Vacuum-matter transition of solar neutrino oscillations with the Borexino experiment

Thanks to the excellent levels of achieved radiopurity and to the accurate data analysis techniques, Borexino has performed the first real time measurement of the 7Be solar neutrino flux. The efficient software rejection of cosmogenic background also allows to investigate the recoiled electron spectrum induced by 8B solar neutrinos down to 3 MeV, the lowest energy threshold ever reached in real time detection. This is the first observation of solar 8B neutrinos in a liquid scintillator detector. For the first time, the same apparatus can measure the two different oscillation regions (vacuum-driven and matter-enhanced) predicted by the MSW-LMA model. Borexino also quotes the ratio between the survival probabilities, corresponding to 1.93 ± 0.75, validating the presence of the transition region predicted by the MSW-LMA solution

Future large-scale water-Cherenkov detector

MEMPHYS (MEgaton Mass PHYSics) is a proposed large-scale water-Cherenkov experiment to be performed deep underground. It is dedicated to nucleon decay searches and the detection of neutrinos from supernovae, solar, and atmospheric neutrinos, as well as neutrinos from a future beam to measure the CP violating phase in the leptonic sector and the mass hierarchy. This paper provides an overview of the latest studies on the expected performance of MEMPHYS in view of detailed estimates of its physics reach, mainly concerning neutrino beams

Study of the performance of a large scale water-Cherenkov detector (MEMPHYS)

MEMPHYS (MEgaton Mass PHYSics) is a proposed large-scale water Cherenkov experiment to be performed deep underground. It is dedicated to nucleon decay searches, neutrinos from supernovae, solar and atmospheric neutrinos, as well as neutrinos from a future Super-Beam or Beta-Beam to measure the CP violating phase in the leptonic sector and the mass hierarchy. A full simulation of the detector has been performed to evaluate its performance for beam physics. The results are given in terms of "Migration Matrices" of reconstructed versus true neutrino energy, taking into account all the experimental effects.Comment: Updated after JCAP's referee's comment

Measurement of Muon Antineutrino Oscillations with an Accelerator-Produced Off-Axis Beam

T2K reports its first measurements of the parameters governing the disappearance of ν-μ in an off-axis beam due to flavor change induced by neutrino oscillations. The quasimonochromatic ν-μ beam, produced with a peak energy of 0.6 GeV at J-PARC, is observed at the far detector Super-Kamiokande, 295 km away, where the ν-μ survival probability is expected to be minimal. Using a data set corresponding to 4.01×1020 protons on target, 34 fully contained μ-like events were observed. The best-fit oscillation parameters are sin2(θ-23)=0.45 and |Δm-322|=2.51×10-3 eV2 with 68% confidence intervals of 0.38-0.64 and 2.26-2.80×10-3 eV2, respectively. These results are in agreement with existing antineutrino parameter measurements and also with the νμ disappearance parameters measured by T2K

First measurement of the muon neutrino charged current single pion production cross section on water with the T2K near detector

The T2K off-axis near detector, ND280, is used to make the first differential cross section measurements of muon neutrino charged current single positive pion production on a water target at energies ∼0.8 GeV. The differential measurements are presented as a function of the muon and pion kinematics, in the restricted phase space defined by pπ+\u3e200 MeV/c, pμ\u3e200 MeV/c, cos(θπ+)\u3e0.3 and cos(θμ)\u3e0.3. The total flux integrated νμ charged current single positive pion production cross section on water in the restricted phase space is measured to be

Measurement of Coherent π+ Production in Low Energy Neutrino-Carbon Scattering

We report the first measurement of the flux-averaged cross section for charged current coherent π+ production on carbon for neutrino energies less than 1.5 GeV, and with a restriction on the final state phase space volume in the T2K near detector, ND280. Comparisons are made with predictions from the Rein-Sehgal coherent production model and the model by Alvarez-Ruso et al., the latter representing the first implementation of an instance of the new class of microscopic coherent models in a neutrino interaction Monte Carlo event generator. We observe a clear event excess above background, disagreeing with the null results reported by K2K and SciBooNE in a similar neutrino energy region. The measured flux-averaged cross sections are below those predicted by both the Rein-Sehgal and Alvarez-Ruso et al. models

