Exclusive ρ0\rho^0 electroproduction on the proton at CLAS

The $e p\to e^\prime p \rho^0$ reaction has been measured, using the 5.754 GeV electron beam of Jefferson Lab and the CLAS detector. This represents the largest ever set of data for this reaction in the valence region. Integrated and differential cross sections are presented. The $W$, $Q^2$ and $t$ dependences of the cross section are compared to theoretical calculations based on $t$-channel meson-exchange Regge theory on the one hand and on quark handbag diagrams related to Generalized Parton Distributions (GPDs) on the other hand. The Regge approach can describe at the $\approx$ 30% level most of the features of the present data while the two GPD calculations that are presented in this article which succesfully reproduce the high energy data strongly underestimate the present data. The question is then raised whether this discrepancy originates from an incomplete or inexact way of modelling the GPDs or the associated hard scattering amplitude or whether the GPD formalism is simply inapplicable in this region due to higher-twists contributions, incalculable at present.Comment: 29 pages, 29 figure

Physical and emotional health outcomes after 12 months of public-sector antiretroviral treatment in the Free State Province of South Africa: a longitudinal study using structural equation modelling

<p>Abstract</p> <p>Background</p> <p>African and Asian cohort studies have demonstrated the clinical efficacy of antiretroviral treatment (ART) in resource-limited settings. However, reports of the long-term changes in the physical and emotional quality of life (QoL) of patients on ART in these settings are still scarce. In this study, we assessed the physical and emotional QoL after six and 12 months of ART of a sample of 268 patients enrolled in South Africa's public-sector ART programme. The study also tested the impact of the adverse effects of medication on patients' physical and emotional QoL.</p> <p>Methods</p> <p>A stratified random sample of 268 patients undergoing ART was interviewed at baseline (< 6 months ART) and follow-up (< 12 months ART). A model of the relationships between the duration of ART, the adverse effects of medication, and physical and emotional QoL (measured using EUROQOL-5D) was tested using structural equation modelling.</p> <p>Results</p> <p>The improved physical and emotional QoL shown at baseline was sustained over the 12-month study period, because treatment duration was not significantly associated with changes in the patients' QoL. Physical QoL significantly and positively influenced the patients' emotional QoL (subjective well-being [SWB]) (β = 0.33, <it>P </it>< 0.01). Longitudinal data showed that patients reported significantly fewer adverse effects at follow-up than at baseline (β = -0.38, <it>P </it>< 0.001) and that these adverse effects negatively influenced physical (β = -0.27, <it>P </it>< 0.01) and emotional QoL (β = -0.15, <it>P </it>< 0.05).</p> <p>Conclusion</p> <p>This study provides evidence that the South African public-sector ART programme is effective in delivering sustained improvement in patient well-being. However, the results should encourage clinicians and lay health workers to be vigilant regarding the adverse effects of treatment, because they can seriously affect physical and emotional QoL.</p

The extraction of ϕ−N\phi-N total cross section from d(γ,pK+K−)nd(\gamma,pK^{+}K^{-})n

We report on the first measurement of the differential cross section of $\phi$-meson photoproduction for the $d(\gamma,pK^{+}K^{-})n$ exclusive reaction channel. The experiment was performed using a \textcolor{black}{tagged-photon} beam and the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. A combined analysis using data from the $d(\gamma,pK^{+}K^{-})n$ channel and those from a previous publication on coherent $\phi$ production on the deuteron has been carried out to extract the $\phi-N$ total cross section, $\sigma_{\phi N}$. The extracted $\phi-N$ total cross section favors a value above 20 mb. This value is larger than the value extracted using vector-meson dominance models for $\phi$ photoproduction on the proton.Comment: 7 pages 4 figure

First measurement of target and double spin asymmetries for polarized e- polarized p --> e p pi0 in the nucleon resonance region above the Delta(1232)

The exclusive channel polarized proton(polarized e,e prime p)pi0 was studied in the first and second nucleon resonance regions in the Q2 range from 0.187 to 0.770 GeV2 at Jefferson Lab using the CEBAF Large Acceptance Spectrometer (CLAS). Longitudinal target and beam-target asymmetries were extracted over a large range of center-of-mass angles of the pi0 and compared to the unitary isobar model MAID, the dynamic model by Sato and Lee, and the dynamic model DMT. A strong sensitivity to individual models was observed, in particular for the target asymmetry and in the higher invariant mass region. This data set, once included in the global fits of the above models, is expected to place strong constraints on the electrocoupling amplitudes A_{1/2} and S_{1/2} for the Roper resonance N(1400)P11, and the N(1535)S11 and N(1520)D13 states.Comment: 13 pages, 13 figure

Photoproduction of pi(+)pi(-) meson pairs on the proton

The cross section for photoproduction of pion pairs from hydrogen has been calculated from the cut-off static theory, assuming the energy is sufficiently low that one of the mesons is produced in an S state, the other in a P state. It is shown that the cross section for this process can be expressed exactly in terms of the P-wave scattering phase shifts, provided the S-wave meson-nucleon interactions and the meson-meson interaction can be neglected. The theoretical predictions obtained here are in general agreement with preliminary experimental results

First measurement of target and double spin asymmetries for ep -\u3e ep pi(0) in the nucleon resonance region above the Delta(1232)

The exclusive channel p⃗(e⃗,e\u27p)π0 was studied in the first and second nucleon resonance regions in the Q2 range from 0.187 to 0.770 GeV2 at Jefferson Lab using the CEBAF Large Acceptance Spectrometer. Longitudinal target and beam-target asymmetries were extracted over a large range of center-of-mass angles of the π0 and compared to the unitary isobar model MAID, the dynamic model by Sato and Lee, and the dynamic model DMT. A strong sensitivity to individual models was observed, in particular for the target asymmetry and in the higher invariant mass region. This data set, once included in the global fits of the above models, is expected to place strong constraints on the electrocoupling amplitudes A1/2 and S1/2 for the Roper resonance N(1400)P11 and the N(1535)S11 and N(1520)D13 states