Erice: INTERNATIONAL SCHOOL OF NUCLEAR PHYSICS, 47th COURSE

Neutrino mixing, arising from the misalignment between flavor and mass eigenstates, leads to oscillations that firmly establish nonzero neutrino masses and physics beyond the minimal Standard Model. This talk provides an overview of the three-flavor mixing framework, parameterized by three mixing angles, two mass-squared differences, and a CP-violating phase. I will summarize the current global constraints from solar, atmospheric, reactor, and accelerator neutrino data, and highlight key open questions, including the neutrino mass ordering, the size of leptonic CP violation, and the possible existence of new physics beyond the Standard Model that next-generation experiments aim to address.

In this talk I will review the most prominent anomalous results in neutrino oscillation experiments, which may be interpreted as hints towards the existence of extra sterile neutrino states beyond the three known active ones. After discussing the individual findings, we will put emphasis on the synergies between different classes of experiments, showing how the interplay among solar, atmospheric, reactor and accelerator data pose challenges to a common interpretation of all data under the sterile neutrino paradigm.

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The neutrino mass is one of the outstanding problems in particle physics and cosmology. Lower limits obtained from neutrino oscillations are in tension with upper limits derived from cosmological measurements. Direct kinematic measurements provide the most promising avenue to determine the absolute neutrino mass scale. KATRIN has finished data taking, and the new technologies necessary for the next-generation neutrino mass experiment are currently being developed and prototyped. I will discuss the various concepts that are being explored for a future neutrino mass experiment.

The PTOLEMY project exploits the innovative concept of the transverse drift filter, in which the synergic action of on uniform magnetic field and electric one play a key role. This is used to achieve a controlled reduction of the kinetic energy of electrons within a one-meter transport length. Before implementing this approach in the PTOLEMY demonstrator, a proof-of-principle test will be carried out. To this aim, a cylindrical Halbach permanent magnet — capable of generating a 1 T dipolar magnetic field orthogonal to the cylinder axis inside the hollow — can be employed together with an electron gun as the particle source. The design of the experimental setup and dedicated simulations are presented in this talk.

The determination of the absolute neutrino mass scale remains one of the most pressing open challenges in modern physics. Although the Standard Model assumes massless neutrinos, flavor oscillations unequivocally prove the existence of massive, non-degenerate eigenstates. State-of-the-art experiments like KATRIN are currently pushing the sensitivity limits of tritium $\beta$-decay spectroscopy, while upcoming projects such as PTOLEMY aim to further expand this frontier, including the long-term goal of detecting the Cosmic Neutrino Background. The method relies on the analysis of the kinematic distortion at the endpoint of the energy spectrum; however, the extreme statistical and systematic precision required by these measurements makes standard theoretical approximations insufficient.The present work focuses on the rigorous advancement of the formalism for describing the $\beta$ spectrum. Starting from the $V-A$ theory of the weak interaction, the study extends the treatment into a complete Quantum Field Theory (QFT) framework. This approach allows the calculation of the decay rate by overcoming the traditional factorization approximation of the leptonic wave functions and exactly integrating the solutions of the Dirac equation. Particular attention will be devoted to the evaluation of radiative and nuclear corrections within this new framework.While this theoretical framework has already proven its validity in low-energy neutrino physics—offering, for instance, an interpretation for the so-called "gallium anomaly" [1] through the redetermination of absorption rates—the talk will specifically focus on the application of this formalism to tritium decay. It will be shown how theoretical control at the QFT level is essential to extract the neutrino mass parameter by minimizing theoretical systematics at the kinematic endpoints.

Neutrinos in dense astrophysical environments play an important role in shaping the dynamics and nucleosynthesis of systems such as core-collapse supernovae and binary neutron star mergers. We have recently investigated collective neutrino-antineutrino pairing phenomena within an extended mean-field framework that incorporates neutrino-antineutrino pairing correlations [1]. Unlike conventional studies focusing on flavor conversion, our analysis emphasizes pairing conversion driven by collective pairing instabilities. Using toy models with discretized momentum modes, we study the conditions under which collective pairing conversions can occur in anisotropic neutrino media. We find that pairing instabilities emerge when the excessive pair-occupation number—defined as the sum of neutrino and antineutrino occupation numbers minus unity—changes sign across momentum space. In single-energy systems, the instability can trigger significant collective pairing conversions between different momentum modes. However, in multi-energy configurations, the overall amount of collective pairing conversions are generally suppressed because the instability only develops in limited energy bins and cannot coherently involve the entire neutrino ensemble. Our results motivate further studies to assess the relevance of neutrino-antineutrino pairing effects in realistic astrophysical and cosmological environments.
[1] S.-J. Huang, M.-R. Wu, arXiv:2604.25687.

