MEDEX'22

Jun 13, 2022, 8:00 AM → Jun 17, 2022, 3:00 PM Europe/Prague

Conference room (Institute of Experimental and Applied Physics, CTU in Prague)

Ivan Stekl (IEAP CTU in Prague), Rastislav Hodák (IEAP CTU in Prague)

MEDEX (Matrix Elements for the Double beta decay EXperiments) conference is dedicated to the presentation of different methods of nuclear matrix elements (NME) calculations in connection with the nuclear double beta decay processes. Several double beta decay experiments have been taking data with quantities of enriched isotopes around or above 100 kg and plans are under way for tonne-scale experiments. These efforts revolve around several isotopes and use a broad array of detection techniques (KamLAND-Zen, SNO+, EXO-200/nEXO, NEXT, LEGEND (GERDA + Majorana), CUORE, CUPID, SuperNEMO, COBRA,...). Experiments of such scale make enormous demands on the progress and reliability of the nuclear matrix elements calculations. Also the research in the field of special modes of ββ, such as β+β+ or 2νECEC starts to be more and more interesting from experimental and theoretical points of view (e.g. COBRA, TGV,...). Further development of the theory of such processes is crucial for continuation of the experimental activities in this field. Extended scope of the MEDEX conference include also other areas where the same sort of techniques are applied, namely: in dark matter detection, rare electroweak decays, and in neutrino-nucleus scattering processes. The MEDEX meeting is organized by the Institute of Experimental and Applied Physics, Czech Technical University in Prague (Czech Republic); by the University of La Plata (La Plata, Argentina) and by the University of Jyväskylä (Jyväskylä, Finland) each second year since 1997.

 

AIP_Conference_Proceedings_LaTeX-template.zip

AIP_Conference_Proceedings_License_Agreement.pdf

MEDEX22_1st_Circular.pdf

MEDEX22_2nd_Circular.pdf

MEDEX22_Agenda_9.6.2022_final.pdf

MEDEX'22.group.photo.png

MEDEX22_logo.png

Monday, June 13

8:30 AM → 9:15 AM MEDEX'22 Registration

Convener: Martina Vanišová (IEAP CTU in Prague)

9:15 AM → 9:30 AM Opening of the MEDEX'22 conference

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

9:30 AM → 10:30 AM Theory

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

9:30 AM Neutrino Properties from Beta and Double Beta Decay

Beta-decay and double-beta-decay experiments measure neutrino masses by using as large a source mass as possible. At present, there are many of these experiments running, notable examples being KATRIN (beta-minus decay of tritium), ECHo (electron capture in holmium) and NEMO (double beta decays of several nuclear species). The first two experiments are clean experiments in the sense that they do not need detailed information on nuclear structure which is hard to get under control. In addition, they exploit the quite small Q value of the decays to enhance the detection sensitivity. Contrary to beta experiments, the third category of experiments, namely double beta experiments, prefer as high a Q value as possible and need knowledge of nuclear structure in the form of nuclear matrix elements (NMEs) in order to unravel the elusive secrets of neutrinos. The talk is aimed at giving some new vistas on beta-decay experiments, like proposals for new low-Q decay candidates. Concerning the double beta experiments, some particular aspects of concern for these experiments and complementary ways to address these concerns by beta spectral analyses and the nuclear muon capture will be discussed.

Speaker: Prof. Jouni Suhonen (University of Jyväskylä)

MEDEX2022.pdf

10:00 AM Exotic Contributions to Two-Neutrino Double Beta Decay

The observation of neutrinoless double beta decay would have far-reaching consequences for particle physics, as it would be a clear manifestation of lepton number violation and it would give a hint on the origin of neutrino masses. While searching for neutrinoless double beta decay, a significant amount of the two-neutrino double beta decay data has been collected by a number of experiments. Although these events are typically regarded and studied as the background of the neutrinoless process, I will show they can be also used to probe physics beyond the Standard Model. Specifically, I will discuss two-neutrino double beta decay contributions induced by right-handed vector currents, sterile neutrinos and neutrino self-interactions.

Speaker: Lukas Graf (Max Planck Institute for Nuclear Physics)

Graf-MEDEX.pdf

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Experiment

Convener: Hiro Ejiri (RCNP Osaka University)

11:00 AM Latest results from EXO-200

EXO-200 is a current generation experiment to search for neutrinoless double beta (0νββ) decay of 136Xe. It was the first of only a few detectors of this scale to run and operated between 2010 and 2018 at the underground Waste Isolation Pilot Plant (WIPP) in southern New Mexico, USA. EXO-200 used 200 kg of 80%-enriched liquid xenon in a single phase, cylindrical time projection chamber (TPC) with scintillator light readout. The experiment set a lower bound on the 0νββ decay of 136Xe of 3.5x10^25 years (90% C.L.), measured the electron spectrum of the 2νββ decay in the same isotope with <3% precision, and searched for the ββ decays of 136Xe to the excited states of 136Ba and of 134Xe. The data collected with EXO-200 have also enabled the search for non-standard physics processes and accurate understanding of the response of large xenon detectors to MeV ionizing radiation. The analysis of EXO-200 data continues past the decommissioning of its hardware. This talk presents an update on searches performed with the so-called Phase-II data set, including a more sensitive search for the 2νββ decay of 136Xe to the first 0+ excited state of 136Ba and the investigation on the existence of exotic dark matter.

