Time-like observables: differential cross section and angular asymmetry

Time-like electromagnetic form factors can be obtained from unpolarized measurements of the differential cross section in proton antiproton annihilation in a pair of leptons, as $\overline{p}$ + p ↔ e+ + e− , with the PANDA detector at FAIR. We study the sensitivity of such measurements and focus on observables such as the angular asymmetry and the ratio of electric to magnetic form factors. We also collect useful formulas and references for future simulations and studies

Study of exclusive one-pion and one-eta production using hadron and dielectron channels in pp reactions at kinetic beam energies of 1.25 GeV and 2.2 GeV with HADES

We present measurements of exclusive ensuremathπ+,0 and η production in pp reactions at 1.25GeV and 2.2GeV beam kinetic energy in hadron and dielectron channels. In the case of π+ and π0 , high-statistics invariant-mass and angular distributions are obtained within the HADES acceptance as well as acceptance-corrected distributions, which are compared to a resonance model. The sensitivity of the data to the yield and production angular distribution of Δ (1232) and higher-lying baryon resonances is shown, and an improved parameterization is proposed. The extracted cross-sections are of special interest in the case of pp → pp η , since controversial data exist at 2.0GeV; we find \ensuremathσ=0.142±0.022 mb. Using the dielectron channels, the π0 and η Dalitz decay signals are reconstructed with yields fully consistent with the hadronic channels. The electron invariant masses and acceptance-corrected helicity angle distributions are found in good agreement with model predictions

Studying Time-Like Electromagnetic Baryon Transitions with HADES in π\piN Reactions

International audienceA dedicated program to study electromagnetic baryonic transitions in the time-like region has started using the pion beam and the High Acceptance Di-Electron Spectrometer set-up at GSI. Combined measurements of hadronic and dielectron final states have been performed for the first time in $\pi$ -N reactions, using polyethylene and carbon targets. Differential cross sections of the exclusive channels with two pions in the final state ( $\pi ^-\pi ^+ n$ , $\pi ^0\pi ^- p$ ) were obtained in the second resonance region with an unprecedented statistics. These new data were included in the partial wave analysis of the Bonn–Gatchina group together with the world data from pion and photon beam facilities. The obtained solution provides the excitation function of the two-pion production in photo- and pion- induced reactions around the pole of the D$_{13}$ resonance N(1520) and of its decomposition into the different resonant, non-resonant and $\rho$ contributions. Moreover, the exclusive $ne^+e^-$ production gives insight into time-like electromagnetic structure of baryons using both $e^+e^-$ invariant masses and angular distributions as most sensitive observables for model comparison. In addition, the extraction of the $\rho$ contribution in the two-pion production channels can be used to investigate the validity of the Vector Dominance Model for electromagnetic baryon transitions. The prospects for future experiments in the third resonance region is also discussed

Studying time-like electromagnetic baryonic transitions with HADES in pion induced reactions

A dedicated programme aiming at studying electromagnetic baryonic transitions in the time-like region has started at GSI using the pion beam and the High Acceptance Di-Electron Spectrometer (HADES) set-up. A pioneering experiment has been carried out in the second resonance region, at a center-of-mass energy of 1.49 GeV, using carbon and polyethylene targets, allowing for an analysis of the inclusive e+e- production and of the exclusive quasi-free π-p → ne+e- reaction, in complement to hadronic channels. Predictions for the Dalitz decay of N(1520) and N(1535) based on real photon couplings strongly underestimate the e+e- yield at invariant masses larger than 300 MeV/c2, which signals effects of time-like baryon transition form factors, in qualitative agreement with the Vector Dominance Models (VDM). A quantitative description of the observed e+e- yield is achieved by taking into account the contribution from off-shell ρs. The latter was provided by the preliminary results of a Bonn-Gatchina Partial Wave Analysis of the two-pion production channels, which were measured simultaneously in our experiment. A good agreement is also obtained using a covariant model for the time-like electromagnetic form factors for the N-N(1520) transition. The angular distributions for the e+e- production contain additional selective information on the spin structure of the different transitions. The measurements with the pion beam will be extended in future in the third resonance region. Hyperon Dalitz decay studies in proton induced reactions are also foreseen

Mesures exclusives avec le spectromètre HADES en réactions proton-proton à 1,25 GeV

