144 research outputs found
Search for the exotic resonance in the NOMAD experiment
A search for exotic Theta baryon via Theta -> proton +Ks decay mode in the
NOMAD muon neutrino DIS data is reported. The special background generation
procedure was developed. The proton identification criteria are tuned to
maximize the sensitivity to the Theta signal as a function of xF which allows
to study the Theta production mechanism. We do not observe any evidence for the
Theta state in the NOMAD data. We provide an upper limit on Theta production
rate at 90% CL as 2.13 per 1000 of neutrino interactions.Comment: Accepted to European Physics Journal
Search for nu(mu)-->nu(e) Oscillations in the NOMAD Experiment
We present the results of a search for nu(mu)-->nu(e) oscillations in the
NOMAD experiment at CERN. The experiment looked for the appearance of nu(e) in
a predominantly nu(mu) wide-band neutrino beam at the CERN SPS. No evidence for
oscillations was found. The 90% confidence limits obtained are delta m^2 < 0.4
eV^2 for maximal mixing and sin^2(2theta) < 1.4x10^{-3} for large delta m^2.
This result excludes the LSND allowed region of oscillation parameters with
delta m^2 > 10 eV^2.Comment: 19 pages, 8 figures. Submitted to Phys. Lett.
A Study of Strange Particles Produced in Neutrino Neutral Current Interactions in the NOMAD Experiment
Results of a detailed study of strange particle production in neutrino
neutral current interactions are presented using the data from the NOMAD
experiment. Integral yields of neutral strange particles (K0s, Lambda,
Lambda-bar) have been measured. Decays of resonances and heavy hyperons with an
identified K0s or Lambda in the final state have been analyzed. Clear signals
corresponding to K* and Sigma(1385) have been observed. First results on the
measurements of the Lambda polarization in neutral current interactions have
been obtained.Comment: Accepted for publication in Nuclear Physics B as a rapid
communicatio
A Precise Measurement of the Muon Neutrino-Nucleon Inclusive Charged Current Cross-Section off an Isoscalar Target in the Energy Range 2.5 < E_\nu < 40 GeV by NOMAD
We present a measurement of the muon neutrino-nucleon inclusive charged
current cross-section, off an isoscalar target, in the neutrino energy range
GeV. The significance of this measurement is its
precision, % in GeV, and % in GeV regions, where significant uncertainties in previous
experiments still exist, and its importance to the current and proposed long
baseline neutrino oscillation experiments.Comment: 14 pages, 3 figures, submitted to Phys.Lett.
A Measurement of Coherent Neutral Pion Production in Neutrino Neutral Current Interactions in NOMAD
We present a study of exclusive neutral pion production in neutrino-nucleus
Neutral Current interactions using data from the NOMAD experiment at the CERN
SPS. The data correspond to muon-neutrino Charged Current
interactions in the energy range GeV. Neutrino
events with only one visible in the final state are expected to result
from two Neutral Current processes: coherent production, {\boldmath
} and single production in
neutrino-nucleon scattering. The signature of coherent production is an
emergent almost collinear with the incident neutrino while 's
produced in neutrino-nucleon deep inelastic scattering have larger transverse
momenta. In this analysis all relevant backgrounds to the coherent
production signal are measured using data themselves. Having determined the
backgrounds, and using the Rein-Sehgal model for the coherent
production to compute the detection efficiency, we obtain {\boldmath } corrected coherent- events with GeV. We measure {\boldmath }.
This is the most precise measurement of the coherent production to
date.Comment: 23 pages, 9 figures, accepted for publication in Phys. Lett.
