MEDEX'19

May 27, 2019, 8:30 AM → May 31, 2019, 2:15 PM UTC

Balling Hall (ground floor) (The Czech National Library of Technology)

The MEDEX (Matrix Elements for the Double beta decay EXperiments) meeting is dedicated to the presentation of different methods of nuclear matrix elements (NME) calculations in connection with 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, LEGEND (GERDA + Majorana), CUORE, 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.

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.

 

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Licence Agreement AIP_Conference_Proceedings_License_Agreement.pdf

MEDEX19_Agenda MEDEX19_Agenda_23.5.2019.pdf

MEDEX19_Circular MEDEX19_Circular_24.5.2019.pdf

MEDEX19_group_photo MEDEX19_group_photo.JPG

MEDEX19_logo MEDEX19_logo.png

Monday, May 27

REGISTRATION

OPENNING of the MEDEX'19 conference

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

Session (Chair: O. Civitarese)

1 Theory Challenges in Neutrinoless Double Beta Decay

The recent progress in theoretical description of the 0νββ-decay is shortly reviewed. Several simplified benchmark scenarios within left-right symmetric models are discussed. The question is raised whether light and heavy neutrino contributions to 0νββ-decay are experimentally distinguishable. New modes of the double-beta decay are introduced. The present-day results of the calculation of double-beta decay nuclear matrix elements are discussed. A connection between the 2νββ-decay and 0νββ-decay matrix elements is analyzed. An impact of the quenching of the axial-vector coupling constant on double-beta decay processes is addressed and a novel approach to determine quenched value of axial-vector coupling constant is presented.

Speaker: Prof. Fedor Simkovic (Comenius University and JINR Dubna)

Slides Simkovic_Fedor_MEDEX_0519.pdf

2 Neutrino-nuclear responses and the value of the weak axial coupling

The value of the weak axial coupling, g$_A$, has pervasive impact on neutrino-nucleus interactions in many fields: Nuclear astrophysics, neutrino physics and particle physics. In particular, nuclear beta decays and double beta decays, as also astro-(anti)neutrino-nucleus scattering and nuclear muon capture imply effective quenched or enhanced values of g$_A$, sometimes deviating a lot from the default PCAC value g$_A$ = 1.27, valid for a free neutron. This quenching or enhancement of g$_A$ in finite nuclei stems from, e.g., deficiencies of the nuclear many-body approaches used to describe the involved nuclear structures (restrictions in single-particle model spaces and/or configuration spaces, neglect of three-body forces, etc.), interference of non-nucleonic degrees of freedom, nuclear medium effects, like meson-exchange (two-body) currents, and so on. In my talk I try to highlight these features by several different examples.

Speaker: Prof. Jouni Suhonen (University of Jyväskylä)

Slides MEDEX19-Suhonen.pdf

10:30 AM Coffee break

Session (Chair: O. Civitarese)

3 Neutrinoless Double Beta Decay of Atomic Nuclei

Neutrinos are elusive particles interacting weekly with the atomic nuclei and electron plasma. Most of the atomic nuclei that are stable from the strong interaction point of view can decay emitting neutrinos or antineutrinos. The properties of weak interaction are essential for the understanding of the fundamental symmetries that constrain the Standard Model of particle physics. Neutrinoless double beta decay, if observed, would signal physics beyond the Standard Model (BSM). In my talk I will analyze the neutrino physics relevant for the double beta decay of the atomic nuclei. Contributions to the decay rate from different terms in the BSM Lagrangian will be presented, and their relevance for the analysis of the experimental data will be discussed.

