278 research outputs found

    Regge description of two pseudoscalar meson production in antiproton-proton annihilation

    Full text link
    A Regge-inspired model is used to discuss the hard exclusive two-body hadronic reactions (pbar p ----> pi+ pi-, pi0 pi0, K+ K-, Kbar0 K0) for the FAIR facility project at GSI with the Panda detector. The comparison between the differential cross sections predictions and the available data is shown to determine the values of the few parameters of the model.Comment: 9 pages, 13 figure

    Evidence for Strange Quark Contributions to the Nucleon's Form Factors at Q2Q^2 = 0.108 (GeV/c)2^2

    Full text link
    We report on a measurement of the parity violating asymmetry in the elastic scattering of polarized electrons off unpolarized protons with the A4 apparatus at MAMI in Mainz at a four momentum transfer value of Q2Q^2 = \Qsquare (GeV/c)2^2 and at a forward electron scattering angle of 30∘<θe<40∘^\circ < \theta_e < 40^\circ. The measured asymmetry is ALR(e⃗p)A_{LR}(\vec{e}p) = (\Aphys ±\pm \Deltastatstat_{stat} ±\pm \Deltasystsyst_{syst}) ×\times 10−6^{-6}. The expectation from the Standard Model assuming no strangeness contribution to the vector current is A0_0 = (\Azero ±\pm \DeltaAzero) ×\times 10−6^{-6}. We have improved the statistical accuracy by a factor of 3 as compared to our previous measurements at a higher Q2Q^2. We have extracted the strangeness contribution to the electromagnetic form factors from our data to be GEsG_E^s + \FakGMs GMsG_M^s = \GEsGMs ±\pm \DeltaGEsGMs at Q2Q^2 = \Qsquare (GeV/c)2^2. As in our previous measurement at higher momentum transfer for GEsG_E^s + 0.230 GMsG_M^s, we again find the value for GEsG_E^s + \FakGMs GMsG_M^s to be positive, this time at an improved significance level of 2 σ\sigma.Comment: 4 pages, 3 figure

    The first determination of Generalized Polarizabilities of the proton by a Virtual Compton Scattering experiment

    Get PDF
    Absolute differential cross sections for the reaction (e+p -> e+p+gamma) have been measured at a four-momentum transfer with virtuality Q^2=0.33 GeV^2 and polarization \epsilon = 0.62 in the range 33.6 to 111.5 MeV/c for the momentum of the outgoing photon in the photon-proton center of mass frame. The experiment has been performed with the high resolution spectrometers at the Mainz Microtron MAMI. From the photon angular distributions, two structure functions which are a linear combination of the generalized polarizabilities have been determined for the first time.Comment: 4 pages, 3 figure

    Single-neutron transfer from 11Be gs via the (p,d) reaction with a radioactive beam

    Full text link
    The 11Be(p,d)10Be reaction has been performed in inverse kinematics with a radioactive 11Be beam of E/A = 35.3 MeV. Angular distributions for the 0+ ground state, the 2+, 3.37 MeV state and the multiplet of states around 6 MeV in 10Be were measured at angles up to 16 deg CM by detecting the 10Be in a dispersion-matched spectrometer and the coincident deuterons in a silicon array. Distorted wave and coupled-channels calculations have been performed to investigate the amount of 2+ core excitation in 11Be gs. The use of "realistic" 11Be wave functions is emphasised and bound state form factors have been obtained by solving the particle-vibration coupling equations. This calculation gives a dominant 2s component in the 11Be gs wave function with a 16% [2+ x 1d] core excitation admixture. Cross sections calculated with these form factors are in good agreement with the present data. The Separation Energy prescription for the bound state wave function also gives satisfactory fits to the data, but leads to a significantly larger [2 x 1d] component in 11Be gs.Comment: 39 pages, 12 figures. Accepted for publication in Nuclear Physics A. Added minor corrections made in proof to pages 26 and 3

    Measurement of Strange Quark Contributions to the Nucleon's Form Factors at Q^2=0.230 (GeV/c)^2

    Get PDF
    We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a Q2Q^2 of 0.230 (GeV/c)^2 and a scattering angle of \theta_e = 30^o - 40^o. Using a large acceptance fast PbF_2 calorimeter with a solid angle of \Delta\Omega = 0.62 sr the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is A_{phys} =(-5.44 +- 0.54_{stat} +- 0.27_{\rm sys}) 10^{-6}. The Standard Model expectation assuming no strangeness contributions to the vector form factors is A0=(−6.30+−0.43)10−6A_0=(-6.30 +- 0.43) 10^{-6}. The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is G^s_E + 0.225 G^s_M = 0.039 +- 0.034 or F^s_1 + 0.130 F^s_2 = 0.032 +- 0.028.Comment: 5 pages, 3 figures, submitted to Phys. Rev. Letters on Dec 11, 200