While most research on sterile neutrinos focuses on the sub-eV mass scale associated with the surprising oscillation effects at a scale of L/GeV ~ 1 m/eV, this master’s research project aims to explore an alternative and far less investigated scenario: that of superlight sterile neutrinos (sub-meV scale).
This scenario becomes particularly relevant with the advent of next-generation long-baseline experiments, especially JUNO (Jiangmen Underground Neutrino Observatory). The remarkable precision expected from JUNO provides a unique opportunity to probe subtle deviations in the electron antineutrino disappearance channel, making it possible either to place strong constraints on or to uncover signatures of new neutrino families.
The main goal of this work is therefore to carry out a detailed investigation of the sensitivity and exclusion limits associated with the superlight sterile neutrino scenario (with masses in the sub-meV range well below 1 eV^2), using the experimental framework and infrastructure of JUNO, while updating current constraints based on the accumulated data from the former KamLand experiment.

Abstract: Lepton number violation (LNV) as underlying neutrinoless nuclear double beta decay (DBD) and equal-charged lepton pair plus di-jet production in ultra-relativistic hadron collisions are expected to deliver the heavily searched on signatures for physics beyond the standard model (BSM). Direct probes for LNV are lepton DCE (LDCE) reactions at accelerators, apparently and surprisingly never considered before. Theoretical concepts are discussed, merging into a second order approach. As a first application. total cross sections of $\Delta L=+2$ (e-,e+) reactions on nuclear targets are estimated [1,2]. At beam energies beyond 10 GeV, cross sections of magnitudes are predicted which might be
measurable at existing facilities.
1. H. Lenske et al., Lepton Double Charge Exchange Reactions as Probes for Lepton Number Violation, PRL (in print), e-Print: 2603.21997 [nucl-th]
2. H. Lenske, Reaction Studies of Lepton Number Violation, Nuovo Cimento (in print), e-Print:2603.21903 [nucl-

Relativistic energy density functionals provide a universal self-consistent description of nuclear ground states across the nuclear chart. The resulting ground states can be to obtain the excited states of the nucleus. These excited states play a major role in determining the cross sections of low-energy neutrino-nucleus interactions. The interaction is described by a charged-current weak Hamiltonian, whose nuclear transition matrix elements determine the nuclear response. In this work, we use the relativistic quasiparticle random-phase approximation to obtain the excited states and use them to calculate the charge-exchange neutrino-nucleus cross sections for nuclei relevant to astrophysical processes and neutrino detection.

We investigate the late-time accelerated expansion of the Universe within the framework of power law f(Q) gravity, adopting a logarithmic parametrization of dark energy. This approach enables a smooth evolution of the equation of state across different redshifts. The model parameters are constrained using a Markov Chain Monte Carlo (MCMC) analysis based on recent observational data, including the Pantheon+ Type Ia supernovae sample, DESI DR2 Baryon Acoustic Oscillations, and Cosmic Chronometers. We also compare our results with the standard ΛCDM model using statistical criteria. Our findings indicate that this model offers a viable and flexible alternative to standard dark energy scenarios, exhibiting a richer dynamical behavior at low redshifts.

We discuss the effect of multiple mediators influencing the scattering of astrophysical neutrinos at the ultra-high energies — 100 TeV and beyond — against relic neutrinos from the Cosmic neutrino background, demonstrating unique features in the resulting spectral shape as detected at neutrino telescopes like IceCube. We specifically discuss the effect of superposition of scattering amplitudes involving interactions mediated by bosons of close but distinct masses and the importance of considering off-resonant T/U channel scattering in scenarios like these, in addition to the resonant S channels. As an example, we consider the case of L_μ – L_τ symmetry in a KK extra-dimensional scenario, leading to the existence of a tower of multiple vector bosons capable of mediating such neutrino self interactions. We show that in this specific case, the features in the flux spectrum, especially at the higher energies of the astrophysical neutrino spectrum, would be clearly distinctive from that expected in standard model scenarios.

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Although heavy elements like gold and platinum are known to form through the rapid neutron capture process (r-process), their exact cosmic origins remain uncertain. Neutron star mergers account for some r-process production, but a substantial second component may come from other environments, such as magnetorotational supernovae. I will discuss a few key open questions surrounding the r-process, including the influence of neutrinos, neutron capture physics, and observational prospects with gamma-ray satellites.

Scaling Cyclotron Radiation Emission Spectroscopy(CRES) to large volumes in the Project 8 neutrino mass experiment

Abstract

Project 8 is a next-generation experiment aiming to perform a direct measurement of the neutrino mass using the endpoint region of the tritium beta-decay spectrum, with a final target sensitivity of 40 meV. To achieve this goal, Project 8 employs Cyclotron Radiation Emission Spectroscopy (CRES), a technique in which the kinetic energy of beta-decay electrons is reconstructed from the frequency of their cyclotron radiation. After successful proof-of-principle demonstrations of CRES for tritium end point measurements, the next challenge is to scale the technique to much larger source volumes while improving upon the precision of the measured signal.

A promising way to achieve this goal is to use a cylindrical resonant cavity, in which the cyclotron radiation from magnetically trapped electrons is enhanced on-resonance. The Low Frequency Apparatus(LFA) is the bridge between proof-of-principle cavity CRES tests and the future neutrino-mass experiment. It will establish resonant, mode-filtered cavities as cubic-meter CRES detectors compatible with atomic-tritium operations and yield a competitive neutrino-mass upper limit.

In this talk, I will discuss the challenges of scaling CRES to large volumes, focusing on recent progress in multi-mode cavity design.

