Abstract
The Borexino detector measures solar neutrino fluxes via neutrino-electron elastic scattering. Observed spectra are determined by the solar-νe survival probability Pee(E), and the chiral couplings of the neutrino and electron. Some theories of physics beyond the Standard Model postulate the existence of Non-Standard Interactions (NSI’s) which modify the chiral couplings and Pee(E). In this paper, we search for such NSI’s, in particular, flavor-diagonal neutral current interactions that modify the νee and ντe couplings using Borexino Phase II data. Standard Solar Model predictions of the solar neutrino fluxes for both high- and low-metallicity assumptions are considered. No indication of new physics is found at the level of sensitivity of the detector and constraints on the parameters of the NSI’s are placed. In addition, with the same dataset the value of sin2θW is obtained with a precision comparable to that achieved in reactor antineutrino experiments.
Highlights
Using Borexino to constrain Non-Standard Interactions (NSI’s) was originally discussed by Berezhiani, Raghavan, and Rossi in refs. [20, 21]. They argued that the monochromatic nature of 7Be solar neutrinos results in an electron recoil spectrum whose Compton-like shape is more sensitive to the νe couplings than that from a continuous neutrino energy spectrum
One can see that the sensitivity of Borexino to the NSI parameter εLe is more pronounced as compared to its sensitivity to εRe
For the sake of comparison, in the forth column, we present the global bounds from ref. [55], where the authors analyzed the data from the Large Electron-Positron Collider (LEP) experiment, LSND and CHARM II accelerator experiments, and Irvine, MUNU, and Rovno reactor experiments
Summary
[18], a high-energy region of 3.2 < T < 16 MeV was considered to measure 8B neutrinos with a continuous energy spectrum extending up to about 16.5 MeV. At momentum transfers relevant for Borexino (Q2 MW2 , MZ2 ), the CC and NC processes are well approximated by the point interaction:. Where we have used the Fierz transformation [29, 30] to rewrite the CC interaction into NC form, and we follow the notation of the Review of Particle Physics [31] for the NC coupling constants. For a monochromatic neutrino of energy E and flavor α scattering off an electron at rest, the interaction (2.4) predicts the spectrum of the kinetic energy T of the recoiling electrons to be [24, 32]
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