420 research outputs found

    Assessment of reward responsiveness in the response bias probabilistic reward task in rats: implications for cross-species translational research

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    Mood disorders, such as major depressive disorder, are characterized by abnormal reward responsiveness. The Response Bias Probabilistic Reward Task (hereafter referred to as probabilistic reward task (PRT)) quantifies reward responsiveness in human subjects, and an equivalent animal assessment is needed to facilitate preclinical translational research. Thus, the goals of the present studies were to develop, validate and characterize a rat analog of the PRT. Adult male Wistar and Long–Evans rats were trained in operant testing chambers to discriminate between two tone stimuli that varied in duration (0.5 and 2 s). During a subsequent test session consisting of 100 trials, the two tones were made ambiguous (0.9 and 1.6 s) and correct identification of one tone was reinforced with a food pellet three times more frequently than the other tone. In subsequent experiments, Wistar rats were administered either a low dose of the dopamine D2/D3 receptor agonist pramipexole (0.1 mg kg−1, subcutaneous) or the psychostimulant amphetamine (0.5 mg kg−1, intraperitoneal) before the test session. Similar to human subjects, both rat strains developed a response bias toward the more frequently reinforced stimulus, reflecting robust reward responsiveness. Mirroring prior findings in humans, a low dose of pramipexole blunted response bias. Moreover, in rats, amphetamine potentiated response bias. These results indicate that in rats, reward responsiveness can be quantified and bidirectionally modulated by pharmacological manipulations that alter striatal dopamine transmission. Thus, this new procedure in rats, which is conceptually and procedurally analogous to the one used in humans, provides a reverse translational platform to investigate abnormal reward responsiveness across species

    Azimuthal and Single Spin Asymmetries in Hard Scattering Processes

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    In this article we review the present understanding of azimuthal and single spin asymmetries for inclusive and semi-inclusive particle production in unpolarized and polarized hadronic collisions at high energy and moderately large transverse momentum. After summarizing the experimental information available, we discuss and compare the main theoretical approaches formulated in the framework of perturbative QCD. We then present in some detail a generalization of the parton model with inclusion of spin and intrinsic transverse momentum effects. In this context, we extensively discuss the phenomenology of azimuthal and single spin asymmetries for several processes in different kinematical configurations. A comparison with the predictions of other approaches, when available, is also given. We finally emphasize some relevant open points and challenges for future theoretical and experimental investigation.Comment: 70 pages, 34 ps figures. Invited review paper to be published in Progress in Particle and Nuclear Physic

    Subleading-twist effects in single-spin asymmetries in semi-inclusive deep-inelastic scattering on a longitudinally polarized hydrogen target

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    Single-spin asymmetries in the semi-inclusive production of charged pions in deep-inelastic scattering from transversely and longitudinally polarized proton targets are combined to evaluate the subleading-twist contribution to the longitudinal case. This contribution is significantly positive for (\pi^+) mesons and dominates the asymmetries on a longitudinally polarized target previously measured by \hermes. The subleading-twist contribution for (\pi^-) mesons is found to be small

    Measurement of single-spin azimuthal asymmetries in semi-inclusive electroproduction of pions and kaons on a longitudinally polarised deuterium target

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    Single-spin asymmetries have been measured for semi-inclusive electroproduction of π+\pi^+, π\pi^-, π0\pi^0 and K+K^+ mesons in deep-inelastic scattering off a longitudinally polarised deuterium target. The asymmetries appear in the distribution of the hadrons in the azimuthal angle ϕ\phi around the virtual photon direction, relative to the lepton scattering plane. The corresponding analysing powers in the sinϕ\sin \phi moment of the cross section are 0.012±0.002(stat.)±0.002(syst.)0.012 \pm 0.002 {(stat.)} \pm 0.002 {(syst.)} for π+\pi^+, 0.006±0.003(stat.)±0.002(syst.)0.006 \pm 0.003 {(stat.)} \pm 0.002 {(syst.)} for π\pi^-, 0.021±0.005(stat.)±0.003(syst.)0.021 \pm 0.005 {(stat.)} \pm 0.003 {(syst.)} for π0\pi^0 and 0.013±0.006(stat.)±0.003(syst.)0.013 \pm 0.006 {(stat.)} \pm 0.003 {(syst.)} for K+K^+. The sin2ϕ\sin 2\phi moments are compatible with zero for all particles.Comment: Revised version shortened 9 pages, 3 tables, 7 figure

    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

    Single-spin Azimuthal Asymmetries in Electroproduction of Neutral Pions in Semi-inclusive Deep-inelastic Scattering

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    A single-spin asymmetry in the azimuthal distribution of neutral pions relative to the lepton scattering plane has been measured for the first time in deep-inelastic scattering of positrons off longitudinally polarized protons. The analysing power in the sin(phi) moment of the cross section is 0.019 +/- 0.007(stat.) +/- 0.003(syst.). This result is compared to single-spin asymmetries for charged pion production measured in the same kinematic range. The pi^0 asymmetry is of the same size as the pi^+ asymmetry and shows a similar dependence on the relevant kinematic variables. The asymmetry is described by a phenomenological calculation based on a fragmentation function that represents sensitivity to the transverse polarization of the struck quark.Comment: 4 pages, 1 figure, replaced to correct eprint author field, 2nd replacement to correct figure; upper limit of model predictions are corrected. No correction to data or conclusion

    Measurement of Angular Distributions and R= sigma_L/sigma_T in Diffractive Electroproduction of rho^0 Mesons

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    Production and decay angular distributions were extracted from measurements of exclusive electroproduction of the rho^0(770) meson over a range in the virtual photon negative four-momentum squared 0.5< Q^2 <4 GeV^2 and the photon-nucleon invariant mass range 3.8< W <6.5 GeV. The experiment was performed with the HERMES spectrometer, using a longitudinally polarized positron beam and a ^3He gas target internal to the HERA e^{+-} storage ring. The event sample combines rho^0 mesons produced incoherently off individual nucleons and coherently off the nucleus as a whole. The distributions in one production angle and two angles describing the rho^0 -> pi+ pi- decay yielded measurements of eight elements of the spin-density matrix, including one that had not been measured before. The results are consistent with the dominance of helicity-conserving amplitudes and natural parity exchange. The improved precision achieved at 47 GeV, reveals evidence for an energy dependence in the ratio R of the longitudinal to transverse cross sections at constant Q^2.Comment: 15 pages, 15 embedded figures, LaTeX for SVJour(epj) document class Revision: Fig. 15 corrected, recent data added to Figs. 10,12,14,15; minor changes to tex

    Evidence for Quark-Hadron Duality in the Proton Spin Asymmetry A1A_1

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    Spin-dependent lepton-nucleon scattering data have been used to investigate the validity of the concept of quark-hadron duality for the spin asymmetry A1A_1. Longitudinally polarised positrons were scattered off a longitudinally polarised hydrogen target for values of Q2Q^2 between 1.2 and 12 GeV2^2 and values of W2W^2 between 1 and 4 GeV2^2. The average double-spin asymmetry in the nucleon resonance region is found to agree with that measured in deep-inelastic scattering at the same values of the Bjorken scaling variable xx. This finding implies that the description of A1A_1 in terms of quark degrees of freedom is valid also in the nucleon resonance region for values of Q2Q^2 above 1.6 GeV2^2.Comment: 5 pages, 1 eps figure, table added, new references added, in print in Phys. Rev. Let
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