A Pilot Experiment with Reactor Neutrinos in Taiwan

A Collaboration comprising Taiwan and mainland Chinese scientists has been built up since 1996 to pursue a experimental program in neutrino and astro-particle physics in Taiwan. A pilot experiment to be performed at the Nuclear Power Station II in Taiwan is now under intense preparation. It will make use of a 600 kg CsI(Tl) crystal calorimeter to study various neutrino interactions. The feasibility of performing a long baseline reactor neutrino experiment will also be investigated. The conceptual design and the physics to be addressed by the pilot experiment are presented.Comment: 14 pages, 8 figures, 2 table

Are there sterile neutrinos at the eV scale?

New predictions for the anti-neutrino flux emitted by nuclear reactors suggest that reactor experiments may have measured a deficit in the anti-neutrino flux, which can be interpreted in terms of oscillations between the known active neutrinos and new sterile states. Motivated by this observation, we perform a re-analysis of global short-baseline neutrino oscillation data in a framework with one or two sterile neutrinos. While one sterile neutrino is still not sufficient to reconcile the signals suggested by reactor experiments and by the LSND and MiniBooNE experiments with null results from other searches, we find that, with the new reactor flux prediction, the global fit improves considerably when the existence of two sterile neutrinos is assumed.Comment: 5 pages, 5 figures, v2: reference and acknowledgements adde

The 51^{51}Cr neutrino source and Borexino: a desirable marriage

Exposure to a $^{51}$Cr neutrino source as that used in Gallex will provide an excellent overall performance test of Borexino, which should collect about 1400 source induced events, with an initial rate of about 35 counts per day. This will be particularly important if MSW-small-angle turns out to be the solution of the solar neutrino problem. In addition, if an independent, accurate calibration is available, one will have an interesting experiment on neutrino properties: as an example, a neutrino magnetic moment of the order $5\cdot10^{-11}\mu_B$could be detected/excluded at the 90\% C.L.Comment: 7 pages, RevTeX, plus 3 postscripts figures, tarred, compresse

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

On mixing angles and magnetic moment of heavy tau neutrino

If the magnetic moment of unstable tau neutrinos with the mass of $O$(MeV) is in the region of $10^{-8}\mu_{B} \lesssim \mu_{\nu_{\tau}} \lesssim 10^{-6}\mu_{B}$, it is compatible with the present experimental and cosmological bounds. It is pointed out here, that if the tau neutrino has such a large magnetic moment and can oscillate into a neutrino of another flavour the results from $\nu e$ scattering experiment at LAMPF constrain the tau neutrino mixing angles to $sin^{2}2\theta_{e \tau} \lesssim 2\times 10^{-6} - 2\times 10^{-2}$ and $sin^{2}2\theta_{\mu\tau} \lesssim 10^{-6} - 10^{-2}$ depending on the magnetic moment value in the allowed region.Comment: 5 pages, LaTe

Does the neutrino magnetic moment have an impact on solar neutrino physics?

Solar neutrino observations coupled with the recent KamLAND data suggest that spin-flavor precession scenario does not play a major role in neutrino propagation in the solar matter. We provide approximate analytical formulas and numerical results to estimate the contribution of the spin-flavor precession, if any, to the electron neutrino survival probability when the magnetic moment and magnetic field combination is small.Comment: 7 pages, 1 figure

Implications of sterile neutrinos for medium/long-baseline neutrino experiments and the determination of θ13\theta_{13}

We revisit some of the recent neutrino observations and anomalies in the context of sterile neutrinos. Based on a general parametrization motivated in the presence of sterile neutrinos, the consistency of the MINOS disappearance data with additional sterile neutrinos is discussed. We also explore the implications of sterile neutrinos for the measurement of $|U_{\mu3}|$ in this case. Regarding the determination of $|U_{e3}|$, we observe that the existence of sterile neutrinos may induce a significant modification of the $\theta_{13}$ angle in neutrino appearance experiments like T2K and MINOS, over and above the ambiguities and degeneracies that are already present in 3-neutrino parameter extractions. The modification is less significant in reactor neutrino experiments like Double-CHOOZ, Daya Bay and RENO and therefore the extracted $|U_{e3}|$ value when sterile neutrinos are present is close to the one that would be obtained in the 3-neutrino case. We also conclude that the results from T2K imply a 90% C.L. lower-bound on $|U_{e3}|$, in the "$\,3+2$" neutrino case, which is still within the sensitivity of future reactor neutrino experiments like Daya Bay, and consistent with the one-$\sigma$ range of $\sin^22\theta_{13}$ recently reported by the Double-CHOOZ experiment. Finally, we argue that for the recently determined best-fit parameters, the results in the "$\,3+1$" scenario would be very close to the medium/long baseline results obtained in the "$\,3+2$" case analyzed in this work.Comment: 25 pages, 9 figures, revtex4-1. Typos corrected, published versio

Global neutrino data and recent reactor fluxes: status of three-flavour oscillation parameters

We present the results of a global neutrino oscillation data analysis within the three-flavour framework. We include latest results from the MINOS long-baseline experiment (including electron neutrino appearance as well as anti-neutrino data), updating all relevant solar (SK II+III), atmospheric (SK I+II+III) and reactor (KamLAND) data. Furthermore, we include a recent re-calculation of the anti-neutrino fluxes emitted from nuclear reactors. These results have important consequences for the analysis of reactor experiments and in particular for the status of the mixing angle $\theta_{13}$. In our recommended default analysis we find from the global fit that the hint for non-zero $\theta_{13}$ remains weak, at 1.8$\sigma$ for both neutrino mass hierarchy schemes. However, we discuss in detail the dependence of these results on assumptions concerning the reactor neutrino analysis.Comment: 15 pages, 10 figures and 2 tables, v2: corrected version, main conclusions unchanged, references adde

Prospects for Detecting a Neutrino Magnetic Moment with a Tritium Source and Beta-beams

We compare the prospects for detecting a neutrino magnetic moment by the measurement of neutrinos from a tritium source, reactors and low-energy beta-beams. In all cases the neutrinos or antineutrinos are detected by scattering of electrons. We find that a large (20 MCurie) tritium source could improve the limit on the neutrino magnetic moment significantly, down to the level of a few $\times 10^{-12}$ while low-energy beta-beams with sufficiently rapid production of ions could improve the limits to the level of a few $\times 10^{-11}$. The latter would require ion production at the rate of at least $10^{15}$ s$^{-1}$.Comment: 6 pages, 3 figure

Sensitivities of Low Energy Reactor Neutrino Experiments

The low energy part of the reactor neutrino spectra has not been experimentally measured. Its uncertainties limit the sensitivities in certain reactor neutrino experiments. The origin of these uncertainties are discussed, and the effects on measurements of neutrino interactions with electrons and nuclei are studied. Comparisons are made with existing results. In particular, the discrepancies between previous measurements with Standard Model expectations can be explained by an under-estimation of the low energy reactor neutrino spectra. To optimize the experimental sensitivities, measurements for \nuebar-e cross-sections should focus on events with large ($>$1.5 MeV) recoil energy while those for neutrino magnetic moment searches should be based on events $<$100 keV. The merits and attainable accuracies for neutrino-electron scattering experiments using artificial neutrino sources are discussed.Comment: 25 pages, 9 figure