Speaker: Andrea Pocar (University of Massachusetts, Amherst)

20220613_Medex-praga-exo200.pdf

11:30 AM Latest results from the CUORE 130Te Double Beta Decay Experiment

The Cryogenic Underground Observatory for Rare Events (CUORE) is the first bolometric experiment searching for 0νββ decay that has been able to reach 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 in April 2021 released its 3rd result of the search for 0νββ, corresponding to a tonne-year of TeO2 exposure. This is the largest amount of data ever acquired with a solid state detector and the most sensitive measurement of 0νββ decay in 130Te ever conducted, with a median exclusion sensitivity of 2.8×10^25 yr. We find no evidence of 0νββ decay and set a lower bound of 2.2 ×10^25 yr at a 90% credibility interval on the 130Te half-life for this process. In this talk, we present the current status of CUORE search for 0νββ with the updated statistics of one tonne-yr. We finally give an update of the CUORE background model and the measurement of the 130Te 2νββ decay half-life, study performed using an exposure of 300.7 kg⋅yr.

Speaker: Miriam Olmi (Laboratori del Gran Sasso)

MEDEX2022_OlmiM_CUORE-v4.pdf

12:00 PM New results on the Ge76 double-beta decay with neutrinos and exotic decay modes from GERDA Phase II

Two-neutrino double beta (2$\nu\beta\beta$) decays are amongst the rarest nuclear processes ever observed. Precision studies of the electron sum energies require ultra-low background and an excellent understanding of the experiment’s response. Both are key features of the Germanium Detector Array (GERDA) experiment, which main goal was to search for neutrino-less double beta (0$\nu\beta\beta$) decay with enriched high purity germanium detectors in Liquid Argon at Laboratori Nazionali del Gran Sasso (LNGS) in Italy. The measurement of the Standard Model 2$\nu\beta\beta$ decay half-life of $^{76}$Ge was performed with unprecedented precision, profiting from the high signal-to-background ratio and the small systematic uncertainties. It provides essential inputs for nuclear structure calculations, that benefit the interpretation of 0$\nu\beta\beta$ decay results. Furthermore, the search for distortions of the 2$\nu\beta\beta$ decay spectrum allows exploring new physics, like 0$\nu\beta\beta$ decay with Majoron emission, Lorentz invariance, or search for sterile neutrinos.
The new results of the $^{76}$Ge 2$\nu\beta\beta$ decay half-life and improved limits on exotic decay modes will be presented in this talk.

Speaker: Elisabetta Bossio

MEDEX22_BossioE.pdf

12:45 PM → 2:15 PM Lunch

2:15 PM → 3:15 PM Experiment

Convener: Hiro Ejiri (RCNP Osaka University)

2:15 PM Search for $\alpha$ and $\beta$ decays of naturally occurring osmium nuclides accompanied by $\gamma$ quanta

A search for $\alpha$ and $\beta\beta$ decays of naturally occurring osmium isotopes to the excited levels of daughter nuclei has been performed using an ultra-low-background broad-energy germanium $\gamma$ detector and an ultrapure osmium sample at the Gran Sasso National Laboratory of the INFN (Italy).

The isotopic composition of the osmium sample has been measured with a high precision using negative thermal ionization mass spectrometry.

During the data taking with the $\gamma$ detector, no effect has been detected, and lower limits of the half-life of $\alpha$ and $\beta\beta$ decays were set at the level of $10^{15}–10^{20}$ yr.
In the case of $\alpha$ decays of $^{184}$Os and $^{186}$Os to the first excited levels of daughter nuclei, the limits substantially exceed the present theoretical estimates of the decays probabilities. This gives hope to the possibility to detect such transitions in the next data taking.

The present talk will describe a review of recent new measurements and new experimental perspectives.

Speaker: Vincenzo Caracciolo

Caracciolo-Os-Medex22.pdf

2:45 PM Study of double beta decay processes in $^{106}$Cd using a $^{106}$CdWO$_4$ crystal scintillator

An experiment to study double-beta decay processes in $^{106}$Cd using a $^{106}$CdWO$_4$ crystal scintillator (mass 215.4 g) enriched in $^{106}$Cd to 66$\%$ is in progress in the DAMA/R&D setup at LNGS. The enriched crystal was placed in a close geometry with two CdWO$_4$ crystal scintillators in order to increase the detection efficiency to $\gamma$'s that can be emitted in the double-beta decay processes in $^{106}$Cd. The data has been accumulated for 467 days considering the coincidence and/or anticoincidence events in the three detectors. No effects have been observed and only lower limits on the half-lives for the double-beta decay processes in $^{106}$Cd have been set. They are at the level of lim T$_{1/2}$$\sim$10$^{20}$-10$^{22}$ years. The limit on the half-life for the $2\nu\varepsilon\beta^+$ in $^{106}$Cd was preliminarily estimated as T$_{1/2}$ $\ge$2.1$\times$10$^{21}$ yr, which approaches the theoretical expectations for this process that are in the range of T$_{1/2}$ = 10$^{21}$-10$^{22}$ yr. Such results could contribute in principle to the estimation of the effective nuclear matrix elements for $2\beta$ decay processes, which can be considered one of the most challenging theoretical problem that hinders precision studies of $0\nu2\beta$ decay in the case of the event of a discovery.

Speaker: Alice Leoncini (Università di Roma Tor Vergata)

aliceleoncini_medex22.pdf

3:15 PM → 3:45 PM Coffee break

3:45 PM → 4:15 PM Theory

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

3:45 PM New results from the double-beta decay study

In my talk I will first give a brief review of the last results in the theoretical study of double-beta decay obtained by our Bucharest group. Next, I will focus on testing the Lorentz invariance violation (LIV) in double beta decay. I will present the calculation of the LIV perturbations in the energy electron spectra and in angular correlation between electrons and show possible experimental LIV signatures. Also, I will propose a new method to constrain the parameter that governs the magnitude of LIV effects by measuring the angular correlation coefficient.