The multi-staged Project 8 experiment aims for a direct neutrino mass measurement, investigating on the atomic Tritium's beta decay electron energy spectrum. It employs the non-destructive technique of Cyclotron radiation emission spectroscopy (CRES), which measures the electron’s energy from the cyclotron radiation it emits when moving in a magnetic field. While recent measurements have shown that the technique is successful, enhancing the sensitivity down to the final goal of a neutrino mass of <40 meV remains a challenge which will be tackled by moving to a cubic-meter low-frequency cavity readout. This allows for higher statistics and a better reconstruction of the exact electron motion, as well as for an enhancement in the electromagnetic coupling between the emitted radiation and the field.

In this talk, I will describe recent progress on the CRES signal phenomenology and sensitivity in Project 8 and follow up with an overview on the challenges and advances in both topics when moving to the projected big volume cavity stages.

The effective electron neutrino mass can be derived from the analysis of the endpoint region of electron capture spectra, since the finite mass distorts the spectral shape near the Q value. In ECHo the shape of the Ho-163 electron capture spectrum is studied. During the first phase of the ECHo experiment, more than 200 million Ho-163 events were acquired using 2 arrays of metallic magnetic calorimeters enclosing Ho-163. For a reliable analysis of the endpoint region, a precise calibration of the spectrum was obtained by applying a tailored procedure determined in a dedicated calibration measurement. Since theoretical models fail to provide an accurate analytical description of the spectral shape, we have tested two different approaches for the determination of a phenomenological function. The obtained functions were tested for stability of fit in the endpoint region of the acquired Ho-163 spectrum. We present the analysis of the ECHo-1k data leading to the present best limit of 15 eV (90%) credibility interval (18 eV 95% C.I.) and discuss the study of systematic uncertainties.

The analysis of the endpoint region of β-decay or electron capture decay spectra is a model independent method for the determination of the effective electron (anti-)neutrino mass. The ECHo collaboration aims to achieve this goal by building a ‘Large scale Experiment’, named ‘ECHo-LE’, with the objective of attaining — for the first time — sub-eV sensitivity on the effective neutrino mass with a ${}^{163}\textrm{Ho}$ based experiment, by realizing a high energy resolution and high statistics measurement of the electron capture spectrum in ${}^{163}\textrm{Ho}$. This new experiment will operate large metallic magnetic calorimeters enclosing $10$ $\textrm{Bq}$ ${}^{163}\textrm{Ho}$ each. More than 20,000 single pixels will be read out using the Microwave SQUID Multiplexing technique. The goal is to achieve the acquisition of more than $10^{13}$ ${}^{163}\textrm{Ho}$ events with an energy resolution better than $5 ~\textrm{eV}$ (FWHM), with two years of measurement.
We present the results obtained in the ECHo-1k experiment. The present status of the optimization of the hardware for the preparation of ECHo-LE will be summarized and the outlook towards upcoming developments will be discussed.

We model the effects of decoherence induced by quantum gravity phenomenologically using an open quantum system framework. In addition to the three known active neutrinos, we allow for an arbitrary number of dark fermion generations, such as particle dark matter or sterile neutrinos. Assuming that quantum gravity is flavour blind, we expect democratic transition probabilities across all neutrinos and dark fermions with respect to gravitational interactions, thus resulting in an equally distributed final flavour ratio in the high-energy limit. Therefore, the damping of neutrino flavour oscillation probabilities as a function of energy and propagation length encodes information about quantum gravity effects and the number of fermion generations in the dark sector. By analysing the SN1987A data, we obtain bounds on gravitationally induced neutrino quantum decoherence.

The KATRIN experiment aims at a direct kinematic measurement of the absolute neutrino mass with an expected sensitivity below 300 meV (90% CL), achieved through high-resolution, high-statistics spectroscopy of tritium beta decay. To reach this sensitivity, systematic effects that modify the measured electron spectrum must be modeled and controlled via dedicated calibration measurements. One key systematic effect is related to the starting potential of electrons in the gaseous molecular tritium source, which behaves as a cold plasma in a tesla-scale magnetic field. In this talk, after introducing the starting-potential-related effects, we present the analysis of calibration measurements using gaseous krypton-83m. Steps toward a robust source-potential description are discussed and the impact on the neutrino mass analysis is evaluated.
This work is supported by the Helmholtz Association and by the Ministry of Research, Technology and Space BMFTR (grant numbers 05A23PMA, 05A23PX2, 05A23VK2 and 05A23WO6).

Core-collapse supernovae (CCSN) emit neutrinos and antineutrinos of all flavors with distinct luminosities and energy spectra. As neutrinos propagate through the dense and anisotropic stellar interior, their interactions with the surrounding medium introduce several characteristic energy scales -- including neutrino self-interactions, neutrino-electron forward scattering, and vacuum mixing -- which shape their flavor evolution and ultimately determine the flavor-dependent signal observed on Earth. In this talk, I will discuss slow and fast flavor conversion mechanisms and investigate how, under what conditions and to what extent the spatially inhomogeneous neutrino-electron forward scattering influences these flavor conversion processes, CCSN dynamics, and the resulting neutrino signal. I will also present analytical strategies to incorporate these effects into supernova hydrodynamical simulations while maintaining computational efficiency, and explore their signatures using realistic supernova matter profiles at different stages of evolution.

