147 research outputs found
Signature of exotic particles in light by light scattering
We discuss the implications on light by light scattering of two kind of
exotic particles: doubly charged scalar bosons and doubly charged fermions; the
virtual effects of a nonstandard singly charged gauge boson are also examined.
These particles, if their masses lie in the range 0.1--1.0 TeV, will have a
clear signature in the future linear colliders. The present analysis has the
advantage that it depends only on electromagnetic symmetry, so it is applicable
to any model which predicts this class of particles. In particular, our results
have interesting consequences on left-right models and their supersymmetric
extension.Comment: 6 eps figures. Requires elsevier.cl
Tests of Higgs and Top Effective Interactions
We study the possibility to detect heavy physics effects in the interactions
of Higgs bosons and the top quark at future colliders using the effective
Lagrangian approach. The modification of the interactions may enhance the
production of Higgs bosons at hadron colliders through the mechanisms of gluon
fusion and associated production with a W boson or pairs. The most
promising signature is through the decay of the Higgs boson into two photons,
whose branching ratio is also enhanced in this approach. As a consequence of
our analysis we get a bound on the chromomagnetic dipole moment of the top
quark.Comment: 14 pages, Latex, two figures available by fax under request. To be
published in Phys. Lett
An effective lagrangian description of charged Higgs decays H^+ -> Wg, WZ and Wh
Charged Higgs decays are discussed within an effective lagrangian extension
of the two-higgs doublet model, assuming new physics appearing in the Higgs
sector of this model. Low energy constrains are used to imposse bounds on
certain dimension -six operators that describe the modified charged Higgs
interactions. These bounds are used then to study the decays H^+ -> Wg, WZ and
Wh, which can have branching ratios of order 10^-5, 10^-1 and O(1),
respectively; thse modes are thus sensitive probes of the symmetries of the
Higgs sector that could be tested at future colliders.Comment: 15 pages, 3 figure
Exact formulae for Higgs production through e gamma --> e H in the non-linear R_\xi gauge
We study the production of the SM Higgs boson (H^0) at future e gamma
colliders, through the reaction e gamma --> e H^0. The amplitude is evaluated
using the non-linear R_\xi gauge, which greatly simplifies the calculation.
Complete analytical expressions for the amplitudes are presented, which include
the contributions from 1-loop triangles "gamma gamma^* H^0" and "gamma Z^* H^0"
as well as the W- and Z-boxes with their related triangle graphs. The
resulting cross section for this mechanism indicates that it could be used to
detect the Higgs signal and to test its properties.Comment: 6 pages, 2 figures, RevTe
New Physics Effects on Higgs Production at Colliders
We study heavy physics effects on the Higgs production in
fusion using the effective Lagrangian approach. We find that the effects coming
from new physics may enhance the standard model predictions for the number of
events expected in the final states , , and up to one order
of magnitude, whereas the corresponding number of events for the final state
may be enhanced up to two orders of magnitude.Comment: Latex, 6 pages, 4 eps figures, to appear in the Proceedings of the V
Mexican Workshop of Particles and Fields, Puebla, Mexico, October 199
Magnetic interactions in EuTe epitaxial layers and EuTe/PbTe superlattices
The magnetic properties of antiferromagnetic (AFM) EuTe epitaxial layers and
short period EuTe/PbTe superlattices (SLs), grown by molecular beam epitaxy on
(111) BaF substrates, were studied by magnetization and neutron diffraction
measurements. Considerable changes of the N\'eel temperature as a function of
the EuTe layer thickness as well as of the strain state were found. A mean
field model, taking into account the variation of the exchange constants with
the strain-induced lattice distortions, and the nearest neighbor environment of
a Eu atoms, was developed to explain the observed changes in wide
range of samples. Pronounced interlayer magnetic correlations have been
revealed by neutron diffraction in EuTe/PbTe SLs with PbTe spacer thickness up
to 60 \AA. The observed diffraction spectra were analyzed, in a kinematical
approximation, assuming partial interlayer correlations characterized by an
appropriate correlation parameter. The formation of interlayer correlations
between the AFM EuTe layers across the nonmagnetic PbTe spacer was explained
within a framework of a tight-binding model. In this model, the interlayer
coupling stems from the dependence of the total electronic energy of the
EuTe/PbTe SL on the spin configurations in adjacent EuTe layers. The influence
of the EuTe and PbTe layer thickness fluctuations, inherent in the epitaxial
growth process, on magnetic properties and interlayer coupling is discussed.Comment: 17 pages, 19 figures, accepted to PR
Performance of the First ANTARES Detector Line
In this paper we report on the data recorded with the first Antares detector
line. The line was deployed on the 14th of February 2006 and was connected to
the readout two weeks later. Environmental data for one and a half years of
running are shown. Measurements of atmospheric muons from data taken from
selected runs during the first six months of operation are presented.
