Unambiguously Resolving the Potential Neutrino Magnetic Moment Signal at Large Liquid Scintillator Detectors

Non-vanishing electromagnetic properties of neutrinos have been predicted by many theories beyond the Standard Model, and an enhanced neutrino magnetic moment can have profound implications for fundamental physics. The XENON1T experiment recently detected an excess of electron recoil events in the 1–7 keV energy range, which can be compatible with solar neutrino magnetic moment interaction at a most probable value of μν = 2.1 × 10−11 μ B. However, tritium backgrounds or solar axion interaction in this energy window are equally plausible causes. Upcoming multi-tonne noble liquid detectors will test these scenarios more in depth, but will continue to face similar ambiguity. We report a unique capability of future large liquid scintillator detectors to help resolve the potential neutrino magnetic moment scenario. With O(100) kton⋅year exposure of liquid scintillator to solar neutrinos, a sensitivity of μν < 10−11 μ B can be reached at an energy threshold greater than 40 keV, where no tritium or solar axion events but only neutrino magnetic moment signal is still present.

Deuteron disintegration by reactor antineutrinos

The existence of a new interaction involving the electron neutrino and the nucleons, which has received a convincing confirmation through a good agreement between the theoretical and experimental results concerning all observable processes with solar neutrinos, should also inevitably manifest itself in the deuteron disintegration by the neutral currents of reactor antineutrinos. The special attention is drawn to the problem of finding the neutron registration efficiency, discussed in the preparation of the experiment at the Sudbury Neutrino Observatory and in a number of special studies. Lessons are noted that can be learned from three long-standing experiments on the deuteron disintegration by reactor neutrinos.

Confirming $$U(1)_{L_\mu -L_{\tau }}$$ as a solution for $$(g-2)_\mu $$ with neutrinos

The recent measurement of the muon anomalous magnetic moment by the Fermilab E989 experiment, when combined with the previous result at BNL, has confirmed the tension with the SM prediction at $$4.2\,\sigma $$ 4.2 σ CL, strengthening the motivation for new physics in the leptonic sector. Among the different particle physics models that could account for such an excess, a gauged $$U(1)_{L_\mu -L_{\tau }}$$ U ( 1 ) L μ - L τ stands out for its simplicity. In this article, we explore how the combination of data from different future probes can help identify the nature of the new physics behind the muon anomalous magnetic moment. In particular, we contrast $$U(1)_{L_\mu -L_{\tau }}$$ U ( 1 ) L μ - L τ with an effective $$U(1)_{L_\mu }$$ U ( 1 ) L μ -type model. We first show that muon fixed target experiments (such as NA64$$\mu $$ μ ) will be able to measure the coupling of the hidden photon to the muon sector in the region compatible with $$(g-2)_\mu $$ ( g - 2 ) μ , and will have some sensitivity to the hidden photon’s mass. We then study how experiments looking for coherent elastic neutrino-nucleus scattering (CE$$\nu $$ ν NS) at spallation sources will provide crucial additional information on the kinetic mixing of the hidden photon. When combined with NA64$$\mu $$ μ results, the exclusion limits (or reconstructed regions) of future CE$$\nu $$ ν NS detectors will also allow for a better measurement of the mediator mass. Finally, the observation of nuclear recoils from solar neutrinos in dark matter direct detection experiments will provide unique information about the coupling of the hidden photon to the tau sector. The signal expected for $$U(1)_{L_\mu -L_{\tau }}$$ U ( 1 ) L μ - L τ is larger than for $$U(1)_{L_\mu }$$ U ( 1 ) L μ with the same kinetic mixing, and future multi-ton liquid xenon proposals (such as DARWIN) have the potential to confirm the former over the latter. We determine the necessary exposure and energy threshold for a potential $$5\,\sigma $$ 5 σ discovery of a $$U(1)_{L_\mu -L_{\tau }}$$ U ( 1 ) L μ - L τ boson, and we conclude that the future DARWIN observatory will be able to carry out this measurement if the experimental threshold is lowered to $$1\,{\mathrm {keV}}_{\mathrm {nr}} $$ 1 keV nr .