Speaker: Prof. Mihai Horoi (Central Michigan University)

Slides mhoroi-medex19.pdf

4 Nuclear matrix element of neutrinoless double-β decay: Relativity and short-range correlations

The discovery of neutrinoless double-$β$ ($0νββ$) decay would demonstrate the nature of neutrinos, have profound implications for our understanding of matter-antimatter mystery, and solve the mass hierarchy problem of neutrinos. The calculations for the nuclear matrix elements $M^{0ν}$ of $0νββ$ decay are crucial for the interpretation of this process. We study the effects of relativity and nucleon-nucleon short-range correlations on the nuclear matrix elements $M^{0ν}$ by assuming the mechanism of exchanging light or heavy neutrinos for the $0νββ$ decay. The nuclear matrix elements $M^{0ν}$ are calculated within the framework of covariant density functional theory. The dynamic effects of particle-number and angular-momentum conservations as well as quadrupole shape fluctuations are considered with projections and generator coordinate method for both initial and final nuclei. The full relativistic transition operator is adopted to calculate the NMEs. The nuclear matrix elements $M^{0ν}$ are obtained for ten $0νββ$-decay candidate nuclei. The impact of relativity is illustrated by adopting relativistic or nonrelativistic decay operators. The effects of short-range correlations are evaluated. The effects of relativity and short-range correlations play an important role in the mechanism of exchanging heavy neutrinos though the influences are marginal for light neutrinos. Combining the nuclear matrix elements $M^{0ν}$ with the observed lower limits on the $0νββ$-decay half-lives, the predicted strongest limits on the effective masses are less than 0.06 eV for light neutrinos and larger than 3.065 × 10$^8$ GeV for heavy neutrinos.

Speaker: Prof. Jie Meng (School of Physics, Peking University, Beijing 100871, China)

Slides 4-20190527@Czech_Technical_University.pptx

5 Effective field theory approach to neutrinoless double beta decay

In this talk I will discuss a theoretical approach to neutrinoless double beta decay based on effective field theory (EFT). I will describe an end-to-end analysis that starts from the high scale where lepton number violation originates and evolves the dynamics all the way down to nuclear scales, using at each stage the appropriate effective theory (from the Standard Model EFT to chiral EFT). After an overview of the method, I will focus on the light Majorana neutrino exchange mechanism.

Speaker: Dr Vincenzo Cirigliano (Los Alamos National Laboratory)

Slides MEDEX_Cirigliano.pdf

12:45 PM Lunch

www.avantgarderestaurant.cz/en

Session (Chair: K. Zuber)

6 Average and recommended half-life values for two-neutrino double beta decay: upgrade-2019

All existing positive results on two-neutrino double beta decay in different nuclei were analyzed. Using the procedure recommended by the Particle Data Group, weighted average values for half-lives of 48Ca, 76Ge, 82Se, 96Zr, 100Mo, 100Mo– 100Ru (0+1 ), 116Cd, 130Te, 136Xe, 150Nd, 150Nd– 150Sm (0+1 ) and 238U have been obtained. Existing geochemical data were analyzed and recommended values for half-lives of 128Te and 130Ba are proposed. Finally, previous results [NPA 935 (2015) 52)] were updated. Situation with 78Kr result is discussed.

Speaker: Dr Alexander Barabash (ITEP)

Slides barabash_MEDEX_19.pdf

7 Neutrinoless double beta decay search with EXO: EXO-200 results and status of nEXO

EXO-200 is a liquid xenon experiment whose primary goal is to search for the neutrinoless double-beta decay of Xe-136. Such a process would violate the lepton number conservation and provide an insight into nature and absolute mass scale of neutrinos. EXO-200 has finished data taking in December 2018, accumulating more than 200 kg*yr of Xe-136 exposure. The EXO-200 data will remain to be useful for testing new approaches to analysis, such as deep learning, and for additional searches for new physics. In parallel, an effort to develop a next generation experiment, nEXO, has begun. This talk presents the latest EXO-200 results and describes goals and status of nEXO.

Speaker: Dr Igor Ostrovskiy (The University of Alabama)

Slides Ostrovskiy_MEDEX2019_May2019.pdf

3:15 PM Coffee break

Session (Chair: K. Zuber)

