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The MEDEX (Matrix Elements for the Double beta decay EXperiments) conference is dedicated to presenting different methods of nuclear matrix elements (NMEs) calculations in connection with the nuclear double beta decay processes.
Several double beta decay experiments have been collecting data with quantities of enriched isotopes around or above 100 kg, and plans are underway for tonne-scale experiments. These efforts involve various isotopes and utilize a broad array of detection techniques (e.g., KamLAND-Zen, SNO+, EXO-200/nEXO, NEXT, LEGEND (GERDA + Majorana), CUORE, CUPID, SuperNEMO, AMoRE, BINGO, COBRA, etc.). Experiments of this scale place enormous demands on the progress and reliability of nuclear matrix element calculations. Additionally, research in special modes of ββ decay, such as β+β+ or 2νECEC, is becoming increasingly interesting from both experimental and theoretical perspectives (e.g., XENON1T, COBRA, TGV, etc.). Further development of the theory behind these processes is crucial for the continuation of experimental activities in this field.
The extended scope of the MEDEX conference also includes other areas where the same techniques are applied, namely in dark matter detection, rare electroweak decays, and neutrino-nucleus scattering processes.
The MEDEX conference has been organized every second year since 1997 by the Institute of Experimental and Applied Physics, Czech Technical University in Prague (Prague, Czech Republic); the University of La Plata (La Plata, Argentina); and the University of Jyväskylä (Jyväskylä, Finland).
The MEDEX proceedings are published by the American Institute of Physics (AIP) Conference Proceedings.
A new Quantum Field Theory (QFT) formalism for neutrino oscillations in a vacuum is proposed. The neutrino emission and detection are identified with the charged-current vertices of a single second-order Feynman diagram for the underlying process, enclosing neutrino propagation between these two points. The critical point of this approach is the definition of the space-time setup typical for neutrino oscillation experiments, implying macroscopically large but finite volumes of the source and detector separated by a sufficiently large distance, L. The L-dependent master formula for the charged lepton production rate is derived, which provides the QFT basis for analyzing neutrino oscillations. It is demonstrated that our QFT formula coincides with the conventional one under some assumptions for some particular choice of the underlying process. Further, techniques are developed for constructing amplitudes of neutrino-related processes in terms of the neutrino mass matrix, with no reference to the neutrino mixing matrix. The proposed approach extensively uses Frobenius covariants within the framework of Sylvester’s theorem on matrix functions. It is maintained that fitting experimental data in terms of the neutrino mass matrix can provide better statistical accuracy in determining the neutrino mass matrix compared to methods using the neutrino mixing matrix at intermediate stages.
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Recently, sensitive experiments operating in frontier muon facilities like MuSEUM (J‐PARC), Mu-MASS (PSI), etc. provide ultra‐high‐precision measurements for quantum electrodynamics (QED) and non-standard (BSM) physics. Historically, the spectroscopy of conventional atoms played essential role in understanding physics (Lamb shift, bound state QED, etc.). However, the proton finite size prevents testing of QED and BSM physics, while structureless purely leptonic atoms, particularly the Muonium (
In this talk we are presenting and discussing our results for some
Double Charge Exchange (DCX) systems. The calculations are performed for
light and heavy nuclei participant in the reactions. The microscopic structure
( wave functions and energy spectra) of the light nuclei is given in terms of
shell model results. For the heavy mass partners we use the Quasiparticle Ran-
dom Phase Approximation (QRPA). Attention is paid to the explicit equations
which described the transfer of neutrons and protons between projectile and
target nuclei, as well as to the dependence of the currents upon the momentum
transferred between nuclei. The present results are compared with other re-
sults available in the literature and the differences between them are discussed.
The possible relationship between DBD and DCX nuclear matrix elements is
analysed as a function of the momentum.
The Cryogenic Underground Observatory for Rare Events (CUORE) is the first bolometric experiment searching for 0νββ decay that has successfully reached the one-tonne mass scale. The detector, located at the LNGS in Italy, consists of an array of 988 TeO2 crystals arranged in a compact cylindrical structure of 19 towers. CUORE began its first physics data run in 2017 at a base temperature of about 10 mK and has been collecting data continuously since 2019, reaching a TeO2 exposure of 2 tonne-year in spring 2023. This is the largest amount of data ever acquired with a solid state cryogenic detector, which allows for further improvement in the CUORE sensitivity to 0νββ decay in 130Te. In this talk, we will present the new CUORE data release, based on the full available statistics and on new, significant enhancements of the data processing chain and high-level analysis.
