sin2 θ W estimate and bounds on nonstandard interactions at source and detector in the solar neutrino low-energy regime

Abstract

Abstract:We explore the implications of the Borexino experiment's real time measurements of the lowest energy part of the neutrino spectrum from the primary pp fusion process up to 0.420 MeV through the 7 Be decay at 0.862 MeV to the pep reaction at 1.44 MeV. We exploit the fact that at such low energies, the large mixing angle solution to the MikheyevSmirnov-Wolfenstein matter effects in the sun are small for 7 Be and pep and negligible for pp. Consequently, the neutrinos produced in the sun change their flavor almost entirely through vacuum oscillations during propagation from the sun's surface and through possible nonstandard interactions acting at the solar source and Borexino detector. We combine the different NSI effects at source and detector in a single framework and use the current Borexino data to bound NSI non-universal and flavor-changing parameters at energies below the reach of reactor neutrino experiments. We also study the implication of the current data for the weak-mixing angle at this "low-energy frontier" data from the Borexino experiment, where it is expected to be slightly larger than its value at the Z mass. We find sin 2 θ W = 0.224 ± 0.016, the lowest energy-scale estimate to date. Looking to the future, we use projected sensitivities to solar neutrinos in next generation dedicated solar experiments and direct dark matter detection experiments and find a potential factor five improvement in determination of the weak-mixing angle and up to an order of magnitude improvement in probing the NSI parameters space.

Neutrino Oscillations and Non-standard Interactions

“…As can be seen, the NSI constraints obtained from Borexino and the combined analysis of solar (mainly Super-Kamiokande) and KamLAND data are comparable. It is expected that future results from Borexino Phase II, as well as the combination of all solar data, including Borexino, plus KamLAND data would allow a significant improvement on the current knowledge of neutrino NSI with matter [134].…”

Borexino and general neutrino interactions

“…The statistical analysis we have implemented here has already been used for phenomenological new physics studies in Refs. [33,36] and others. The validity of the χ 2 model used here has been cross-checked for estimating the neutrino magnetic moments for the same data in Ref.…”

“…For vector or axial-vector interactions, this case has been well studied in the context of the usual nonstandard interactions (NSI) in Ref. [33] for the Borexino data.…”

“…As solar neutrinos change their flavor from production to detection, we need to consider the survival probabilities for the pp, 7 Be and pep neutrinos that we will use for our model to fit with the data. We follow the notation from [33]. If there were no matter effects, the oscillation amplitude would be…”

Probing muonic charged current nonstandard interactions at decay-at-rest facilities in conjunction with T2HK

“…Typically, the interactions of neutrinos at source and detector are CC interactions involving both leptons and quarks. The impact of these NSIs on neutrino oscillation phenomenology has been studied extensively, for example, in the context of ESSνSB [25], DUNE [18,26], astrophysical neutrinos [27], neutrino factory [28], explaining data from MiniBoone and liquid scintillator neutrino detector (LSND) [29], as well as solar and reactor neutrino experiments [30][31][32][33][34][35][36]. In addition, neutrinos may be also produced via muon-decay process, and it is worthwhile to investigate impact of NSIs on processes involving muons especially in light of the various anomalies (involving muons) such as muon g − 2 or results involving B-meson decays [37,38].…”