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

SStoica_MEDEX'22.pptx

4:15 PM → 5:15 PM Round-Table Discussion

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

Tuesday, June 14

9:00 AM → 10:30 AM Theory

Convener: Jouni Suhonen (University of Jyväskylä)

9:00 AM The non-observation of $0 \nu \beta \beta$ decay as a tool for dark matter studies

Abstract: Among cold dark-matter candidates are low-mass neutral bosons. The existence of such pseudo-scalar particles has been proposed long ago by Peccei and Quinn to explain the spontaneous breaking of CP in the early Universe. In this talk we discuss a possible mechanism to explain for non-zero neutrino masses, which is based on the treatment of neutrino-axions interactions.From the known limits to the values of the neutrino mass, extracted from the non-observation of the neutrinoless double beta decay, we set relations between the axion-neutrino coupling, the axion mass and the neutrino mass.

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

apendice.pdf

talk(civitarese).pdf

9:30 AM Improvements and constraints on neutrinoless double-beta-decay matrix elements

Reliable nuclear matrix elements play a crucial role in planning future neutrinoless double-beta-decay experiments, and in extracting the exciting new physics from them. Unfortunately, currently the nuclear matrix elements are not well constrained, and different many-body methods notably disagree on the values of them. Another open question is the possible need of quenching the axial-vector coupling constant – which enters the half-life expression of double-beta decay in fourth power.

In my talk, I will tackle these questions by discussing the impact of the recently acknowledged leading-order short-range term and hadronic two-body currents on the nuclear matrix elements of medium-heavy nuclei in pnQRPA framework. Furthermore, I will talk about complementary ways to constrain the nuclear matrix elements by using data on other nuclear observables. Specially, I will present our recent ab initio study on ordinary muon capture and discuss its potential to shed light on the need of quenching of the couplings at high-momentum-exchange regime relevant for neutrinoless double-beta decay.

Speaker: Lotta Jokiniemi (TRIUMF, University of Barcelona)

MEDEX2022_Jokiniemi.pdf

10:00 AM Towards interferometry of neutrino electromagnetism

It is well known that the neutrino medium, such as the cosmic neutrino background, produces a tiny birefringence effect on electromagnetic waves. Recently, it was claimed that this effect may be enhanced by an additional presence of a plasma characterized by the electron plasma frequency. In our work, instead of considering the plasma, we consider a ordinary transparent refractive medium characterized by its index of refraction. To stay general we keep the mutual velocity of the refractive and neutrino media nonzero. For that situation we estimate the strength of the birefringence effect, analyze its dependence on the angle between the velocities of the two media, and compare the obtained results with other cases analyzed previously.

Speaker: Adam Smetana (IEAP CTU in Prague)

Towards Interferometry of Neutrino Electromagnetism_xxx.pdf

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Experiment

Convener: Igor Ostrovskiy (The University of Alabama)

11:00 AM Nuclear matrix elements for double beta decays and spin dipole giant resonances studied by charge-exchange nuclear reactions

Experimental studies of charge-exchange nuclear and leptonic reactions are useful for evaluating nuclear matrix elements (NMEs) for double beta decays (DBDs). The sin-dipole (SD) NME is one of the major components of the DBD NME. The experimental SD giant resonance energy and the SD strength are shown to be closely related with pnQRPA NME. The NME is obtained by using the particle hole interaction derived from the experimental SD giant resonance energy and the quenching coefficient (0.65) for the axial-vector coupling derived from the experimental GT and SD strengths. The NME is given as a smooth function of the mass number A as M ~ 5.2-0.023 A for medium heavy nuclei wit A = 76 - 136, which are of current interest. The quenching is partly due to the delta isobar effect, which is not explicitly included in the pnQRPA. Impact of the NME on future DBD experiment is discussed.

Speaker: Hiro Ejiri (RCNP Osaka University)

Ejiri MEDEX22DBD-SD .pdf

11:30 AM LEGEND: An Overview & the Commissioning Status of LEGEND-200

The discovery that neutrinos are Majorana fermions would have profound implications for particle physics and cosmology. The Majorana character of neutrinos would make neutrinoless double-beta decay, a matter-creating process without the balancing emission of antimatter, possible. The LEGEND Collaboration pursues a phased, ⁷⁶Ge-based double-beta decay experimental program with a discovery potential that covers the inverted hierarchy. The first phase, LEGEND-200,will deploy 200 kg of germanium detectors enriched in ⁷⁶Ge. It will have a discovery potential of 10²⁷ years and a background index of 0.6 cts/(ROI t yr). The second phase, LEGEND-1000, will deploy 1000 kg of enriched germanium and will have a discovery sensitivity beyond 10²⁸ years. Using high-purity materials, sophisticated analysis routines and novel subdetector systems to identify background events, the LEGEND experiment will be virtually background-free in the region of interest. This talk will provide an overview of LEGEND and report on the work currently underway to commission LEGEND-200.

Speaker: Patrick Krause (TUM)

A journey through the LEGEND-200 cryostat [video]

MEDEX22_slides.pdf

12:00 PM Current status and perspectives of the ACCESS project

The ACCESS project (Array of Cryogenic Calorimeters to Evaluate Spectral Shapes) aims to establish a novel technique to perform precision measurements of forbidden beta-decays, whose spectral shape is a crucial benchmark for Nuclear Physics calculations and plays a pivotal role in Astroparticle Physics experiments. ACCESS will operate a pilot array of four tellurium dioxide crystals as cryogenic calorimeters at 10 mK. Three of them will be doped with different beta emitters ($^{99}$Tc, $^{115}$Sm, $^{210}$Pb/$^{210}$Bi), while the last natural one will be used for effective background subtraction. In the intermediate steps of the project also natural crystals such as cadmium tungstate (CdWO${4}$) and indium dioxide (In${2}$O$_{3}$) will be used to investigate the beta decay of $^{113}$Cd and $^{115}$In respectively. In this contribution, we will describe the ACCESS project, summarizing the current status and the future perspectives. Moreover, we will discuss the preliminary results obtained with indium-based crystals.

