207 research outputs found
Review of Reactor Neutrino Oscillation Experiments
In this document we will review the current status of reactor neutrino
oscillation experiments and present their physics potentials for measuring the
neutrino mixing angle. The neutrino mixing angle is
currently a high-priority topic in the field of neutrino physics. There are
currently three different reactor neutrino experiments, \textsc{Double Chooz},
\textsc{Daya Bay} and \textsc{Reno} and a few accelerator neutrino experiments
searching for neutrino oscillations induced by this angle. A description of the
reactor experiments searching for a non-zero value of is given,
along with a discussion of the sensitivities that these experiments can reach
in the near future.Comment: 15 pages, 4 figure
Last CPT-Invariant Hope for LSND Neutrino Oscillations
It is shown that the 99% confidence limits from the analyses of the data of
cosmological and neutrino experiments imply a small marginally allowed region
in the space of the neutrino oscillation parameters of 3+1 four-neutrino mixing
schemes. This region can be confirmed or falsified by experiments in the near
future.Comment: 6 pages, added predictions for neutrinoless double beta decay and
tritium experiment
Neutrino Phenomenology in a 3+1+1 Framework
Evidence continues to grow in the MiniBooNE (MB) antineutrino mode supporting
a low-energy excess compatible with the MB neutrino mode and possibly also
confirming the results of the LSND experiment. At least one sterile neutrino is
required to explain the anomalies consistent with the observations of other
experiments. At the same time, there is a strong tension between the positive
signals of LSND and MB and the null results of nu_e and nu_mu disappearance
experiments. We explore a scenario, first proposed in \cite{Nelson:2010hz},
where the presence of an additional heavy sterile neutrino (with mass well
above an eV) can alleviate tension between LSND, MB and the null results of
disappearance experiments. We compare and contrast this 3+1+1 scenario with the
more standard 3+1 scenario and carry out global fits to all oscillation data
including new 2011 MB anti-nu data. We find that the tension can be somewhat
alleviated and that a phenomenologically viable window for the heavy neutrino,
consistent with rare decays and BBN constraints, can be found if the fifth
neutrino has a mass of order 0.3 - 10 GeV. We also find, however, that the 2011
MB anti-nu data exacerbates the tension with null experiments in both the 3+1
and 3+1+1 models when the lowest energy bins are included, resulting in little
improvement in the global fit. We also discuss the implications of an
additional neutrino for the reactor and gallium anomalies, and show that an
oscillation explanation of the anomalies is disfavored by cosmological
considerations, direct searches, and precision electroweak tests.Comment: 22 pages, 5 figures; replaced to reflect journal versio
Local demands on sterile neutrinos
In a model independent manner, we explore the local implications of a single
neutrino oscillation measurement which cannot be reconciled within a
three-neutrino theory. We examine this inconsistency for a single region of
baseline to neutrino energy . Assuming that sterile neutrinos account for
the anomaly, we find that the {\it local} demands of this datum can require the
addition to the theory of one to three sterile neutrinos. We examine the
constraints which can be used to determine when more than one neutrino would be
required. The results apply only to a given region of . The question of
the adequacy of the sterile neutrinos to satisfy a global analysis is not
addressed here. Finally, using the results of a 3+2 analysis, we indicate
values for unknown mixing matrix elements which would require two sterile
neutrinos due to local demands only.Comment: 11 pages, 1 figure, discussion adde
Confronting mass-varying neutrinos with MiniBooNE
We study the proposal that mass-varying neutrinos could provide an
explanation for the LSND signal for \bar\nu_mu to \bar\nu_e oscillations. We
first point out that all positive oscillation signals occur in matter and that
three active mass-varying neutrinos are insufficient to describe all existing
neutrino data including LSND. We then examine the possibility that a model with
four mass-varying neutrinos (three active and one sterile) can explain the LSND
effect and remain consistent with all other neutrino data. We find that such
models with a 3+1 mass structure in the neutrino sector may explain the LSND
data and a null MiniBooNE result for 0.10 < \sin^2 2\theta_x < 0.30.