In this talk, I will introduce the nEXO experiment, a proposed next-generation search for the neutrinoless double beta decay (0νβꞵ) of 136Xe with a projected half-life sensitivity of 1.35 x 1028 years, nearly two orders of magnitude beyond existing experiments. Building on techniques developed for the successful EXO-200 experiment, the primary detector will be a 5-tonne, monolithic liquid xenon time projection chamber with a source enriched to 90% in 136Xe. I will discuss the science goals of nEXO and describe how the experiment addresses the stringent low-background requirements of next-generation 0νβꞵ searches using a combination of established design choices (driven by EXO-200 experience) and novel readout schemes.
Among the potentially double-beta decay (DBD) active natural isotopes,
The ordinary muon capture (OMC) is a process where a nucleus captures a negative muon from the lowest atomic orbital, the 1s orbital, and modern muon facilities in Japan and Switzerland can produce these muons and shoot them at target atoms. The mass of the captured muon is some 100 MeV, thus introducing momentum exchanges in the range of 100 MeV, in the ballpark of the momentum exchanges involved in the neutrinoless double beta decay (NDBD). In NDBD-minus decaying nuclei the OMC on the NDBD daughter populates the states of the intermediate nucleus of the NDBD, like in the case of 136-Xe NDBD the capture on 136-Ba populates the states of 136-Cs. Both processes, NDBD and OMC, populate intermediate/final states of high excitation energies and high angular momentum. This is how the OMC probes effectively the wave functions of all the intermediate states relevant for the NDBD. Furthermore, the rates of both processes depend strongly on the value of the weak axial coupling,
Ordinary muon capture is a nuclear-weak process in which a negatively charged muon, initially bound on an atomic orbit, is captured by the atomic nucleus, resulting in atomic number reduction by one and emission of a muon neutrino. Thanks to the high momentum transfer involved in the process, it is one of the most promising probes for as yet hypothetical neutrinoless double-beta decay. With the recent renaissance of muon-capture experiments, reliable theory predictions for muon capture are now of paramount importance.
In my talk, I will discuss recent progress in ab initio studies on muon capture on light nuclei, focusing in particular in ab initio no-core shell model studies. Starting from nuclear interactions derived from chiral effective field theory, the computed partial muon-capture rates are found to be in good agreement with available experimental counterparts. This motivates future experimental and theoretical studies in the same mass region.
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We investigate the atomic exchange effect between the final atom's bound electrons and those emitted in the allowed
Double-beta decay of nuclei, especially neutrinoless double-beta decay, is one of the most intriguing topics in nuclear physics. Observing the neutrinoless double-beta decay would mean physics beyond the standard model. In this presentation, I will cover some of the results of the studies of giant resonances in double-beta decay nuclei and the corresponding daughter nuclei. The strength functions for different multipoles have been obtained for all the studied nuclei. From the strength functions, the average energies have been calculated.
Also, I will present preliminary results for the study of nuclear matrix elements and phase space factors for
Predictions of neutrinoless double-beta decay (0nbb) nuclear matrix elements are challenging, and markedly differ from each other when different many-body methods are used. One possible avenue to improve this current status is to use data from other observables related to 0nbb to test the theoretical calculations, and to use correlations of these observables with 0nbb matrix elements to predict them more confidently. In my talk I will present recent work focused on using nuclear spectroscopy data to test calculations and double-gamma and two-neutrino double-beta decays to predict 0nbb nuclear matrix elements.
In addition, I will discuss recent efforts to improve nuclear shell model 0nbb calculations. First, I will present nuclear matrix elements taking into account the recently acknowledged short-range contribution. Second, I will present a novel way to improve shell-model wavefunctions, by incorporating short-range correlations obtained from high-quality ab initio quantum Monte Carlo calculations.
