281 research outputs found

    A Precision Measurement of pp Elastic Scattering Cross Sections at Intermediate Energies

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    We have measured differential cross sections for \pp elastic scattering with internal fiber targets in the recirculating beam of the proton synchrotron COSY. Measurements were made continuously during acceleration for projectile kinetic energies between 0.23 and 2.59 GeV in the angular range 30θc.m.9030 \leq \theta_{c.m.} \leq 90 deg. Details of the apparatus and the data analysis are given and the resulting excitation functions and angular distributions presented. The precision of each data point is typically better than 4%, and a relative normalization uncertainty of only 2.5% within an excitation function has been reached. The impact on phase shift analysis as well as upper bounds on possible resonant contributions in lower partial waves are discussed.Comment: 23 pages 29 figure

    OGLE-2005-BLG-018: Characterization of Full Physical and Orbital Parameters of a Gravitational Binary Lens

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    We present the analysis result of a gravitational binary-lensing event OGLE-2005-BLG-018. The light curve of the event is characterized by 2 adjacent strong features and a single weak feature separated from the strong features. The light curve exhibits noticeable deviations from the best-fit model based on standard binary parameters. To explain the deviation, we test models including various higher-order effects of the motions of the observer, source, and lens. From this, we find that it is necessary to account for the orbital motion of the lens in describing the light curve. From modeling of the light curve considering the parallax effect and Keplerian orbital motion, we are able to measure not only the physical parameters but also a complete orbital solution of the lens system. It is found that the event was produced by a binary lens located in the Galactic bulge with a distance 6.7±0.36.7\pm 0.3 kpc from the Earth. The individual lens components with masses 0.9±0.3 M0.9\pm 0.3\ M_\odot and 0.5±0.1 M0.5\pm 0.1\ M_\odot are separated with a semi-major axis of a=2.5±1.0a=2.5 \pm 1.0 AU and orbiting each other with a period P=3.1±1.3P=3.1 \pm 1.3 yr. The event demonstrates that it is possible to extract detailed information about binary lens systems from well-resolved lensing light curves.Comment: 19 pages, 6 figure

    OGLE-2005-BLG-153: Microlensing Discovery and Characterization of A Very Low Mass Binary

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    The mass function and statistics of binaries provide important diagnostics of the star formation process. Despite this importance, the mass function at low masses remains poorly known due to observational difficulties caused by the faintness of the objects. Here we report the microlensing discovery and characterization of a binary lens composed of very low-mass stars just above the hydrogen-burning limit. From the combined measurements of the Einstein radius and microlens parallax, we measure the masses of the binary components of 0.10±0.01 M0.10\pm 0.01\ M_\odot and 0.09±0.01 M0.09\pm 0.01\ M_\odot. This discovery demonstrates that microlensing will provide a method to measure the mass function of all Galactic populations of very low mass binaries that is independent of the biases caused by the luminosity of the population.Comment: 6 pages, 3 figures, 1 tabl

    Limits on additional planetary companions to OGLE-2005-BLG-390L

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    We investigate constraints on additional planets orbiting the distant M-dwarf star OGLE-2005-BLG-390L, around which photometric microlensing data has revealed the existence of the sub-Neptune-mass planet OGLE-2005-BLG-390Lb. We specifically aim to study potential Jovian companions and compare our findings with predictions from core-accretion and disc-instability models of planet formation. We also obtain an estimate of the detection probability for sub-Neptune mass planets similar to OGLE-2005-BLG-390Lb using a simplified simulation of a microlensing experiment. We compute the efficiency of our photometric data for detecting additional planets around OGLE-2005-BLG-390L, as a function of the microlensing model parameters and convert it into a function of the orbital axis and planet mass by means of an adopted model of the Milky Way. We find that more than 50 % of potential planets with a mass in excess of 1 M_J between 1.1 and 2.3 AU around OGLE-2005-BLG-390L would have revealed their existence, whereas for gas giants above 3 M_J in orbits between 1.5 and 2.2 AU, the detection efficiency reaches 70 %; however, no such companion was observed. Our photometric microlensing data therefore do not contradict the existence of gas giant planets at any separation orbiting OGLE-2005-BLG-390L. Furthermore we find a detection probability for an OGLE-2005-BLG-390Lb-like planet of around 2-5 %. In agreement with current planet formation theories, this quantitatively supports the prediction that sub-Neptune mass planets are common around low-mass stars.Comment: 10 pages, 4 figures, accepted by A&

