22 research outputs found
Prompt atmospheric neutrinos and muons: dependence on the gluon distribution function
We compute the next-to-leading order QCD predictions for the vertical flux of
atmospheric muons and neutrinos from decays of charmed particles, for different
PDF's (MRS-R1, MRS-R2, CTEQ-4M and MRST) and different extrapolations of these
at small partonic momentum fraction x. We find that the predicted fluxes vary
up to almost two orders of magnitude at the largest energies studied, depending
on the chosen extrapolation of the PDF's. We show that the spectral index of
the atmospheric leptonic fluxes depends linearly on the slope of the gluon
distribution function at very small x. This suggests the possibility of
obtaining some bounds on this slope in ``neutrino telescopes'', at values of x
not reachable at colliders, provided the spectral index of atmospheric leptonic
fluxes could be determined.Comment: 20 pages including 8 figure
Measurement of the gluon PDF at small x with neutrino telescopes
We analyze the possibility that neutrino telescopes may provide an
experimental determination of the slope lambda of the gluon distribution in the
proton at momentum fractions x smaller than the accelerator reach. The method
is based on a linear relation between lambda and the spectral index (slope) of
the down-going atmospheric muon flux above 100 TeV, for which there is no
background. Considering the uncertainties in the charm production cross section
and in the cosmic ray composition, we estimate the error on the measurement of
lambda through this method, excluding the experimental error of the telescopes,
to be ~ +/- 0.2Comment: 16 pages with 16 figures - new version, comments added, same results
and figure
FORTE satellite constraints on ultra-high energy cosmic particle fluxes
The FORTE (Fast On-orbit Recording of Transient Events) satellite records
bursts of electromagnetic waves arising from near the Earth's surface in the
radio frequency (RF) range of 30 to 300 MHz with a dual polarization antenna.
We investigate the possible RF signature of ultra-high energy cosmic-ray
particles in the form of coherent Cherenkov radiation from cascades in ice. We
calculate the sensitivity of the FORTE satellite to ultra-high energy (UHE)
neutrino fluxes at different energies beyond the Greisen-Zatsepin-Kuzmin (GZK)
cutoff. Some constraints on supersymmetry model parameters are also estimated
due to the limits that FORTE sets on the UHE neutralino flux. The FORTE
database consists of over 4 million recorded events to date, including in
principle some events associated with UHE neutrinos. We search for candidate
FORTE events in the period from September 1997 to December 1999. The candidate
production mechanism is via coherent VHF radiation from a UHE neutrino shower
in the Greenland ice sheet. We demonstrate a high efficiency for selection
against lightning and anthropogenic backgrounds. A single candidate out of
several thousand raw triggers survives all cuts, and we set limits on the
corresponding particle fluxes assuming this event represents our background
level.Comment: added a table, updated references and Figure 8, this version is
submitted to Phys. Rev.
TeV-scale bileptons, see-saw type II and lepton flavor violation in core-collapse supernova
Electrons and electron neutrinos in the inner core of the core-collapse
supernova are highly degenerate and therefore numerous during a few seconds of
explosion. In contrast, leptons of other flavors are non-degenerate and
therefore relatively scarce. This is due to lepton flavor conservation. If this
conservation law is broken by some non-standard interactions, electron
neutrinos are converted to muon and tau-neutrinos, and electrons - to muons.
This affects the supernova dynamics and the supernova neutrino signal. We
consider lepton flavor violating interactions mediated by scalar bileptons,
i.e. heavy scalars with lepton number 2. It is shown that in case of TeV-mass
bileptons the electron fermi gas is equilibrated with non-electron species
inside the inner supernova core at a time-scale of order of (1-100) ms. In
particular, a scalar triplet which generates neutrino masses through the
see-saw type II mechanism is considered. It is found that supernova core is
sensitive to yet unprobed values of masses and couplings of the triplet.Comment: accepted to Eur.Phys.J.
Resistência de Bidens subalternans aos herbicidas inibidores da enzima acetolactato sintase utilizados na cultura da soja
O uso contínuo e prolongado de produtos com o mesmo mecanismo de ação pode provocar a manifestação de biótipos resistentes. Para verificar possíveis novos casos de resistência, bem como alternativas para prevenção e manejo, foram coletadas sementes de Bidens subalternans na região de São Gabriel D' Oeste-MS, em plantas que sobreviveram a tratamentos em que inibidores da ALS foram sistematicamente utilizados. Em experimento conduzido em vasos em casa de vegetação, o biótipo com histórico de resistente foi comparado ao suscetível quando submetido aos diversos herbicidas com diferentes mecanismos de ação usados em pós-emergência, os quais foram aplicados nas doses de zero, uma, duas, quatro e oito vezes a recomendada. Decorridos 20 dias, foram avaliadas a porcentagem de controle e a produção da fitomassa verde, visando estabelecimento de curvas de dose-resposta e obtenção dos fatores de resistência. O biótipo oriundo de área com histórico de aplicações repetidas de inibidores da ALS apresentou elevado nível de resistência aos herbicidas chlorimuron-ethyl e imazethapyr, demonstrando ser portador de resistência cruzada aos inibidores da ALS dos grupos das sulfoniluréias e imidazolinonas. Entretanto, esse biótipo foi eficientemente controlado pelos herbicidas fomesafen, lactofen, bentazon, glufosinato de amônio e glyphosate