5 research outputs found
A High Statistics Search for Ultra-High Energy Gamma-Ray Emission from Cygnus X-3 and Hercules X-1
We have carried out a high statistics (2 Billion events) search for
ultra-high energy gamma-ray emission from the X-ray binary sources Cygnus X-3
and Hercules X-1. Using data taken with the CASA-MIA detector over a five year
period (1990-1995), we find no evidence for steady emission from either source
at energies above 115 TeV. The derived upper limits on such emission are more
than two orders of magnitude lower than earlier claimed detections. We also
find no evidence for neutral particle or gamma-ray emission from either source
on time scales of one day and 0.5 hr. For Cygnus X-3, there is no evidence for
emission correlated with the 4.8 hr X-ray periodicity or with the occurrence of
large radio flares. Unless one postulates that these sources were very active
earlier and are now dormant, the limits presented here put into question the
earlier results, and highlight the difficulties that possible future
experiments will have in detecting gamma-ray signals at ultra-high energies.Comment: 26 LaTeX pages, 16 PostScript figures, uses psfig.sty to be published
in Physical Review
Exclusion limits on the WIMP-nucleon cross-section from the Cryogenic Dark Matter Search
The Cryogenic Dark Matter Search (CDMS) employs low-temperature Ge and Si
detectors to search for Weakly Interacting Massive Particles (WIMPs) via their
elastic-scattering interactions with nuclei while discriminating against
interactions of background particles. For recoil energies above 10 keV, events
due to background photons are rejected with >99.9% efficiency, and surface
events are rejected with >95% efficiency. The estimate of the background due to
neutrons is based primarily on the observation of multiple-scatter events that
should all be neutrons. Data selection is determined primarily by examining
calibration data and vetoed events. Resulting efficiencies should be accurate
to about 10%. Results of CDMS data from 1998 and 1999 with a relaxed
fiducial-volume cut (resulting in 15.8 kg-days exposure on Ge) are consistent
with an earlier analysis with a more restrictive fiducial-volume cut.
Twenty-three WIMP candidate events are observed, but these events are
consistent with a background from neutrons in all ways tested. Resulting limits
on the spin-independent WIMP-nucleon elastic-scattering cross-section exclude
unexplored parameter space for WIMPs with masses between 10-70 GeV c^{-2}.
These limits border, but do not exclude, parameter space allowed by
supersymmetry models and accelerator constraints. Results are compatible with
some regions reported as allowed at 3-sigma by the annual-modulation
measurement of the DAMA collaboration. However, under the assumptions of
standard WIMP interactions and a standard halo, the results are incompatible
with the DAMA most likely value at >99.9% CL, and are incompatible with the
model-independent annual-modulation signal of DAMA at 99.99% CL in the
asymptotic limit.Comment: 40 pages, 49 figures (4 in color), submitted to Phys. Rev. D;
v.2:clarified conclusions, added content and references based on referee's
and readers' comments; v.3: clarified introductory sections, added figure
based on referee's comment