Performance figures in terms of time residuals and angular resolution are
given. Finally the angular distribution of atmospheric muons is presented and
from this the depth profile of the muon intensity is derived.Comment: 14 pages, 9 figure
Acoustic and optical variations during rapid downward motion episodes in the deep north-western Mediterranean Sea
An Acoustic Doppler Current Profiler (ADCP) was moored at the deep-sea site
of the ANTARES neutrino telescope near Toulon, France, thus providing a unique
opportunity to compare high-resolution acoustic and optical observations
between 70 and 170 m above the sea bed at 2475 m. The ADCP measured downward
vertical currents of magnitudes up to 0.03 m s-1 in late winter and early
spring 2006. In the same period, observations were made of enhanced levels of
acoustic reflection, interpreted as suspended particles including zooplankton,
by a factor of about 10 and of horizontal currents reaching 0.35 m s-1. These
observations coincided with high light levels detected by the telescope,
interpreted as increased bioluminescence. During winter 2006 deep dense-water
formation occurred in the Ligurian subbasin, thus providing a possible
explanation for these observations. However, the 10-20 days quasi-periodic
episodes of high levels of acoustic reflection, light and large vertical
currents continuing into the summer are not direct evidence of this process. It
is hypothesized that the main process allowing for suspended material to be
moved vertically later in the year is local advection, linked with topographic
boundary current instabilities along the rim of the 'Northern Current'.Comment: 30 pages, 7 figure
An improved method for measuring muon energy using the truncated mean of dE/dx
The measurement of muon energy is critical for many analyses in large
Cherenkov detectors, particularly those that involve separating
extraterrestrial neutrinos from the atmospheric neutrino background. Muon
energy has traditionally been determined by measuring the specific energy loss
(dE/dx) along the muon's path and relating the dE/dx to the muon energy.
Because high-energy muons (E_mu > 1 TeV) lose energy randomly, the spread in
dE/dx values is quite large, leading to a typical energy resolution of 0.29 in
log10(E_mu) for a muon observed over a 1 km path length in the IceCube
detector. In this paper, we present an improved method that uses a truncated
mean and other techniques to determine the muon energy. The muon track is
divided into separate segments with individual dE/dx values. The elimination of
segments with the highest dE/dx results in an overall dE/dx that is more
closely correlated to the muon energy. This method results in an energy
resolution of 0.22 in log10(E_mu), which gives a 26% improvement. This
technique is applicable to any large water or ice detector and potentially to
large scintillator or liquid argon detectors.Comment: 12 pages, 16 figure
All-particle cosmic ray energy spectrum measured with 26 IceTop stations
We report on a measurement of the cosmic ray energy spectrum with the IceTop
air shower array, the surface component of the IceCube Neutrino Observatory at
the South Pole. The data used in this analysis were taken between June and
October, 2007, with 26 surface stations operational at that time, corresponding
to about one third of the final array. The fiducial area used in this analysis
was 0.122 km^2. The analysis investigated the energy spectrum from 1 to 100 PeV
measured for three different zenith angle ranges between 0{\deg} and 46{\deg}.
Because of the isotropy of cosmic rays in this energy range the spectra from
all zenith angle intervals have to agree. The cosmic-ray energy spectrum was
determined under different assumptions on the primary mass composition. Good
agreement of spectra in the three zenith angle ranges was found for the
assumption of pure proton and a simple two-component model. For zenith angles
{\theta} < 30{\deg}, where the mass dependence is smallest, the knee in the
cosmic ray energy spectrum was observed between 3.5 and 4.32 PeV, depending on
composition assumption. Spectral indices above the knee range from -3.08 to
-3.11 depending on primary mass composition assumption. Moreover, an indication
of a flattening of the spectrum above 22 PeV were observed.Comment: 38 pages, 17 figure
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