43,746 research outputs found
Gluonic Excitations and Experimental Hall-D at Jefferson Lab
A new tagged photon beam facility is being constructed in experimental Hall-D
at Jefferson Lab as a part of the 12 GeV upgrade program. The 9 GeV
linearly-polarized photon beam will be produced via coherent Bremsstrahlung
using the CEBAF electron beam, incident on a diamond radiator. The GlueX
experiment in Hall-D will use this photon beam to search for and study the
pattern of gluonic excitations in the meson spectrum produced through
photoproduction reactions with a liquid hydrogen target. Recent lattice QCD
calculations predict a rich spectrum of hybrid mesons, that are formed by
exciting the gluonic field that couples the quarks. A subset of these hybrid
mesons are predicted to have exotic quantum numbers which cannot be formed from
a simple pair, and thus provide an ideal laboratory for testing QCD
in the confinement regime. In these proceedings the status of the construction
and installation of the GlueX detector will be presented, in addition to
simulation results for some reactions of interest in hybrid meson searches.Comment: 5 pages, 4 figures, 1 table, contribution to the proceedings of XXII.
International Workshop on Deep-Inelastic Scattering and Related Subjects, 28
Apr - 2 May, 2014, Warsaw, Polan
The STAR W Program at RHIC
The production of bosons in polarized collisions at RHIC provides
an excellent tool to probe the proton's sea quark distributions. At leading
order bosons are produced in collisions,
and parity-violating single-spin asymmetries measured in longitudinally
polarized collisions give access to the flavor-separated light quark and
antiquark helicity distributions. In this proceedings we report preliminary
results for the single-spin asymmetry, from data collected in 2012 by the
STAR experiment at RHIC with an integrated luminosity of 72 pb at
GeV and an average beam polarization of 56%.Comment: Proceedings of the 3rd Workshop on the QCD Structure of the Nucleon
(QCD-N' 2012
The dominant X-ray wind in massive star binaries
We investigate which shocked wind is responsible for the majority of the
X-ray emission in colliding wind binaries, an issue where there is some
confusion in the literature, and which we show is more complicated than has
been assumed. We find that where both winds rapidly cool (typically close
binaries), the ratio of the wind speeds is often more important than the
momentum ratio, because it controls the energy flux ratio, and the faster wind
is generally the dominant emitter. When both winds are largely adiabatic
(typically long-period binaries), the slower and denser wind will cool faster
and the stronger wind generally dominates the X-ray luminosity.Comment: 4 pages, 1 figure, accepted by A&A Letter
Liberation of specific angular momentum through radiation and scattering in relativistic black-hole accretion discs
A key component of explaining the array of galaxies observed in the Universe
is the feedback of active galactic nuclei, each powered by a massive black
hole's accretion disc. For accretion to occur, angular momentum must be lost by
that which is accreted. Electromagnetic radiation must offer some respite in
this regard, the contribution for which is quantified in this paper, using
solely general relativity, under the thin-disc regime. Herein, I calculate
extremised situations where photons are entirely responsible for energy removal
in the disc and then extend and relate this to the standard relativistic
accretion disc outlined by Novikov & Thorne, which includes internal
angular-momentum transport. While there is potential for the contribution of
angular-momentum removal from photons to be >~1% out to ~10^4 Schwarzschild
radii if the disc is irradiated and maximally liberated of angular momentum
through inverse Compton scattering, it is more likely of order 10^2
Schwarzschild radii if thermal emission from the disc itself is stronger. The
effect of radiation/scattering is stronger near the horizons of fast-spinning
black holes, but, ultimately, other mechanisms must drive angular-momentum
liberation/transport in accretion discs.Comment: 6 pages, 2 figures. Accepted for publication in PAS
Tracking and data handling for the pioneer iii and pioneer iv firings
Tracking and data handling systems for Pioneer III space probe and Pioneer IV lunar probe firing
Combinatorics of rational functions and Poincare-Birkhoff-Witt expansions of the canonical U(n-)-valued differential form
We study the canonical U(n-)-valued differential form, whose projections to
different Kac-Moody algebras are key ingredients of the hypergeometric integral
solutions of KZ-type differential equations and Bethe ansatz constructions. We
explicitly determine the coefficients of the projections in the simple Lie
albegras A_r, B_r, C_r, D_r in a conviniently chosen Poincare-Birkhoff-Witt
basis. As a byproduct we obtain results on the combinatorics of rational
functions, namely non-trivial identities are proved between certain rational
functions with partial symmetries.Comment: More typos correcte
Starburst-driven galactic winds: I. Energetics and intrinsic X-ray emission
We have performed an extensive hydrodynamical parameter study of
starburst-driven galactic winds, motivated by the latest observation data on
the best-studied starburst galaxy M82. We study how the wind dynamics,
morphology and X-ray emission depend on the host galaxy's ISM distribution,
starburst star formation history and strength, and presence and distribution of
mass-loading by dense clouds. We find that the soft X-ray emission from
galactic winds comes from low filling factor (ff < 2 per cent) gas, which
contains only a small fraction (f < 10 per cent) of the mass and energy of the
wind, irrespective of whether the wind models are strongly mass-loaded or not.
X-ray observations of galactic winds therefore do not directly probe the gas
that contains the majority of the energy, mass or metal-enriched gas in the
outflow. The soft X-ray emission comes from gas at a wide range different
temperatures and densities. Estimates of the physical properties of the hot gas
in starburst galaxies, based on fitting the standard simple spectral models to
existing X-ray spectra, should therefore be treated with extreme suspicion. The
majority of the thermal and kinetic energy of these winds is in a volume
filling hot, T approx 10^7 K, component which is extremely difficult to probe
observationally due to its low density and hence low emissivity. Most of the
total energy is in the kinetic energy of this hot gas, a factor which must be
taken into account when attempting to constrain wind energetics
observationally. We also find that galactic winds are efficient at transporting
large amounts of energy out of the host galaxy, in contrast to their
inefficiency at transporting mass out of star-forming galaxies. (Abridged)Comment: Accepted for publication in MNRAS. Letter page size postscript
available from http://adcam.pha.jhu.edu/~dks/dks_published.htm
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