MEDEX'23

Sep 4, 2023, 8:00 AM → Sep 8, 2023, 5:00 PM Europe/Prague

the Great Hall (Café Louvre Gallery)

Osvaldo Civitarese (Department of Physics. University of La Plata.Argentina), Jouni Suhonen (University of Jyväskylä), Ivan Stekl (IEAP CTU in Prague), Rastislav Hodák (Institute of Experimental and Applied Physics, CTU in Prague)

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.

AIP_Conference_Proceedings_License_Agreement.pdf

MEDEX23_2st_Circular.pdf

MEDEX23_Agenda_1.9.2023_final.pdf

MEDEX'23_CP_3138.pdf

MEDEX23_logo.png

Mon, September 4

MEDEX'23 Registration

Conveners: Aneta Homolková (IEAP CTU in Prague), Martina Vanišová (IEAP CTU in Prague)

Opening of the MEDEX’23 conference

Conveners: Osvaldo Civitarese (Department of Physics. University of La Plata.Argentina), Rastislav Hodák (Institute of Experimental and Applied Physics, CTU in Prague), Ivan Stekl (IEAP CTU in Prague), Jouni Suhonen (University of Jyväskylä)

Theory

Convener: Jouni Suhonen (University of Jyväskylä)

1 Novel Aspects of Neutrino oscillations

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.

Speaker: Fedor Šimkovic (Comenius University in Bratislava & IEAP CTU in Prague)

FSimkovic_MEDEX_2023.pdf

10:15 AM Coffee Break

Theory

Convener: Jouni Suhonen (University of Jyväskylä)

2 NME for LR symmetric model

TBA

Speaker: DongLiang Fang (Institute of Modern Physics, Chinese Academy of sciences)

37_Fang_LRNME.pdf

3 Testing QED and BSM theories through advanced solutions of the Dirac-Breit-Darwin equations in exotic leptonic atoms

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 ($\mu^+,e^-$), are thoroughly being investigated towards this aim. Their study allows testing of fundamental physical laws like the lepton number conservation in experiments searching for Muonium to anti-Muonium conversion. In general, the exotic leptonic atoms are ideal for testing QED and BSM theories. Theoretically, their energy levels can be calculated with very high accuracy within the bound state QED since there are no complications due to internal nuclear structure and size. Ground state hyperfine splitting, 1S-2S energy interval, etc., can provide testing of QED theory and determinations of fundamental constants (muon mass $m_\mu$, fine structure constant $\alpha$, etc.). Our main goal in this work is to provide advanced algorithms to test these theories based on accurate numerical solutions of the Dirac-Breit-Darwin equations in leptonic atoms.

Speaker: Theocharis Kosmas (University of Ioannina)

Kosmas_MEDEX_2023.pdf

4 On DCX Nuclear Matrix Elements: Shell Model and QRPA results

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.

Speaker: Osvaldo Civitarese (Dept of Physics. University of La Plata, Argentina and IFLP-CONICET.)

Civitarese_talkmedex.pdf

12:15 PM Lunch

Experiment

Convener: Lorenzo Pagnanini (Gran Sasso Science Institute & INFN - LNGS)

5 Latest results from the CUORE experiment

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.

Speaker: Kenny Vetter (UC Berkeley)

Vetter_Medex23_slides_v6.pdf

6 The nEXO search for neutrinoless double beta decay

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.

Speaker: Brian Lenardo (SLAC)