L'étude précise de la décroissance pionique et la première mesure de décroissance Dalitz de la résonance (1232) sont obtenues par la collaboration HADES (High Acceptance Di-Electron Spectrometer) à GSI, Darmstadt. HADES a développé dans les dernières années un programme de réactions élémentaires visant à fournir une information sélective sur les différentes sources d'émission d'électrons en complément des expériences en ions lourds. Les mesures discutées dans cette thèse se réfèrent à l'étude des collisions proton-proton à une énergie de faisceau de 1.25 GeV. Cette énergie, juste en dessous du seuil de production du , est adaptée à l'étude de la décroissance DaIitz du , qui est l'une des sources importantes d'émission d'électrons dans la région de masse intermédiaire (0.15 GeV/c2npp+ réaction à 1.25 Ge V a été réalisée, ce qui constitue la contribution principale de cette thèse. Les résultats, e.g. la distribution en masse, en angle après correction d'acceptance de la production pp->N et les distributions angulaires de la décroissance ->Np sont montrées et les comparaisons aux modèles sont discutées. Une autre contribution de cette thèse est une étude de simulation des distributions d'angle d'hélicité, qui a été proposée d'une part comme un support à l'analyse exclusive de la décroissance Dalitz du et d'autre part comme une référence à des résultats préliminaires de distribution d'angle d'hélicité obtenus dans les mesures inclusives de di-électrons dans les collisions Ar+KCI.The detailed study of the pionic decay and the first measurement of Dalitz decay of (1232) resonance have been carried out with the High Acceptance Di-Electron Spectrometer (HADES) at GSI, Darmstadt. HADES developed in the last years an elementary reaction program aimed at providing selective information on different sources of di-electron emission as a complement to the heavy-ion experiments. The measurements discussed in this thesis refer to one experiment in this program, the study of proton-proton collisions at a kinetic beam energy of 1.25 GeV. This energy is chosen just below the production threshold and devoted to study the Dalitz decay, which is one of the main sources of di-electron emission at intermediate e+e- invariant masses (0.15 GeV/c2npp+ at 1.25 GeV has been performed, which is the main contribution of this PhD work. The results, such as the acceptance corrected mass and angular distributions of the pp->N process and the ->Np decay angular distribution are shown and the comparisons to models are discussed. Another contribution of this PhD is a simulation study on helicity angle distributions, which was proposed on the one band as a support to the data analysis of the Dalitz decay exclusive measurements and on the other hand as a reference to the preliminary results of helicity angle distribution obtained with inclusive e+e- in Ar+KCI collisions.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Study of baryonic resonances in the reaction pp→ppπ+π−pp\to pp\pi^{+}\pi{-} at 3.5 GeV with HADES

International audienceReport on baryon resonance production and decay in the exclusive pp → ppπ + π − channel at a kinetic energy of 3.5 GeV based on data measured with HADES. The invariant masses and angular distributions of the pion-nucleon systems were compared to simulations based on a resonance model assuming an incoherent sum of contributions from baryonic resonances with masses < 2 GeV and using inputs from one pion measured in the same experiment. A very good description of the two pion production is achieved allowing for an estimate of one and double baryon-resonance as well as ρ meson production cross sections

Bridging Time-Like and Space-Like N* Form Factors

International audienceThe study of electromagnetic transitions opens a window into the very nature of the strong interaction. And, indeed, such a study of how a ground-state nucleon transitions to an excited state, over a broad range of $q^2$ , will provide keen insight into the evolution of how dynamically-generated masses emerge from the asymptotically-free, nearly massless quarks of perturbative QCD as well as provide information on the ancillary effects from the meson–baryon cloud. The space-like ( $q^20$ ) region at GSI. We are living in exciting times whereby near-future prospects exist in extracting high-quality data in both the space-like and time-like regimes (JLab12 and FAIR, for example). The recent ECT* workshop, entitled space-like and time-like electromagnetic baryonic transitions, brought together several disparate communities of experimentalists and theorists. The goal and purpose of this workshop was to make the very first steps towards a much needed consistent description spanning the two kinematical regimes in $q^2$ . The discussions included photoproduction measurements (ELSA, JLab, LEPS, and MAMI), wherein the $q^2=0$ point anchors the connection between space-like and time-like regions and meson-beam data (GSI and J-PARC) and amply complements the requisite information for baryon spectroscopy. This paper presents the outcomes from this ECT* workshop, space-like and time-like baryon electromagnetic transitions, held at the European Centre for Theoretical Studies in Nuclear Physics and Related Areas in Trento, Italy, May 8–12, 2017

Stability and physicochemical properties of the bovine brain phosphatidylethanolamine-binding protein

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Time-like observables: differential cross section and angular asymmetry

Time-like electromagnetic form factors can be obtained from unpolarized measurements of the differential cross section in proton antiproton annihilation in a pair of leptons, as $\overline{p}$ + p ↔ e+ + e− , with the PANDA detector at FAIR. We study the sensitivity of such measurements and focus on observables such as the angular asymmetry and the ratio of electric to magnetic form factors. We also collect useful formulas and references for future simulations and studies