Electromagnetic properties of neutrinos from scattering on bound electrons in atom

In this paper, we consider the effects of bound atomic electrons scattered by solar neutrinos due to the electromagnetic properties of neutrinos. This necessitates considering the recoil of atomic nucleus, which should be considered in the momentum conservation, but the effect to the energy conservation is negligible. This effect changes the kinematic behavior of the scattered electron compared to that scattered on free electrons. We apply this effect to the recent XENON1T data, but the bounds obtained from this are not very restrictive. We obtained the bounds: the (transition) magnetic moment [Formula: see text] (times the electron Bohr magneton) and the charge radius [Formula: see text] cm. For a nonvanishing millicharge [Formula: see text], the allowed bound is shown in the [Formula: see text] plane.

Probing neutrino magnetic moment at the Jinping neutrino experiment

Neutrino magnetic moment (νMM) is an important property of massive neutrinos. The recent anomalous excess at few keV electronic recoils observed by the XENON1T collaboration might indicate a ∼ 2.2 × 10−11μB effective neutrino magnetic moment ($$ {\mu}_{\nu}^{\mathrm{eff}} $$ μ ν eff ) from solar neutrinos. Therefore, it is essential to carry out the νMM searches at a different experiment to confirm or exclude such a hypothesis. We study the feasibility of doing νMM measurement with 4 kton fiducial mass at Jinping neutrino experiment (Jinping) using electron recoil data from both natural and artificial neutrino sources. The sensitivity of $$ {\mu}_{\nu}^{\mathrm{eff}} $$ μ ν eff can reach < 1.2 × 10−11μB at 90% C.L. with 10-year data taking of solar neutrinos. Besides the abundance of the intrinsic low energy background 14C and 85Kr in the liquid scintillator, we find the sensitivity to νMM is highly correlated with the systematic uncertainties of pp and 85Kr. Reducing systematic uncertainties (pp and 85Kr) and the intrinsic background (14C and 85Kr) can help to improve sensitivities below these levels and reach the region of astrophysical interest. With a 3 mega-Curie (MCi) artificial neutrino source 51Cr installed at Jinping neutrino detector for 55 days, it could give us a sensitivity to the electron neutrino magnetic moment ($$ {\mu}_{\nu_e} $$ μ ν e ) with < 1.1 × 10−11μB at 90% C.L. . With the combination of those two measurements, the flavor structure of the neutrino magnetic moment can be also probed at Jinping.

The Future of Solar Neutrinos

In this article we review the current state of the field of solar neutrinos, including flavor oscillations, nonstandard effects, solar models, cross section measurements, and the broad experimental program thus motivated and enabled. We describe the historical discoveries that contributed to current knowledge, and define critical open questions to be addressed in the next decade. We discuss standard solar models, including uncertainties and problems related to the solar composition, and review experimental and model solar neutrino fluxes, including future prospects. We review the state of the art of the nuclear reaction data relevant for solar fusion in the proton–proton chain and carbon–nitrogen–oxygen cycle. Finally, we review the current and future experimental programs that can address outstanding questions in this field. Expected final online publication date for the Annual Review of Nuclear and Particle Science, Volume 71 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Borexino Results on Neutrinos from the Sun and Earth

Borexino is a 280-ton liquid scintillator detector located at the Laboratori Nazionali del Gran Sasso in Italy. Since the start of its data-taking in May 2007, it has provided several measurements of low-energy neutrinos from various sources. At the base of its success lie unprecedented levels of radio-purity and extensive thermal stabilization, both resulting from a years-long effort of the collaboration. Solar neutrinos, emitted in the Hydrogen-to-Helium fusion in the solar core, are important for the understanding of our star, as well as neutrino properties. Borexino is the only experiment that has performed a complete spectroscopy of the pp chain solar neutrinos (with the exception of the hep neutrinos contributing to the total flux at 10−5 level), through the detection of pp, 7Be, pep, and 8B solar neutrinos and has experimentally confirmed the existence of the CNO fusion cycle in the Sun. Borexino has also detected geoneutrinos, antineutrinos from the decays of long-lived radioactive elements inside the Earth, that can be exploited as a new and unique tool to study our planet. This paper reviews the most recent Borexino results on solar and geoneutrinos, from highlighting the key elements of the analyses up to the discussion and interpretation of the results for neutrino, solar, and geophysics.