Lenardo_MEDEX23_nEXO_slides.pdf

7 Search for neutrinoless double beta decay in $^{94,96}$Zr isotopes using Cs$_2$ZrCl$_6$ crystal scintillators.

Among the potentially double-beta decay (DBD) active natural isotopes, $^{96}$Zr is promising because of its high energy transition ($Q_{2\beta}=3.35$ MeV) that helps to overcome issues with background events generated by environmental $\gamma$ radioactivity and internal $\beta$-active nuclides from U/Th decay chains. Moreover the $^{94}$Zr isotope has a lower Q$_{2\beta}$-value (1.14 MeV) than $^{96}$Zr but has a high natural abundance ($\delta \sim 17\%$, instead for $^{96}$Zr $\delta \sim 2.8\%$). An experiment to study DBD processes in $^{94,96}$Zr using two Cs$_2$ZrCl$_6$ (CZC) crystal scintillators (11 g and 24 g) has been performed deep underground in the DAMA/CRYS setup at LNGS. These crystals have been studied in terms of chemical purity and residual radioactive contaminants, scintillation and PSD performances. The low-background measurements over 456.5 days supported their high radiopurity leading to a counting rate of 0.17(kg$\cdot$keV$\cdot$y)$^{-1}$ at the $Q_{2\beta}$ of $^{96}$Zr. Limits on different DBD modes of $^{94,96}$Zr were set at the level T$_{1/2} \sim 10^{17}-10^{20}$ yr (90$\%$ C.L.). Such results could contribute in principle to the estimation of the effective nuclear matrix elements for DBD processes, which can be considered one of the most challenging theoretical problem that would hinder precision studies of $0\nu$-DBD in the case of possible future observations.

Speaker: Alice Leoncini (Università di Roma Tor Vergata)

leoncini_medex23_CZC.pdf

3:15 PM Coffee Break

Round-Table Discussion

Convener: Jouni Suhonen (University of Jyväskylä)

FSimkovic_MEDEX_2023muon.pdf

Tue, September 5

Theory

Convener: Javier Menendez (University of Barcelona)

8 Ordinary muon capture, a perfect probe of the $0\nu\beta\beta$ decay

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, $g_{\rm A}$, the effective values of which are not well known in the NDBD nuclei. This dependence of the OMC on weak couplings adds to its importance as a probe of the NDBD.

Speaker: Jouni Suhonen (University of Jyväskylä)

MEDEX2023-talk.pdf

9 Ab Initio studies on muon capture

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.

Speaker: Lotta Jokiniemi (TRIUMF, University of Barcelona)

Jokiniemi_MEDEX23.pdf

10:15 AM Coffee Break

Theory

Convener: Javier Menendez (University of Barcelona)

10 New results from beta and double-beta decays studies

TBA

Speaker: Sabin Stoica (International Centre for Advanced Training and Research in Physics)

SStoica_MEDEX'23.pptx

11 Atomic exchange correction for allowed $\beta$ decay and $2\nu\beta\beta$ decay

We investigate the atomic exchange effect between the final atom's bound electrons and those emitted in the allowed $\beta$ decay and $2\nu\beta\beta$ decay of the initial nucleus. The electron wave functions are obtained with the Dirac-Hartree-Fock-Slater self-consistent method, and we ensure the orthogonality between the continuum and bound electron states of the final atom by modifying the last iteration of the self-consistent method. We show that orthogonality plays an essential role in calculating the exchange correction. We argue that our findings can solve the mismatch between the predictions and experimental measurements in the low-energy region of the $\beta$ spectrum. First, we calculate the exchange effect for four low-energy $\beta$ transitions recently investigated in the literature. Additionally, we present the observables for the $2\nu\beta\beta$ decay of $^{100}$Mo, including exchange and radiative corrections. Next, we compute the exchange correction for the $\beta$ emitters with $Z$ from $1$ to $102$. From the systematic study, we found that for ultra-low energy, i.e., $5$ eV, the $Z$ dependence of total exchange effect is affected by $s_{1/2}$ and $p_{1/2}$ orbitals closure. Finally, we provide an analytical expression of the exchange correction for each atomic number for easy implementation in experimental investigations.

Speaker: Ovidiu Nitescu (Comenius University)

MEDEX23-Nitescu.pdf

12 On the giant resonances of double-beta decay nuclei and nuclear matrix elements and phase space factors for the double-beta decay of 104Ru

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 $^{104}$Ru. This study is done in collaboration with an experimental group, IGISOL (Ion Guide Isotope Separation On-Line), from the University of Jyväskylä. They have precisely measured the Q-value for the double-beta decay of $^{104}$Ru $\rightarrow$ $^{104}$Pd. This Q-value is used in our calculations for the phase space factors. The half-life estimates for the two neutrino and neutrinoless double-beta decay are also calculated.

