The Japan Proton Accelerator Research Complex (J-PARC) currently delivers a 1 MW, 3 GeV proton beam to the Materials and Life Science Experimental Facility (MLF). Power is expected to increase to 1.3 MW, driven by the needs of Hyper-Kamiokande. As a result, the MLF presently provides the highest neutron yield of any spallation source, while potentially holding the best current and foreseeable conditions for Coherent Elastic Neutrino-Nucleus Scattering (CE$\textit{ν}$NS) experimentation. We explore this potential, using as examples detector technologies presently funded for construction and under development. We quantify their sensitivity to a rich variety of particle physics scenarios, finding that very-high-statistics CE$\textit{ν}$NS measurements with significant sensitivity to relevant scenarios are feasible at this facility within the next few years.

United States

Spain

J. Collar

Ivan Esteban

J. Gomez-Cadenas

M. Gonzalez–Garcia

L.C. Ji

L. Larizgoitia

C. Lewis

F. Monrabal

China

João Pinheiro.

A. Simón

S. Yoon

Coherent elastic neutrino-nucleus scattering at the Japan Proton Accelerator Research Complex

First results from the JUNO reactor neutrino experiment already determine with world-leading precision the small neutrino squared-mass splitting $$ \Delta {m}_{21}^2 $$ and the mixing angle $\textit{θ}$ . In this article we perform an exploratory study beyond these, taking advantage of the first JUNO data release to discuss its sensitivity to the large squared-mass splitting, $$ \Delta {m}_{3\ell}^2 $$ . When combined with constraints from global oscillation data, this may already contain some information on the neutrino mass ordering. Indeed, we find that the combination of the complementary $$ \Delta {m}_{3\ell}^2 $$ -determinations gives a slight preference for Normal Ordering, with a $\textit{p}$-value for Inverted Ordering of 2%–2.6% (2$\textit{.}$2$\textit{σ}$–2$\textit{.}$3$\textit{σ}$). We study the robustness of this result with respect to potential systematic uncertainties and statistical fluctuations. Taken at face value, a full global analysis of oscillation data including the publicly available JUNO information and data leads to a preference for Normal Ordering with ∆$\textit{χ}$ = 4.6 and 9.4 without and with Super-K and IceCube-24 atmospheric neutrino data, respectively.

M. Gonzalez-Garcia

Michele Maltoni

United Kingdom

Ivan Martinez-Soler

João Pinheiro

Germany

Thomas Schwetz

Lessons from the first JUNO results

We present an updated global analysis of neutrino oscillation data as of September 2024. The parameters $\textit{θ}$ , $\textit{θ}$ , $$ \Delta {m}_{21}^2 $$ , and $$ \mid \Delta {m}_{3\ell}^2\mid $$ ($\textit{ℓ}$ = 1$\textit{,}$ 2) are well-determined with relative precision at 3$\textit{σ}$ of about 13%, 8%, 15%, and 6%, respectively. The third mixing angle $\textit{θ}$ still suffers from the octant ambiguity, with no clear indication of whether it is larger or smaller than 45 . The determination of the leptonic CP phase $\textit{δ}$ depends on the neutrino mass ordering: for normal ordering the global fit is consistent with CP conservation within 1$\textit{σ}$, whereas for inverted ordering CP-violating values of $\textit{δ}$ around 270$\textit{°}$ are favored against CP conservation at more than 3$\textit{.}$6$\textit{σ}$. While the present data has in principle 2$\textit{.}$5–3$\textit{σ}$ sensitivity to the neutrino mass ordering, there are different tendencies in the global data that reduce the discrimination power: T2K and NOvA appearance data individually favor normal ordering, but they are more consistent with each other for inverted ordering. Conversely, the joint determination of $$ \mid \Delta {m}_{3\ell}^2\mid $$ from global disappearance data prefers normal ordering. Altogether, the global fit including long-baseline, reactor and IceCube atmospheric data results into an almost equally good fit for both orderings. Only when the $\textit{χ}$ table for atmospheric neutrino data from Super-Kamiokande is added to our $\textit{χ}$ , the global fit prefers normal ordering with ∆$\textit{χ}$ = 6$\textit{.}$1. We provide also updated ranges and correlations for the effective parameters sensitive to the absolute neutrino mass from $\textit{β}$-decay, neutrinoless double-beta decay, and cosmology.

