Virtual Compton Scattering and Neutral Pion Electroproduction in the Resonance Region up to the Deep Inelastic Region at Backward Angles

We have made the first measurements of the virtual Compton scattering (VCS) process via the H$(e,e'p)\gamma$ exclusive reaction in the nucleon resonance region, at backward angles. Results are presented for the $W$-dependence at fixed $Q^2=1$ GeV$^2$, and for the $Q^2$-dependence at fixed $W$ near 1.5 GeV. The VCS data show resonant structures in the first and second resonance regions. The observed $Q^2$-dependence is smooth. The measured ratio of H$(e,e'p)\gamma$ to H$(e,e'p)\pi^0$ cross sections emphasizes the different sensitivity of these two reactions to the various nucleon resonances. Finally, when compared to Real Compton Scattering (RCS) at high energy and large angles, our VCS data at the highest $W$ (1.8-1.9 GeV) show a striking $Q^2$- independence, which may suggest a transition to a perturbative scattering mechanism at the quark level.Comment: 20 pages, 8 figures. To appear in Phys.Rev.

Analyse de la mise en œuvre des mesures agri-environnementales à obligation de résultat sur les surfaces herbagères

Les mesures agri-environnementales (MAE) visant la gestion pastorale (Herbe_09) et le maintien de prairies à forte richesse spécifique (Herbe_07) sont analysées : genèse de ces mesures en Europe et en France, conditions de leur mise en oeuvre dans plusieurs territoires et pertinence agri-écologique. Ce type de MAE est susceptible de redonner aux éleveurs une responsabilité valorisante ; leur mise en oeuvre peut entraîner une dynamique territoriale positive dans le débat parfois contradictoire entre agriculture et conservation de la biodiversité ; enfin, elles permettent de concilier production et biodiversité, mais sont peu propices à d'autres fonctions écologiques (pollinisation, séquestration du carbone...). Au final, leur bilan social, écologique et agricole, positif, incite à les généraliser mais en faisant progresser réglementation, concertation entre acteurs agricoles et environnementaux, et connaissances techniques et scientifiques

Analyse de la mise en œuvre des mesures agri-environnementales à obligation de résultat sur les surfaces herbagères

Les mesures agri-environnementales (MAE) visant la gestion pastorale (Herbe_09) et le maintien de prairies à forte richesse spécifique (Herbe_07) sont analysées : genèse de ces mesures en Europe et en France, conditions de leur mise en oeuvre dans plusieurs territoires et pertinence agri-écologique. Ce type de MAE est susceptible de redonner aux éleveurs une responsabilité valorisante ; leur mise en oeuvre peut entraîner une dynamique territoriale positive dans le débat parfois contradictoire entre agriculture et conservation de la biodiversité ; enfin, elles permettent de concilier production et biodiversité, mais sont peu propices à d'autres fonctions écologiques (pollinisation, séquestration du carbone...). Au final, leur bilan social, écologique et agricole, positif, incite à les généraliser mais en faisant progresser réglementation, concertation entre acteurs agricoles et environnementaux, et connaissances techniques et scientifiques

Conception et appropriation de MAE à obligation de résultat sur les surfaces herbagères : comment concilier pertinence écologique et agricole dans l'action publique en faveur de la biodiversité ? (acronyme DIVA2 : MAE Résultat)

Two agri-environmental measures (MAE) tied to an obligation of result aimed at pastureland management (Herbe_09) and preserving species-rich grassland (Herbe_07) were studied: genesis of these measures in Europe and in France, conditions of implementation in different areas and agroecological relevance. This type of MAE restores a sense of responsibility to farmers. Implementing these measures may generate a positive territorial dynamic in the sometimes contradictory debate over the best interests of farmers vs. ecological biodiversity conservation measures. Results show that their positive impact in terms of social, ecological and agricultural benefits supports the idea that they ought to be implemented on a wider scale, along with improved regulations, a better dialogue between farmers and environmental activists, and progress in technical and scientific knowledge.Les mesures agri-environnementales (MAE) visant la gestion pastorale (Herbe_09) et le maintien de prairies à forte richesse spécifique (Herbe_07) sont analysées : genèse de ces mesures en Europe et en France, conditions de leur mise en oeuvre dans plusieurs territoires et pertinence agri-écologique. Ce type de MAE est susceptible de redonner aux éleveurs une responsabilité valorisante ; leur mise en oeuvre peut entraîner une dynamique territoriale positive dans le débat parfois contradictoire entre agriculture et conservation de la biodiversité ; enfin, elles permettent de concilier production et biodiversité, mais sont peu propices à d’autres fonctions écologiques (pollinisation, séquestration du carbone...). Au final, leur bilan social, écologique et agricole, positif, incite à les généraliser mais en faisant progresser réglementation, concertation entre acteurs agricoles et environnementaux, et connaissances techniques et scientifiques