Speaker: Elina Kauppinen (University of Jyväskylä)

Kauppinen_MEDEX.pdf

12:15 PM Lunch

Theory

Convener: Léonard Imbert (IJClab / CNRS - Université Paris-Saclay)

13 Shell model neutrinoless double-beta decay matrix elements based on other observables

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.

Speaker: Javier Menendez (University of Barcelona)

menendez_MEDEX.pdf

Experiment

Convener: Léonard Imbert (IJClab / CNRS - Université Paris-Saclay)

14 Final results of the CUPID-0 combined background model

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 $^{82}$Se with unprecedented accuracy.

Speakers: Lorenzo Pagnanini (Gran Sasso Science Institute & INFN - LNGS), Emanuela Celi (GSSI & INFN)

MEDEX23_CUPID0_Pagnanini.pdf

15 Search for Neutrinoless Double Beta Decay with the MAJORANA DEMONSTRATOR

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 $^{76}$Ge and housed inside a compact shield consisting of lead and copper at the Sanford Underground Research Facility (SURF) in Lead, SD. The experiment achieved a world leading energy resolution of 0.12% FWHM at 2039 keV, one of the lowest background rates in the region of the 0νββ Q-value, 15.7 cnts/(FWHM t y), and set a 0νββ half-life limit of T$_{1/2}$ > 8.3×10$^{25}$ yrs based on full exposure, resulting in the effective neutrino mass range of 113 < m$_{\beta \beta}$ < 269 meV. The DEMONSTRATOR continues to run with a single module with natural abundance BEGe detectors for background studies and other physics searches. This talk will present the MJD results on the search for neutrinoless double beta decay as well as the broader underground physics program.

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.

Speaker: David Tedeschi (University of South Carolina)

MJD_Tedeschi_MEDEX_23.pdf

16 Status of MONUMENT project

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).

Speaker: Mark Shirchenko (Joint Institute for Nuclear Research)

Shirchenko_MEDEX23.pptx

3:15 PM Coffee Break

Round-Table Discussion

Convener: Javier Menendez (University of Barcelona)

FSimkovic_MEDEX_2023muon.pdf

Wed, September 6

Theory

Convener: Osvaldo Civitarese (Department of Physics. University of La Plata.Argentina)

17 Shell model neutrinoless double-beta decay NME of $^{136}$Xe within a statistical approach

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.

Speaker: Andrei Neacsu (CIFRA - Magurele)

medex_23_nanadrei_public.pdf

medex_23_nanadrei_public.pptx

meme competition

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18 Cause of discrepancy problem of calculated running sums to nuclear matrix element of two-neutrino double-$\beta$ decay

A qualitative difference in the running sum to the nuclear matrix element of the two-neutrino double-$\beta$ decay of $^{136}$Xe has been found four years ago between QRPA and shell model calculations. The former result has large increase and decrease with respect to the excitation energy of the intermediate state, and the latter one is an almost monotonically and mildly increasing function. My QRPA calculations independent of the above one do not have a remarkable decrease. This discrepancy is a serious problem affecting the reliability of calculations of the neutrinoless double-$\beta$ decay, and the cause was unknown. I perform several relevant test calculations and consider analytically to find the cause, which is found to be in the strength of the attractive interactions. The possible major local decrease in the running sum is also explained analytically. The interactions of my QRPA calculation are appropriate in terms of the strength, thus, the almost monotonic behavior is reasonable.

Speaker: Jun Terasaki (IEAP CTU in Prague)

Terasaki_Sep2023.pptx

10:15 AM Coffee Break

Theory

Convener: Osvaldo Civitarese (Department of Physics. University of La Plata.Argentina)

19 Probing Lepton Number Violation at Low and High Energies

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.

Speaker: Lukas Graf (University of California, Berkeley)

graf-MEDEX-2023.pdf

20 Looking through the beta spectra

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.

Speaker: Marlom Ramalho (Jyväskylän yliopisto)

Medex23_Marlom.pdf

21 Probing nuclear and electroweak physics with coherent elastic neutrino nucleus scattering

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.

