A road map to solar neutrino fluxes, neutrino oscillation parameters, and tests for new physics

Abstract

We analyze all available solar and related reactor neutrino experiments, as well as simulated future 7 Be, p − p, and pep solar neutrino experiments. We treat all solar neutrino fluxes as free parameters subject to the condition that the total luminosity represented by the neutrinos equals the observed solar luminosity (the 'luminosity constraint'). Existing experiments plus the luminosity constraint show that the p − p solar neutrino flux is 1.02 ± 0.02 (1σ) times the flux predicted by the BP00 standard solar model; the 7 Be neutrino flux is 0.93 +0.25 −0.63 the predicted flux; and the 8 B flux is 1.01 ± 0.04 the predicted flux. The CNO fluxes are very poorly determined. The neutrino oscillation parameters are: ∆m 2 = 7.3 +0.4 −0.6 × 10 −5 eV 2 and tan 2 θ 12 = 0.41 ± 0.04. We evaluate how accurate future experiments must be to determine more precisely neutrino oscillation parameters and solar neutrino fluxes, and to elucidate the transition from vacuum-dominated to matter-dominated oscillations at low energies. A future 7 Be ν − e scattering experiment accurate to ±10% can reduce the uncertainty in the experimentally determined 7 Be neutrino flux by a factor of four and the uncertainty in the p − p neutrino flux by a factor of 2.5 (to ±0.8%). A future p − p experiment must be accurate to better than ±3% to shrink the uncertainty in tan 2 θ 12 by more than 15%. The idea that the Sun shines because of nuclear fusion reactions can be tested accurately by comparing the observed photon luminosity of the Sun with the luminosity inferred from measurements of solar neutrino fluxes. Based upon quantitative analyses of present and simulated future experiments, we answer the question: Why perform low-energy solar neutrino experiments?

Solar model parameters and direct measurements of solar neutrino fluxes

“…[34,35,36], whereas the potential improvements of the precision on these parameters from future solar neutrino experiments has been investigated, e.g., in refs. [30,32,10].…”

“…As long as the luminosity constraint is imposed, a measurement of the Borexino event rate with a 5% error could lead to a determination of φ pp with a 1σ uncertainty of 0.5%. The addition of a high precision data from a "generic pp" experiment is not expected to lead to any significant reduction of the uncertainty in the value of φ pp as long as the luminosity constraint is taken into account [10]. However, the data from these experiments could certainly improve noticeably the precision of the pp flux determination, which can be achieved without using the luminosity constraint.…”

“…However, the data from these experiments could certainly improve noticeably the precision of the pp flux determination, which can be achieved without using the luminosity constraint. Moreover, it should be possible to test the applicability of the photon luminosity constraint itself and, more generally, the thermo-nuclear theory of the energy generation in the Sun, by comparing the measured value of the solar photon luminosity with the value obtained using the results from the LowNu and the other solar neutrino experiments [10].…”

“…The ratio of the CC and NC event rates observed at SNO provided a measure of the solar ν e transition probability at energies of E ∼ (5 − 10) MeV, while the SNO NC data permitted to determine with rather good precision the 8 B component of the solar ν e flux [9]. The global solar neutrino data allowed to obtain information on the other important components of the solar neutrino flux -the fluxes of pp, pep and 7 Be neutrinos, and to constrain the flux of CNO neutrinos [10]. The combined solar neutrino and KamLAND data lead to a determination of the neutrino oscillation parameters which drive the solar ν e oscillations -the neutrino mass squared difference ∆m 2 21 and the mixing angle θ 12 , with an unexpectedly high precision (see, e.g., [11,12]).…”

Solar neutrinos and 1-3 leptonic mixing

“…Indeed, the sin 2 θ 12 can be measured with 3% accuracy at 1σ (1 d.o.f.) in the reactor experiments with baseline 50 -60 km [55,18,56,38].…”