GeV Region Research Articles

Does regenerated emission change the high-energy signal from gamma-ray burst afterglows?

We study regenerated high-energy emission from the gamma-ray burst (GRB) afterglows, and compare its flux with the direct component from the same afterglow. When the intrinsic emission spectrum extends to TeV region, these very high-energy photons are significantly absorbed by the cosmic infrared background (CIB) radiation field, creating electron/positron pairs; since these pairs are highly energetic, they can scatter the cosmic microwave background radiation up to GeV energies, which may change the intrinsic afterglow light curve in the GeV region. Using the theoretical modeling given in literature and the reasonable choice of relevant parameters, we calculate the expected light curve due to the regeneration mechanism. As the result, we find that the regenerated emission could only slightly change the original light curve, even if we take a rather large value for the CIB density, independently of the density profile of surrounding medium, i.e., constant or wind-like profile. This ensures us the reliable estimation of the intrinsic GRB parameters when the high-energy observation is accessible, regardless of a large amount of uncertainty concerning the CIB density as well as extragalactic magnetic field strength.

Optimum target thickness for polarimeters

Polarimeters with thick targets are a tool to measure the proton polarization. However, the question about the optimum target thickness is still the subject of discussion. An attempt to calculate the common parameters concerning this problem, in a few GeV region, is made in this paper.

Radiation of particles in undulators with straight sections taking into account the medium polarization

In some undulators, in particular, in the recently proposed crystalline undulators the particle trajectories after each bending can have straight sections of length not much less than the period of the undulator, L p =2( L+ L 0), where L and L 0 are the projections on the direction of the particle average motion of arcs with alternating sign of curvature radius R and of the straight sections, respectively. The properties of the radiation produced by relativistic particles in such devices are studied theoretically taking into account the dielectric constant of the medium. This polarization effect results in energy threshold of the radiation, which for realistic crystalline undulators is in GeV region. Varying L 0 one can tune the energy region of the emitted photons as well as their spectral distribution.

Polarization observables in high-energy deuteron photo-disintegration within the Quark-Gluon Strings Model

Deuteron two-body photodisintegration is analysed within the framework of the Quark-Gluon Strings Model. The model describes fairly well the recent experimental data from TJNAF in the few GeV region. Angular distributions at different $\gamma$ -energies are presented and the effect of a forward-backward asymmetry is discussed. New results from the QGSM for polarization observables from 1.5-6 GeV are presented and compared with the available data.

Deuteron photodisintegration at high energy

The high-energy two-body deuteron break-up is a very well-suited process to identify quark effects in nuclei. In particular, its study in the few GeV region can clarify the transition from the nucleonic to the QCD picture of hadrons. The CEBAF Large Angle Spectrometer (CLAS) at JLab allowed for the first time the complete measurement of the angular distributions of the two-body deuteron photodisintegration differential cross-section at photon energies from 0.5 to 2.95 GeV. First results from the analysis of 30% of the total collected data show persistent forward-backward asymmetry and are well described by a calculation derived in the non-perturbative framework of the Quark Gluon String Model (QGSM).

Higher twist, ξw scaling, and effective LO PDFs for lepton scattering in the few GeV region

We use a new scaling variable ξw, and add low Q2 modifications to GRV98 leading order parton distribution functions such that they can be used to model electron, muon and neutrino inelastic scattering cross sections (and also photoproduction) at both very low and high energies.

Folding model study ofα−pscattering: Systematics of elastic scattering, effective interaction, and inelastic excitation ofN*resonances