A solid observation of neutrino-less double beta decay (0νDBD) relies on the possibility of operating high-energy resolution detectors with detailed background control. Scintillating cryogenic calorimeters are one of the most promising tools to fulfill the requirements for a next-generation experiment. CUPID-0 has been the first demonstrator of the proposed CUPID experiment based on this experimental technique. The detector, consisting of 24 enriched and 2 natural ZnSe crystals, has been taking data at Laboratori Nazionali del Gran Sasso from March 2017 to December 2018 (Phase I) and from May 2019 to February 2020 (Phase II), for a total exposure of 16.59 kg yr of ZnSe. In this contribution, we present the final results of CUPID-0 phase-I and phase-II combined background model. We identify
with improved precision the background sources in the region of interest for neutrinoless double β-decay, making more solid the foundations for the background budget of the next-generation CUPID
experiment. Relying on the excellent data reconstruction, we measure the two-neutrino double β-decay half-life of
The MAJORANA DEMONSTRATOR recently concluded its search for neutrinoless double-beta decay. The experiment operated an array of up to 40.4 kg of germanium detectors, 27 kg of which were isotopically enriched in
This material is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, the Particle Astrophysics and Nuclear Physics Programs of the National Science Foundation, and the Sanford Underground Research Facility.
We describe the MONUMENT project (Muon Ordinary capture for NUclear Matrix elemENTs calculations) aims to determine ordinary muon capture (OMC) rates, which could help in studying nuclear responses for antineutrinos associated with double beta decays (ββ) and astroneutrino interactions.
The MONUMENT project has conducted a series of meticulous measurements at the PSI muon facility in Switzerland. Utilizing high-precision gamma-spectroscopy with negative slow muons and HPGe detectors, measurements were carried out on solid and are planned to be carried out on gaseous targets. The carefully controlled parameters of the muon beam especialy the beam momentum have enabled measurements on isotopically enriched targets with small masses, enhancing the precision of the study.
OMC presents a valuable supplementary tool for ββ decay matrix element calculations, effectively representing a virtual stage of this decay process. Additionally, the substantial transferred momentum (up to 100 MeV) can excite high-lying level states in intermediate nuclei. This unique feature opens avenues for investigating the details of nuclear structure of the isotopes involved in the ββ decay.
The MONUMENT project's ongoing efforts involve the continuation of these investigations through future experiments. Furthermore, the developed methods will be applied to explore the suppression of Gamow-Teller transitions in nuclei (G_a suppression).
Calculation of the nuclear matrix elements (NMEs) for double-beta decay is of paramount importance for guiding experiments and for analyzing and interpreting the experimental data, especially for the search of the neutrinoless double beta decay mode (0νββ). However, there are currently still large differences between the NME values calculated by different methods, hence a quantification of their uncertainties is very much required. In this paper we propose a statistical analysis of 0νββ NME for the 136Xe isotope, based on the interacting shell model, but using three independent effective Hamiltonians, emphasizing the range of the NMEs' most probable values and its correlations with observables that can be obtained from the existing nuclear data. Consequently, we propose a common probability distribution function for the 0νββ NME, which has a range of (1.55 - 2.65) at 90\% confidence level, with a mean value of 1.99 and a standard deviation of 0.37.
A qualitative difference in the running sum to the nuclear matrix element of the two-neutrino double-
The new particle physics underlying any potential lepton-number-violating signal of neutrinoless double beta decay can be parametrized within the framework of effective field theory in terms of a set of higher-dimensional operators triggering a variety of distinct mechanisms. While it seems to be challenging to unravel the dominant contribution from the observation of this rare nuclear process itself, the (non-)conservation of lepton number can be also tested in a variety of other experiments. Following our recent analysis I will discuss the complementary probes of lepton number violation and their interplay with neutrinoless double beta decay.
Theoretical research is conducted for interesting isotopes using nuclear shell model to predict level schemes, half-lives, and beta spectral shapes. Further studies of these aspects for isotopes of interest shine a light on different phenomena of such as reactor anti-neutrino anomaly in 92Rb, background effects of beta decays such as 214Pb in Dark Matter experiments, and helping Neutrino's mass research with Low-Q beta decay analysis.
The approach used in those different phenomena involves and highlights the necessity for further experimental data of nuclear observables such as half-lives, branching ratios, and beta spectral shape studies for further improving the theoretical predictions due to the uncertainty of the effective gA, beta decay Q-values, mesonic enhancement currents and the small relativistic nuclear matrix element.
We highlight the common features of all the different works mentioned to stress the importance and the interconnectedness of the nuclear physics field both in the Experimental and Theoretical fields.