Speaker: Dounia Helis (Gran Sasso Science Institute and INFN - LNGS)

ACCESS_MEDEX22_Dounia_Helis.pdf

12:45 PM → 2:15 PM Lunch

2:15 PM → 3:15 PM Experiment

Convener: Igor Ostrovskiy (The University of Alabama)

2:15 PM Measurements of two neutrino double beta decay of Mo-100 to the excited states of Ru-100

Molybdenum-100 is one of the popular isotopes used to search for double beta decay and to study nuclear matrix elements. The half-lives of the two neutrino double beta decays of Mo-100 to the various excited states of Ru-100 were investigated with two samples of Mo-100-enriched molybdenum trioxide powders. The measurements were performed using an array of fourteen HPGe detectors, CAGe, located in the 700-m-deep Yangyang underground laboratory, Korea. Each detector element has 70% relative efficiency, and the total crystal volume of CAGe is 4093 cm^3. The mass and assay duration of powder #1 was 14.8 kg and 146 days, and powder #2 was 12.0 kg and 170 days, respectively. The half-life of the two neutrino double beta decay to the second excited state was measured to be similar to the previous experiments performed by other groups. On the other hand, the other excited states were found to have higher limits at 90% C.L. than other groups.

Speaker: Dr Su-yeon Park (Center for Underground Physics, Institute for Basic Science)

20220614_MEDEX_Su-yeon_Park.pdf

2:45 PM The MONUMENT Experiment; Ordinary Muon Capture as a benchmark for 0nßß-decay nuclear structure calculations

Extracting particle physics properties from neutrinoless double-beta (0nßß) decay, requires a detailed understanding of the involved nuclear structures. Still, modern calculations of the corresponding nuclear matrix elements (NMEs) differ by factors 2-3.

The high momentum transfer of Ordinary Muon Capture (OMC) provides insight into highly excited states similar to those that contribute virtually to 0nßß transitions.
The precise study of the gammas following the OMC process, makes this a promising tool to validate NME calculations, and test the quenching of the axial vector coupling g_A.

The MONUMENT collaboration is performing a series of explorative OMC measurements involving typical ßß decay daughter isotopes such as Se76 and Ba136, as well as other benchmark isotopes. In this presentation the experiment carried out at the Paul Scherrer Institute and first results from the beam-time in 2021 will be presented.

This research is supported by the DFG Grant 448829699 and RFBR-DFG with project number 21-52-12040.

Speaker: Mrs Elizabeth Mondragon (Technical University of Munich)

Monument_E-Mondragon.pdf

3:15 PM → 3:45 PM Coffee break

3:45 PM → 5:00 PM Round-Table Discussion

Convener: Jouni Suhonen (University of Jyväskylä)

Wednesday, June 15

9:00 AM → 10:30 AM Theory

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

9:00 AM Novel insights on double-beta decay: role of short-range and nuclear correlations

Reliable nuclear matrix elements for the neutrinoless double-beta decay of Germanium, Molibdenum, Tellurium and Xenon are necessary to determine the physics reach of next generation experiments and to fully exploit their findings. In this talk I will present recent improvements in calculations with the nuclear shell model, one of the leading many-body methods to obtain these nuclear matrix elements. I will make emphasis on the inclusion of short-range correlations based on a comparison with ab initio calculations, and I will introduce the impact of the short-range contribution to the nuclear matrix element, which was only acknowledged recently. I will also discuss the correlation between double-beta decay matrix elements and other nuclear observables which may be easier to measure experimentally.

Speaker: Javier Menendez (University of Barcelona)

menendez_praguePublic.pdf

9:30 AM Finding the Dominant Mechanism Contributing to Neutrinoless Double-Beta Decay

Although the neutrinoless double-beta decay has not been experimentally proven yet, there is work undergoing to improve the theoretical description of the decay.
In this work, we computed the nuclear matrix elements using the shell model techniques and the electron phase-space factors for several nuclei of interest. The latter were computed using three different descriptions for the potential generated by the nucleus and the electronic shells, accounting for finer ingredients like the finite size of the nucleus and the screening effect of the electrons.
Using the above results and the experimental limits for the half-life times, upper bounds for the neutrino mass were obtained. To isolate the dominant mechanism that could possibly drive the neutrinoless double-beta decay, we investigated the ratio of the predicted half-lives, and the shapes of the calculated angular and energy distributions of the emitted electrons.

References
[1] Andrei Neacsu, Vasile Alin Sevestrean and Sabin Stoica, Front. Phys., 21 May (2021)
[2] Sabin Stoica and Mihail Mirea, Front. Phys., 15 February (2019)

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

Sevestrean Vasile Alin MEDEX2022.pdf

10:00 AM Toward reliable neutrinoless ββ-decay nuclear matrix elements: exploring the potential of measuring γγ-transitions in ββ final nuclei

Neutrinoless double beta decay ($0\nu\beta\beta$) is a proposed decay which turns out to be the most promising process to observe lepton number violation in the laboratory, and to establish whether neutrinos are its own antiparticle. Due to this unique potential, a very active experimental program aims to detect this rare decay. In order to plan these searches, reliable estimations for the decay lifetimes, which are known to exceed $10^{26}$ years, are crucial as well as to extract precise new physics parameters or constrains from these experiments. However, nuclear matrix elements (NMEs) are not well known, as state-of-the-art nuclear structure methods disagree in their predictions.

An alternative avenue to learn about $0\nu\beta\beta$ NMEs is to find other observables correlated with $0\nu\beta\beta$ decay that may be easier to access experimentally. In my talk, I will discuss results for double dipole magnetic transitions of the double isobaric analog state, which show a good correlation with $0\nu\beta\beta$ decay. This could be used to constrain $0\nu\beta\beta$ NMEs from measurements of nuclear 2\gamma M1M1 decays.

