Solar Neutrino Observables Sensitive to Matter Effects

Abstract

We discuss constraints on the coefficientAMSWwhich is introduced to simulate the effect of weaker or stronger matter potential for electron neutrinos with the current and future solar neutrino data. The currently available solar neutrino data leads to a boundAMSW=1.47+0.54−0.42(+1.88−0.82)at 1σ(3σ) CL, which is consistent with the Standard Model predictionAMSW=1. For weaker matter potential (AMSW<1), the constraint which comes from the flat8B neutrino spectrum is already very tight, indicating the evidence for matter effects. However for stronger matter potential (AMSW>1), the bound is milder and is dominated by the day-night asymmetry of8B neutrino flux recently observed by Super-Kamiokande. Among the list of observables of ongoing and future solar neutrino experiments, we find that (1) an improved precision of the day-night asymmetry of8B neutrinos, (2) precision measurements of the low-energy quasi-monoenergetic neutrinos, and (3) the detection of the upturn of the8B neutrino spectrum at low energies are the best choices to improve the bound onAMSW.