Coherent elastic neutrino-nucleus scattering (CEνNS) is a weak neutral current process where the neutrino interacts coherently with the nucleus as a whole. It that has been demonstrated to be a powerful tool to investigate nuclear and electroweak physics since its first observation in 2017 at COHERENT exploiting a CsI detector.
In this presentation, I will present the state-of-the-art results on nuclear and electroweak physics obtained with the latest CsI and LAr dataset.
These observations allow us to achieve a precise measurement of the average neutron rms radius of such elements, as well as intriguing determinations of the weak mixing angle at low energy.
We combine the CsI dataset with the atomic parity violation (APV) experimental result on Cs, deriving the most precise measurement of the neutron rms radii of 133Cs and 127I, disentangling the contributions of the two nuclei.
This analysis allows us to also obtain a data-driven APV+COHERENT measurement of the low-energy weak mixing angle with a percent uncertainty, independent of the value of the average neutron rms radius of 133Cs and 127I.
To conclude, prospects for the future will be reviewed, with particular emphasis on the current limiting factors and a list of desiderata to improve these measurements.
Neutrinoless double-beta decay (0
In our talk, we will present the current status of CUPID and outline the forthcoming steps towards the construction of the experiment.
In this presentation, we will report two new studies on the spectral shape: the
The experiment is an array of 20 enriched Li
We will present a study of a CdWO
An experiment to study double beta decay processes in
Experimental studies of nuclear matrix elements for double beta decays are crucial since theoretically evaluated NMEs are very sensitive to the nuclear models and the nuclear parameters used for the calculations. Single and double charge exchange reactions have been used to study experimentally the GT NMEs associated with DBD NMEs. We show in the present work that M1 and E1 gamma transitions from isobaric analogue states excited by charge exchange reactions are used to study axial-vector and vector nuclear matrix elements associated with double beta decays. The effective axial-vector and vector weak couplings are derived experimentally by comparing the observed M1 and EI gamma nuclear matrix elements with the QRPA calculations. Then, these experimental results on the electro-magmetic nuclear matrix elements are well used to help theoretical calculations for the nuclear matrix elements for double beta decays. The gamma transitions are measured in coincidence with the chage exchange reactions. The gamma transition rates are evaluated to show the feasibility of the gamma experiments. It is recently discussed in H. Ejiri, Phys. Rev. C. Letters 108 Lo11302 (2023).
A question of high interest is how to relate double charge exchange (DCE) reactions and double beta decay [1-3]. DCE reaction theory predicts two interfering reaction mechanisms, namely second order Double Single Charge Exchange (DSCE) and first order Meson-Nucleon Majorana DCE (MDCE).
The DSCE mechanism is a distorted wave (DW) two-step reaction wher a reaction amplitude is related to the nuclear matrix elements (NME) of
The MDCE mode is given by a combination of off-shell (
The DCE formalism will be introduced with main focus on the MDCE theory. In closure approximation a striking similarity to the NMEs of
The structureless purely leptonic atoms are ideal for testing quantum electrodynamics (QED) and beyond the Standard Model theories (BSM). In recent years, Muonium (Mu) and Positronium (Ps) are considered prominent examples of leptonic atoms that are thoroughly being investigated towards the above aim. A non-relativistic description of leptonic systems provides a simplified quantum mechanical approach to such systems through the analytic solutions to the Schrödinger equation. Nonetheless, accurate theoretical predictions necessarily require the inclusion of relativistic corrections and fine structure terms in addition to corrections related to new interactions between the leptons of the exotic atoms. To this purpose, the relativistic description of the Dirac equation (which includes the particle’s spin) constitutes a more realistic and optimal approach to the problem. Furthermore, the energy correction terms of the Breit-Darwin type that describe additional interactions between the system's particles are also included in the discussion. One of our main goals in this work is to provide an advanced mathematical formulation of the Dirac equation involving Breit-Darwin terms in order to compute high-accuracy theoretical predictions for (i) the bound states of purely leptonic atoms like the Mu and Ps, (ii) as well as exotic (BSM) processes like the Muonium to anti-Muonium conversion.