    Beam-Induced Nuclear Depolarisation in a Gaseous Polarised Hydrogen Target

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    Spin-polarised atomic hydrogen is used as a gaseous polarised proton target in high energy and nuclear physics experiments operating with internal beams in storage rings. When such beams are intense and bunched, this type of target can be depolarised by a resonant interaction with the transient magnetic field generated by the beam bunches. This effect has been studied with the HERA positron beam in the HERMES experiment at DESY. Resonances have been observed and a simple analytic model has been used to explain their shape and position. Operating conditions for the experiment have been found where there is no significant target depolarisation due to this effect.Comment: REVTEX, 6 pages, 5 figure

    Measurement of the Spin Asymmetry in the Photoproduction of Pairs of High-pT Hadrons at HERMES

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    We present a measurement of the longitudinal spin asymmetry A_|| in photoproduction of pairs of hadrons with high transverse momentum p_T. Data were accumulated by the HERMES experiment using a 27.5 GeV polarized positron beam and a polarized hydrogen target internal to the HERA storage ring. For h+h- pairs with p_T^h_1 > 1.5 GeV/c and p_T^h_2 > 1.0 GeV/c, the measured asymmetry is A_|| = -0.28 +/- 0.12 (stat.) +/- 0.02 (syst.). This negative value is in contrast to the positive asymmetries typically measured in deep inelastic scattering from protons, and is interpreted to arise from a positive gluon polarization.Comment: 5 pages (latex), 4 figures (eps

    Measurement of the Proton Spin Structure Function g1p with a Pure Hydrogen Target

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    A measurement of the proton spin structure function g1p(x,Q^2) in deep-inelastic scattering is presented. The data were taken with the 27.6 GeV longitudinally polarised positron beam at HERA incident on a longitudinally polarised pure hydrogen gas target internal to the storage ring. The kinematic range is 0.021<x<0.85 and 0.8 GeV^2<Q^2<20 GeV^2. The integral Int_{0.021}^{0.85} g1p(x)dx evaluated at Q0^2 of 2.5 GeV^2 is 0.122+/-0.003(stat.)+/-0.010(syst.).Comment: 7 pages, 3 figures, 1 table, RevTeX late

    The Flavor Asymmetry of the Light Quark Sea from Semi-inclusive Deep-inelastic Scattering

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    The flavor asymmetry of the light quark sea of the nucleon is determined in the kinematic range 0.02<x<0.3 and 1 GeV^2<Q^2<10 GeV^2, for the first time from semi-inclusive deep-inelastic scattering. The quantity (dbar(x)-ubar(x))/(u(x)-d(x)) is derived from a relationship between the yields of positive and negative pions from unpolarized hydrogen and deuterium targets. The flavor asymmetry dbar-ubar is found to be non-zero and x dependent, showing an excess of dbar over ubar quarks in the proton.Comment: 7 Pages, 2 figures, RevTeX format; slight revision in text, small change in extraction of dbar-ubar and comparison with a high q2 parameterizatio

    Determination of the Deep Inelastic Contribution to the Generalised Gerasimov-Drell-Hearn Integral for the Proton and Neutron

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    The virtual photon absorption cross section differences [sigma_1/2-sigma_3/2] for the proton and neutron have been determined from measurements of polarised cross section asymmetries in deep inelastic scattering of 27.5 GeV longitudinally polarised positrons from polarised 1H and 3He internal gas targets. The data were collected in the region above the nucleon resonances in the kinematic range nu < 23.5 GeV and 0.8 GeV**2 < Q**2 < 12 GeV**2. For the proton the contribution to the generalised Gerasimov-Drell-Hearn integral was found to be substantial and must be included for an accurate determination of the full integral. Furthermore the data are consistent with a QCD next-to-leading order fit based on previous deep inelastic scattering data. Therefore higher twist effects do not appear significant.Comment: 6 pages, 3 figures, 1 table, revte
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