We present a determination of the gluon polarization ΔG/G in the nucleon, based on the helicity asymmetry of quasi-real photoproduction events, Q2<1 (GeV/c)2, with a pair of large transverse-momentum ...hadrons in the final state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarized muon beam scattered on a polarized 6LiD target. The helicity asymmetry for the selected events is 〈A∥/D〉=0.002±0.019(stat)±0.003(syst). From this value, we obtain in a leading-order QCD analysis ΔG/G=0.024±0.089(stat)±0.057(syst) at xg=0.095 and μ2≃3 (GeV/c)2.
The inner 10 pc of our Galaxy contains many counterpart candidates of the very high energy (VHE; >100 GeV) γ-ray point source HESS J1745−290. Within the point spread function of the H.E.S.S. ...measurement, at least three objects are capable of accelerating particles to VHE and beyond and of providing the observed γ-ray flux. Previous attempts to address this source confusion were hampered by the fact that the projected distances between these objects were of the order of the error circle radius of the emission centroid (34 arcsec, dominated by the pointing uncertainty of the H.E.S.S. instrument). Here we present H.E.S.S. data of the Galactic Centre region, recorded with an improved control of the instrument pointing compared to H.E.S.S. standard pointing procedures. Stars observed during γ-ray observations by optical guiding cameras mounted on each H.E.S.S. telescope are used for off-line pointing calibration, thereby decreasing the systematic pointing uncertainties from 20 to 6 arcsec per axis. The position of HESS J1745−290 is obtained by fitting a multi-Gaussian profile to the background-subtracted γ-ray count map. A spatial comparison of the best-fitting position of HESS J1745−290 with the position and morphology of candidate counterparts is performed. The position is, within a total error circle radius of 13 arcsec, coincident with the position of the supermassive black hole Sgr A* and the recently discovered pulsar wind nebula candidate G359.95−0.04. It is significantly displaced from the centroid of the supernova remnant Sgr A East, excluding this object with high probability as the dominant source of the VHE γ-ray emission.
A scintillating fibre hodoscope for high rate applications Bisplinghoff, J; Eversheim, D; Eyrich, W ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2002, Letnik:
490, Številka:
1
Journal Article
Recenzirano
A scintillating fibre hodoscope was developed for application in a high rate environment such as the central region of external beam experiments. It accommodates rates of several
10
6
s
−1
per fibre ...channel while maintaining a time resolution of about
400
ps
. Its central elements are highly efficient radiation-hard scintillating fibres and a photomultiplier tube capable of operating at such rates without appreciable loss of signal amplitude.
We present a new measurement of the longitudinal spin asymmetry A1d and the spin-dependent structure function g1d of the deuteron in the range 1<Q2<100 GeV2 and 0.004<x<0.7. The data were obtained by ...the COMPASS experiment at CERN using a 160 GeV polarised muon beam and a large polarised 6LiD target. The results are in agreement with those from previous experiments and improve considerably the statistical accuracy in the region 0.004<x<0.03.
The first detailed measurement of the dependence on target nuclear mass of the average squared transverse momentum 〈pt2〉 of π+, π−, and K+ mesons from deep-inelastic lepton scattering is obtained as ...a function of several kinematic variables. The data were accumulated at the Hermes experiment at Desy, in which the Hera 27.6 GeV lepton beam was scattered off several nuclear gas targets. The average squared transverse momentum was clearly observed to increase with atomic mass number. The effect increases as a function of Q2 and x and remains constant as a function of both the virtual photon energy ν and the fractional hadron energy z, except that it vanishes as z approaches unity.
Observations of the globular clusters (GCs) NGC 6388 and M15 were carried out by the High Energy Stereoscopic System array of Cherenkov telescopes for a live time of 27.2 and 15.2 hr, respectively. ...No gamma-ray signal is found at the nominal target position of NGC 6388 and M15. In the primordial formation scenario, GCs are formed in a dark matter (DM) halo and DM could still be present in the baryon-dominated environment of GCs. This opens the possibility of observing a DM self-annihilation signal. The DM content of the GCs NGC 6388 and M15 is modeled taking into account the astrophysical processes that can be expected to influence the DM distribution during the evolution of the GC: the adiabatic contraction of DM by baryons, the adiabatic growth of a black hole in the DM halo, and the kinetic heating of DM by stars. Ninety-five percent confidence level exclusion limits on the DM particle velocity-weighted annihilation cross section are derived for these DM halos. In the TeV range, the limits on the velocity-weighted annihilation cross section are derived at the 10--25 cm3 s--1 level and a few 10--24 cm3 s--1 for NGC 6388 and M15, respectively.
Longitudinal double-spin asymmetries of charged hadrons with high transverse momentum
p
T
have been measured in electroproduction using the H
ermes
detector at H
era
. Processes involving gluons in ...the nucleon have been enhanced relative to others by selecting hadrons with
p
T
typically above 1 GeV. In this kinematic domain the gluon polarization has been extracted in leading order making use of the model embedded in the Monte Carlo Generator P
ythia
6.2. The gluon polarization obtained from single inclusive hadrons in the
p
T
range 1 GeV <
p
T
< 2.5 GeV using a deuterium target is
at a scale
and
. For different final states and kinematic domains, consistent values of
have been found within statistical uncertainties using hydrogen and deuterium targets.
Hard exclusive electroproduction of
ω
mesons is studied with the HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and electron beams off a transversely polarized hydrogen ...target. The amplitudes of five azimuthal modulations of the single-spin asymmetry of the cross section with respect to the transverse proton polarization are measured. They are determined in the entire kinematic region as well as for two bins in photon virtuality and momentum transfer to the nucleon. Also, a separation of asymmetry amplitudes into longitudinal and transverse components is done. These results are compared to a phenomenological model that includes the pion pole contribution. Within this model, the data favor a positive
π
ω
transition form factor.
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