Speaker: Beatriz Romeo (DIPC)

MEDEX22_beatriz_romeo.pdf

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Experiment

Convener: Andrea Pocar (University of Massachusetts, Amherst)

11:00 AM Measurement of the spectral shapes of the beta decay of 137Xe with EXO-200

The reactor neutrino anomaly and $g_A$ “quenching” in neutrinoless double-β decay are two of the outstanding issues in nuclear physics. Measurement of the first-forbidden nonunique β decay of $^{137}$Xe can provide helpful input to both issues but is difficult to perform accurately. EXO-200 is a low-background neutrinoless double-β decay experiment that used close to 200 kg of $^{136}$Xe as a target. An ultraminiature AmBe neutron source was deployed in EXO-200, which allowed one to accumulate a pure sample of $^{137}$Xe β decays. The spectrum of the decay to the ground state of $^{137}$Cs was measured accurately and found to agree with the theoretical prediction, suggesting that the effects of the first-forbidden β decays lead to mitigation of the reactor anomaly and a possible explanation of the origins of the spectral bump. Extracting an accurate spectrum of the decay to the first excited state of $^{137}$Cs is more difficult and still ongoing, but it is advantageous due to the sensitivity of this mode to the effective value of the $g_A$. This talk presents the result of the first measurement and discusses the current status and outlook of the second one.

Speaker: Igor Ostrovskiy (The University of Alabama)

MEDEX2022_Belov_Ostrovskiy_Xe137.pdf

11:30 AM Spectrum-shape method for the $^{210}$Bi forbidden beta decay study using PbMoO$_4$ cryogenic detectors.

The spectrum-shape method has been proposed to determine the effective value of the axial-vector coupling constant, $g_A$ with the vector coupling constant, $g_v = 1$ in forbidden nonunique $\beta$ decays. $^{210}$Bi nuclear is the isotope of first nonunique forbidden beta decay, the shape function of which strongly depends on the $g_A$.
Due to the short half-life of the $^{210}$Bi, the $^{210}$Pb ($\beta$, 22.3 y) $\rightarrow$ $^{210}$Bi ($\beta$, 5.0 d) $\rightarrow$ 210Po ($\alpha$, 138 d) decay chain has been adopted. PbMoO$_4$ cryogenic detectors have been used for high detection efficiency (source = detector) and high energy resolution. We prepared 2 detectors of same detector geometric design and same crystal size (1 cm$^3$). One PbMoO$_4$ contains a modern lead and the $^{210}$Pb radioactivity was about 30 Bq/kg. The other PbMoO$_4$ crystal contains an archeological lead with low radioactivity of $^{210}$Pb (about 0.2 Bq/kg) and has been used to reject the backgrounds with low systematic error. They were installed next to each other in a cryogen-free dilution refrigerator.
We will present the details of the detectors and properness of the pure beta decay spectrum collected by this detection system.

Speaker: Dr Hyelim Kim (Institute for Basic Science)

202206_MEDEX2022_hlkim_pdf.pdf

12:00 PM Status of nEXO

nEXO is a proposed next-generation liquid xenon experiment to search for neutrino-less double beta decay (0νββ) of $^{136}$Xe. The experiment will use a 5-tonne liquid xenon (LXe) monolithic time projection chamber (TPC) with xenon enriched to 90% the isotope 136. While the nEXO design is validated by EXO-200, the larger detector will employ novel techniques to collect charge and scintillation light, and employ ASIC electronics installed directly in the LXe, only transmitting out digitized signals. Ionization electrons and scintillation photons from energy deposits in the detector will be recorded by a segmented anode and a large area SiPM array.
This talk will present recent progress in the detector design and prototyping, and an improved modelling of the readout system and analysis. New simulations result in a 90% CL 0νββ halflife sensitivity of 1.35×10$^{28}$yrs in 10 years of data taking and a Majorana mass reach that, for most models, entirely covers the inverted hierarchy.

Speaker: Prof. Giorgio Gratta (Stanford University, USA)

nEXO_Gratta_MEDEX2022.pdf

12:45 PM → 2:15 PM Lunch

2:15 PM → 3:15 PM Experiment

Convener: Andrea Pocar (University of Massachusetts, Amherst)

2:15 PM Constraints on partial half-lives of 136Ce and 138Ce double electron captures

The gamma-ray emissions from a radiopure cerium-bromide crystal with a mass of 4381 g were measured for a total of 497.4 d by means of high-resolution gamma-ray spectrometry in the HADES underground laboratory at a depth of 500 m.w.e.
Publikation: Phys. Rev. C 105, 045801 (2022)

Speaker: Kai Zuber (TU Dresden)

Cer-MEDEX.pdf

2:45 PM BINGO: Bi-Isotope 0ν2β Next Generation Observatory

Neutrinoless double-beta decay (0νββ) is a hypothetical rare nuclear transition. Its observation would provide an important insight about the nature of neutrinos (Dirac or Majorana particle) demonstrating that the lepton number is not conserved. BINGO aims to set the technological and conceptual grounds for future bolometric 0νββ experiments. It is based on a dual heat-light readout, i.e. a main absorber embedding the double-beta decay isotope faced by a light detector. Dual heat-light readout helps to reject the α background component, thanks to the lower light output of α’s compared to β/γ’s. BINGO will study two of the most promising isotopes: $^{100}$Mo embedded in Li$_2$MoO$_4$ and $^{130}$Te embedded in TeO$_2$. BINGO’s proposed technology aims at reducing dramatically the background in the region of interest, thus boosting the discovery sensitivity of 0νββ. This can be achieved by fulfilling the following goals: (i) increasing the light detector sensitivity thanks to Neganov-Luke amplification; (ii) having a revolutionary detector assembly that will reduce the total surface radioactivity contribution; (iii) using an active shield, based on ZnWO$_4$ or BGO scintillator with bolometric readout, to suppress the external gamma background. The proposed solutions will have a high impact on next-generation bolometric tonne-scale experiments, like CUPID. In this contribution we present the first results on the bolometric veto and the new detector assembly.