Search for Lorentz and CPT violation using sidereal time dependence of neutrino flavor transitions over a short baseline

A class of extensions of the Standard Model allows Lorentz and CPT violations, which can be identified by the observation of sidereal modulations in the neutrino interaction rate. A search for such modulations was performed using the T2K on-axis near detector. Two complementary methods were used in this study, both of which resulted in no evidence of a signal. Limits on associated Lorentz and CPT-violating terms from the Standard Model extension have been derived by taking into account their correlations in this model for the first time. These results imply such symmetry violations are suppressed by a factor of more than 1020 at the GeV scale

Updated T2K measurements of muon neutrino and antineutrino disappearance using 1.5×1021 protons on target

We report measurements by the T2K experiment of the parameters θ23 and Δm322 governing the disappearance of muon neutrinos and antineutrinos in the three-flavor neutrino oscillation model. Utilizing the ability of the experiment to run with either a mainly neutrino or a mainly antineutrino beam, the parameters are measured separately for neutrinos and antineutrinos. Using 7.482×1020 POT in neutrino running mode and 7.471×1020 POT in antineutrino mode, T2K obtained sin2(θ23)=0.51-0.07+0.08 and Δm322=2.53-0.13+0.15×10-3 eV2/c4 for neutrinos, and sin2(θ-23)=0.42-0.07+0.25 and Δm-232=2.55-0.27+0.33×10-3 eV2/c4 for antineutrinos (assuming normal mass ordering). No significant differences between the values of the parameters describing the disappearance of muon neutrinos and antineutrinos were observed

Measurement of neutrino and antineutrino oscillations by the T2K experiment including a new additional sample of ve interactions at the far detector

The T2K experiment reports an updated analysis of neutrino and antineutrino oscillations in appearance and disappearance channels. Asample of electron neutrino candidates at Super-Kamiokande in which a pion decay has been tagged is added to the four single-ring samples used in previous T2K oscillation analyses. Through combined analyses of these five samples, simultaneous measurements of four oscillation parameters, j?m2 32j, sin2 ?23, sin2 ?13, and dCP and of the mass ordering are made. A set of studies of simulated data indicates that the sensitivity to the oscillation parameters is not limited by neutrino interaction model uncertainty. Multiple oscillation analyses are performed, and frequentist and Bayesian intervals are presented for combinations of the oscillation parameters with and without the inclusion of reactor constraints on sin2 ?13.When combined with reactor measurements, the hypothesis of CP conservation (dCP 0 or p) is excluded at 90% confidence level. The 90% confidence region for dCP is -2.95;-0.44(-1.47;-1.27) for normal (inverted) ordering. The central values and 68% confidence intervals for the other oscillation parameters for normal (inverted) ordering are ?m2 32 2.540.082.510.08 10-3 eV2=c4 and sin2?23 0.55+0.05 -0.09 (0.55+0.05 -0.08 ), compatible with maximal mixing. In the Bayesian analysis, the data weakly prefer normal ordering (Bayes factor 3.7) and the upper octant for sin2 ?23 (Bayes factor 2.4)

First measurement of the νμ charged-current cross section on a water target without pions in the final state

This paper reports the first differential measurement of the charged-current interaction cross section of νμ on water with no pions in the final state. This flux-averaged measurement has been made using the T2K experiment\u27s off-axis near detector, and is reported in doubly differential bins of muon momentum and angle. The flux-averaged total cross section in a restricted region of phase space was found to be σ=(0.95±0.08(stat)±0.06(det syst)±0.04(model syst)±0.08(flux))×10-38 cm2/n