21,498 research outputs found
ROSAT Detection and High Precision Localization of X-ray Sources in the November 19, 1978 Gamma-Ray Burst Error Box
We report on observations of the 1978, November 19 Gamma-Ray Burst source,
performed with the ROSAT X-ray HRI experiment. Two sources were detected, one
of which is possibly variable. The latter source is identical to the source
discovered in 1981 by the EINSTEIN satellite, and recently detected by ASCA.
The precise localization of these sources is given, and our data are compared
with optical, radio and previous X-ray data.Comment: 10 pages with 2 figures, Accepted for publication in the
Astrophysical Journal (Letters), Latex, aastex macros neede
Single spin asymmetries in the Drell-Yan process
We discuss single transverse spin asymmetries in the Drell-Yan process
originating from so-called gluonic poles in twist-three hadronic matrix
elements, as first considered by Qiu and Sterman. Even though time-reversal
invariance is not broken, the effects of such poles cannot be distinguished
from those of time-reversal odd distribution functions. We show the connection
between gluonic poles and large distance gluon fields, in particular we focus
on boundary conditions. We identify the possible single spin asymmetries in the
Drell-Yan process.Comment: 10 pages, Latex, 4 Postscript figure, uses epsfig.sty. Invited talk
presented at the workshop 'Deep inelastic scattering off polarized targets:
theory meets experiment', DESY-Zeuthen, September 1-5, 199
Spin asymmetries in jet-hyperon production at LHC
We consider polarized Lambda hyperon production in proton-proton scattering,
p p -> (\Lambda^\uparrow jet) jet X, in the kinematical region of the LHC
experiments, in particular the ALICE experiment. We present a new Lambda
polarization observable that arises from the Sivers effect in the fragmentation
process. It can be large even at midrapidity and therefore, is of interest for
high energy hadron collider experiments. Apart from its potential to shed light
on the mechanisms behind the phenomenon of Lambda polarization arising in
unpolarized hadronic collisions, the new observable in principle also allows to
test the possible color flow dependence of single spin asymmetries and the
(non)universality of transverse momentum dependent fragmentation functions.Comment: 11 pages, 10 eps figures; minor modifications, conclusions unchanged,
version to be publishe
Operator analysis of -widths of TMDs
Transverse momentum dependent (TMD) parton distribution functions (PDFs),
TMDs for short, are defined as the Fourier transform of matrix elements of
nonlocal combinations of quark and gluon fields. The nonlocality is bridged by
gauge links, which for TMDs have characteristic paths (future or past
pointing), giving rise to a process dependence that breaks universality. It is
possible, however, to construct sets of universal TMDs of which in a given
process particular combinations are needed with calculable, process-dependent,
coefficients. This occurs for both T-odd and T-even TMDs, including also the
{\it unpolarized} quark and gluon TMDs. This extends the by now well-known
example of T-odd TMDs that appear with opposite sign in single-spin azimuthal
asymmetries in semi-inclusive deep inelastic scattering or in the Drell-Yan
process. In this paper we analyze the cases where TMDs enter multiplied by
products of two transverse momenta, which includes besides the -broadening
observable, also instances with rank two structures. To experimentally
demonstrate the process dependence of the latter cases requires measurements of
second harmonic azimuthal asymmetries, while the -broadening will require
measurements of processes beyond semi-inclusive deep inelastic scattering or
the Drell-Yan process. Furthermore, we propose specific quantities that will
allow for theoretical studies of the process dependence of TMDs using lattice
QCD calculations.Comment: 10 pages, no figures; expanded discussions, matches version accepted
by JHE
Cancellation of quantum mechanical higher loop contributions to the gravitational chiral anomaly
We give an explicit demonstration, using the rigorous Feynman rules developed
in~\0^{1}, that the regularized trace \tr \gamma_5 e^{-\beta \Dslash^2} for
the gravitational chiral anomaly expressed as an appropriate quantum mechanical
path integral is -independent up to two-loop level. Identities and
diagrammatic notations are developed to facilitate rapid evaluation of graphs
given by these rules.Comment: 10 pages, LaTeX and psfig (many figures
In-flight measurements of energetic radiation from lightning and thunderclouds
In the certification procedure aircraft builders carry out so-called icing
tests flights, where the zero degree Celsius altitude is deliberately sought
and crossed in or under thunderstorms. Airbus also used these flights to test
ILDAS, a system aimed to determine lightning severity and attachment points
during flight from high speed data on the electric and magnetic field at the
aircraft surface. We used this unique opportunity to enhance the ILDAS systems
with two x-ray detectors coupled to high speed data recorders in an attempt to
determine the x-rays produced by lightning in-situ, with synchronous
determination of the lightning current distribution and electric field at the
aircraft. Such data are of interest in a study of lightning physics. In
addition, the data may provide clues to the x-ray dose for personnel and
equipment during flights. The icing campaign ran in April 2014; in six flights
we collected data of 61 lightning strikes on an Airbus test aircraft. In this
communication we briefly describe ILDAS and present selected results on three
strikes, two aircraft initiated and one intercepted. Most of the x-rays have
been observed synchronous with initiating negative leader steps, and as bursts
immediately preceding the current of the recoil process. Those processes
include the return stroke. The bursts last one to four micro-second and attain
x-ray energies up to 10 MeV. Intensity and spectral distribution of the x-rays
and the association with the current distribution are discussed. ILDAS also
continuously records x-rays at low resolution in time and amplitude.Comment: 28 pages, 9 figure
ORFEUS II echelle spectra: Absorption by H_2 in the LMC
We present the first detection of molecular hydrogen (H_2) UV absorption
profiles on the line of sight to the LMC. The star LH 10:3120 in the LMC was
measured with the ORFEUS telescope and the Tuebingen echelle spectrograph
during the space shuttle mission of Nov./Dec. 1996. 16 absorption lines from
the Lyman band are used to derive the column densities of H_2 for the lowest 5
rotational states in the LMC gas. For these states we find a total column
density of N(H_2)=6.6 x 10^18$ cm^-2 on this individual line of sight. We
obtain equivalent excitation temperatures of T < 50 K for the rotational ground
state and T = 470 K for 0 < J < 6 by fitting the population densities of the
rotational states to theoretical Boltzmann distributions. We conclude that UV
pumping dominates the population of the higher rotational levels, as known from
the H_2 gas in the Milky Way. (Research supported in part by the DARA)Comment: Astronomy & Astrophysics, Letter, in pres
Double Sivers effect asymmetries and their impact on transversity measurements at RHIC
We study double transverse spin asymmetries in the Drell-Yan process at
measured transverse momentum of the lepton pair. Contrary to what a collinear
factorization approach would suggest, a nonzero double transverse spin
asymmetry in the laboratory frame a priori does not imply nonzero transversity.
TMD effects, such as the double Sivers effect, in principle form a background.
Using the current knowledge of the relevant TMDs we estimate their contribution
in the laboratory frame for Drell-Yan and W production at RHIC and point out a
cross check asymmetry measurement to bound the TMD contributions. We also
comment on the transverse momentum integrated asymmetries that only receive
power suppressed background contributions.Comment: 12 pages, 11 eps figures, minor changes, matches the published
versio
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