Speaker: Antoine Armatol (CEA IRFU/DPhP)

Pres-BINGO-MEDEX22-vf.pdf

3:15 PM → 3:45 PM Coffee break

3:45 PM → 5:00 PM Round-Table Discussion

Convener: Hiro Ejiri (RCNP Osaka University)

7:00 PM → 10:00 PM Banquet - Social Dinner

Žižkov Television Tower

Thursday, June 16

9:00 AM → 10:30 AM Theory

Convener: Lukas Graf (Max Planck Institute for Nuclear Physics)

9:00 AM A Statistical Analysis for the Neutrinoless Double-Beta Decay Matrix element of 48Ca

Neutrinoless double beta decay (0νββ) nuclear matrix elements (NME) are the object of many theoretical calculation methods, and are very important for analysis and guidance of a large number of experimental efforts. However, there are large discrepancies between the NME values provided by different methods. In this paper we propose a statistical analysis of the 48Ca 0νββ NME using the interacting shell model, emphasizing the range of the NME probable values and its correlations
with observables that can be obtained from the existing nuclear data. Based on this statistical analysis with three independent effective Hamiltonians we propose a common probability distribution function for the 0νββ NME, which has a range of (0.45 - 0.95) at 90% confidence level of, and a mean value of 0.68.

Speaker: Andrei Neacsu (CIFRA - Magurele)

NaN-Medex22-16june.pdf

PSF-resources effective_psf_calculation.nb PRD_plots.nb

9:30 AM Estimation of nuclear matrix elements of double-β decay from shell model and quasiparticle random-phase approximation

The nuclear matrix element of neutrinoless double-β decay is an essential input for determining the neutrino effective mass, if the half-life of this decay is measured. Reliable calculation of this nuclear matrix element has been a long-standing problem because of the diversity of the predicted values of the nuclear matrix element, which depends on the calculation method. In this study, we focus on the shell model and the quasiparticle random-phase approximation. We propose a new method to modify phenomenologically the results of the two methods compensating for the insufficiencies of each method using the information of other methods in a complementary manner. Extrapolations of the nuclear matrix element of the shell model are made toward a very large valence single-particle space referring to the running sum of the nuclear matrix element of the quasiparticle random-phase approximation. We introduce a modification factor to the nuclear matrix element of the quasiparticle random-phase approximation referring to the charge-change strength function of the shell model in a low-energy region. The discrepancy of the original nuclear matrix elements of the two methods is reduced dramatically for Ca-48.

Speaker: Jun Terasaki (Czech Technical University in Prague)

Terasaki_16Jun2022.pptx

10:00 AM Impact of the leading-order short-range term on neutrinoless double-beta decay

Precise calculations of nuclear matrix elements provide a solid foundation in order to extract relevant data from current and upcoming neutrinoless double-beta decay experiments. These searches are key to unveil the nature of neutrinos as well as to access physics beyond the Standard Model due to the violation of the lepton number conservation in neutrinoless double-beta decay.
In this matter, the aim of this study consists on the evaluation of the impact of a newly acknowledged leading-order short-range term on the neutrinoless double-beta decay nuclear matrix element of medium-mass and heavy nuclei in the Nuclear Shell Model framework. As such, I will discuss the relative contribution of this leading-order short-range term to the total nuclear matrix element in the nuclei most relevant for experiments, ranging from 48Ca to 136Xe. I will also talk about the implications of the still-unknown relative sign of this term.

Speaker: Pablo Soriano Fajardo (Universitat de Barcelona)

MEDEX'22 Talk.pdf

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Experiment

Convener: Giorgio Gratta (Stanford University, USA)

11:00 AM The CUPID-Mo experiment

The CUPID-Mo experiment, located in the Laboratoire Souterrain de Modane (France), 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. The experiment has collected data from spring 2019 to summer 2020, for a total exposure of 2.71 kg.yr. Within this exposure, no event in the region of interest and hence no evidence for 0νββ is observed. It has been possible to set a new world-leading limit on the half-life of 0νββ decay of $^{100}$Mo (T$_{1/2}$ > 1.8 x 10$^{24}$ yr (stat. + syst.) at 90% C.L.). This corresponds to an effective Majorana mass limit of 〈𝑚$_{𝛽𝛽}$〉 < (0.28 - 0.49) eV, in the light Majorana neutrino exchange interpretation. In this contribution, the detector technology, the experimental set-up, the performed analysis for the 0νββ decay search, the results for the half-life of the excited states ($^{100}$Mo->$^{100}$Ru), and the background model will be presented.

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

CUPIDMo_MEDEX22.pdf

11:30 AM Recent results of the COBRA experiment

The COBRA experiment aims to search for neutrinoless double-beta decay using CdZnTe room-temperature semiconductor detectors. It is located at the Gran Sasso underground laboratory and has been operated stably for several years. In 2018, an upgrade of the COBRA demonstrator to the extended demonstrator was performed by adding nine 6 cm3 CdZnTe detectors to the existing array with 64 1 cm3 detectors. The new detectors have an improved sensitivity as well as a reduced background level. Besides the investigation of nine naturally present ββ nuclides in the detector material, the “source = detector” concept of the COBRA experiment allows the study of exotic decay modes with high inherent detection efficiency. The charge non-conserving decay of 113Cd with the event signature of γ-rays at 391.7 keV resulting from the de-excitation of the isomeric state 113mIn is of particular interest. An improved limit for this process can be achieved using the dataset collected from the two setups.