NuFit-6.0: updated global analysis of three-flavor neutrino oscillations

Neutrinos remain mysterious. As an example, enhanced self-interactions (<math><mi>ν</mi><mi>SI</mi></math>), which would have broad implications, are allowed. At the high neutrino densities within core-collapse supernovae, <math><mi>ν</mi><mi>SI</mi></math> should be important, but robust observables have been lacking. We show that <math><mi>ν</mi><mi>SI</mi></math> make neutrinos form a tightly coupled fluid that expands under relativistic hydrodynamics. The outflow becomes either a burst or a steady-state wind; which occurs here is uncertain. Though the diffusive environment where neutrinos are produced may make a wind more likely, further work is needed to determine when each case is realized. In the burst-outflow case, <math><mi>ν</mi><mi>SI</mi></math> increase the duration of the neutrino signal, and even a simple analysis of SN 1987A data has powerful sensitivity. For the wind-outflow case, we outline several promising ideas that may lead to new observables. Combined, these results are important steps toward solving the 35-year-old puzzle of how <math><mi>ν</mi><mi>SI</mi></math> affect supernovae.

Po-Wen Chang

John F. Beacom

Todd A. Thompson

Christopher M. Hirata

Toward Powerful Probes of Neutrino Self-Interactions in Supernovae

Recently, the ANITA collaboration announced the detection of new, unsettling upgoing Ultra-High-Energy (UHE) events. Understanding their origin is pressing to ensure success of the incoming UHE neutrino program. In this work, we study their internal consistency and the implications of the lack of similar events in IceCube. We introduce a generic, simple parametrization to study the compatibility between these two observatories in Standard Model-like and Beyond Standard Model scenarios: an incoming flux of particles that interact with Earth nucleons with cross section σ, producing particle showers along with long-lived particles that decay with lifetime τ and generate a shower that explains ANITA observations. We find that the ANITA angular distribution imposes significant constraints, and when including null observations from IceCube only τ ~ 10 −3–10 −2 s and σ ~ 10 −33– 10 −32 cm2 can explain the data. This hypothesis is testable with future IceCube data. Finally, we discuss a specific model that can realize this scenario. Our analysis highlights the importance of simultaneous observations by high-energy optical neutrino telescopes and new UHE radio detectors to uncover cosmogenic neutrinos or discover new physics.

Toni Bertólez-Martínez

Carlos Argüelles

Jacobo Lopez-Pavon

Jordi Salvado

IceCube and the origin of ANITA-IV events

The exchange of a pair of neutrinos with Standard Model weak interactions generates a long-range force between fermions. The associated potential is extremely feeble, ∝   <math> <msubsup> <mi>G</mi> <mi>F</mi> <mn>2</mn> </msubsup> <mo>/</mo> <msup> <mi>r</mi> <mn>5</mn> </msup> </math>  $$ {G}_F^2/{r}^5 $$  for massless neutrinos, which renders it far from observable even in the most sensitive experiments testing fifth forces. The presence of a neutrino background has been argued to induce a correction to the neutrino propagator that enhances the potential by orders of magnitude. In this brief note, we point out that such modified propagators are invalid if the background neutrino wavepackets have a finite width. By reevaluating the 2-ν exchange potential in the presence of a neutrino background including finite width effects, we find that the background-induced enhancement is reduced by several orders of magnitude. Unfortunately, this pushes the resulting 2-ν exchange potential away from present and near-future sensitivity of tests of new long-range forces.

