1,721,057 research outputs found
nu(e) disappearance in MiniBooNE
No full textThe anomalous excess of low-energy nu(e) events measured in the MiniBooNE experiment is explained through a renormalization of the absolute neutrino flux and a simultaneous disappearance of the nu(e)'s in the beam, which is compatible with that indicated by the results of gallium radioactive source experiments. We present the results of the fit of MiniBooNE data (P(nu e)->nu(e) = 0.64(-0.07)(+0.08)) and the combined fit of MiniBooNE data and the nu(e) disappearance measured in the gallium radioactive source experiments, which gives P(nu e)->nu(e)=0.82 +/- 0.04. We show that our interpretation of the data is also compatible with an old indication in favor of nu(e) disappearance found from the analysis of the results of beam-dump experiments, leading to P(nu e)->nu(e)=0.80(-0.04)(+0.03)
Large nu(mu)->nu(tau) and nu(e)->nu(tau) transitions in short-baseline experiments?
Full text linkConsidering four-neutrino schemes of type 3 + 1, we identify four small regions of the neutrino mixing parameter space compatible with all data. Assuming a small mixing between the sterile neutrino and the isolated mass eigenstate we show that large nu (mu) --> nu (tau) and nu (e) --> nu (tau) transitions are predicted in short-baseline experiments and could be observed in the near future in dedicated experiments. We discuss also implications for solar, atmospheric and long-baseline neutrino experiments and we present a formalism that allows to describe in 3+1 schemes atmospheric neutrino oscillations, long-baseline nu (mu) disappearance and nu (mu) --> nu (tau) transitions in matter
The physical significance of confidence intervals
No full textWe 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
The power of confidence intervals
Full text linkWe 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
Short-baseline active-sterile neutrino oscillations?
Full text linkWe suggest the possibility that the anomalies in the LSND experiment and the Gallium radioactive source experiments may be due to neutrino oscillations generated by a large squared-mass difference of about 20-30 eV(2). We consider the simplest 3+1 four-neutrino scheme that can accommodate also the observed solar and atmospheric neutrino oscillations. We show that, in this framework, the disappearance nu((-))(e) and nu((-))(mu) in short-baseline neutrino oscillation experiments is mainly due to active-sterile transitions. The implications of the first MiniBooNE, appeared after the completion of this paper, are discussed in an addendum
Crossing different energy scales: a summary
No full textThis proceeding summarizes the content of the talks presented in the 5th parallel session of the NOW2006 Workshop and dealing with several Physics items, including Neutrino mass and mixing textures (as resulting from both global analyses and theoretical models), lepton physics (flavour violation and leptogenesis), and future programs in neutrino physics (roadmaps and megaton detectors)
Limits on nu(e) and (nu)overbar(e) disappearance from Gallium and reactor experiments
No full textThe deficit observed in the Gallium radioactive source experiments is interpreted as a possible indication of the disappearance of electron neutrinos. In the effective framework of two-neutrino mixing we obtain sin(2)2 Theta greater than or similar to 0.03 and Delta m(2)greater than or similar to 0.1 eV(2). The compatibility of this result with the data of the Bugey and Chooz reactor short-baseline antineutrino disappearance experiments is studied. It is found that the Bugey data present a hint of neutrino oscillations with 0.02 less than or similar to sin(2)2 Theta less than or similar to 0.08 and Delta m(2)approximate to 1.8 eV(2), which is compatible with the Gallium allowed region of the mixing parameters. This hint persists in the combined analyses of Bugey and Chooz data, of Gallium and Bugey data, and of Gallium, Bugey, and Chooz data
Statistical significance of the gallium anomaly
Full text linkWe calculate the statistical significance of the anomalous deficit of electron neutrinos measured in the radioactive source experiments of the GALLEX and SAGE solar neutrino detectors, taking into account the uncertainty of the detection cross section. We found that the statistical significance of the anomaly is similar to 3.0 sigma. A fit of the data in terms of neutrino oscillations favors at similar to 2.7 sigma short-baseline electron neutrino disappearance with respect to the null hypothesis of no oscillations
3+1 and 3+2 sterile neutrino fits
Full text linkWe present the results of fits of short-baseline neutrino-oscillation data in 3 + 1 and 3 + 2 neutrino-mixing schemes. In spite of the presence of a tension in the interpretation of the data, 3 + 1 neutrino mixing is attractive for its simplicity and for the natural correspondence of one new entity (a sterile neutrino) with a new effect (short-baseline oscillations). The allowed regions in the oscillation parameter space can be tested in near-future experiments. In the framework of 3 + 2 neutrino mixing, there is less tension in the interpretation of the data, at the price of introducing a second sterile neutrino. Moreover, the improvement of the parameter goodness of fit is mainly a statistical effect due to an increase in the number of parameters. The CP violation in short-baseline experiments allowed in 3 + 2 neutrino mixing can explain the positive -> (nu) over bar (e) signal and the negative -> (nu) over bar (e) measurement in the MiniBooNE experiment. For the CP-violating phase, we obtained two minima of the marginal chi(2) close to the two values where CP violation is maximal
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