224 research outputs found

    Neutrino induced threshold production of two pions and N^*(1440) electroweak form factors

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    We study the threshold production of two pions induced by neutrinos in nucleon targets. The contribution of nucleon, pion and contact terms are calculated using a chiral Lagrangian. The contribution of the Roper resonance, neglected in earlier studies, has also been taken into account. The numerical results for the cross sections are presented and compared with the available experimental data. It has been found that in the two pion channels with π+π\pi^+\pi^- and π0π0\pi^0\pi^0 in the final state, the contribution of the N(1440)N^*(1440) is quite important and could be used to determine the N(1440)N^*(1440) electroweak transition form factors if experimental data with better statistics become available in the future.Comment: This version corrects a mistake on the helicity amplitudes sign. Additional comments on resonance-background relative sign are added. Other minor corrections. Matches published version. 17 pages, 7 figure

    Disappearance of Elliptic Flow: A New Probe for the Nuclear Equation of State

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    Using a relativistic hadron transport model, we investigate the utility of the elliptic flow excitation function as a probe for the stiffness of nuclear matter and for the onset of a possible quark-gluon-plasma (QGP) phase-transition at AGS energies 1 < E_Beam < 11 AGeV. The excitation function shows a strong dependence on the nuclear equation of state, and exhibits characteristic signatures which could signal the onset of a phase transition to the QGP.Comment: 11 pages, 4 Postscript figures, uses epsf.sty, submitted to Physical Review Letter

    The total yields of K^+(892), Sigma^+(1385) and Sigma^0 in neutrino-induced reactions at <E_nu> = 10 GeV

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    Using the data obtained with SKAT bubble chamber, the total yields of K+(892)K^+(892), Σ+(1385)\Sigma^+(1385) and Σ0\Sigma^0 are estimated for the first time in neutrino-induced reactions at moderate energies ( = 10.4 GeV). It is shown, that the recently observed \cite{ref1,ref2} enhancement of the K0K^0 and Λ\Lambda yields in νA\nu A interactions (as compared to νN\nu N interactions) is contributed only slightly by the K+(892)K^+(892) and Σ+(1385)\Sigma^+(1385) production, respectively. The decay contribution to the K0K^0 and Λ\Lambda yields is found to be in qualitative agreement with higher energy ( \geq 40 GeV) data. It is shown, that the energy dependence of the K+(892)K^+(892) mean multiplicity in νN\nu N interactions is approximately linear in the range of \approx 10-60 GeV, while that for Σ0\Sigma^0 in νA\nu A interactions (for AA = 20-21) is approximately logarithmic in the range of \approx 10-150 GeV.Comment: 6 pages, 3 figure

    Charged-Particle Multiplicities in Charged-Current Neutrino-- and Anti-Neutrino--Nucleus Interactions

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    The CHORUS experiment, designed to search for νμντ\nu_{\mu}\to\nu_{\tau} oscillations, consists of a nuclear emulsion target and electronic detectors. In this paper, results on the production of charged particles in a small sample of charged-current neutrino-- and anti-neutrino--nucleus interactions at high energy are presented. For each event, the emission angle and the ionization features of the charged particles produced in the interaction are recorded, while the standard kinematic variables are reconstructed using the electronic detectors. The average multiplicities for charged tracks, the pseudo-rapidity distributions, the dispersion in the multiplicity of charged particles and the KNO scaling are studied in different kinematical regions. A study of quasi-elastic topologies performed for the first time in nuclear emulsions is also reported. The results are presented in a form suitable for use in the validation of Monte Carlo generators of neutrino--nucleus interactions.Comment: 17 pages, 5 figure

    A Search for Selectrons and Squarks at HERA

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    Data from electron-proton collisions at a center-of-mass energy of 300 GeV are used for a search for selectrons and squarks within the framework of the minimal supersymmetric model. The decays of selectrons and squarks into the lightest supersymmetric particle lead to final states with an electron and hadrons accompanied by large missing energy and transverse momentum. No signal is found and new bounds on the existence of these particles are derived. At 95% confidence level the excluded region extends to 65 GeV for selectron and squark masses, and to 40 GeV for the mass of the lightest supersymmetric particle.Comment: 13 pages, latex, 6 Figure

