89 research outputs found
Plankton rotifers from a tropical lake: differences in distribution and migration patterns in two mixing events, with similar abiotic conditions.
Vertical distribution of plankton rotifers is not random. Although the causes of this behavior are still under debate, it has been suggested, mainly from the study of stratified environments, that abiotic parameters play an important role in determining the presence and position of a species in the water column. We compared the composition and vertical distribution of planktonic rotifers in a tropical monomictic lake in Mexico during the mixing period of two years in which abiotic conditions were similar. We recorded 28 rotifer species. Total average densities ranged from 238±39 ind l-1 to 517±97 ind l-1. The similarity of rotifer assemblages between the two compared dates was 46.4%. Our results showed that temperature and dissolved oxygen in the upper 13 meters and pH upper 8 meters, respectively, were homogeneous in the two dates. Nevertheless, the rotifer assemblages showed important differences in: a) the absolute population densities, b) the dominance ranking of species in the community, c) the preferential position of a specific species in the water column, d) the relationship between such preference and the studied abiotic factors and, e) the types and amplitudes of species migrations. Given the resemblance of the abiotic factors in the analyzed years, we suggest that changes in rotifers distribution and abundance would involve biological factors, such as food availability, competition and predation.
Single neutral pion production by charged-current interactions on hydrocarbon at 3.6 GeV
Single neutral pion production via muon antineutrino charged-current
interactions in plastic scintillator (CH) is studied using the \minerva
detector exposed to the NuMI low-energy, wideband antineutrino beam at
Fermilab. Measurement of this process constrains models of neutral pion
production in nuclei, which is important because the neutral-current analog is
a background for appearance oscillation experiments. The
differential cross sections for momentum and production angle, for
events with a single observed and no charged pions, are presented and
compared to model predictions. These results comprise the first measurement of
the kinematics for this process.Comment: 6 pages, 5 figures, submitted to Physics Letters
First evidence of coherent meson production in neutrino-nucleus scattering
Neutrino-induced charged-current coherent kaon production,
, is a rare, inelastic electroweak process
that brings a on shell and leaves the target nucleus intact in its ground
state. This process is significantly lower in rate than neutrino-induced
charged-current coherent pion production, because of Cabibbo suppression and a
kinematic suppression due to the larger kaon mass. We search for such events in
the scintillator tracker of MINERvA by observing the final state ,
and no other detector activity, and by using the kinematics of the final state
particles to reconstruct the small momentum transfer to the nucleus, which is a
model-independent characteristic of coherent scattering. We find the first
experimental evidence for the process at significance.Comment: added ancillary file with information about the six kaon candidate
Measurement of Total and Differential Cross Sections of Neutrino and Antineutrino Coherent Production on Carbon
Neutrino induced coherent charged pion production on nuclei,
, is a rare inelastic interaction in
which the four-momentum squared transfered to the nucleus is nearly zero,
leaving it intact. We identify such events in the scintillator of MINERvA by
reconstructing |t| from the final state pion and muon momenta and by removing
events with evidence of energetic nuclear recoil or production of other final
state particles. We measure the total neutrino and antineutrino cross sections
as a function of neutrino energy between 2 and 20 GeV and measure flux
integrated differential cross sections as a function of , and
. The dependence and equality of the neutrino and
anti-neutrino cross-sections at finite provide a confirmation of Adler's
PCAC hypothesis
Measurement of Partonic Nuclear Effects in Deep-Inelastic Neutrino Scattering using MINERvA
The MINERvA collaboration reports a novel study of neutrino-nucleus
charged-current deep inelastic scattering (DIS) using the same neutrino beam
incident on targets of polystyrene, graphite, iron, and lead. Results are
presented as ratios of C, Fe, and Pb to CH. The ratios of total DIS cross
sections as a function of neutrino energy and flux-integrated differential
cross sections as a function of the Bjorken scaling variable x are presented in
the neutrino-energy range of 5 - 50 GeV. Good agreement is found between the
data and predicted ratios, based on charged-lepton nucleus scattering, at
medium x and low neutrino energies. However, the data rate appears depleted in
the vicinity of the nuclear shadowing region, x < 0.1. This apparent deficit,
reflected in the DIS cross-section ratio at high neutrino energy , is
consistent with previous MINERvA observations and with the predicted onset of
nuclear shadowing with the the axial-vector current in neutrino scattering
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