Solar neutrino physics with low-threshold dark matter detectors

J. Billard, L. E. Strigari, and E. Figueroa-Feliciano

Phys. Rev. D 91, 095023 – Published 29 May 2015

Abstract

Dark matter detectors will soon be sensitive to Solar neutrinos via two distinct channels: coherent neutrino-nucleus and neutrino-electron elastic scatterings. We establish an analysis method for extracting Solar model properties and neutrino properties from these measurements, including the possible effects of sterile neutrinos which have been hinted at by some reactor experiments and cosmological measurements. Even including sterile neutrinos, through the coherent scattering channel, a 1 ton-year exposure with a low-threshold background free Germanium detector could improve on the current measurement of the normalization of the ${}^{8}B$ Solar neutrino flux down to 3% or less. Combining with the neutrino-electron elastic scattering data will provide constraints on both the high- and low-energy survival probability and will improve on the uncertainty on the active-to-sterile mixing angle by a factor of 2. This sensitivity to active-to-sterile transitions is competitive and complementary to forthcoming dedicated short baseline sterile neutrino searches with nuclear decays. Finally, we show that such solar neutrino physics potentials can be reached as long as the signal-to-noise ratio is better than 0.1.

Received 29 August 2014

DOI:https://doi.org/10.1103/PhysRevD.91.095023

Authors & Affiliations

J. Billard^*

Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA and IPNL, Université de Lyon, Université Lyon 1, CNRS/IN2P3, 4 rue E. Fermi 69622 Villeurbanne cedex, France

L. E. Strigari^†

Department of Physics and Astronomy, Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, Texas 77843-4242, USA

E. Figueroa-Feliciano

Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

^*j.billard@ipnl.in2p3.fr
^†strigari@physics.tamu.edu

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Vol. 91, Iss. 9 — 1 May 2015

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Images

Figure 1
Neutrino induced backgrounds in a low-threshold Ge dark matter detector as a function of true kinetic energy of the recoil (keV) and ionization energy (keVee). The ${}^{8}B$ induced nuclear recoils (CNS) and the $p p$ induced electronic recoils (ES) are shown as the blue solid and red dashed lines, respectively. These event rates have been computed using the high metallicity standard solar model, $P_{e e} = 0.55$ for $p p$ neutrinos and $P_{e s} = 0$ at all neutrino energies. Also shown in green is a residual gamma background of 5 and $50 evt / ton / year / keVee$ with a 10% uncertainty.
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Figure 2
Marginalized posterior probability density functions for selected model parameters from our MCMC analysis considering only existing the data from the experiments listed in Table 2 and the high metallicity SSM [9] listed in Table 1. Along the off diagonal are the correlations between the different parameters, where the thick contours reflect the 68% and 95% C.L. of the joint distributions. The other parameters ${f_{{}^{7}{Be}}, f_{p e p}, f_{p p}, f_{h e p}, f_{CNO}}$ , not shown here, have been marginalized over.
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Figure 3
Derived 90% C.L. contours from our MCMC analyses for the normalization of the ${}^{8}B$ flux vs the solar mixing angle $\sin^{2} θ_{12}$ (left), the active mixing angle $\sin^{2} θ_{13}$ (middle), and the sterile mixing angle $\sin^{2} θ_{14}$ (right), when combining current Solar and KamLAND data with future CNS and ES data from a background free dark matter detector. The top (bottom) panels assume a 1 (10) ton-yr exposure for a Ge detector with a 0.1 keV threshold. These panels highlight the improvement in the measurement of the normalization of the ${}^{8}B$ flux and on the estimation of the neutrino mixing angles with the addition of CNS and ES data from a dark matter detector.
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Figure 4
Left: Contours at 95% C.L. on the electron neutrino survival probability $P_{e e}$ (cyan) and transition probability into a sterile neutrino $P_{e s}$ (red) as a function of the neutrino energy. The two set of bands correspond to the case $Solar + KamLAND$ (dashed lines) and to the case $Solar + KamLAND + CNS + ES$ with a background free 10 ton-year exposure (filled contours). The contours are determined from Bayesian marginalization of the previously discussed MCMC analyses. Transition in the electron survival probability from the low- to the high-energy neutrinos around a few MeV is clearly visible and is known as the transition between vacuum- to matter-dominated oscillation regimes. Also shown are the current constraints on the neutrino-electron survival probability derived assuming no existence of sterile neutrinos [54]. Right: Projected limits on the active-to-sterile mixing angle $\sin^{2} θ_{14} \equiv \sin^{2} θ_{e e}$ using all current Solar and KamLAND data plus a 1 (green) and 10 (blue) ton-year exposure of a Ge dark matter detector sensitive to both CNS and ES neutrino induced events. The blue long (short) dashed lines correspond to the sensitivity for a 10 ton-year Ge detector with a residual gamma background of $5 (50) evt / ton / year / keVee$ with a 10% uncertainty. The highlighted regions are the favored solutions for the reactor anomaly at the 95% and 99% C.L. [55]. The red contour corresponds to the 99% C.L. constraint and best fit point derived from a global analysis of both neutrino disappearance and appearance data [56]. The dashed grey curves are the projected limit from the SOX experiment [57, 58].
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