For a description of elastic and inelastic $\ensuremath{\alpha}\ensuremath{-}p$ scattering exciting ${N}^{*}$ resonances optical potentials and transition potentials were derived by folding nucleon and nucleus mass densities with a variable range effective interaction. For elastic $\ensuremath{\alpha}\ensuremath{-}p$ scattering in forward direction, a reasonable description of essentially all data has been obtained from low energies up to the GeV region. Also, $\ensuremath{\alpha}$ scattering from ${}^{4}\mathrm{He}$ and ${}^{12}\mathrm{C}$ is quite well described with potentials, which indicate that the used folding method is a valid approach for the systems in question. The strong energy dependence of the deduced potentials can be accounted for by a sum of scalar and vector meson-exchange potentials and a soft Pomeron-exchange contribution. The scalar meson-exchange potential falls off rapidly with energy and has a large radius in agreement with theoretical predictions. Consistent with the flavor SU(3) quark model, the vector-meson coupling is rather weak in the central potential, but is strong in the spin-orbit potential, for which a soft Pomeron contribution is negligible. The differences between the deduced $\ensuremath{\alpha}\ensuremath{-}p$ and nucleon-nucleon $(\mathrm{NN})$ potentials are understood; further, an excellent description of the energy dependence of the s-wave $\mathrm{NN}$ amplitudes is obtained in the folding model framework. Distorted wave Born approximation calculations for inelastic $\ensuremath{\alpha}\ensuremath{-}p$ scattering show a t-dependence of the $L=0$ cross section consistent with empirical form factors. Absolute yields for excitation of the resonances ${P}_{11}(1440),$ ${D}_{13}(1520)$ and ${F}_{15}(1680)$ were calculated, using resonance shapes from $\ensuremath{\pi}\ensuremath{-}N$ scattering. A quantitative description of the data at ${E}_{\ensuremath{\alpha}}=4.2\mathrm{GeV}$ is obtained using fluid-dynamical transition densities and strengths exhausting large fractions of scalar energy weighted sum rules. The rather pure scalar (non-spin-isospin-flip) character of these excitations and the observed cross sections are in severe conflict with the constituent quark model. Finally, a prediction is made for $p\ensuremath{-}\ensuremath{\alpha}$ scattering at an incident energy of ${E}_{p}=2.2\mathrm{GeV},$ which yields strongly increased cross sections for ${N}^{*}$ excitations.

Experimental studies of π+π− and K+K− production in two-photon collisions

We have measured the cross section for the processes, γγ → π + π − and γγ → K + K −, with high statistics data collected by the Belle detector at the KEKB e + e − collider. We find resonant peaks in the two-photon c.m. energy region from 1.6 – 2.4 GeV in both processes. The cross sections in the 2.5 – 4.1 GeV region are compared with QCD predictions.

The reaction pd→(pp)n at high momentum transfer and short-range NN properties

A recent cross section measurement of the deuteron breakup reaction pd→(pp)(0°)+n(180°), in the GeV region in a kinematics similar to backward pd elastic scattering, strongly contradicts predictions of a pd→dp model based on the one-nucleon exchange, single pN scattering and Δ excitation mechanisms, and on the wave functions of the Reid soft core and Paris NN potentials. We show within the same model that for the CD Bonn NN potential there is qualitative agreement with the data. It is attributed to a reduction of the one-nucleon exchange at energies above 1 GeV and an increase of the Δ(1232)-isobar contribution, both related to the short-range properties of the wave functions generated by this potential.

Deuteron photodisintegration in the quark-hadron picture

The study of the two-body photodisintegration of the deuteron in the few GeV region is the ideal reaction to clarify the transition from the nucleonic degrees of freedom to the QCD picture of hadrons. The CLAS large angle spectrometer of Hall B at Jlab allowed for the first time the complete measurement of the angular distribution of the differential cross section at photon energy between 0.5 and 3 GeV. Preliminary results of the E93-017 experiment from the analysis of the 30% of the total statistic accumulated show persistent forward-backward asymmetry and are well described by the recent calculation of the deuteron photodisintegration cross section derived in the framework of the Quark Gluon String Model.

Study of electron identification in a few GeV region by an emulsion cloud chamber

We have performed an experimental study of electron identification using an emulsion cloud chamber detector with electron-enriched π− beams at 2 and 4 GeV/c produced by the proton synchrotron source at CERN. This study shows that the efficiency of electron identification is about 90% with little (6%) contamination from pions. These results are in agreement with those obtained using a Cherenkov counter and are reproduced well by the simulation.

Modeling deep inelastic cross sections in the few GeV region

We present preliminary results on simple modifications and corrections to GRV94 leading order parton distribution functions such that they can be used to model electron,muon and neutrino deep-inelastic scattering cross sections at low energies.

Neutrino interactions at low and medium energies

We discuss the calculations for several neutrino induced reactions from low energies to the GeV region. Special attention is paid to nuclear corrections when the targets are medium or heavy nuclei. Finally, we present several ratios of neutral to charged current reactions whose values on isoscalar targets can be estimated accurately. The ratios are useful for investigating neutrino oscillations in Long Baseline experiments.