... for your entertainment.

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Neutrino oscillations are a fundamental quantum phenomenon demonstrating that neutrinos have non-zero mass and that the Standard Model in its minimal form must be extended. Their precise measurement plays a central role in particle physics and astroparticle physics, providing unique insight into the properties of neutrinos and their role in the Universe.

The Jiangmen Underground Neutrino Observatory (JUNO) in China, first proposed more than 15 years ago, started taking data in August 2025, only ten years after the start of civil construction. With its 20-kiloton liquid scintillator target, JUNO is the first multi-kiloton liquid scintillator detector designed to combine its large size with unprecedented energy resolution. This unique combination enables the observation of the fine oscillation pattern of reactor antineutrinos, opening a new era of precision neutrino oscillation measurements while providing sensitivity to a broad range of neutrino and astroparticle physics topics.

In this lecture, I will review the physics of reactor neutrino oscillations, the experimental challenges of precision measurements, and the design and performance of the JUNO detector. I will present the latest oscillation results based on 207.2 days of data taking, which establish JUNO as the world's leading experiment for precision measurements of the solar oscillation parameters. I will further discuss the first percent-level measurement of the atmospheric mass-squared splitting, the current sensitivity to the neutrino mass ordering, and the implications of these results for our understanding of neutrino oscillations. Finally, I will present JUNO's broader scientific program, including its first geoneutrino results. Finally, I will provide an overview of JUNO's broader scientific program and present the experiment's first measurement of geoneutrinos.

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The SNO+ experiment is a large multi-purpose neutrino detector, based 2km underground in Sudbury, Canada. A phased approach to its target deployment has allowed for a variety of neutrino physics to be explored, including reactor, geo-, solar, and supernova neutrinos. It also allows for effective background and detector characterisation in preparation for the loading of tellurium into the liquid scintillator target, enabling a search for neutrinoless double beta decay. This talk will give an overview of the detector, major results that have been recently published, and the status of the neutrinoless double beta decay project.

The Jiangmen Underground Neutrino Observatory (JUNO) is a next-generation multipurpose liquid scintillator detector with a 20-kiloton target mass, located in southern China. One of its primary goals is to determine the neutrino mass ordering (NMO) with a significance of at least 3σ by precisely measuring the oscillation pattern of reactor antineutrinos over a 53 km baseline. Beyond reactor neutrinos, JUNO also provides a unique opportunity to study atmospheric neutrinos, which play an important role in enhancing the NMO sensitivity through matter effects. The construction of the detector has been completed, and JUNO has already started physics data taking. Detecting atmospheric neutrinos in a liquid scintillator detector poses several challenges, such as the reconstruction of complex event topologies and the separation of interaction channels. Advanced machine learning methods, in particular deep-learning–based reconstruction techniques, offer promising solutions to address these difficulties. This talk will present recent progress in using such methods to reconstruct the energy and direction of atmospheric neutrino events, as well as their performance in particle identification from Monte Carlo studies, highlighting both the challenges and the advantages of these innovative approaches.

Neutrinos play a major role in the core-collapse supernova mechanism. In the supernova core, the neutrino density is so large, that neutrino self-interaction dominates the flavor evolution with major implications on the supernova mechanism, neutron-star kicks, and the nucleosynthesis of the elements heavier than iron. Our work advances the understanding of flavor conversion in core-collapse supernovae by means of multi-dimensional simulations of the neutrino kinetics. We find a very rich phenomenology, shaped by the streaming of neutrinos and their collisions with the surrounding medium.

Single kaon production in neutrino interactions is a rare process with relevance for both neutrino–nucleus studies and searches for physics beyond the Standard Model. In particular, neutral-current flavor transitions such as $\bar{d} \rightarrow \bar{s}$ are strongly suppressed in the Standard Model, making the reaction $\nu p \rightarrow \nu K^+ n$ a possible probe of non-standard interactions.

Motivated by the recent MicroBooNE measurement of $K^+$ production in charged-current interactions, we have studied Cabbibo-suppressed single-kaon production including so far unaccounted nuclear effects. We analyze the role of this reaction mechanism in the measured signal and compare our results to the GiBUU and GENIE predictions, aiming to understand how strangeness production is implemented in these generators and which channels contribute to the observed $K^+$ events.

We have also extended the model to the neutral-current case, relating the corresponding hadronic matrix elements to the charged-current ones through isospin rotations, and expressing the cross section in terms of an unknown Wilson coefficient for the still poorly constrained axial flavor-changing transition. We investigate if, with the current bounds, neutral current $K^+$ induced by atmospheric neutrinos could coexist with potential signatures of proton decay in the channel $p \rightarrow \bar{\nu} K^+$, searched for at Super-Kamiokande and expected to be further explored at DUNE and Hyper-Kamiokande.

