New high precision measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarised
6LiD target are presented. The data ...were taken in 2003 and 2004 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160
GeV
/
c
. Both the Collins and Sivers asymmetries turn out to be compatible with zero, within the present statistical errors, which are more than a factor of 2 smaller than those of the published COMPASS results from the 2002 data. The final results from the 2002, 2003 and 2004 runs are compared with naive expectations and with existing model calculations.
The cross section for the production of ω mesons in proton–proton collisions has been measured in a previously unexplored region of incident energies. Cross sections of σ=(7.5±1.9) μb and ...σ=(30.8±3.4) μb (with 20% systematic uncertainties) were extracted at ϵ=92 MeV and 173 MeV excess energy above the ω threshold, respectively. The angular distribution of the ω at ϵ=173 MeV is strongly anisotropic, demonstrating the importance of partial waves beyond pure s-wave production at this energy.
First measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarized 6LiD target are presented. The data were taken ...in 2002 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. The Collins asymmetry turns out to be compatible with zero, as does the measured Sivers asymmetry within the present statistical errors.
A search for dark matter linelike signals iss performed in the vicinity of the Galactic Center by the H.E.S.S. experiment on observational data taken in 2014. An unbinned likelihood analysis iss ...developed to improve the sensitivity to linelike signals. The upgraded analysis along with newer data extend the energy coverage of the previous measurement down to 100 GeV. The 18 h of data collected with the H.E.S.S. array allow one to rule out at 95% C.L. the presence of a 130 GeV line (at l=-1.5°, b=0° and for a dark matter profile centered at this location) previously reported in Fermi-LAT data. This new analysis overlaps significantly in energy with previous Fermi-LAT and H.E.S.S.
No significant excess associated with dark matter annihilations was found in the energy range of 100 GeV to 2 TeV and upper limits on the gamma-ray flux and the velocity weighted annihilation cross section are derived adopting an Einasto dark matter halo profile. Expected limits for present and future large statistics H.E.S.S. observations are also given.
Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. The ...asymmetry depends on the azimuthal angles of both the pion (phi) and the target spin axis (phi(S)) about the virtual-photon direction and relative to the lepton scattering plane. The extracted Fourier component sin((phi+phi(S))(pi)(UT) is a signal of the previously unmeasured quark transversity distribution, in conjunction with the Collins fragmentation function, also unknown. The component sin((phi-phi(S)(pi)(UT) arises from a correlation between the transverse polarization of the target nucleon and the intrinsic transverse momentum of quarks, as represented by the previously unmeasured Sivers distribution function. Evidence for both signals is observed, but the Sivers asymmetry may be affected by exclusive vector meson production.
The reaction
pp→
K
+
Λp was measured exclusively at the cooler synchrotron COSY at beam momenta of p
Beam = 2.50
GeV/c and p
Beam = 2.75
GeV/c using the TOF detector. Angular and momentum ...distributions were obtained for the full phase space of the reaction products. Total cross sections were extracted to be (2.7 ± 0.3)
μb and (12.0 ± 0.4)
μb, respectively. The polarization of the
Λ-hyperon was determined as a function of its transversal momentum and was found to be negative for transverse momentum transfers of p
T
≥ 0.3
GeV/c. The results together with existing data are compared with phenomenological parametrizations and model calculations on the basis of meson exchange.
► Lorentz Invariance Violation as an observational window on Quantum Gravity (QG). ► Reanalysis of PKS 2155-304 flare in 2006 by H.E.S.S. ► Use of a precise likelihood fit procedure on individual ...photons. ► Previous limits on QG energy scale improved by a factor of 3.
Several models of Quantum Gravity predict Lorentz Symmetry breaking at energy scales approaching the Planck scale (∼10
19
GeV). With present photon data from the observations of distant astrophysical sources, it is possible to constrain the Lorentz Symmetry breaking linear term in the standard photon dispersion relations. Gamma Ray Bursts (GRB) and flaring Active Galactic Nuclei (AGN) are complementary to each other for this purpose, since they are observed at different distances in different energy ranges and with different levels of variability. Following a previous publication of the High Energy Stereoscopic System (H.E.S.S.) collaboration
1, a more sensitive event-by-event method consisting of a likelihood fit is applied to PKS 2155-304 flare data of MJD 53944 (July 28, 2006) as used in the previous publication. The previous limit on the linear term is improved by a factor of ∼3 up to
M
QG
l
>
2.1
×
10
18
GeV and is currently the best result obtained with blazars. The sensitivity to the quadratic term is lower and provides a limit of
M
QG
q
>
6.4
×
10
10
GeV, which is the best value obtained so far with an AGN and similar to the best limits obtained with GRB.
Single-spin asymmetries were investigated in inclusive electroproduction of charged pions and kaons from transversely polarized protons at the Hermes experiment. The asymmetries were studied as a ...function of the azimuthal angle ψ about the beam direction between the target-spin direction and the hadron production plane, the transverse hadron momentum PT relative to the direction of the incident beam, and the Feynman variable xF. The sinψ amplitudes are positive for π+ and K+, slightly negative for π− and consistent with zero for K−, with particular PT but weak xF dependences. Especially large asymmetries are observed for two small subsamples of events, where also the scattered electron was recorded by the spectrometer.
The region around the supernova remnant (SNR) W41 contains several TeV sources and has prompted the HESS Collaboration to perform deep observations of this field of view. This resulted in the ...discovery of the new very high energy (VHE) source HESS J1832-093, at the position ..., spatially coincident with a part of the radio shell of the neighbouring remnant G22.7-0.2. The photon spectrum is well described by a power law of index ... and a normalization at 1 TeV of ... The location of the gamma-ray emission on the edge of the SNR rim first suggested a signature of escaping cosmic rays illuminating a nearby molecular cloud. Then a dedicated XMM-Newton observation led to the discovery of a new X-ray point source spatially coincident with the TeV excess. Two other scenarios were hence proposed to identify the nature of HESS J1832-093. Gamma-rays from inverse Compton radiation in the framework of a pulsar wind nebula scenario or the possibility of gamma-ray production within a binary system are therefore also considered. Deeper multiwavelength observations will help to shed new light on this intriguing VHE source. (ProQuest: ... denotes formulae/symbols omitted.)
PDF