Atmospheric gamma-ray observation with the BETS detector for calibrating atmospheric neutrino flux calculations

We observed atmospheric gamma-rays around 10 GeV at balloon altitudes (15~25 km) and at a mountain (2770 m a.s.l). The observed results were compared with Monte Carlo calculations to find that an interaction model (Lund Fritiof1.6) used in an old neutrino flux calculation was not good enough for describing the observed values. In stead, we found that two other nuclear interaction models, Lund Fritiof7.02 and dpmjet3.03, gave much better agreement with the observations. Our data will serve for examining nuclear interaction models and for deriving a reliable absolute atmospheric neutrino flux in the GeV region.

Path integral bosonization of the 't Hooft determinant: fluctuations and multiple vacua

The 't Hooft six-quark flavor mixing interaction ( N f =3) is bosonized by the path integral method. The considered complete Lagrangian is constructed on the basis of the combined 't Hooft and U(3)× U(3) extended chiral four fermion Nambu–Jona-Lasinio interactions. The method of the steepest descents is used to derive the effective mesonic Lagrangian. Additionally to the known lowest order stationary phase (SP) result of Reinhardt and Alkofer we obtain the contribution from the small quantum fluctuations of bosonic configurations around their stationary phase trajectories. It affects the vacuum state of hadrons at low energies: whereas without the inclusion of quantum fluctuations the vacuum is uniquely defined for a fixed set of the model parameters, fluctuations give rise to multivalued solutions of the gap equations, marked at instances by drastic changes in the quark condensates. We derive the new gap equations and analyze them in comparison with known results. We classify the solutions according to the number of extrema they may accommodate. We find up to four solutions in the 0< m u , m s <3 GeV region.

Thermodynamics of clan production

Scenarios for particle production in the GeV and TeV regions are reviewed. The expected increase with c.m. energy of the average number of clans for the soft component and the decrease for the semihard one indicate possible classical and quantum behaviour of gluons, respectively. Clan thermodynamics, discussed in the paper, appears as the natural framework to deal with such phenomena.

Mathematical simulation of proton polarimeters with carbon-like analyzing target

The program of the mathematical simulation of the different polarimeters of protons with carbon-like analyzers, working in the 1–5 GeV region of energies, is created. Using the POLO2P version of program the optimization of main parameters of analyzing filter has been carried out. The characteristics of the “focal plane” polarimeters with low dense carbon, polyethylene and graphite (single or double) targets are compared. Optimal parameters of filter and maximal achievable value of polarimeter efficiency was calculated.

Late decaying axino as CDM and its lifetime bound

The axino with mass in the GeV region can be cold dark matter (CDM) in the galactic halo. However, if R-parity is broken, for example by the bilinear terms μ α , then axino (ã) can decay to ν + γ . In this case, the most stringent bound on the axino lifetime comes from the diffuse photon background and we obtain that the axino lifetime should be greater than 3.9×10 24 Ω a ̃ h [s] which amounts to a very small bilinear R-parity violation, i.e., μ α <1 keV. This invalidates the atmospheric neutrino mass generation through bilinear R-violating terms within the context of axino CDM.

Scalar mesons, glueballs, instantons and the glueball/sigma

We include instanton effects in QCD sum rules for coupled scalar glueballs and mesons. We find a light glueball/sigma as in earlier studies without instantons, but in a lattice-type pure instanton model the light glueball/sigma is not found. In the 1-2 Gev region we now find that lightest I=0 meson, in the region of the f$_o$(1370), has no direct glueball mixing, with the instanton loop replacing the glueball component. The lightest scalar mainly glueball in the region of the f$_o$(1500) is sensitive to the choice of nonperturbative gluonic parameters.

Scalar glueball- $q\bar{q}$ mixing above 1 GeV and implications for lattice QCD

Lattice QCD predictions have motivated several recent studies of the mixing between the predicted JPC = 0++ glueball and a qqbar nonet in the 1.3 to 1.7 GeV region. We show that results from apparently different approaches have some common features, explain why this is so and abstract general conclusions. We place particular emphasis on the flavour dependent constraints imposed by decays of the f0(1370), f0(1500) and f0(1700) to all pairs of pseudoscalar mesons. From these results we identify a systematic correlation between glueball mass, mixing, and flavour symmetry breaking and conclude that the glueball may be rather lighter than some quenched lattice QCD computations have suggested. We identify experimental tests that can determine the dynamics of a glueball in this mass region and discuss quantitatively the feasibility of decoding glueball-qqbar mixing.