Speaker: Mattia Atzori Corona (University of Cagliari; INFN of Cagliari)

CEvNS_MEDEX2023_Mattia_Atzori_Corona.pdf

CEvNS_MEDEX2023_Mattia_Atzori_Corona.pptx

12:15 PM Lunch

Experiment

Convener: Ivan Stekl (IEAP CTU in Prague)

22 The CUPID neutrinoless double beta decay experiment

Neutrinoless double-beta decay (0$\nu\beta\beta$) is a key process to address some of the major outstanding issues in particle physics, such as the lepton number conservation and the Majorana nature of the neutrino. Several efforts have taken place in the last decades in order to reach higher and higher sensitivity on its half-life. The next-generation of experiments aims at covering the Inverted-Ordering region of the neutrino mass spectrum, with sensitivities on the half-lives greater than 10$^{27}$ years. Among the exploited techniques, low-temperature calorimetry has proved to be a very promising one. CUPID (CUORE Upgrade with Particle IDentification) will search for 0$\nu\beta\beta$ decay of $^{100}$Mo and will exploit the existing cryogenic infrastructure as well as the gained experience of CUORE, at the Laboratori Nazionali del Gran Sasso in Italy. Thanks to 1596 scintillating Li$_2$MoO$_4$ crystals, enriched in $^{100}$Mo, coupled to 1710 light detectors CUPID will have a simultaneous readout of heat and light that will allow for particle identification, and thus a powerful alpha background rejection.
In our talk, we will present the current status of CUPID and outline the forthcoming steps towards the construction of the experiment.

Speakers: Pia Loaiza (LAL), The CUPID Collaboration

CUPID_MEDEX.pdf

23 Spectral shape studies of the $^{100}$Mo $2\nu\beta\beta$ decay and the $^{113}$Cd $\beta$ decay

In this presentation, we will report two new studies on the spectral shape: the $2\nu\beta\beta$ decay of the $^{100}$Mo in the CUPID-Mo experiment, and the $^{113}$Cd $\beta$ decay in the framework of the CROSS project. The CUPID-Mo experiment is a demonstrator for the next generation 0νββ experiment CUPID.
The experiment is an array of 20 enriched Li$_2$$^{100}$MoO$_4$ bolometers and 20 Ge light detectors, working at 20 mK. We will present the measurement of $2\nu\beta\beta$ decay half-life of $^{100}$Mo to the ground state of $^{100}$Ru, which is the most precise measurement to date of a $2\nu\beta\beta$ decay rate in $^{100}$Mo. We will also present a measurement of higher-order corrections to the spectral shape which provides complementary nuclear structure information. We will report a novel measurement of the shape factor $\xi_{3,1}$, which is compared to theoretical predictions for different values of the effective axial-vector coupling constant.
We will present a study of a CdWO$_4$ scintillating crystal which allows to extract the $\beta$ decay spectrum of $^{113}$Cd. Within the spectrum-shape method, we performed a fit of the experimental data to extract the $g_A^{\text{eff}}$ and the small relativistic nuclear matrix element. This method allows to fit the spectral shape as well as the half-life.

Speaker: Léonard Imbert (IJClab / CNRS - Université Paris-Saclay)

MEDEX23-1.pdf

24 Low-background experiment to search for double beta decay of $^{106}$Cd with enriched $^{106}$CdWO$_4$ scintillator

An experiment to study double beta decay processes in $^{106}$Cd using a $^{106}$CdWO$_4$ crystal scintillator (mass 215 g) enriched in $^{106}$Cd at 66$\%$ is in progress at the Laboratori Nazionali del Gran Sasso (LNGS), in Italy. Events in the $^{106}$CdWO$_4$ detector are recorded in (anti)coincidences with two large-volume CdWO$_4$ scintillation counters. The design of the detector system, calibration and background measurements, methods and results of data analysis to determine key detector characteristics are described. The experimental data are compared with Monte Carlo simulation results, and a background model is constructed. The radioactive contamination of the setup components is studied. After 3 yr of data taking the experimental sensitivity to $2\beta$ decay processes in $^{106}$Cd is at the level of lim T$_{1/2} \sim 10^{21-22}$ yr.