The KArlsruhe TRItium Neutrino (KATRIN) experiment measures the effective electron antineutrino mass by precision spectroscopy of the endpoint region of the kinematic tritium β-decay spectrum. Using a high-luminosity gaseous molecular tritium source with an electrostatic spectrometer with magnetic adiabatic collimation, an upper limit of 0.45 eV/c² (90% C.L.) on the neutrino mass is currently set by KATRIN, using the first 25% of the total dataset. For the upcoming analysis of the final data set, corresponding to 1000 days of data taking and thus strongly enhanced statistics, a very precise knowledge of all systematic effects is essential. The dominant systematic contributions are source-related: The energy loss due to inelastic scatterings in the source and the gas density. This talk focuses on calibration measurements and methods to determine source-related systematic contributions with the monoenergetic angular-selective photoelectron source (arXiv: 2603.15918).

Following the completion of its neutrino mass measurement program at the end of 2025, the KATRIN experiment aims to probe keV-scale sterile neutrinos by analyzing the full tritium beta decay spectrum with a novel detector system, TRISTAN. Leveraging KATRIN's high source activity, this search is sensitive to mixing amplitudes at the parts-per-million level. However, extracting a potential sterile neutrino signature is challenging, as it relies on detailed modeling of the observed tritium spectrum and requires computationally intensive Monte Carlo simulations. To address this challenge, we implement neural simulation-based inference using normalizing flows to approximate the underlying probability density of the physics simulation. We demonstrate that continuous normalizing flows trained via conditional flow-matching enable modeling of experimental spectra and discuss the challenges involved. Furthermore, we cast the signal extraction as a neural ratio estimation problem to infer the sterile-neutrino mixing amplitude directly from the spectrum without an explicit likelihood, complemented by a model-independent cross-check of any candidate signature.

Coherent elastic neutrino–nucleus scattering (CE$\nu$NS) is a Standard Model process in which a neutrino scatters coherently off an entire nucleus, provided that the momentum transfer is sufficiently small compared to the inverse nuclear size. This process serves as a powerful probe of weak interactions, neutron distributions within nuclei, and potential new physics scenarios, including non-standard neutrino interactions, light mediators, and neutrino electromagnetic properties.

The Mitchell Institute Neutrino Experiment at Reactor (MINER) employs 72 g cryogenic sapphire ($\mathrm{Al_2O_3}$) detectors instrumented with phonon sensors and operated at millikelvin temperatures. In a recent search for CE$\nu$NS, MINER observed no statistically significant excess above background, with the measurement sensitivity being primarily limited by reactor-correlated backgrounds. In addition, an excess of low-energy events was observed that could not be fully explained by the simulated background model. This unexplained component constitutes one of the dominant limitations to the sensitivity of the present measurement.

Similar low-energy excesses have been reported in several cryogenic detector experiments. Although their physical origin remains uncertain, common phenomenological features have emerged. The event rate typically rises steeply toward lower energies and often reappears following detector warm-up cycles, subsequently decreasing with detector operation time. Understanding and mitigating this background is therefore crucial for future CE$\nu$NS and rare-event searches employing cryogenic detector technologies.

Within MINER, we investigated this background using deep-learning-based waveform analysis techniques. We identified a characteristic long rise-time feature in the pre-pulse region and developed a classification framework capable of rejecting approximately 50% of the low-energy excess events. The resulting background reduction improves the projected CE$\nu$NS detection sensitivity by about 10%, demonstrating the potential of machine-learning approaches for enhancing the performance of future cryogenic neutrino experiments. The developed methodology is broadly applicable to experiments employing similar cryogenic detector technologies and can be used to mitigate low-energy backgrounds, thereby extending their physics reach. These studies provide new insight into the nature of low-energy backgrounds in cryogenic detectors and represent an important step toward improving the sensitivity of future CE$\nu$NS and other rare-event searches.

The Diffuse Supernova Neutrino Background (DSNB) constitutes a steady and isotropic flux of neutrinos originating from all past core-collapse supernovae across the observable universe. Despite decades of theoretical development and increasingly stringent limits from experiments such as Super-Kamiokande, the DSNB remains undetected. Its eventual observation would provide a unique probe of supernova dynamics and neutrino properties over cosmological distances, while a continued absence of signal may indicate physics beyond the Standard Model.

In this talk, we investigate the impact of secret neutrino interactions ($\nu$SI), or non-standard neutrino self-interactions, on the DSNB flux. Such interactions are well motivated by scenarios of neutrino mass generation, including models with light mediators such as the Majoron, and can be significantly stronger than Standard Model interactions. While laboratory tests of $\nu$SI are challenging due to limited neutrino fluxes, astrophysical environments and long-baseline propagation offer a natural setting to probe these effects.

We focus on the attenuation of DSNB neutrinos due to scattering with the cosmic neutrino background in the presence of $\nu$SI. In particular, we explore the possibility of resonant enhancement in the case where one relic neutrino remains relativistic, leading to distinctive distortions in the DSNB energy spectrum. We present the resulting spectral modifications and assess their detectability at current and upcoming neutrino observatories, including Jiangmen Underground Neutrino Observatory, Hyper-Kamiokande, and Deep Underground Neutrino Experiment. These results demonstrate the potential of DSNB measurements as a sensitive probe of new neutrino interactions beyond the Standard Model.

This talk will summarise the current state of the experimental pursuit for neutrinoless double beta decay.