Speaker: Yingjie Chu (TU Dresden)

ychu_2022_medex.pdf

12:00 PM Search for Exotic Modes of Double Beta Decay within the SuperNEMO Experiment

The SuperNEMO experiment is a one-of-a-kind detector searching for neutrinoless double beta decay (0νββ). The unique design of this heterogeneous detector takes advantage of the combination of 2034 drift cells operating in Geiger Mode (tracker) with 712 plastic scintillator modules (calorimeter) placed around a 6.3kg thin foil of Se-82 – the source of the double beta decay (DBD). This design allows for the study of the kinematics of the decay, ie. single electron tracks and spectra. The detector is being commissioned in the Modane Underground Laboratory (Laboratoire Souterrain de Modane - LSM) in France. While the main goal of the experiment is the search for 0νββ, its capabilities of producing large amounts of DBD data – as well as the possibility of obtaining full kinematics of the decay – make it a prime candidate for the study of more exotic (newly proposed) modes of DBD. This contribution reports both on the progress of the construction and commissioning of the SuperNEMO detector as well as on the potential uses of the detector as a tool for the studies of exotic DBD modes.

Speaker: Maros Petro (IEAP CTU in Prague)

Medex2022_MarosPetro-FINAL.pdf

12:45 PM → 2:15 PM Lunch

2:15 PM → 3:15 PM Experiment

Convener: Giorgio Gratta (Stanford University, USA)

2:15 PM Investigation of neutron-induced 𝛾-rays from Ge-nuclides in the region of interest of GERDA/LEGEND

GERDA has been a pioneering experiment in the search for the still undetected neutrinoless double beta (0𝜈𝛽𝛽)-decay of Ge-76 and this will also hold for the successor experiment LEGEND. The discovery of this extremely rare process would prove the Majorana character of neutrinos and consequently physics beyond the Standard Model. For an explicit identification of a signal caused by the 0𝜈𝛽𝛽-decay, which correspond to an energy of 2039 keV for Ge-76, a precise understanding of all background contributions in the region of interest is crucial.

Previous experiments indicated 𝛾-lines, produced by (n,p) reactions on Ge-76 and Ge-74, but until now, no significant indications for their existence were found. In order to confirm the existence of the 𝛾-lines, an enriched Ge-sample was alternately irradiated by neutrons from a DT generator and measured by a HP Ge detector. The combined 𝛾-ray spectra from 51 irradiation cycles show three peaks in the signal region of GERDA/LEGEND. The experimental procedure and the analysis of the peaks will be presented.

Speaker: Marie Pichotta

Powerpoint_MEDEX_MariePichotta.pdf

2:45 PM Search for new physics in double beta decay of 82Se with the CUPID-0 Background Model

CUPID-0 is a pilot experiment in scintillating cryogenic calorimetry for the search of neutrino-less double beta decay. 26 ZnSe crystals coupled to bolometric light detectors were operated continuously for two years. From its successful experience comes a demonstration of full alpha to beta/gamma background separation, the most stringent limit on the 82Se neutrino-less double beta decay, as well as the most precise measurement of the 82Se two-neutrino double beta decay half-life. We developed a model to constrain the contribution of several sources in a wide energy region, demonstrating that CUPID-0 reached unprecedented low levels of background in the region of interest at the Q-value of 82Se. CUPID-0 is sensitive to the spectral shape of the two-neutrino double beta decay, and it already provided evidence for its single state dominance. In this contribution we search for spectral distortions due to exotic decay modes. Through a Bayesian approach we investigate the Lorentz violation in the two-neutrino double beta decay and several conjuctured models providing the neutrino-less double beta decay with the emission of a Majoron-like particle

Speaker: Alberto Ressa (University of Rome La Sapienza)

Search for new physics in double beta decay of 82Se with the CUPID-0 Background Model (1).pdf

3:15 PM → 3:45 PM Coffee break

3:45 PM → 5:00 PM Round-Table Discussion

Convener: Giorgio Gratta (Stanford University, USA)

5:00 PM → 5:30 PM Theory

5:00 PM Constraining neutrinoless double beta decay matrix elements from ab initio nuclear theory

As experiments searching for neutrinoless double beta decay are in the planning phase of a next generation with hopes to completely probe the inverted mass hierarchy, the need for reliable nuclear matrix elements, which govern the rate of this decay, is stronger than ever. Since a large discrepancy is found when computing this quantity with different nuclear models, a large unknown still exists on the sensitivity of these experiments to the effective neutrino mass. We tackle this problem from first principle using the valence-space in medium similarity renormalization group ab initio method, which allows to assign rigorous theoretical uncertainties. We present converged results for isotopes of interests for mass number up to A=136 with multiple nuclear interactions obtain from chiral effective field theory. Furthermore, we study correlations with other observables such as the double Gamow-Teller giant resonance in an attempt to betterr constrain our uncertainties.

Speaker: Antoine Belley (TRIUMF Vancouver)

Belley_MEDEX2022 .pdf

Friday, June 17

9:00 AM → 10:30 AM Theory

Convener: Javier Menendez (University of Barcelona)

9:00 AM On the implications of the 92Rb total beta spectrum for the reactor flux anomaly

Theoretical and experimental studies on the beta decays of the most prominent fission products in nuclear reactors are needed to unravel the source of the anomalies detected in the related anti-neutrino flux. One of these fission products, 92Rb, was recently studied for its beta decay to 92Sr by using large-scale nuclear shell-model (NSM) calculations to analyze the role of forbidden beta transitions in the theoretical prediction of the total electron spectral shape. Our calculations of the total electron spectrum rely on experimental branching data obtained from a recent TAGS (Total Absorption Gamma Spectroscopy) of the same isotope. These branchings are used for pinpointing the effective values of the weak axial-vector coupling $g_{\rm A}$ and the mesonic enhancement factor ($\varepsilon_{\rm MEC}$). Our calculations take into account all allowed and forbidden decay transitions, making it a pioneering study of the total spectral shape for a beta decay with a high decay Q value. We show that the first-forbidden non-unique transitions can be behind the so-called 'bump' in the measured reactor anti-neutrino flux. Considering this is one of the many important isotopes, further studies on the spectral shapes are called for. Our main interest is to show the necessity of further studies of the beta decays of the most prominent isotopes contributing to the anti-neutrino flux, and additionally to show the necessity to further understand the role of $g_{\rm A}$ in the building of the total electron spectral shape.