    Low Q^2 Jet Production at HERA and Virtual Photon Structure

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    The transition between photoproduction and deep-inelastic scattering is investigated in jet production at the HERA ep collider, using data collected by the H1 experiment. Measurements of the differential inclusive jet cross-sections dsigep/dEt* and dsigmep/deta*, where Et* and eta* are the transverse energy and the pseudorapidity of the jets in the virtual photon-proton centre of mass frame, are presented for 0 < Q2 < 49 GeV2 and 0.3 < y < 0.6. The interpretation of the results in terms of the structure of the virtual photon is discussed. The data are best described by QCD calculations which include a partonic structure of the virtual photon that evolves with Q2.Comment: 20 pages, 5 Figure

    Hadron Production in Diffractive Deep-Inelastic Scattering

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    Characteristics of hadron production in diffractive deep-inelastic positron-proton scattering are studied using data collected in 1994 by the H1 experiment at HERA. The following distributions are measured in the centre-of-mass frame of the photon dissociation system: the hadronic energy flow, the Feynman-x (x_F) variable for charged particles, the squared transverse momentum of charged particles (p_T^{*2}), and the mean p_T^{*2} as a function of x_F. These distributions are compared with results in the gamma^* p centre-of-mass frame from inclusive deep-inelastic scattering in the fixed-target experiment EMC, and also with the predictions of several Monte Carlo calculations. The data are consistent with a picture in which the partonic structure of the diffractive exchange is dominated at low Q^2 by hard gluons.Comment: 16 pages, 6 figures, submitted to Phys. Lett.

    Measurement of D* Meson Cross Sections at HERA and Determination of the Gluon Density in the Proton using NLO QCD

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    With the H1 detector at the ep collider HERA, D* meson production cross sections have been measured in deep inelastic scattering with four-momentum transfers Q^2>2 GeV2 and in photoproduction at energies around W(gamma p)~ 88 GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe the differential cross sections within theoretical and experimental uncertainties. Using these calculations, the NLO gluon momentum distribution in the proton, x_g g(x_g), has been extracted in the momentum fraction range 7.5x10^{-4}< x_g <4x10^{-2} at average scales mu^2 =25 to 50 GeV2. The gluon momentum fraction x_g has been obtained from the measured kinematics of the scattered electron and the D* meson in the final state. The results compare well with the gluon distribution obtained from the analysis of scaling violations of the proton structure function F_2.Comment: 27 pages, 9 figures, 2 tables, submitted to Nucl. Phys.

    The A - dependence of K0K^{0} and Λ\Lambda neutrinoproduction on nuclei

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    For the first time, the A- dependence of the production of K0K^0, Λ\Lambda and, for comparison, π\pi^- mesons is investigated in neutrinonuclear reactions, using the data obtained with SKAT bubble chamber. An exponential parametrization (Aβ\sim A^{\beta}) of the particle yields results in βV0=0.20±0.05{\beta}_{V^0} = 0.20 \pm 0.05 for V0V^0 particles (combined K0K^0 and Λ\Lambda), while for π\pi^- mesons the A- dependence is much weaker, βπ=0.068±0.007{\beta}_{\pi^-} = 0.068 \pm 0.007. A nuclear enhancement of the ratio K0/πK^0/\pi^- is found; this ratio increases from 0.055±0.0130.055 \pm 0.013 for νN\nu N- interactions up to 0.070±0.0110.070 \pm 0.011 at A21A \approx 21 and 0.099±0.0110.099 \pm 0.011 at A45A \approx 45. It is observed, that the multiplicity rise of V0V^0's occures predominantely in the backward hemisphere of the hadronic c.m.s. It is shown, that the A- dependence of the nuclear enhancement of the Λ0{\Lambda}^0 and π\pi^- yields can be reproduced in the framework of a model, incorporating the secondary intranuclear interactions of pions originating from the primary νN\nu N- interactions, while only (29±\pm9)% of that for K0K^0 at A45A \approx 45 can be attributed to intranuclear interactions.Comment: 18 pages, 8 figure

    The yields of light meson resonances in neutrinonuclear interactions at <E_nu> = 10 GeV

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    The total yields of the all well-established light mesonic resonances (up to the ϕ\phi(1020) meson) are estimated in neutrinonuclear interactions at < E_nu > = 10 GeV, using the data obtained with SKAT bubble chamber. For some resonances, the yields in the forward and backward hemispheres in the hadronic c.m.s. are also extracted. From the comparison of the obtained and available higher-energy data, an indication is obtained that the resonance yields rise almost linearly as a function of the mean mass of the neutrinoproduced hadronic system. The fractions of pions originating from the light resonance decays are inferred.Comment: 15 pages, 7 figure
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