16,333 research outputs found
Search for the Standard Model Higgs boson at LEP
The combined results of the search for the Standard Model Higgs boson from
the four LEP experiments are given. These results are based on the full data
sample collected by ALEPH, DELPHI, L3 and OPAL at centre-of-mass energies up to
209GeV, corresponding to a total integrated luminosity of about 2.5fb-1. A
slight excess of events over the background expectation is found at the 2sigma
level, originating mainly from the ALEPH 4-jet channel. This excess is
compatible with what expected for the production of a SM Higgs boson with a
mass of 115.6GeV/c2. A combined 95% confidence level lower limit of 114.1GeV/c2
on the mass of the Standard Model Higgs boson is derived.Comment: 12 pages, 4 figures, La Thuile 2002 proceeding
Is there new physics in the 1999 ALEPH data ?
The first results on searches performed by ALEPH on the 1999 data sample are
presented here. They are based on an integrated luminosity of about 54 pb
collected at the two centre-of-mass energies of 192 and 196 GeV. Preliminary
results on searches for supersymmetric particles and for the neutral Higgs
bosons are shown.Comment: 3 page
What caused the GeV flare of PSR B1259-63 ?
PSR B1259-63 is a gamma-ray binary system composed of a high spindown pulsar
and a massive star. Non-thermal emission up to TeV energies is observed near
periastron passage, attributed to emission from high energy e+e- pairs
accelerated at the shock with the circumstellar material from the companion
star, resulting in a small-scale pulsar wind nebula. Weak gamma-ray emission
was detected by the Fermi/LAT at the last periastron passage, unexpectedly
followed 30 days later by a strong flare, limited to the GeV band, during which
the luminosity nearly reached the spindown power of the pulsar. The origin of
this GeV flare remains mysterious. We investigate whether the flare could have
been caused by pairs, located in the vicinity of the pulsar, up-scattering
X-ray photons from the surrounding pulsar wind nebula rather than UV stellar
photons, as usually assumed. Such a model is suggested by the geometry of the
interaction region at the time of the flare. We compute the gamma-ray
lightcurve for this scenario, based on a simplified description of the
interaction region, and compare it to the observations. The GeV lightcurve
peaks well after periastron with this geometry. The pairs are inferred to have
a Lorentz factor ~500. They also produce an MeV flare with a luminosity ~1e34
erg/s prior to periastron passage. A significant drawback is the very high
energy density of target photons required for efficient GeV emission. We
propose to associate the GeV-emitting pairs with the Maxwellian expected at
shock locations corresponding to high pulsar latitudes, while the rest of the
non-thermal emission arises from pairs accelerated in the equatorial region of
the pulsar wind termination shock.Comment: 6 pages, 3 figures, accepted for publication in A&
Beam-Material Interaction
Th is paper is motivated by the growing importance of better understanding of
the phenomena and consequences of high- intensity energetic particle beam
interactions with accelerator, generic target , and detector components. It
reviews the principal physical processes of fast-particle interactions with
matter, effects in materials under irradiation, materials response, related to
component lifetime and performance, simulation techniques, and methods of
mitigating the impact of radiation on the components and envir onment in
challenging current and future applicationComment: 28 pages, contribution to the 2014 Joint International Accelerator
School: Beam Loss and Accelerator Protection, Newport Beach, CA, USA , 5-14
Nov 201
k-Fractional trigonometric functions
Based on the k-Mittag-Lefler function and the k-α-Exponential Function we introduce families of functions that allows us define new fractional trigonometric functions that contain the classical trigonometric functions as particular case for some convenient election of parameters. We study some elementary properties and obtain the Laplace transform of some elements of the families.Fil: Cerutti, Ruben Alejandro. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura; ArgentinaFil: Luque, Luciano Leonardo. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
High-energy radiation from the relativistic jet of Cygnus X-3
Cygnus X-3 is an accreting high-mass X-ray binary composed of a Wolf-Rayet
star and an unknown compact object, possibly a black hole. The gamma-ray space
telescope Fermi found definitive evidence that high-energy emission is produced
in this system. We propose a scenario to explain the GeV gamma-ray emission in
Cygnus X-3. In this model, energetic electron-positron pairs are accelerated at
a specific location in the relativistic jet, possibly related to a
recollimation shock, and upscatter the stellar photons to high energies. The
comparison with Fermi observations shows that the jet should be inclined close
to the line of sight and pairs should not be located within the system.
Energetically speaking, a massive compact object is favored. We report also on
our investigations of the gamma-ray absorption of GeV photons with the
radiation emitted by a standard accretion disk in Cygnus X-3. This study shows
that the gamma-ray source should not lie too close to the compact object.Comment: 4 pages, 3 figures, Proceedings of the SF2A conference held in
Marseille, 21-24 June 201
Modeling high-energy pulsar lightcurves from first principles
Current models of gamma-ray lightcurves in pulsars suffer from large
uncertainties on the precise location of particle acceleration and radiation.
Here, we present an attempt to alleviate these difficulties by solving for the
electromagnetic structure of the oblique magnetosphere, particle acceleration,
and the emission of radiation self-consistently, using 3D spherical
particle-in-cell simulations. We find that the low-energy radiation is
synchro-curvature radiation from the polar-cap regions within the light
cylinder. In contrast, the high-energy emission is synchrotron radiation that
originates exclusively from the Y-point and the equatorial current sheet where
relativistic magnetic reconnection accelerates particles. In most cases,
synthetic high-energy lightcurves contain two peaks that form when the current
sheet sweeps across the observer's line of sight. We find clear evidence of
caustics in the emission pattern from the current sheet. High-obliquity
solutions can present up to two additional secondary peaks from energetic
particles in the wind region accelerated by the reconnection-induced flow near
the current sheet. The high-energy radiative efficiency depends sensitively on
the viewing angle, and decreases with increasing pulsar inclination. The
high-energy emission is concentrated in the equatorial regions where most of
the pulsar spindown is released and dissipated. These results have important
implications for the interpretation of gamma-ray pulsar data.Comment: 14 pages, 11 figures, Accepted for publication in MNRA
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