Proton elastic form factor ratios to Q2Q^2=3.5 GeV2^2 by polarization transfer

PHASEThe ratio of the proton elastic electromagnetic form factors, $G_{Ep}/G_{Mp}$, was obtained by measuring $P_{t}$ and $P_{\ell}$, the transverse and longitudinal recoil proton polarization components, respectively, for the elastic $\vec e p \to e\vec p$ ~reaction in the four-momentum transfer squared range of 0.5 to 3.5 GeV$^2$. In the single-photon exchange approximation, the ratio $G_{Ep}/G_{Mp}$ is directly proportional to the ratio $P_t/P_{\ell}$. The simultaneous measurement of $P_{t}$ and $P_{\ell}$ in a polarimeter reduces systematic uncertainties. The results for the ratio $G_{Ep}/G_{Mp}$ show a systematic decrease with increasing $Q^2$, indicating for the first time a definite difference in the distribution of charge and magnetization in the proton. The data have been re-analyzed and systematic uncertainties have become significantly smaller than previously published results

GEp/GMpG_{E_p}/G_{M_p} ratio by polarization transfer in e⃗p→ep⃗\vec{e}p\rightarrow e\vec{p}

The ratio of the proton's elastic electromagnetic form factors was obtained by measuring the transverse and longitudinal polarizations of recoiling protons from the elastic scattering of polarized electrons with unpolarized protons. The ratio of the electric to magnetic form factor is proportional to the ratio of the transverse to longitudinal recoil polarizations. The ratio was measured over a range of four-momentum transfer squared between 0.5 and 3.5 GeV-squared. Simultaneous measurement of transverse and longitudinal polarizations in a polarimeter provides good control of the systematic uncertainty. The results for the ratio of the proton's electric to magnetic form factors show a systematic decrease with increasing four momentum squared, indicating for the first time a marked difference in the spatial distribution of charge and magnetization currents in the proton

Dynamical relativistic effects in quasielastic 1p-shell proton knockout from 16^{16}O

We have measured the cross section for quasielastic 1p-shell proton knockout in the 16O(e,e′p) reaction at ω=0.439GeV and Q2=0.8(GeV/c)2 for missing momentum Pmiss≤355MeV/c. We have extracted the response functions RL+TT, RT, RLT, and the left-right asymmetry, ALT, for the 1p1/2 and the 1p3/2 states. The data are well described by relativistic distorted wave impulse approximation calculations. At large Pmiss, the structure observed in ALT indicates the existence of dynamical relativistic effects. (APS

Measurements of the deuteron elastic structure function A(Q2)A(Q^2) for 0.7≤Q2≤6.00.7\leq Q^2\leq 6.0 (GeV/c)2^2 at Jefferson Laboratory

The deuteron elastic structure function A(Q^2) has been extracted in the Q^2 range 0.7 to 6.0 (GeV/c)^2 from cross section measurements of elastic electron-deuteron scattering in coincidence using the Hall A Facility of Jefferson Laboratory. The data are compared to theoretical models based on the impulse approximation with inclusion of meson-exchange currents, and to predictions of quark dimensional scaling and perturbative quantum chromodynamic

Virtual compton scattering in the resonance region up to the deep inelastic region at backward angles and momentum transfer squared of Q2Q^2 = 1.0 GeV2GeV^2

PHASEInternational audienceWe have made the first measurements of the virtual Compton scattering process via the e p -> e p gamma exclusive reaction at Q**2 = 1 GeV**2 in the nucleon resonance region. The cross section is obtained at center of mass (CM) backward angle, theta_gamma_gamma*, in a range of total (gamma* p) CM energy W from the proton mass up to W = 1.91 GeV. The data show resonant structures in the first and second resonance regions, and are well reproduced at higher W by the Bethe-Heitler+Born cross section, including t-channel pi0-exchange. At high W, our data, together with existing real photon data, show a striking Q**2 independence. Our measurement of the ratio of H(e,e'p)gamma to H(e,e'p)pi0 cross sections is presented and compared to model predictions