Atomic nuclei are ideal probes to test fundamental symmetries. For instance, nuclei are used as targets to detect dark matter particles, and electric dipole moments of nuclei can help to unveil why there is more matter than antimatter in the universe.

Nuclear $\beta\beta$ decays also play a paramount role in understanding the nature of neutrinos. If no neutrinos happen to be emitted in the decay, this would immediately imply that the neutrino and the antineutrino are the same particle, as proposed by Ettore Majorana in the early days of quantum field theory. Nonetheless, the rate of the Majorana $\beta\beta$ decays depend on nuclear matrix elements that need to be predicted by nuclear theory, as these decays have not been observed yet experimentally.

In this talk, I will present recent advancements on the calculation of the rates of Majorana $\beta\beta$ decays (or neutrinoless $\beta\beta$ decays) of the nuclei used in current experimental searches. I will emphasize on the estimation of the theoretical uncertainties in the calculations.

In this talk I'll discuss the challenges of building the world's largest water Cherenkov detector and present details of the current status of the Hyper-Kamiokande Experiment, before taking a walk through the project's physics goals.

The unitary Fermi gas is a scale invariant, strongly correlated
non-relativistic fluid. This system can be created in the Lab using
ultra-cold atoms, and it is an important model system for dilute
neutron matter and other strongly correlated fluids. We will
discuss what we can learn about properties of neutron matter
that are of interest to neutrino astrophysics. This includes
the equation of state, the role of short-range correlations,
the neutrino opacity, and the onset of hydrodynamics.

The first detection of supernova burst neutrinos was achieved through the observation
of SN1987A [1], almost four decades ago. However, neutrinos produced during the
burning stages of a massive star prior to core collapse are yet to be detected. In
particular, neutrinos from the silicon core and shell burning phases, with typical
energies of a few MeV [2], may be detectable with current and next generation neutrino
detectors [3]. Integrating pre-supernova models into a neutrino event generator would
help to provide a unified framework for studying this source of neutrinos.

sntools [4] is a neutrino event generator for supernova burst neutrinos, originally
developed to study supernova model discrimination with Hyper-Kamiokande [5]. It
currently supports a range of detector geometries, detection materials, input formats
for neutrino fluxes generated from computer simulations and can use any core collapse
supernova model implemented within the Python package SNEWPY [6]. The output file
produced can be directly fed into detector simulation software to simulate the detector
response to these interactions.

In this talk, I will begin by introducing pre-supernova neutrinos and the importance of
their detection. Following this, I will describe work to add support for pre-supernova
event generation to sntools, emphasizing how time binning can be optimised for a
robust simulation. Finally, I will present the progress I have made towards using sntools
to generate the signal MC for a pre-supernova neutrino sensitivity study for the Hyper
Kamiokande Experiment, outlining the current status and future plans for the work.

[1] K. Hirata et al., “Observation of a neutrino burst from the supernova SN1987a,” Physical Review
Letters, vol. 58, no. 14, pp. 1490–1493, Apr. 6, 1987. doi: 10.1103/PhysRevLett.58.1490.
[2] C. Kato, K. Ishidoshiro, and T. Yoshida, “Theoretical prediction of presupernova neutrinos and their
detection,” Annual Review of Nuclear and Particle Science, vol. 70, pp. 121–145, Volume 70, 2020 Oct. 19,
2020, issn: 0163-8998, 1545-4134. doi: 10.1146/annurev-nucl-040620-021320.
[3] A. Odrzywolek, M. Misiaszek, and M. Kutschera, “Detection possibility of the pair annihilation
neutrinos from the neutrino-cooled pre-supernova star,” Astroparticle Physics, vol. 21, no. 3, pp. 303
313, Jun. 1, 2004, issn: 0927-6505. doi: 10.1016/ j.astropartphys.2004.02.002.
[4] J. Migenda et al., “Sntools: An event generator for supernova burst neutrinos,” Journal of Open Source
Software, vol. 6, no. 60, p. 2877, Apr. 15, 2021, issn: 2475 9066. doi: 10.21105/joss.02877
[5] K. Abe et al., “Supernova model discrimination with hyper-kamiokande,” The Astrophysical Journal,
vol. 916, no. 1, p. 15, Jul. 2021, issn: 0004-637X. doi: 10.3847/1538-4357/abf7c4.
[6] A. Baxter et al., “SNEWPY: A data pipeline from supernova simulations to neutrino signals,” Journal of
Open Source Software, vol. 6, no. 67, p. 3772, Nov. 27, 2021, issn: 2475-9066. doi: 10.21105/joss.03772.

Located at LNGS, LEGEND (Large Enriched Germanium Experiment for Neutrinoless ββ Decay) aims to probe the Majorana nature of the neutrino by observing the neutrinoless double beta (0νββ) decay in high-purity germanium crystals (HPGe) enriched in 76Ge and immersed in an ultra-pure instrumented liquid argon (LAr) volume. The first phase, LEGEND-200, has collected data since spring 2023. Beyond its primary physics goal, the excellent energy resolution (FWHM ∼0.1% at 2 MeV) and ultra-low background achieved by LEGEND enable searches for other rare nuclear processes.
One such process is the neutrinoless double electron capture (0νDEC), a lepton-number-violating process that can occur only if neutrinos are Majorana particles. Searches for the 0νDEC are complementary to the 0νββ study and probe the same fundamental physics.