    A versatile method for simulating pp -> ppe+e- and dp -> pne+e-p_spec reactions

    Get PDF
    We have developed a versatile software package for the simulation of di-electron production in pppp and dpdp collisions at SIS energies. Particular attention has been paid to incorporate different descriptions of the Dalitz decay Δ→Ne+e−\Delta \to N e^+e^- via a common interface. In addition, suitable parameterizations for the virtual bremsstrahlung process NN→NNe+e−NN \to NN e^+e^- based on one-boson exchange models have been implemented. Such simulation tools with high flexibility of the framework are important for the interpretation of the di-electron data taken with the HADES spectrometer and the design of forthcoming experiments

    Transverse Beam Spin Asymmetries in Forward-Angle Elastic Electron-Proton Scattering

    Get PDF
    We have measured the beam-normal single-spin asymmetry in elastic scattering of transversely-polarized 3 GeV electrons from unpolarized protons at Q^2 = 0.15, 0.25 (GeV/c)^2. The results are inconsistent with calculations solely using the elastic nucleon intermediate state, and generally agree with calculations with significant inelastic hadronic intermediate state contributions. A_n provides a direct probe of the imaginary component of the 2-gamma exchange amplitude, the complete description of which is important in the interpretation of data from precision electron-scattering experiments.Comment: 5 pages, 3 figures, submitted to Physical Review Letters; shortened to meet PRL length limit, clarified some text after referee's comment

    Strange Quark Contributions to Parity-Violating Asymmetries in the Forward G0 Electron-Proton Scattering Experiment

    Get PDF
    We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers 0.12 < Q^2 < 1.0 GeV^2. These asymmetries, arising from interference of the electromagnetic and neutral weak interactions, are sensitive to strange quark contributions to the currents of the proton. The measurements were made at JLab using a toroidal spectrometer to detect the recoiling protons from a liquid hydrogen target. The results indicate non-zero, Q^2 dependent, strange quark contributions and provide new information beyond that obtained in previous experiments.Comment: 5 pages, 2 figure

    The G0 Experiment: Apparatus for Parity-Violating Electron Scattering Measurements at Forward and Backward Angles

    Full text link
    In the G0 experiment, performed at Jefferson Lab, the parity-violating elastic scattering of electrons from protons and quasi-elastic scattering from deuterons is measured in order to determine the neutral weak currents of the nucleon. Asymmetries as small as 1 part per million in the scattering of a polarized electron beam are determined using a dedicated apparatus. It consists of specialized beam-monitoring and control systems, a cryogenic hydrogen (or deuterium) target, and a superconducting, toroidal magnetic spectrometer equipped with plastic scintillation and aerogel Cerenkov detectors, as well as fast readout electronics for the measurement of individual events. The overall design and performance of this experimental system is discussed.Comment: Submitted to Nuclear Instruments and Method

    Prebiotic Effects of Wheat Arabinoxylan Related to the Increase in Bifidobacteria, Roseburia and Bacteroides/Prevotella in Diet-Induced Obese Mice

    Get PDF
    BACKGROUND: Alterations in the composition of gut microbiota--known as dysbiosis--has been proposed to contribute to the development of obesity, thereby supporting the potential interest of nutrients targeting the gut with beneficial effect for host adiposity. We test the ability of a specific concentrate of water-extractable high molecular weight arabinoxylans (AX) from wheat to modulate both the gut microbiota and lipid metabolism in high-fat (HF) diet-induced obese mice. METHODOLOGY/PRINCIPAL FINDINGS: Mice were fed either a control diet (CT) or a HF diet, or a HF diet supplemented with AX (10% w/w) during 4 weeks. AX supplementation restored the number of bacteria that were decreased upon HF feeding, i.e. Bacteroides-Prevotella spp. and Roseburia spp. Importantly, AX treatment markedly increased caecal bifidobacteria content, in particular Bifidobacterium animalis lactis. This effect was accompanied by improvement of gut barrier function and by a lower circulating inflammatory marker. Interestingly, rumenic acid (C18:2 c9,t11) was increased in white adipose tissue due to AX treatment, suggesting the influence of gut bacterial metabolism on host tissue. In parallel, AX treatment decreased adipocyte size and HF diet-induced expression of genes mediating differentiation, fatty acid uptake, fatty acid oxidation and inflammation, and decreased a key lipogenic enzyme activity in the subcutaneous adipose tissue. Furthermore, AX treatment significantly decreased HF-induced adiposity, body weight gain, serum and hepatic cholesterol accumulation and insulin resistance. Correlation analysis reveals that Roseburia spp. and Bacteroides/Prevotella levels inversely correlate with these host metabolic parameters. CONCLUSIONS/SIGNIFICANCE: Supplementation of a concentrate of water-extractable high molecular weight AX in the diet counteracted HF-induced gut dysbiosis together with an improvement of obesity and lipid-lowering effects. We postulate that hypocholesterolemic, anti-inflammatory and anti-obesity effects are related to changes in gut microbiota. These data support a role for wheat AX as interesting nutrients with prebiotic properties related to obesity prevention
    • …
    corecore