Predictions of the model include a null result at Double-CHOOZ, but positive
signals for underground reactor experiments and for \nu_\mu to \nu_e
oscillations in long-baseline experiments.Comment: 22 pages, 3 figures, 1 table. Comment added about recent MINOS dat
Sterile neutrinos: direct mixing effects versus induced mass matrix of active neutrinos
Mixing of active neutrinos with sterile ones generate ``induced''
contributions to the mass matrix of active neutrinos , where is the Majorana mass of the sterile neutrino
and is the active-sterile mixing angle. We study possible effects
of the induced matrix which can modify substantially the implications of
neutrino oscillation results. We have identified the regions of and
where the induced matrix (i) provides the dominant
structures, (ii) gives the sub-dominant effects and (iii) where its effects can
be neglected. The induced matrix can be responsible for peculiar properties of
the lepton mixing and neutrino mass spectrum, in particular, it can generate
the tri-bimaximal mixing. We update and discuss bounds on the induced masses
from laboratory measurements, astrophysics and cosmology. We find that
substantial impact of the induced matrix is possible if eV and
or MeV and
. The bounds can be relaxed in cosmological
scenarios with low reheating temperature, if sterile neutrinos decay
sufficiently fast, or their masses change with time.Comment: Figures updated, version to be published in Phys. Rev.
SEARCH FOR NEUTRINO OSCILLATION AT BUGEY
The high flux of low energy [MATH]e produced by the core of a PWR reactor of Bugey power plant has been used to search for evidence of neutrino oscillations through the inverse beta decay reaction [MATH]e + p → e+ + n. Measurements have been performed at two distances (13.5 and 18.5m). About 50 000 [MATH]e events have been collected at the first position and 25 000 [MATH]e events at the second one. Data analysis is almost completed
Leptonic CP violation studies at MiniBooNE in the (3+2) sterile neutrino oscillation hypothesis
We investigate the extent to which leptonic CP-violation in (3+2) sterile
neutrino models leads to different oscillation probabilities for
and oscillations at
MiniBooNE. We are using a combined analysis of short-baseline (SBL) oscillation
results, including the LSND and null SBL results, to which we impose additional
constraints from atmospheric oscillation data. We obtain the favored regions in
MiniBooNE oscillation probability space for both (3+2) CP-conserving and (3+2)
CP-violating models. We further investigate the allowed CP-violation phase
values and the MiniBooNE reach for such a CP violation measurement. The
analysis shows that the oscillation probabilities in MiniBooNE neutrino and
antineutrino running modes can differ significantly, with the latter possibly
being as much as three times larger than the first. In addition, we also show
that all possible values of the single CP-violation phase measurable at short
baselines in (3+2) models are allowed within 99% CL by existing data.Comment: Fixed a typo following PRD Erratum. 8 pages, 5 figure
Neutrino-induced deuteron disintegration experiment
Cross sections for the disintegration of the deuteron via neutral-current
(NCD) and charged-current (CCD) interactions with reactor antineutrinos are
measured to be 6.08 +/- 0.77 x 10^(-45) cm-sq and 9.83 +/- 2.04 x 10^(-45)
cm-sq per neutrino, respectively, in excellent agreement with current
calculations. Since the experimental NCD value depends upon the CCD value, if
we use the theoretical value for the CCD reaction, we obtain the improved value
of 5.98 +/- 0.54 x 10^(-45) for the NCD cross section. The neutral-current
reaction allows a unique measurement of the isovector-axial vector coupling
constant in the hadronic weak interaction (beta). In the standard model, this
constant is predicted to be exactly 1, independent of the Weinberg angle. We
measure a value of beta^2 = 1.01 +/- 0.16. Using the above improved value for
the NCD cross section, beta^2 becomes 0.99 +/- 0.10.Comment: 22pages, 9 figure
A combined analysis of short-baseline neutrino experiments in the (3+1) and (3+2) sterile neutrino oscillation hypotheses
We investigate adding two sterile neutrinos to resolve the apparent tension
existing between short-baseline neutrino oscillation results and
CPT-conserving, four-neutrino oscillation models. For both (3+1) and (3+2)
models, the level of statistical compatibility between the combined dataset
from the null short-baseline experiments Bugey, CHOOZ, CCFR84, CDHS, KARMEN,
and NOMAD, on the one hand; and the LSND dataset, on the other, is computed. A
combined analysis of all seven short-baseline experiments, including LSND, is
also performed, to obtain the favored regions in neutrino mass and mixing
parameter space for both models. Finally, four statistical tests to compare the
(3+1) and the (3+2) hypotheses are discussed. All tests show that (3+2) models
fit the existing short-baseline data significantly better than (3+1) models.Comment: 16 pages, 15 figures. Added NOMAD data to the analysis, one
statistical test, and two figures. References and text added. Version
submitted to PR
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