201241327
RECENT HERMES RESULTS ON MESON PRODUCTION
An overview is given of selected recent HERMES results involving hadron production. Topics including transversity, hard exclusive production of pion pairs, observation of the Θ+ pentaquark state and quark fragmentation in nuclei will be presented.
202096488
Particle identification with the HERMES RICH
Abstract In early 1998 a dual-radiator RICH detector was installed into the HERMES spectrometer. It is designed to allow hadron identification over the HERMES kinematic range (2–20 GeV) using both an aerogel and C 4 F 10 gas radiator. Three different approaches that are currently pursued for particle identification are presented.
119748220
New results from hermes
13891794
Vector meson production at HERMES.
Diiractive production of , , ! and J== mesons is observed at the Hermes experiment at DESY. Hermes scatters the 27.5 GeV longitudinally polarised positrons of the HERA storage ring oo an internal gas storage cell target. Polarised and unpolarised gas targets of diierent types are used. The exclusive production from diierent nuclear targets (H, D, 3 He and 14 N) shows coherent and incoherent contributions that depend on the atomic mass A and Q 2. For 3 He the incoherent contribution is smaller than for H and D. The nuclear transparency T has been extracted as a function of Q 2 and and shows no signiicant signal of color transparency eeects. The polari-sation of beam and target at Hermes will allow for the world's rst measurement of double-spin asymmetries in combination with decay angle information. This will allow a nearly complete characterization of the angular momentum structure of the reaction. First results for the longitudinal and linear polarisation of-mesons and for the ratio of the longitudinal versus transverse cross section of-mesons as a function of Q 2 are presented. J== mesons are observed at Hermes in the muonic and the electronic decay channel. As they are produced by photon-gluon fusion processes, the observed spin asymmetry from polarised target data contains information about the gluon spin distribution in the nucleon. As the available statistics is marginal for a determination of G, Hermes currently performs an upgrade of the spectrometer. A ring image Cerenkov detector, a muon detector and a small angle spectrometer will be installed in 1998 and an additional vertex detector in 1999. The upgrade will improve the identiication of charmed and strange mesons, the detection of heavy decaying and slow recoil particles and the detection of the scattered positron in low-Q 2 (photoproduction) events.
125760852
Diffractive vector meson production at intermediate energies.
122512363
Exclusive meson production at HERMES
Abstract.Hard exclusive production of mesons in deep-inelastic scattering allows one to probe the so-far unknown Generalized Parton Distributions (GPDs) of the nucleon. The HERMES experiment has measured several different observables in exclusive meson production by scattering the 27.6GeV HERA lepton beam off an internal fixed gaseous target. Recent results on exclusive π+, ρ0 and pion pair production will be presented.
119185262
Complementarity of Galactic radio and collider data in constraining WIMP dark matter models
In this work we confront dark matter models to constraints that may be derived from radio synchrotron radiation from the Galaxy, taking into account the astrophysical uncertainties and we compare these to bounds set by accelerator and complementary indirect dark matter searches. Specifically we apply our analysis to three popular particle physics models. First, a generic effective operator approach, in which case we set bounds on the corresponding mass scale, and then, two specific UV completions, the Z' and Higgs portals. We show that for many candidates, the radio synchrotron limits are competitive with the other searches, and could even give the strongest constraints (as of today) with some reasonable assumptions regarding the astrophysical uncertainties.
121055806
A light scalar WIMP through the Higgs portal
In these proceedings, I report on the status of a simple singlet scalar dark matter model in the light of recent results from both direct detection experiments, in particular DAMA, CoGeNT, CDMS-II and Xenon10/100, and indirect searches, in particular Fermi-LAT. Specifically, I confront the light scalar WIMP candidates, MDM ∼ few GeV, that are consistent with CoGeNT and/or DAMA, to constraints that may be set using the recent Fermi-LAT data on Milky Way dwarf spheroidal galaxies (dSphs) and the isotropic diffuse gamma-ray emission. I show that the latter observations set relevant exclusion limits on the lightest WIMP candidates. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
15529188
Inflation from a tachyon fluid
Motivated by recent works of Sen [hep-th/0203211, hep-th/0203265] and Gibbons [hep-th/0204008], we study the evolution of a flat and homogeneous universe dominated by tachyon matter. In particular, we analyze the necessary conditions for inflation in the early roll of a single tachyon field. Comparison with string theory reveals that the potential is too steep to explain the fluctuations in the CMBR. We suggest a scenario based on the simultaneous decay of many branes and comment on the issue of reheating of the universe after tachyon rolling.
15985068
Species doubling and effective lagrangians
Coupling gauge fields to the chiral currents from an effective Lagrangian for pseudoscalar mesons naturally gives rise to a species doubling phenomenon similar to that seen with fermionic fields in lattice gauge theory. 17 refs.
53052824
What if Dark Matter Gamma-Ray Lines come with Gluon Lines?
In dark matter (DM) models, the production of a $\ensuremath{\gamma}$ line (or of a ``box-shaped'' $\ensuremath{\gamma}$-ray spectrum) from DM annihilation proceeds in general from a loop diagram involving a heavy charged particle. If the charged particle in the loop carries also a color charge, this leads inevitably to DM annihilation to gluons, with a naturally larger rate. We consider a scenario in which DM candidates annihilate dominantly into gluon pairs, and determine (as far as possible, model-independent) constraints from a variety of observables: (a) the dark matter relic density, (b) the production of antiprotons, (c) DM direct detection and (d) gluon-gluon fusion processes at LHC. Among other things, we show that this scenario together with the recent claim for a possible $\ensuremath{\gamma}$ line from the Galactic center in the Fermi-LAT data, leads to a relic abundance of DM that may be naturally close to the cosmological observations.