Speaker: Alice Leoncini (Università di Roma Tor Vergata)

aliceleoncini_medex23.pdf

3:15 PM Coffee Break

Round-Table Discussion

Convener: Osvaldo Civitarese (Department of Physics. University of La Plata.Argentina)

FSimkovic_MEDEX_2023muon.pdf

6:00 PM Social event - Banquet

Thu, September 7

Theory

Convener: Fedor Simkovic (Comenius University and JINR Dubna)

25 Gamma transitions from isobaric analogue states to study nuclear matrix elements for double beta decays

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).

Speaker: Hiroyasu Ejiri (RCNP Osaka University)

MEDEX23Ejiri.pdf

26 Nuclear Matrix Elements from Heavy Ion Double Charge Exchange Reactions

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 $2\nu 2\beta$ decay, albeit defined by meson exchange.

The MDCE mode is given by a combination of off-shell ($\pi^\pm,\pi^\mp$) reactions in the interacting ions by the isovector pion-nucleon T-matrix [3], described by box diagrams and inducing ($p^2n^{-2}$) and ($n^2p^{-2}$) DCE transitions.

The DCE formalism will be introduced with main focus on the MDCE theory. In closure approximation a striking similarity to the NMEs of $0\nu 2\beta$ DBD is found. Physics aspects of DSCE and MDCE processes will be illustrated and compared to data [3-5].

1. H. Lenske et al., Prog. Part. Nucl. Phys., 109:103716, 2019.
2. H. Lenske et al., Phys. Rev., C98:044620, 2018.
3. F. Cappuzzello et al., Prog. Part. Nucl. Phys. 128 (2023) 103999.
4. H. Lenske et al., Universe, 7(4):98, 2021.
5. J. Bellone et al., Phys. Lett. B, 807:135528, 2020.

Speaker: Horst Lenske (Univ. Giessen)

Lenske_MEDEX_2023.pptx

10:15 AM Coffee Break

Theory

Convener: Fedor Simkovic (Comenius University and JINR Dubna)

27 Mathematical formulation of the Dirac, Breit-Darwin equation for purely leptonic atoms

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.

Speaker: Theodora Papavasileiou (Department of Informatics, University of Western Macedonia)

Mathematical formulation of the Dirac, Breit-Darwin.pdf

28 Computational modelling and designing of the advanced DiracBreitDarwinAlgo code

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.

Speaker: Athanasios Gkrepis (Department of Physics, University of Ioannina, Ioannina, Greece)

medex23Gkrepis.pdf

29 Improved calculations for atomic electron capture ratios

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).

Speaker: Vasile-Alin Sevestrean (Centre International de Formation et de Recherche Avancees en Physique)

MEDEX-2023-Sevestrean-Vasile.pdf

12:15 PM Lunch

Experiment

Convener: Pia Loaiza (LAL)

30 A study of 2υββ decay of 100Mo to the excited states of 100Ru at AMoRE

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.

Speaker: Daehoon Ha (Department of Physics, Kyungpook National University)

230907_Medex2023_A study of 2υββ decay of 100Mo to the excited states of 100Ru at AMoRE.pdf

31 BINGO: Investigation of the Majorana nature of neutrinos at the few meV level of the neutrino mass scale

BINGO is a prototype experiment to demonstrate a path towards a nearly background free tonne-scale cryogenic $0\nu\beta\beta$ experiment with O(10000) detectors with the isotopes $^{100}$Mo and $^{130}$Te. The major design aspects to achieve this goal are (1) a novel detector assembly reducing the exposed surface area of un-instrumented (passive) materials in the detector array by more than an order of magnitude, (2) an additional tightly packed array of BGO scintillators that surrounds the detector array and acts as active cryogenic veto system and (3) the use of Neganov-Trofimov-Luke based light detectors that help mitigate the pile-up background for Mo-100 and ensure the alpha-beta discrimination in Te-130. In this talk we will describe the technical design of these concepts for the BINGO demonstrator and recent individual proof-of concept validations of the technologies. We will also provide an initial outlook on the effect of these improvements in a CUORE/CUPID size experiment.