In this contribution, we present a search for the 0νDEC of 36Ar, a naturally occurring isotope in the LAr volume of LEGEND-200. The signature is a 430 keV γ-ray from the de-excitation of the daughter nucleus 36S, detected by the HPGe array. From the γ-ray mean free path in LAr, we estimate that approximately 24 t of LAr contribute to the observable signal. For the exposure accumulated during the first LEGEND-200 science run, Monte Carlo simulations indicate a detection efficiency ∼1.8 times higher than that achieved by GERDA, the predecessor experiment that first conducted this search.

We are also investigating signal-background discrimination techniques not exploited in GERDA. In particular, the predominantly multi-site topology of the 430 keV γ-ray can be distinguished from the single-site backgrounds arising from 39Ar β decay and 76Ge 2νββ decay. Using the newly developed LEGEND pulse shape simulation framework, we are studying dedicated pulse shape discrimination cuts optimized with machine-learning approaches based on transformer architectures.

In the absence of a signal, thanks to the improved detection efficiency and enhanced background rejection, LEGEND-200 has the potential to extend the current GERDA lower limit of $1.5×10^{22}$ yr (90% C.L.).

A Xenon Electroluminescence (AXEL) detector is a high-pressure xenon gas time projection chamber for searching for neutrinoless double beta decay (0$\nu\beta\beta$), which is a key to solve neutrino mass mechanism and matter-antimatter asymmetry in the universe. For a high-sensitivity 0$\nu\beta\beta$ search, achieving both of backgrounds discrimination and large mass of decay nuclei is essential. To meet these requirements, AXEL detector has a unique ionization-electron detection plane called Electroluminescence Light Collection Cell (ELCC). Since ionization-electrons are detected thorough Electroluminescence process, it can measure the energy with high resolution. Also, due to the rigid cell structure, it enables track pattern recognition and has a scalability to increase the nuclei.
Detector’s performance has been evaluated using 180L-size prototype at 6.8 bar, demonstrating the energy resolution of (0.67$\pm$0.08) % FWHM at 2615 keV. This was achieved with the drift electric field supplied by –34.3 kV generated by a dedicated Cockcroft-Walton (CW) multiplier installed inside the gas vessel. Furthermore, tracks possessing characteristics that enable the discrimination of 0$\nu\beta\beta$ from environmental radiation have been successfully imaged. A machine learning model to do this discrimination has been trained using simulated tracks and achieved 95 % background rejection efficiency with 60 % signal efficiency. Clearer track images have been obtained by the Richardson-Lucy deconvolution method, which would enhance the discrimination power.
Many R&D for the next 1000L-size detector construction is on progress. An ELCC structure with more resistance to creeping discharge is being developed. We use Multi Pixel Photon Counter (MPPC) for the photon detection on ELCC. To enhance the detection efficiency, large sensitive region MPPC was developed. It is confirmed that new MPPC has enough performance, and readout electronics for this MPPC is also under development. To reduce backgrounds contamination and also to lower the manufacturing cost, a field shaper cage made with Flexible Printed circuit (FPC) was assembled. Its voltage endurance and the potential charging-up on its surface are being investigated. CW multiplier update is underway, and generated voltage is up to –76.4 kV in the air. Also, to reduce contamination in capacitors in CW circuits, development of FPC-made capacitors is ongoing. To enhance the position-reconstruction accuracy, a novel scintillation light timing counter is under development to replace the conventional photomultiplier tubes. To improve the understanding of energy resolution, the fluctuation in MPPC non-linearity correction is under study using simulation data. With 1000L-size detector, we will demonstrate AXEL detector’s performance and its excellent sensitivity for 0$\nu\beta\beta$ search.

The Hyper-Kamiokande (Hyper-K) is the third generation of underground water Cherenkov detectors in Japan. It will serve as: (1) the far detector for a long-baseline neutrino oscillation experiment for the upgraded, 1.3 MW power, J-PARC muon neutrino/antineutrino beam, and (2) a detector capable of observing proton decays, atmospheric neutrinos, and neutrinos from astronomical sources. The fiducial region of the Hyper-K detector, with a mass of 186 kton, will be instrumented with 20,000 20-inch photomultipliers (PMTs) and 800 multi-PMT modules, each containing 19 3-inch PMTs. Tests of detector components are underway, and operation is scheduled to begin in 2028. The status of the Hyper-Kamiokande experiment, its broad neutrino physics programme, and its sensitivities to key processes, including CP violation, proton decay, and astrophysical neutrinos, will be presented.

The Hyper-Kamiokande experiment is a future water Cherenkov neutrino experiment located in Japan. It will be an order of magnitude larger than its predecessor Super-Kamiokande, with improved detection technology. The experiment will target a broad physics program, including precisely measuring neutrino oscillation parameters, alongside determining whether charge parity is violated, searches for nucleon decay, and observation of astrophysical signals.
To achieve a detector systematic uncertainty of better than 1%, which is required for the successful completion of these physics goals, a robust and extensive calibration system is included in the detector design. Hosting a wide range of different calibration source technologies, from light injection to radioactive sources, the detector response should be well characterized, leading to decreased systematic uncertainties.
This talk will cover the calibration scheme, including technological details of the detector components, and a description of the analysis methods under development.

