535 research outputs found
Supernova neutrino oscillations: A simple analytical approach
Analyses of observable supernova neutrino oscillation effects require the
calculation of the electron (anti)neutrino survival probability P_ee along a
given supernova matter density profile. We propose a simple analytical
prescription for P_ee, based on a double-exponential form for the crossing
probability and on the concept of maximum violation of adiabaticity. In the
case of two-flavor transitions, the prescription is shown to reproduce
accurately, in the whole neutrino oscillation parameter space, the results of
exact numerical calculations for generic (realistic or power-law) profiles. The
analytical approach is then generalized to cover three-flavor transitions with
(direct or inverse) mass spectrum hierarchy, and to incorporate Earth matter
effects. Compact analytical expressions, explicitly showing the symmetry
properties of P_ee, are provided for practical calculations.Comment: 22 pages (RevTeX) + 5 figures (PostScript
Quasi-energy-independent solar neutrino transitions
Current solar, atmospheric, and reactor neutrino data still allow oscillation
scenarios where the squared mass differences are all close to 10^-3 eV^2,
rather than being hierarchically separated. For solar neutrinos, this situation
(realized in the upper part of the so-called large-mixing angle solution)
implies adiabatic transitions which depend weakly on the neutrino energy and on
the matter density, as well as on the ``atmospheric'' squared mass difference.
In such a regime of ``quasi-energy-independent'' (QEI) transitions,
intermediate between the more familiar ``Mikheyev-Smirnov-Wolfenstein'' (MSW)
and energy-independent (EI) regimes, we first perform analytical calculations
of the solar nu_e survival probability at first order in the matter density,
beyond the usual hierarchical approximations. We then provide accurate,
generalized expressions for the solar neutrino mixing angles in matter, which
reduce to those valid in the MSW, QEI and EI regimes in appropriate limits.
Finally, a representative QEI scenario is discussed in some detail.Comment: Title changed; text and acronyms revised; results unchanged. To
appear in PR
Mastectomy rates are decreasing in the era of service screening: a population-based study in Italy (1997-2001)
We enrolled all 2162 in situ and 21 148 invasive cases of breast cancer in 17 areas of Italy, diagnosed in 1997-2001. Rates of early cancer increased by 13.7% in the screening age group (50-69 years), and breast conserving surgery by 24.6%. Advanced cancer rates decreased by 19.4%, and mastectomy rates by 24.2%. Service screening did not increase mastectomy rates in the study population
Global Analysis with SNO: Toward the Solution of the Solar Neutrino Problem
We perform a global analysis of the latest solar neutrino data including the
SNO result on the CC-event rate. This result further favors the LMA solution of
the solar neutrino problem. The best fit values of parameters we find are:
\Delta m^2 = (4.8 - 5.0)10^{-5} eV^2, tan^2 \theta = 0.35 - 0.38, f_B = 1.08 -
1.12, and f_{hep} = 1 - 4. With respect to this best fit the LOW solution is
accepted at 90% C.L.. The Vacuum oscillation solution with \Delta m^2 = 1.4
10^{-10} eV^2, gives good fit of the data provided that the boron neutrino flux
is substantially smaller than the SSM flux (f_B \sim 0.5). The SMA solution is
accepted only at 3\sigma level. We find that vacuum oscillations to sterile
neutrino, VAC(sterile), with f_B \sim 0.5 also give rather good global fit of
the data. All other sterile solutions are strongly disfavored. We check the
quality of the fit by constructing the pull-off diagrams of observables.