Speaker: Benjamin Schmidt (CEA\IRFU\DPHP)

2023-09_07_Medex_BINGO_BenjaminSchmidt.pdf

32 ACCESS: research program and preliminary results on the spectral shape of In-115

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.

Speaker: Lorenzo Pagnanini (Gran Sasso Science Institute & INFN - LNGS)

MEDEX23_ACCESS_Pagnanini.pdf

3:15 PM Coffee Break

Round-Table Discussion

Convener: Fedor Šimkovic (Comenius University in Bratislava)

FSimkovic_MEDEX_2023muon.pdf

Fri, September 8

Experiment

Convener: Mark Shirchenko (Joint Institute for Nuclear Research)

33 An optimized design of the cryogenic detector for the spectrum shape method to study the 99Tc forbidden β decay

The spectrum-shape method has been proposed to determine the effective value of weak coupling constants g$_V$ (vector part) and g$_A$ (axial-vector part) in forbidden β decays. The nuclear transition from $^{99}$Tc(9/2$^+$) to $^{99}$Ru(5/2 $^+$) is 2$\rm^{nd}$ non-unique forbidden β decay, the shape function strongly depends on the g$_A$ of variant nuclear-model frameworks. The maximum energy (Q value) of $^{99}$Tc β decay is 293.5 keV, making it suitable for deposition in a thin gold foil absorber. The metallic magnetic calorimeter (MMC) is a cryogenic detector used for high energy resolution. The detector’s signal amplitude depends on the heat capacity, which directly influences the energy resolution. To enhance the detection efficiency, a perfect solid angle absorber (4π-absorber) is used to contain the radioactive source. It is manufactured by dropping $^{99}$Tc dissolved in a nitric acid solution onto a gold thin foil. After drying, it is covered with another gold foil (sandwich-like structure) and each layers are welded together. The simulation is conducted for complete absorption of energy of particles prepared with various sizes (1 mm$^2$, 4 mm$^2$) and concentrations (2.5 Bq, 5 Bq). We will present manufacturing details of the source, the setup of detectors, and the preliminary results of the measurements.

Speaker: Jiwan Song (Kyungpook National University (KNU) , Korea Research Institute of Standards and Science (KRISS))

MEDEX2023_jwsong.pdf

34 Electron capture of $^{76}$As

The nuclear matrix element for neutrinoless double beta decay of $^{76}$Ge can be expressed as a sum over all transitions along states of the intermediate nucleus $^{76}$As. The dominant contribution is expected to be the ground state of $^{76}$As. Experimentally the contribution of the $^{76}$As ground state can be investigated via the branching ratios of its $\beta^-$ and electron capture decay branches.
An $^{76}$As sample was produced by (n,$\gamma$) reactions on $^{75}$As using the AKR-2 reactor at TU Dresden. The branching ratio of $^{76}$As decaying to various $^{76}$Ge states by electron capture is measured in a low-background coincident counting setup consisting of a high-purity germanium detector and a silicon drift detector both mounted very close to the As sample. The experimental setup is located in the Felsenkeller shallow underground laboratory in Dresden reducing muon induced backgrounds. An additional passive shielding reduces the $\gamma$-induced background. Details of the experimental setup will be introduced.

Speaker: Hans F. R. Hoffmann (TU Dresden)

2023_MEDEX_Hoffmann.pdf

10:15 AM Coffee Break

Theory

Convener: Mark Shirchenko (Joint Institute for Nuclear Research)

35 Constraints on neutrino self-interactions by supernovae and blazars

TBA

Speaker: Mariia Petropavlova (Institute of Experimental and Applied Physics, Czech Technical University in Prague)

Constraints on the coupling constant.pdf

36 $\nu$DoBe - A Python Tool for Neutrinoless Double Beta Decay

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.

Speaker: Oliver Scholer (Max-Planck Institut für Kernphysik)

MEDEX23_Scholer.pdf

Round-Table Discussion

Convener: Mark Shirchenko (Joint Institute for Nuclear Research)

FSimkovic_MEDEX_2023muon.pdf

12:15 PM Lunch

End of the MEDEX'23 conference