1,630 research outputs found
Short-Baseline Electron Neutrino Disappearance, Tritium Beta Decay and Neutrinoless Double-Beta Decay
We consider the interpretation of the MiniBooNE low-energy anomaly and the
Gallium radioactive source experiments anomaly in terms of short-baseline
electron neutrino disappearance in the framework of 3+1 four-neutrino mixing
schemes. The separate fits of MiniBooNE and Gallium data are highly compatible,
with close best-fit values of the effective oscillation parameters Delta m^2
and sin^2 2 theta. The combined fit gives Delta m^2 >~ 0.1 eV^2 and 0.11 <
sin^2 2 theta < 0.48 at 2 sigma. We consider also the data of the Bugey and
Chooz reactor antineutrino oscillation experiments and the limits on the
effective electron antineutrino mass in beta-decay obtained in the Mainz and
Troitsk Tritium experiments. The fit of the data of these experiments limits
the value of sin^2 2 theta below 0.10 at 2 sigma. Considering the tension
between the neutrino MiniBooNE and Gallium data and the antineutrino reactor
and Tritium data as a statistical fluctuation, we perform a combined fit which
gives Delta m^2 \simeq 2 eV and 0.01 < sin^2 2 theta < 0.13 at 2 sigma.
Assuming a hierarchy of masses m_1, m_2, m_3 << m_4, the predicted
contributions of m_4 to the effective neutrino masses in beta-decay and
neutrinoless double-beta-decay are, respectively, between about 0.06 and 0.49
and between about 0.003 and 0.07 eV at 2 sigma. We also consider the
possibility of reconciling the tension between the neutrino MiniBooNE and
Gallium data and the antineutrino reactor and Tritium data with different
mixings in the neutrino and antineutrino sectors. We find a 2.6 sigma
indication of a mixing angle asymmetry.Comment: 14 pages; final version published in Phys.Rev.D82:053005,201
The Physical Significance of Confidence Intervals
We define some appropriate statistical quantities that indicate the physical
significance (reliability) of confidence intervals in the framework of both
Frequentist and Bayesian statistical theories. We consider the expectation
value of the upper limit in the absence of a signal (that we propose to call
"exclusion potential", instead of "sensitivity" as done by Feldman and Cousins)
and its standard deviation, we define the "Pull" of a null result, expressing
the reliability of an experimental upper limit, and the "upper and lower
detection functions", that give information on the possible outcome of an
experiment if there is a signal. We also give a new appropriate definition of
"sensitivity", that quantifies the capability of an experiment to reveal the
signal that is searched for at the given confidence level.Comment: 16 page
The Power of Confidence Intervals
We consider the power to reject false values of the parameter in Frequentist
methods for the calculation of confidence intervals. We connect the power with
the physical significance (reliability) of confidence intervals for a parameter
bounded to be non-negative. We show that the confidence intervals (upper
limits) obtained with a (biased) method that near the boundary has large power
in testing the parameter against larger alternatives and small power in testing
the parameter against smaller alternatives are physically more significant.
Considering the recently proposed methods with correct coverage, we show that
the physical significance of upper limits is smallest in the Unified Approach
and highest in the Maximum Likelihood Estimator method. We illustrate our
arguments in the specific cases of a bounded Gaussian distribution and a
Poisson distribution with known background.Comment: 13 pages, 5 figure
Statistical Analysis of Solar Neutrino Data
We calculate with Monte Carlo the goodness of fit and the confidence level of
the standard allowed regions for the neutrino oscillation parameters obtained
from the fit of the total rates measured in solar neutrino experiments. We show
that they are significantly overestimated in the standard method. We also
calculate exact allowed regions with correct frequentist coverage. We show that
the exact VO, LMA and LOW regions are much larger than the standard ones and
merge together giving an allowed band at large mixing angles for all Delta m^2
> 10^{-10} eV^2.Comment: 4 pages. Talk presented by C. Giunti at NOW 2000, Conca Specchiulla
(Otranto, Italy), 9-16 Sep. 200
Lepton Numbers in the framework of Neutrino Mixing
In this short review we discuss the notion of lepton numbers. The strong
evidence in favor of neutrino oscillations obtained recently in the
Super-Kamiokande atmospheric neutrino experiment and in solar neutrino
experiments imply that the law of conservation of family lepton numbers L_e,
L_mu and L_tau is strongly violated. We consider the states of flavor neutrinos
nu_e, nu_mu and nu_tau and we discuss the evolution of these states in space
and time in the case of non-conservation of family lepton numbers due to the
mixing of light neutrinos. We discuss and compare different flavor neutrino
discovery experiments. We stress that experiments on the search for
nu_mu->nu_tau and nu_e->nu_tau oscillations demonstrated that the flavor
neutrino nu_tau is a new type of neutrino, different from nu_e and nu_mu. In
the case of neutrino mixing, the lepton number (only one) is connected with the
nature of massive neutrinos. Such conserved lepton number exist if massive
neutrinos are Dirac particles. We review possibilities to check in future
experiments whether the conserved lepton number exists.Comment: 20 page
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