Diego Blas

On neutrino-mediated potentials in a neutrino background

The ultrahigh energy range of neutrino physics (above <math><mrow><mo>∼</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>7</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>), as yet devoid of detections, is an open landscape with challenges to be met and discoveries to be made. Neutrino-nucleon cross sections in that range—with center-of-momentum energies <math><msqrt><mi>s</mi></msqrt><mo>≳</mo><mn>4</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math>—are powerful probes of unexplored phenomena. We present a simple and accurate model-independent framework to evaluate how well these cross sections can be measured for an unknown flux and generic detectors. We also demonstrate how to characterize and compare detector sensitivity. We show that cross sections can be measured to <math><msubsup><mo>≃</mo><mrow><mo>−</mo><mn>30</mn></mrow><mrow><mo>+</mo><mn>65</mn></mrow></msubsup><mo>%</mo></math> precision over <math><msqrt><mi>s</mi></msqrt><mo>≃</mo><mn>4</mn><mi>–</mi><mn>140</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> (<math><msub><mi>E</mi><mi>ν</mi></msub><mo>=</mo><msup><mn>10</mn><mn>7</mn></msup><mo>−</mo><msup><mn>10</mn><mn>10</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>) with modest energy and angular resolution and <math><mo>≃</mo><mn>10</mn></math> events per energy decade. Many allowed novel-physics models (extra dimensions, leptoquarks, etc.) produce much larger effects. In the distant future, with <math><mo>≃</mo><mn>100</mn></math> events at the highest energies, the precision would be <math><mo>≃</mo><mn>15</mn><mo>%</mo></math>, probing even QCD saturation effects.

Steven Prohira

Detector requirements for model-independent measurements of ultrahigh energy neutrino cross sections

Coherent elastic neutrino-nucleus scattering was first experimentally established five years ago by the COHERENT experiment using neutrinos from the spallation neutron source at Oak Ridge National Laboratory. The first evidence of observation of coherent elastic neutrino-nucleus scattering with reactor antineutrinos has now been reported by the Dresden-II reactor experiment, using a germanium detector. In this paper, we present constraints on a variety of beyond the Standard Model scenarios using the new Dresden-II data. In particular, we explore the constraints imposed on neutrino non-standard interactions, neutrino magnetic moments, and several models with light scalar or light vector mediators. We also quantify the impact of their combination with COHERENT (CsI and Ar) data. In doing so, we highlight the synergies between spallation neutron source and nuclear reactor experiments regarding beyond the Standard Model searches, as well as the advantages of combining data obtained with different nuclear targets. We also study the possible signal from beyond the Standard Model scenarios due to elastic scattering off electrons (which would pass selection cuts of the COHERENT CsI and the Dresden-II experiments) and find more stringent constraints in certain parts of the parameter space than those obtained considering coherent elastic neutrino-nucleus scattering.

Pilar Coloma

Leire Larizgoitia

Francesc Monrabal

Sergio Palomares-Ruiz

Bounds on new physics with data of the Dresden-II reactor experiment and COHERENT

Do neutrinos have sizable self-interactions? They might. Laboratory constraints are weak, so strong effects are possible in astrophysical environments and the early Universe. Observations with neutrino telescopes can provide an independent probe of neutrino self (“secret”) interactions, as the sources are distant and the cosmic neutrino background intervenes. We define a roadmap for making decisive progress on testing secret neutrino interactions governed by a light mediator. This progress will be enabled by IceCube-Gen2 observations of high-energy astrophysical neutrinos. Critical to this is our comprehensive treatment of the theory, taking into account previously neglected or overly approximated effects, as well as including realistic detection physics. We show that IceCube-Gen2 can realize the full potential of neutrino astronomy for testing neutrino self-interactions, being sensitive to cosmologically relevant interaction models. To facilitate forthcoming studies, we release nusiprop, a code that can also be used to study neutrino self-interactions from a variety of sources.

India

Sujata Pandey

Vedran Brdar

Probing secret interactions of astrophysical neutrinos in the high-statistics era

In this addendum we re-assess the constraints on Non-Standard Interactions (NSI) from the global analysis of neutrino oscillation data after including the new results released since the publication of ref. [1], in particular those presented at the Neutrino2020 conference. The new data considered here includes the total energy spectrum and the day-night asymmetry of the 2970-day SK4 solar neutrino sample [2], as well as the latest results from long-baseline (LBL) experiments T2K [3, 4] and NOvA [5, 6]. In addition, we have updated the reactor experiments Double-Chooz [7, 8] to 1276/587 days of far/near detector data and RENO [9, 10] to 2908 days of exposure.

Addendum to: Updated constraints on non-standard interactions from global analysis of oscillation data