preprint SSF94-02-0

Exclusive Four-pion Photoproduction in Ultra-peripheral Heavy-ion Collisions at RHIC and LHC Energies

We study the photoproduction of exclusive 2π+2π− mesons in ultra-peripheral heavy-ion collisions at the RHIC and LHC energies. Predictions in photon–nucleus interactions are calculated for various resonances at central and forward rapidities. The recent H1 preliminary data are utilized to improve the description of the poorly known γp→4π±p process. We present the comparisons of our results to the available STAR data at RHIC, and made predictions for the LHC energies