A key requirement for realizing the full physics potential of current and future neutrino experiments – including T2K, NOvA, Hyper-Kamiokande, and DUNE with both accelerator-based and atmospheric neutrino measurements – is the reduction of uncertainties in neutrino flux predictions. A major source of these uncertainties comes from the limited understanding of primary and secondary hadron-nucleus interactions within the beamline or the atmosphere. With the goal of measuring these interactions in thin and replica targets, a dedicated program was developed at the NA61/SHINE experiment at CERN. This contribution will present the plans and results for concurrent analyses on the hadron production measurements conducted at NA61/SHINE using thin and replica targets for T2K, the NuMI experiments, and DUNE.

The finite temperature and edge induced effects on the charge and current densities are studied for a massive spinor field localized on a 2D conical space threaded by a magnetic flux. The field operator is constrained on a circular boundary, concentric with the cone apex, by the bag boundary condition and by the condition with the opposite sign in front of the term containing the normal to the edge. In two-dimensional spaces there exist two inequivalent representations of the Clifford algebra and the analysis is presented for both the fields realizing those representations. The circular boundary divides the conical space into two parts, referred as interior (I-) and exterior (E-) regions. The radial current density vanishes. The edge induced contributions in the expectation values of the charge and azimuthal current densities are explicitly separated in the both regions for the general case of the chemical potential. They are periodic functions of the magnetic flux and odd functions under the simultaneous change of the signs of magnetic flux and chemical potential. An important difference from the fermion condensate, considered previously in the literature, is that the mean charge and current densities are finite in the limit when the observation point tends to the boundary. In the E-region all the spinorial modes are regular and the total charge and current densities are continuous functions of the magnetic flux. In the I-region the corresponding expectation values are discontinuous at half-integer values of the ratio of the magnetic flux to the flux quantum. Those discontinuities come from the contribution of the irregular mode in the I-region. 2D fermionic models, symmetric under the parity and time-reversal transformations (in the absence of magnetic fields) combine two spinor fields realizing the inequivalent representations of the Clifford algebra. The total charge and current densities in those models are discussed for different combinations of the boundary conditions for separate fields. Applications are discussed for electronic subsystem in graphitic cones described by the 2D Dirac model. The investigation of conical spaces with circular edges is motivated by their close mathematical relation to spacetime geometries generated by topological defects such as cosmic strings. Such geometries provide a useful framework for studying localized curvature and singularities in general relativity and quantum field theory in curved spacetime. Understanding field propagation and geometric effects in these backgrounds may contribute to broader problems in cosmology, astrophysics, and particle physics, including the behavior of neutrinos and other quantum fields in nontrivial gravitational environments.

Neutrinos propagating in environments with extremely strong magnetic fields can undergo spin and flavour transitions due to their non-zero magnetic moment, a phenomenon commonly referred to as neutrino spin-flavour precession. Such effects are expected to play an important role in dense and magnetized astrophysical settings, including supernovae and pulsars, where magnetic-field-induced transitions may significantly modify neutrino flavour and spin composition. Understanding these processes is therefore essential for accurate modelling of neutrino transport and flavour evolution in astrophysical media.
In the presence of strong magnetic fields, the effective Hamiltonian governing neutrino evolution includes contributions from vacuum flavour mixing, matter-induced interactions, and magnetic-field-driven spin–flavour transitions. In this work, we study the spin–flavour precession of neutrinos using a quantum simulation framework, focusing on a two-flavour neutrino system consisting of electron and muon neutrinos with both left- and right-handed helicity states. The resulting four-dimensional Hilbert space is evolved according to the Schrodinger equation.
We consider an initial left-handed electron neutrino state and encode it onto a two-qubit quantum system. The effective Hamiltonian is diagonalised via a suitable unitary transformation, enabling an efficient implementation of the time-evolution operator within a quantum-circuit model. After transforming the initial state into the Hamiltonian eigenbasis, phase gates corresponding to the eigenvalues are applied to simulate time evolution. The evolved state is subsequently transformed back into the flavour basis, allowing for the extraction of transition probabilities into the remaining spin–flavour states. The simulations are implemented using the Qiskit Aer simulator, and the resulting transition probabilities are systematically compared with analytical theoretical predictions. We find excellent agreement between the simulated and theoretical results, validating the accuracy of the quantum-circuit implementation. These results demonstrate that quantum simulation techniques can reliably reproduce key features of neutrino spin–flavour dynamics in strong magnetic-field environments.
This work provides a proof-of-principle demonstration of encoding neutrino spin–flavour evolution on a quantum platform, capturing essential neutrino-physics effects such as flavour mixing and magnetic-field induced transitions. The framework can be extended to include more realistic matter profiles, time-dependent magnetic fields, and additional neutrino flavours, offering a promising avenue for studying neutrino coherence and flavour evolution under supernova-like conditions relevant to next-generation neutrino observations.