Bose-Einstein correlations in charged current muon-neutrino interactions in the NOMAD experiment at CERN
Bose-Einstein correlations in one and two dimensions have been studied, with high statistics, in charged current muon-neutrino interaction events collected with the NOMAD detector at CERN. In one dimension the Bose-Einstein effect has been analyzed with the Goldhaber and the Kopylov-Podgoretskii phenomenological parametrizations. The Goldhaber parametrization gives the radius of the pion emission region R-G = 1.01 +/- 0.05(stat)(-0.06)(+0,09)(sys) fm and for the chaoticity parameter the value lambda = 0.40 +/- 0.03(stat)(-0.06)(+0.01) (sys). Using the Kopylov-Podgoretskii parametrization yields R-KP = 2.07 +/- 0.04(stat)(-0.14)(+0.01) (sys) fm and lambda(KP) = 0.29 +/- 0.06(stat)(-0.04)(+0,01) (sys) Different parametrizations of the long-range correlations have been also studied. The two-dimensional shape of the source has been investigated in the longitudinal comoving frame. A significant difference between the transverse and the longitudinal dimensions is observed. The high statistics of the collected sample allowed the study of the Bose-Einstein correlations as a function of rapidity, charged particle multiplicity and hadronic energy. A weak dependence of both radius and chaoticity on multiplicity and hadronic energy is found
A Study of Strange Particle Production in Muon Neutrino Charged Current Interactions in the NOMAD Experiment
A study of strange particle production in muon neutrino charged current
interactions has been performed using the data from the NOMAD experiment.
Yields of neutral strange particles K0s, Lambda, AntiLambda have been measured.
Mean multiplicities are reported as a function of the event kinematic variables
Enu, W2 and Q2 as well as of the variables describing particle behaviour within
a hadronic jet: xF, z and pT2. Decays of resonances and heavy hyperons with
identified K0s and Lambda in the final state have been analyzed. Clear signals
corresponding to K*+-, Sigma*+-, Xi- and Sigma0 have been observed.Comment: 43 pages, accepted for publication in the Nuclear Physics B as a
Rapid Communication in Experimental High-Energy Physic
A Search for Single Photon Events in Neutrino Interactions
We present a search for neutrino-induced events containing a single,
exclusive photon using data from the NOMAD experiment at the CERN SPS where the
average energy of the neutrino flux is GeV. The search is motivated
by an excess of electron-like events in the 200--475 MeV energy region as
reported by the MiniBOONE experiment. In NOMAD, photons are identified via
their conversion to in an active target embedded in a magnetic field.
The background to the single photon signal is dominated by the asymmetric decay
of neutral pions produced either in a coherent neutrino-nucleus interaction, or
in a neutrino-nucleon neutral current deep inelastic scattering, or in an
interaction occurring outside the fiducial volume. All three backgrounds are
determined {\it in situ} using control data samples prior to opening the
`signal-box'. In the signal region, we observe {\bf 155} events with a
predicted background of {\bf 129.2 8.5 3.3}. We interpret this as
null evidence for excess of single photon events, and set a limit. Assuming
that the hypothetical single photon has a momentum distribution similar to that
of a photon from the coherent decay, the measurement yields an upper
limit on single photon events, {\boldmath } per \nm\
charged current event. Narrowing the search to events where the photon is
approximately collinear with the incident neutrino, we observe {\bf 78} events
with a predicted background of {\bf 76.6 4.9 1.9} yielding a more
stringent upper limit, {\boldmath } per \nm\ charged
current event
Integrating sequence and array data to create an improved 1000 Genomes Project haplotype reference panel
A major use of the 1000 Genomes Project (1000GP) data is genotype imputation in genome-wide association studies (GWAS). Here we develop a method to estimate haplotypes from low-coverage sequencing data that can take advantage of single-nucleotide polymorphism (SNP) microarray genotypes on the same samples. First the SNP array data are phased to build a backbone (or 'scaffold') of haplotypes across each chromosome. We then phase the sequence data 'onto' this haplotype scaffold. This approach can take advantage of relatedness between sequenced and non-sequenced samples to improve accuracy. We use this method to create a new 1000GP haplotype reference set for use by the human genetic community. Using a set of validation genotypes at SNP and bi-allelic indels we show that these haplotypes have lower genotype discordance and improved imputation performance into downstream GWAS samples, especially at low-frequency variants. © 2014 Macmillan Publishers Limited. All rights reserved
On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection
A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)
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