Speaker: Marlom Ramalho (Jyväskylän yliopisto)

Ramalho_Medex22.pdf

9:30 AM Unraveling the Mechanisms of Neutrinoless Double Beta Decay

We will discuss possibilities of how to experimentally distinguish different mechanisms of $0\nu\beta\beta$-decay and thereby identify potential non-standard contributions. The different mechanisms possibly contributing to $0\nu\beta\beta$-decay are classified following an effective field theory approach. We find that when utilizing measurements of the leptonic phase space, i.e., the spectra and angular correlation of the outgoing electrons as well as measurements of the half-life in multiple isotopes one can sort the 32 different low-energy effective operators into multiple groups that in principle can result in different experimental signatures. Based on nuclear matrix elements from IBM2 we determine the required theoretical precision of the nuclear part of the $0\nu\beta\beta$-decay rate calculation that would be necessary to identify non-standard mechanisms via half-life measurements in multiple isotopes. Besides the uncertainties involved in the calculation of nuclear matrix elements, we find that the currently unknown low-energy constants that parameterize couplings in the chiral effective field theory are a limiting factor. Finally, we will present a Python tool developed alongside this work that can be used to study different models of $0\nu\beta\beta$. We are working towards making this tool publicly available in the near future.

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

MEDEX22Scholer.pdf

10:00 AM Angular Distributions of Emitted Electrons in the Two-Neutrino Double-Beta Decay

The two-neutrino double-beta decay ($2\nu\beta\beta$-decay) process is attracting more and more attention from the physics community due to its potential to explain nuclear structure aspects of involved atomic nuclei and constrain new (beyond the Standard Model) physics scenarios. Topics of interest are energetical and angular distributions of the emitted electrons, which might allow the deduction of valuable information about fundamental properties and interactions of neutrinos once a new generation of the double-beta decay experiments is realized. These tasks require an improved theoretical description of the $2\nu\beta\beta$-decay differential decay rates, which is presented. The dependence of the denominators in nuclear matrix elements on lepton energies is taken into account via the Taylor expansion. Both the Fermi and Gamow-Teller matrix elements are considered. For nuclei of experimental interest, relevant phase-space factors are calculated using exact Dirac wave functions with finite nuclear size and electron screening. The dependence of the angular correlation factor on nuclear structure parameters is discussed. It is emphasized that the effective axial-vector coupling constant can be determined more reliably by accurately measuring the angular correlation factor.

Speaker: Ovidiu Nitescu (Comenius University)

MEDEXNitescu.pdf

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:00 PM Experiment

Convener: Kai Zuber (TU Dresden)

11:00 AM Determination of a high neutron flux produced by a DT generator

Many of today's double beta experiments go deep underground in order to reduce cosmic backgrounds.
Neutrons still can origin from the surrounding rock. This motivates the investigation of neutron induced reactions on the present materials with thermal but also with fast neutrons. For neutron cross section measurements it is necessary to know the applied neutron intensity.
TU Dresden runs a DT neutron generator which is able to produce $10^{12}$ neutrons per second.
A $300\,$keV deuteron beam hits a tritium target. Via the 2-body-reaction $^3$H($^2$H,n)$^4$He, a quasi-monoenergetic neutron field of $14\,$MeV is produced. The neutron fluence can be measured via the activation method.
An exemplary irradiation procedure and neutron flux analysis will be presented. An Ar gas sample contained in an Al sphere was irradiated in a $14\,$MeV neutron field produced by TU Dresden's neutron generator. The sample was positioned in close geometry in order to gain a high neutron flux. Each 2 metal foils consisting of Al, Zr and Nb respectively, served as neutron monitors. After the irradiation, the monitors' activities were measured using a germanium detector surrounded by a lead shielding. An efficiency calibration of the detector was done using point sources of known activity and supported by simulations.

Speaker: Hans Hoffmann (TU Dresden)

Hans-Hoffmann-DT-neutron-generator.pdf

11:30 AM Development of software for energy calibration of the SuperNEMO detector

The SuperNEMO experiment was designed to search for neutrinoless double-beta decay. It is an improved version of a very successful predecessor experiment, NEMO-3. The detector uses a tracker-calorimeter technique to detect individual particles’ trajectories and energies. Energies are measured by a segmented calorimeter composed of polystyrene scintillator blocks.
The calorimeter will be calibrated periodically using an automatic deployment system of 42 $^{207}$Bi calibration sources, which undergo internal conversion emitting electrons of known energies, and automatic calibration software. The aim of the presented work is to study possible effects which can potentially influence the quality and efficiency of the calibration. On their trajectory from the calibration source to the calorimeter the electrons lose energy, causing an artificial shift of the calibration spectrum to lower energies. It is possible to account for these losses by applying a correction. In the study, we also tested several fitting procedures, which could be applied on energy spectrum obtained during calibration and compared them.
The effects were studied using the Monte Carlo simulations of the $^{207}$Bi sources in the detector. In the future, we will use real data to deliver the final automatic calibration script.

Speaker: Filip Koňařík (IEAP CTU in Prague)

medex_f_konarik_final.pdf

medex_f_konarik_final.pptx

12:00 PM → 12:45 PM Round-Table Discussion

Convener: Kai Zuber (TU Dresden)

12:45 PM → 2:15 PM Lunch

2:15 PM → 2:20 PM End of the conference!