Standard Model Tested with Neutrinos

Abstract

The Standard Model (SM) of particle physics effectively explains most observed phenomena, though some anomalies, especially in the neutrino sector, suggest the need for extensions. In this Letter, we perform the first global fit of elastic neutrino-nucleus and neutrino-electron scattering data to further test the SM within a consistent framework. Our results on the neutrino charge radius, the only nonzero electromagnetic property of neutrinos in the SM, show no significant deviation, indicating no large beyond the SM flavor-dependent effects for electron and muon neutrinos. By incorporating solar neutrino data from dark matter direct detection experiments, we also place the most stringent constraints on the tau neutrino charge radius obtained from neutrino scattering experiments. Additionally, we determine updated constraints on the vector and axial-vector neutrino-electron neutral current couplings, adjusting for flavor-dependent effects and for the different experimental momentum transfers. The global analysis reveals two allowed solutions: one close to the SM prediction, and a degenerate solution that is favored. We show that future dark matter detectors could achieve sufficient precision to resolve the degeneracy. As we move toward the precision era, this Letter demonstrates the crucial need to properly account for flavor- and momentum-dependent effects to avoid misinterpretations of the data.

Figures (3)

• Figure 1: Left: contours at 90% CL for 2 degrees of freedom ($\Delta\chi^2\simeq4.61$) obtained from the analysis of $\nu$ES data from TEXONO TEXONO:2009knm, LSND LSND:2001akn, LAMPF Allen:1992qe, CHARM-II CHARM-II:1994dzwCHARM-II:1994aeb, BNL-E734 Ahrens:1990fp, and CCFR CCFR:1997zzq along with the constraints obtained by combining the available CE$\nu$NS data AtzoriCorona:2025ygnAtzoriCorona:2024rtv with the addition of $\nu$GEN data nuGeN:2025mla, and their combination (green contour). The red cross indicates the SM value of the NCRs. Right: the same constraints shown around the SM prediction and at different CLs. The dashed vertical band indicates the combined $\nu_e-e$ and $\overline{\nu}_e-e$ result, while the horizontal one the combined $\nu_\mu-e$ and $\overline{\nu}_\mu-e$ one at 1$\sigma$ CL for 2 degrees of freedom ($\Delta\chi^2\simeq2.30$).
• Figure 2: Marginal $\Delta\chi^2$'s obtained from the analysis of direct detection dark matter experiments (DMDDs) DeRomeri:2024iawDeRomeri:2024hvcGiunti:2023yhaAtzoriCorona:2022jeb analyzing the signals due to solar neutrino CE$\nu$NS and $\nu$ES. The solid green curve indicates the result from the global fit.
• Figure 3: Left: constraints at $1\sigma$ CL on the flavor-independent neutral current couplings $\tilde{g}_V^{\nu\,e}(M_Z)$ and the $g_A^{\nu\,e}$ from the different $\nu$ES data along with their combination. The red cross indicates the SM prediction while the green star indicates the best fit. The dark red striped contour shows the potentiality of a future DMDD experiment DARWIN:2020bnc. In the inset, we show an enlargement of the contours around the SM prediction. Right: comparison of the global fit results with the sensitivity from a future DMDD experiment, including (solid) or not (dashed) the correction due to the momentum transfer.