262 research outputs found
Addendum to: Solar neutrino oscillation parameters after first KamLAND results
In a previous paper [1], we presented a three-flavour oscillation analysis of
the solar neutrino measurements and of the first data from the KamLAND
experiment, in terms of the relevant mass-mixing parameters (delta m^2,
theta_12, theta_13). The analysis, performed by including the terrestrial
neutrino constraints coming from the CHOOZ (reactor), KEK-to-Kamioka (K2K,
accelerator) and Super-Kamiokande (SK, atmospheric) experiments, provided a
stringent upper limit on theta_13, namely, sin^2(theta_13)<0.05 at 3 sigma. We
reexamine such upper bound in the light of a recent (although preliminary)
reanalysis of atmospheric neutrino data performed by the SK collaboration,
which seems to shift the preferred value of the largest neutrino square mass
difference Delta m^2 downwards. By taking the results of the SK official
reanalysis at face value, and by repeating the analysis in [1] with such a new
input, we find that the upper bound on theta_{13} is somewhat relaxed:
sin^2(theta_13)<0.067 at 3 sigma. Related phenomenological issues are briefly
discussed
Solar Neutrinos (with a tribute to John. N. Bahcall)
John N. Bahcall championed solar neutrino physics for many years. Thanks to
his pioneering and long-lasting contributions, this field of research has not
only reached maturity, but has also opened a new window on physics beyond the
standard electroweak model through the phenomenon of neutrino flavor
oscillations. We briefly outline some recent accomplishments in the field, and
also discuss a couple of issues that do not seem to fit in the ``standard
picture,'' namely, the chemical controversy at the solar surface, and possible
implications of recent gallium radioactive source experiments
Neutrino mass and mixing parameters: A short review
We present a brief review of the current status of neutrino mass and mixing
parameters, based on a comprehensive phenomenological analysis of neutrino
oscillation and non-oscillation searches, within the standard three-neutrino
mixing framework
A phenomenological outlook on three-flavor atmospheric neutrino oscillations
The recent observations of atmospheric nu events from the Super-Kamiokande
experiment are compatible with three-flavor neutrino oscillations, occurring
dominantly in the nu_mu<--->nu_tau channel and subdominantly in the
nu_mu<--->nu_e channel. We present an updated analysis of the three-flavor
mass-mixing parameters consistent with the present phenomenology, including the
latest 45 kTy data sample from Super-Kamiokande. A comparison with our previous
results, based on 33 kTy data, shows that the oscillation evidence is
strengthened, and that the neutrino mass-mixing parameters are constrained in
smaller ranges
Neutrino Oscillations: A Global Analysis
We review the status of the neutrino oscillation physics (as of June 2003),
with a particular emphasis on the present knowledge of the neutrino mass-mixing
parameters in a three generation approach. We consider first the nu_mu-->nu_tau
flavor transitions of atmospheric neutrinos. It is found that standard
oscillations provide the best description of the SK+K2K data, and that the
associated mass-mixing parameters are determined at 1 sigma (and dof=1) as:
Delta m^2=(2.6 +-0.4) x 10^-3 eV^2 and sin^2(2theta)=1.00+0.00-0.05. Such
indications, presently dominated by SK, could be strengthened by further K2K
data. Then we analyze the energy spectrum of reactor neutrino events recently
observed at KamLAND and combine them with solar and terrestrial neutrino data.
We find that the solution to the solar neutrino problem at large mixing angle
(LMA) is basically split into two sub-regions, that we denote as LMA-I and
LMA-II. The LMA-I solution, characterized by lower values of the squared
neutrino mass gap, is favored by the global data fit. Finally, we briefly
illustrate how prospective data from the SNO and KamLAND can increase our
confidence in the occurrence of standard matter effects in the Sun, which are
starting to emerge from current data
Earth regeneration effect in solar neutrino oscillations: an analytic approach
We present a simple and accurate method for computing analytically the
regeneration probability of solar neutrinos in the Earth. We apply this method
to the calculation of several solar model independent quantities than can be
measured by the SuperKamiokande and Sudbury Neutrino Observatory experiments
Effects of matter density variations on dominant oscillations in long baseline neutrino experiments
Variations around the average density and composition of the Earth mantle may
affect long-baseline (anti)neutrino oscillations through matter effects. For
baselines not exceeding a few thousand km, such effects are known to be very
small, and can be practically regarded as fractional contributions to the
theoretical uncertainties. We perturbatively derive compact expressions to
evaluate such contributions in phenomenologically interesting scenarios with
three or four neutrinos and a dominant mass scale
Indications on neutrino oscillations parameters from initial K2K and current SK data
We briefly discuss the impact of initial data from the KEK-to-Kamioka (K2K)
neutrino experiment on the nu_mu-->nu_tau oscillation parameters (m^2,tan^2
psi) currently indicated by the Super-Kamiokande (SK) atmospheric neutrino
experiment. After showing the very good agreement between K2K and SK, we
combine the two separate pieces of information. We find that the 99% C.L. range
for m^2 allowed by SK only, m^2=[1.3, 5.6]x10^-3 eV^2, is reduced to [1.5,
4.8]x10^-3 eV^2 by including K2K data. By halving the uncertainties of the K2K
total rate (with central value unchanged), the m^2 range would be ulteriorly
reduced to [1.8, 4.0]x10^-3 eV^2. Such information appears to be already useful
in planning (very) long baseline neutrino oscillation experiments
Indications from Precision Electroweak Physics Confront Theoretical Bounds on the Mass of the Higgs Boson
An updated fit to the precision electroweak data and to the direct
measurement of the top quark mass provides significant constraints on
and on the Higgs boson mass : and
, with an error correlation .
We integrate the probability distribution found in this analysis
over various zones of the plane defined by one-sided experimental
and theoretical bounds on the Higgs boson mass, both in the Standard Model and
in its minimal supersymmetric extension. The comparison of the cumulative
probabilities gives interesting information on the likelihood that the true
value of is compatible with different theoretical scenarios
Neutrino mass hierarchy and precision physics with medium-baseline reactors: impact of energy-scale and flux-shape uncertainties
Nuclear reactors provide intense sources of electron antineutrinos,
characterized by few-MeV energy E and unoscillated spectral shape Phi(E).
High-statistics observations of reactor neutrino oscillations over
medium-baseline distances L ~ O(50) km would provide unprecedented
opportunities to probe both the long-wavelength mass-mixing parameters (delta
m^2 and theta_12) and the short-wavelength ones (Delta m^2 and theta_13),
together with the subtle interference effects associated to the neutrino mass
hierarchy (either normal or inverted). In a given experimental setting - here
taken as in the JUNO project for definiteness - the achievable hierarchy
sensitivity and parameter accuracy depend not only on the accumulated
statistics but also on systematic uncertainties, which include (but are not
limited to) the mass-mixing priors and the normalizations of signals and
backgrounds. We examine, in addition, the effect of introducing smooth
deformations of the detector energy scale, E -> E'(E), and of the reactor flux
shape, Phi(E) -> Phi'(E), within reasonable error bands inspired by
state-of-the-art estimates. It turns out that energy-scale and flux-shape
systematics can noticeably affect the performance of a JUNO-like experiment,
both on the hierarchy discrimination and on precision oscillation physics. It
is shown that a significant reduction of the assumed energy-scale and
flux-shape uncertainties (by, say, a factor of two) would be highly beneficial
to the physics program of medium-baseline reactor projects. Our results shed
also some light on the role of the inverse-beta decay threshold, of geoneutrino
backgrounds, and of matter effects in the analysis of future reactor
oscillation data
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