Testing the dark side of neutrino oscillations with the solar neutrino fog at Dark Matter experiments

TL;DR

This work investigates how the solar neutrino CEvNS signal, recently observed at DM direct-detection experiments, can test the LMA-Dark neutrino oscillation degeneracy tied to new vector-like interactions with matter. By computing flavor-dependent CEvNS rates for $^8$B solar neutrinos and incorporating light mediator NSI, the authors map current XENONnT and PandaX-4T constraints in the muon/tau sector and project future sensitivities under idealized and realistic exposure scenarios. They find that present data do not fully exclude LMA-Dark with equal muon and tau couplings, but planned exposures at multi-ten-ton years could rule it out at $3$–$5\sigma$, while also showing how such detectors can distinguish muon vs tau couplings. The electron-neutrino sector remains testable via reactor CEvNS experiments, with Dresden-II already excluding significant regions and future xenon or argon detectors offering complementary coverage. Overall, DM detectors hosting solar CEvNS measurements provide a powerful, flavor-sensitive probe of NSI that can demarcate LMA-Dark parameter space and inform the neutrino mass ordering question.

Abstract

The recent detection of the solar neutrino background at Dark Matter direct detection experiments paves the way to fully explore an important degeneracy in neutrino oscillations in the presence of new interactions, named the LMA-Dark degeneracy. This degeneracy makes it impossible to determine the neutrino mass ordering in oscillation experiments if neutrinos have new vectorial interactions with matter. As the composition of solar neutrinos at the Earth consists of all three neutrino flavors, testing the presence of new neutrino interactions in the muon and tau neutrino sector in scatterings can fully probe the LMA-Dark region for the first time. In this paper we show that current data from XENONnT and PandaX-4T does not yet exclude the LMA-Dark region with equal couplings of a new mediator to muon and tau neutrinos and quarks, and we identify the possible experimental scenarios to do so in the future. We also show that Dark Matter experiments can distinguish new interactions in the muon or tau sector only from new interactions affecting both sectors.

Figures (7)

• Figure 1: Solar neutrino survival and transition probability for each neutrino flavor calculated using the PEANUTS code PEANUTS, and flux of solar $^8$B neutrinos 8BSpectrumShape8BFluxNormalizationbahcall_b8_spectrum (thick line). For concreteness we have used as input parameters $\sin\theta_{12}=0.55$, $\sin\theta_{13}=0.15$, $\sin^2\theta_{23}=0.50$, and $\cos \delta=0$ leading to identical probabilities $P_{e\mu}$ and $P_{e\tau}$ shown in dashed.
• Figure 2: Constraints on the coupling strength of a new light mediator with mass $m_{Z'}$ to quarks and muon and tau neutrinos $\sqrt{g_\nu g_q}$ at 3$\sigma$ C.L. for 2 d.o.f. from the XENONnT and PandaX-4T data XENON:2024ijkPandaX:2024muv. We assume equal couplings to muon and tau neutrinos and equal couplings to up and down quarks. The grey band corresponds to the LMA-Dark region from oscillation data from Esteban:2018ppq drawn at $3\sigma$ for 1 d.o.f. The region to the left is excluded from cosmology at $2\sigma$ (1 d.o.f.) Sabti:2021reh. The green dashed line corresponds to the required exposure of 125 t-yr exposure Xe experiments assuming all other experimental characteristics are similar to PandaX-4T. The solid blue lines show the expected sensitivity of an ideal xenon experiment without background and 100% signal efficiency with an exposure of 40 t-yr and 200 t-yr.
• Figure 3: Required systematic uncertainties on signal $\sigma_\alpha$ and background $\sigma_\beta$ to rule out the LMA-Dark point with $m_{Z'}=3$ MeV and $\sqrt{g_\nu g_q}=10^{-5}$ at 3$\sigma$ (1 d.o.f.) as a function of exposure. Current experiments have $\sigma_\alpha\approx0.2$ and $\sigma_\beta\approx 0.2$. We assume either the current background or a reduced background of 20% or 50%. The current exposures are 3.51 t-yr for XENONnT and 1.04 t-yr for PandaX-4T. See fig. \ref{['fig:5sigbenchmark']} for the results to rule out LMA-Dark at $5\sigma$.
• Figure 4: Allowed regions at 3$\sigma$ (1 d.o.f.) from the XENONnT and PandaX-4T data XENON:2024ijkPandaX:2024muv for a light mediator with $m_{Z'}=3$ MeV with equal couplings to muon and tau neutrinos as a function of its coupling to up-and down quarks at a momentum transfer of 10 MeV. We also show the expected constraints from a future xenon experiment with 200 t-yr exposure. We also show the LMA and LMA-Dark region using the matter densities of the Earth and the Sun. These lines intersect at the stars which means that no oscillation probe can distinguish these cases.
• Figure 5: Distinction power of a PandaX-4T-like experiment between the LMA-Dark scenario and a model where a new mediator couples with a LMA-Dark-like-strength to only muon or only tau neutrinos. Since we assumed $\sin^2\theta_{23}=0.50$ and $\cos\delta=0$ the transition probabilities $P_{e\mu}$ and $P_{e\tau}$ are identical and the results for a mediator coupling either only to muon neutrinos or only tau neutrinos are the same. The solid lines show the result using current PandaX-4T data, while the dashed lines assume an increased exposure of 50 t-yr.