3,673 research outputs found
Crepuscular Rays from the Highly Inclined Active Galactic Nucleus in IC 5063
On Earth near sunset, the sun may cast "crepuscular rays" such that clouds
near the horizon obscure the origin of light scattered in bright rays. In
principle, AGN should be able to produce similar effects. Using new Hubble
Space Telescope (HST) near-infrared and optical observations, we show that the
active galaxy IC 5063 contains broad radial rays extending to 11 kpc
from the nucleus. We argue that the bright rays may arise from dusty scattering
of continuum emission from the active nucleus, while the dark rays are due to
shadowing near the nucleus, possibly by a warped torus. We also consider
alternative AGN-related and stellar origins for the extended light.Comment: Accepted for publication to ApJ Letters. 13 pages, 5 figures.
Facilitated by Twitter discussion (see
https://twitter.com/SpaceGeck/status/1201350966945017856). This version
corrects figure labels and includes other more minor update
First results from the CERN Axion Solar Telescope (CAST)
Hypothetical axion-like particles with a two-photon interaction would be
produced in the Sun by the Primakoff process. In a laboratory magnetic field
(``axion helioscope'') they would be transformed into X-rays with energies of a
few keV. Using a decommissioned LHC test magnet, CAST has been running for
about 6 months during 2003. The first results from the analysis of these data
are presented here. No signal above background was observed, implying an upper
limit to the axion-photon coupling < 1.16 10^{-10} GeV^-1 at 95% CL for m_a
<~0.02 eV. This limit is comparable to the limit from stellar energy-loss
arguments and considerably more restrictive than any previous experiment in
this axion mass range.Comment: 4 pages, accepted by PRL. Final version after the referees comment
CAST constraints on the axion-electron coupling
In non-hadronic axion models, which have a tree-level axion-electron
interaction, the Sun produces a strong axion flux by bremsstrahlung, Compton
scattering, and axio-recombination, the "BCA processes." Based on a new
calculation of this flux, including for the first time axio-recombination, we
derive limits on the axion-electron Yukawa coupling g_ae and axion-photon
interaction strength g_ag using the CAST phase-I data (vacuum phase). For m_a <
10 meV/c2 we find g_ag x g_ae< 8.1 x 10^-23 GeV^-1 at 95% CL. We stress that a
next-generation axion helioscope such as the proposed IAXO could push this
sensitivity into a range beyond stellar energy-loss limits and test the
hypothesis that white-dwarf cooling is dominated by axion emission
CAST constraints on the axion-electron coupling
In non-hadronic axion models, which have a tree-level axion-electron interaction, the Sun produces a strong axion flux by bremsstrahlung, Compton scattering, and axiorecombination, the "BCA processes." Based on a new calculation of this flux, including for the first time axio-recombination, we derive limits on the axion-electron Yukawa coupling gae and axion-photon interaction strength ga using the CAST phase-I data (vacuum phase). For ma <~ 10 meV/c2 we find ga gae < 8.1 × 10−23 GeV−1 at 95% CL. We stress that a next-generation axion helioscope such as the proposed IAXO could push this sensitivity into a range beyond stellar energy-loss limits and test the hypothesis that white-dwarf cooling is dominated by axion emission
Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high
We measured the longitudinal double spin asymmetries for single
hadron muo-production off protons and deuterons at photon virtuality <
1(GeV/) for transverse hadron momenta in the range 0.7
GeV/ to 4 GeV/ . They were determined using COMPASS data taken
with a polarised muon beam of 160 GeV/ or 200 GeV/ impinging on
polarised or targets. The experimental
asymmetries are compared to next-to-leading order pQCD calculations, and are
sensitive to the gluon polarisation inside the nucleon in the range
of the nucleon momentum fraction carried by gluons
First Measurement of Chiral Dynamics in \pi^- \gamma -> \pi^- \pi^- \pi^+
The COMPASS collaboration at CERN has investigated the \pi^- \gamma -> \pi^-
\pi^- \pi^+ reaction at center-of-momentum energy below five pion masses,
sqrt(s) < 5 m(\pi), embedded in the Primakoff reaction of 190 GeV pions
impinging on a lead target. Exchange of quasi-real photons is selected by
isolating the sharp Coulomb peak observed at smallest momentum transfers, t' <
0.001 (GeV/c)^2. Using partial-wave analysis techniques, the scattering
intensity of Coulomb production described in terms of chiral dynamics and its
dependence on the 3\pi-invariant mass m(3\pi) = sqrt(s) were extracted. The
absolute cross section was determined in seven bins of with an
overall precision of 20%. At leading order, the result is found to be in good
agreement with the prediction of chiral perturbation theory over the whole
energy range investigated.Comment: 10 pages, 5 figure
The Spin-dependent Structure Function of the Proton g_1^p and a Test of the Bjorken Sum Rule
The inclusive double-spin asymmetry, A_1^p, has been measured at COMPASS in
deepinelastic polarised muon scattering off a large polarised NH3 target. The
data, collected in the year 2007, cover the range Q2 > 1 (GeV/c)^2, 0.004 < x <
0.7 and improve the statistical precision of g_1^p(x) by a factor of two in the
region x < 0.02. The new proton asymmetries are combined with those previously
published for the deuteron to extract the non-singlet spin-dependent structure
function g_1^NS(x,Q2). The isovector quark density, Delta_q_3(x,Q2), is
evaluated from a NLO QCD fit of g_1^NS. The first moment of Delta_q3 is in good
agreement with the value predicted by the Bjorken sum rule and corresponds to a
ratio of the axial and vector coupling constants g_A/g_V =
1.28+-0.07(stat)+-0.10(syst).Comment: 12 pages, 5 figure
Measurement of the Collins and Sivers asymmetries on transversely polarised protons
The Collins and Sivers asymmetries for charged hadrons produced in deeply
inelastic scattering on transversely polarised protons have been extracted from
the data collected in 2007 with the CERN SPS muon beam tuned at 160 GeV/c. At
large values of the Bjorken x variable non-zero Collins asymmetries are
observed both for positive and negative hadrons while the Sivers asymmetry for
positive hadrons is slightly positive over almost all the measured x range.
These results nicely support the present theoretical interpretation of these
asymmetries, in terms of leading-twist quark distribution and fragmentation
functions.Comment: 9 Pages, 5 figure
Resonance Production and S-wave in at 190 GeV/c
The COMPASS collaboration has collected the currently largest data set on
diffractively produced final states using a negative pion
beam of 190 GeV/c momentum impinging on a stationary proton target. This data
set allows for a systematic partial-wave analysis in 100 bins of three-pion
mass, GeV/c , and in 11 bins of the reduced
four-momentum transfer squared, (GeV/c) . This
two-dimensional analysis offers sensitivity to genuine one-step resonance
production, i.e. the production of a state followed by its decay, as well as to
more complex dynamical effects in nonresonant production. In this paper,
we present detailed studies on selected partial waves with , , , , and . In these waves, we observe
the well-known ground-state mesons as well as a new narrow axial-vector meson
decaying into . In addition, we present the results
of a novel method to extract the amplitude of the subsystem with
in various partial waves from the
data. Evidence is found for correlation of the and
appearing as intermediate isobars in the decay of the known
and .Comment: 96 page
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