Predictions for the day-night asymmetry, spectrum distortion and NC/CC ratio at
SNO are calculated. In the best fit points of the global solutions we find:
A_{DN}^{CC} \approx (7 - 8)% for LMA, \sim 3% for LOW, and (2 - 3)% for SMA. It
will be difficult to see the distortion of the spectrum expected for LMA as
well as LOW solutions. However, future SNO spectral data can significantly
affect the VAC and SMA solutions. We also calculate expectations for the
BOREXINO rate.Comment: 35 pages, latex, 9 figures; results of analysis slightly changed due
to different treatment of the hep neutrino flux; predictions for NC/CC ratio
and Borexino rate adde
Analytical description of quasivacuum oscillations of solar neutrinos
We propose a simple prescription to calculate the solar neutrino survival
probability P_{ee} in the quasivacuum oscillation (QVO) regime. Such
prescription is obtained by matching perturbative and exact analytical results,
which effectively take into account the density distribution in the Sun as
provided by the standard solar model. The resulting analytical recipe for the
calculation of P_{ee} is shown to reach its highest accuracy |\Delta P_{ee}| <
2.6 x 10^{-2} in the whole QVO range) when the familiar prescription of
choosing the solar density scale parameter r_0 at the
Mikheyev-Smirnov-Wolfenstein (MSW) resonance point is replaced by a new one,
namely, when r_0 is chosen at the point of ``maximal violation of
adiabaticity'' (MVA) along the neutrino trajectory in the Sun. The MVA
prescription admits a smooth transition from the QVO regime to the MSW
transition one. We discuss in detail the phase acquired by neutrinos in the
Sun, and show that it might be of relevance for the studies of relatively short
timescale variations of the fluxes of the solar \nu lines in the future
real-time solar neutrino experiments. Finally, we elucidate the role of matter
effects in the convective zone of the Sun.Comment: 25 pages (RevTeX) + 11 figures (postscript
Constraining neutrino oscillation parameters with current solar and atmospheric data
We analyze the impact of recent solar, atmospheric and reactor data in the
determination of the neutrino oscillation parameters, taking into account that
both the solar nu_e and the atmospheric nu_mu may convert to a mixture of
active and sterile neutrinos. We use the most recent global solar neutrino
data, including the 1496-day Super-K neutrino data sample, and we investigate
in detail the impact of the SNO neutral current, spectral and day/night data by
performing also an analysis using only the charged current rate from SNO. The
implications of the first 145.1 days of KamLAND data on the determination of
the solar neutrino parameters are also discussed in detail. We confirm the
clear preference of solar+reactor data for the pure active LMA-MSW solution of
the solar neutrino problem, and obtain that the LOW, VAC, SMA and Just-So^2
solutions are disfavored with a Delta_chi^2 = 22, 22, 36, 44, respectively.
Furthermore, we find that the global solar data constrains the admixture of a
sterile neutrino to be less than 43% at 99% CL. By performing an improved fit
of the atmospheric data, we also update the corresponding regions of
oscillation parameters. We find that the recent atmospheric Super-K (1489-day)
and MACRO data have a strong impact on constraining a sterile component in
atmospheric oscillations: if the nu_mu is restricted to the atmospheric mass
states only a sterile admixture of 16% is allowed at 99% CL, while a bound of
35% is obtained in the unconstrained case. Pure sterile oscillations are
disfavored with a Delta_chi^2 = 34.6 compared to the pure active case.Comment: 28 pages, LaTeX file using RevTEX4, 12 figures and 3 tables included.
Improved version including the new KamLAND dat
Solar neutrino oscillation parameters after first KamLAND results
We analyze the energy spectrum of reactor neutrino events recently observed
in the Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND) and combine
them with solar and terrestrial neutrino data, in the context of two- and
three-family active neutrino oscillations. In the 2-neutrino case, 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. This picture is not significantly modified
in the 3-neutrino mixing case. A brief discussion is given about the
discrimination of the LMA-I and LMA-II solutions with future KamLAND data. In
both the 2- and 3-neutrino cases, we present a detailed analysis of the
post-KamLAND bounds on the oscillation parameters.Comment: Revised version. Two figures adde
Solar neutrinos: global analysis with day and night spectra from SNO
We perform global analysis of the solar neutrino data including the day and
night spectra of events at SNO. In the context of two active neutrino mixing,
the best fit of the data is provided by the LMA MSW solution with Delta m^2 =
6.15 10^{-5} eV^2, tan^2\theta = 0.41, f_B = 1.05, where f_B is the boron
neutrino flux in units of the corresponding flux in the Standard Solar Model
(SSM). At 3 sigma level we find the following upper bounds: tan^2\theta < 0.84
and Delta m^2 < 3.6 10^{-4} eV^2. From 1 sigma-interval we expect the day-night
asymmetries of the charged current and electron scattering events to be:
A_{DN}^{CC} = 3.9 +3.6-2.9 and A_{DN}^{ES} = 2.1 +2.1-1.4. The only other
solution which appears at 3 sigma-level is the VAC solution with Delta m^2 =
4.5 10^{-10} eV^2, tan^2\theta = 2.1 and f_B=0.75. The best fit point in the
LOW region, with Delta m^2 = 0.93 10^{-7} eV^2 and tan^2\theta = 0.64, is
accepted at 99.95% (3.5 sigma) C.L. . The least chi^2 point from the SMA
solution region, with Delta m^2 = 4.6 10^{-6} eV^2 and tan^2\theta = 5 10^{-4},
could be accepted at 5.5 sigma-level only. In the three neutrino context the
influence of theta_{13} is studied. We find that with increase of theta_{13}
the LMA best fit point shifts to larger Delta m^2, mixing angle is practically
unchanged, and the quality of the fit becomes worse. The fits of LOW and SMA
slightly improve. Predictions for KamLAND experiment (total rates, spectrum
distortion) have been calculated.Comment: Typos corrected, reference adde
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