In this work, we first formulate the reduced radial Schrödinger equation for a two-leptons system by separating out the center of mass motion. Then, a neural networks technique is, initially, employed to model the numerical solution of the Schrödinger equation written in terms of the relative coordinate r of the two leptons. Next, for the optimization of the defined error function of the concrete leptonic system of Muonium (Mu), the BFGS and the trust-constr methods (as provided from the SciPy submodule optimize) are being utilized. Finally, the numerical solution is compared with the “analytic” wave function provided by the Schrödinger equation, in order to appreciate the confidential level of the designed algorithm. We conclude that our method provides fast and accurate numerical solutions a fact that encourages us to apply the same scheme to solve the corresponding Dirac equations.
We offer a comprehensive investigation of electron capture ratios, spanning a wide range of atomic numbers. Our study utilizes a self-consistent computational method that accounts for essential factors such as electron screening, electron correlations, overlap, and exchange corrections, alongside shake-up and shake-off atomic effects.
To compute the electronic wave functions, we employ the Dirac-Hartree-Fock-Slater method, selected after a systematic comparison of binding energies, atomic relaxation energies, and Coulomb amplitudes against other established methods and experimental data.
A notable aspect of our calculations is the incorporation of an energy balance using atomic masses, enabling us to avoid approximations in determining the electron total binding energy and facilitating a more precise determination of the neutrino energy. This enhancement leads to significantly improved agreement between our predicted capture ratios and experimental observations, particularly for low-energy transitions.
Unlike previous studies that mainly focused on Q value and nuclear level energies, we extend our analysis by including uncertainties in atomic relaxation energies, broadening the assessment of electron capture observable uncertainties.
Detailed results are presented for nuclei of practical significance in both nuclear medicine and exotic physics searches, especially concerning liquid xenon detectors (67 Ga, 111 In, 123 I, 125 I, and 125 Xe).
The AMoRE (Advanced Mo-based Rare process Experiment) aims to study the double beta decay of 100Mo in order to gain insights into neutrino masses using a cryogenic technique. The study of 2vββ decay from 100Mo to an excited state of 100Ru helps us understand nuclear matrix elements and nuclear models as well as search for the bosonic (symmetric) fraction of the neutrino wave function.
The AMoRE-I consists of 18 enriched 100Mo-based scintillating crystal detectors at the Yangyang underground laboratory. Since in the two-neutrino double beta decay to the excited state two gamma and two beta particles are emitted, coincidence event selection using a multiplicity of crystals can reduce the background significantly. For instance, the detection efficiency for the decay of the 0+ excited state signal is approximately 30 times higher than ground state in multiplicity of 2. Additionally, in the signal with a multiplicity of 3, the beta energy distribution can be measured.
The AMoRE-II is under construction at a 1000 m deep Yemi underground laboratory, aiming for a tonne-year exposure of 100Mo. A simulation study for observing the beta energy of the 0+ and verifying events from the decay to the forbidden 2+ excited state has been initiated.
BINGO is a prototype experiment to demonstrate a path towards a nearly background free tonne-scale cryogenic
The ACCESS (Array of Cryogenic Calorimeters to Evaluate Spectral Shapes) project aims to establish a novel detector to perform a precise study of the spectral shape of forbidden β-decays. These strongly suppressed processes can help to clarify the long-standing issue of the axial coupling constant (gA) quenching. Moreover, such rare decays are also a common source of systematic uncertainty in Dark Matter and Neutrinoless Double Beta Decay experiments, where detailed knowledge of the shape of the background spectrum is required. In this talk, we will present a brief review of the ACCESS research program, aiming to study natural (Cd-113 and In-115) and synthetic isotopes (Tc-99), which will be measured with a common experimental technique. The main attention will be dedicated to the current status of the research program and recent promising results achieved for In-115. Using an InI crystal equipped with a small Ge-NTD thermistor an energy resolution of 3.1 keV FWHM at 60 keV and a low-energy threshold of 17 keV were achieved. The physics data acquired over a 300-h-long cryogenic run were analyzed and presented.
The spectrum-shape method has been proposed to determine the effective value of weak coupling constants g
The nuclear matrix element for neutrinoless double beta decay of
An
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We present νDoBe, a Python tool for the computation of neutrinoless double beta decay (0νββ) rates in terms of lepton-number-violating operators in the Standard Model Effective Field Theory (SMEFT). The tool can be used for automated calculations of 0νββ rates, electron spectra and angular correlations for all isotopes of experimental interest, for lepton-number-violating operators up to and including dimension 9.