8 Status and results of the CUORE experiment

The Cryogenic Underground Observatory for Rare Events (CUORE) is the first bolometric experiment searching for neutrinoless double beta decay ($0\nu\beta\beta$) that has been able to reach the one-ton scale. The detector consists of an array of 988 TeO$_2$ crystals arranged in a compact cylindrical structure of 19 towers. The construction of the experiment was completed in August 2016 with the installation of all towers in the cryostat. Following a cooldown, diagnostic, and optimization campaign, routine data-taking began in spring 2017. In this talk, we present the $0\nu\beta\beta$ results of CUORE from examining a total TeO$_2$ exposure of 86.3 kg$\cdot$yr, characterized by an average energy resolution of 7.7 keV FWHM and a background in the region of interest of 0.014 counts/(keV$\cdot$kg$\cdot$yr). In this physics run, CUORE placed the current best lower limit on the 130Te $0\nu\beta\beta$ half-life of $>1.3\times10^{25}$ yr (90$\%$ C.I.). We then discuss the additional improvements in the detector performance achieved in 2018, the latest evaluation of the CUORE background budget, and we finally present the most precise measurement of the $^{130}$Te $2\nu\beta\beta$ half-life to date.

Speaker: Dr Giovanni Benato (University of California Berkeley)

Slides GiovanniBenato_Medex19.pdf

Round-Table discussion (Leader: S. Stoica)

Tuesday, May 28

Session (Chair: F. Simkovic)

9 Nuclear Physics of Non-Standard Neutrinoless Double Beta Decay

In spite of several attempts by many groups (for review see e.g. [1]), neutrinoless double beta ($0\nu\beta\beta$) decay has not yet been observed. Nonetheless, this observation remains crucial for understanding lepton number violation. After the discovery of neutrino oscillations [2], attention has been mostly focused on the mass mechanism of $0\nu\beta\beta$, wherein the three species of neutrinos have masses $m_i$ and couplings to the electron neutrino $U_{ei}$. However, in view of the difficulties to observe the mass mechanism, investigations of other mechanisms are also in order. These non-standard mechanisms can be divided into short-range and long-range mechanisms. They were previously studied by Doi et al. [3] and Tomoda [4], who investigated L-R models [5], and by Ali et al. [6], who provided a general framework for the investigation of non-standard models. Recently, we have performed systematic study for all possible short-range non-standard mechanisms [7] and all possible long-range non-standard mechanisms [8]. The aim of this study was twofold: I) to provide explicit formulas for the nuclear matrix elements (NMEs) and phase-space factors (PSFs) from which the decay rate for one or a combination of mechanisms operating at the same time can be calculated; II) to provide numerical values of the NMEs and PSFs obtained by making use of the interacting boson model for the NMEs [9] and of exact Dirac wave functions for the PSFs [10]. [1] M. J. Dolinski, A. W. P. Poon, W. Rodejohann, submitted for publication in the Annu. Rev. of Nucl. Part. Sci. 69 (2019), [arXiv:1902.04097]. [2] Y. Fukuda et al. [Super-Kamiokande Collaboration], Phys. Rev. Lett. 81, 1562 (1998); Q. R. Ahmad et al. [SNO Collaboration], Phys. Rev. Lett. 89, 011301 (2002); K. Eguchi et al. [KamLAND Collaboration], Phys. Rev. Lett. 90, 021802 (2003). [3] M. Doi, T. Kotani, H. Nishiura, K. Okuda and E. Takasugi, Prog. Theor. Phys. 66, 1739 (1981) Erratum: [Prog. Theor. Phys. 68, 347 (1982)]; M. Doi, T. Kotani, H. Nishiura and E. Takasugi, Prog. Theor. Phys. 69, 602 (1983). [4] T. Tomoda, Rept. Prog. Phys. 54, 53 (1991). [5] J. C. Pati and A. Salam, Phys. Rev. D 10, 275 (1974) Erratum: [Phys. Rev. D 11, 703 (1975)]; R. N. Mohapatra and J. C. Pati, Phys. Rev. D 11, 566 (1975); G. Senjanovic and R. N. Mohapatra, Phys. Rev. D 12, 1502 (1975); M. Doi, T. Kotani and E. Takasugi, Prog. Theor. Phys. Suppl. 83, 1 (1985); M. Hirsch, H. V. Klapdor-Kleingrothaus and O. Panella, Phys. Lett. B 374, 7 (1996). [6] A. Ali, A. V. Borisov and D. V. Zhuridov, Phys. Rev. D 76, 093009 (2007) [arXiv:0706.4165v3]. [7] L. Graf, F. F. Deppisch, F. Iachello and J. Kotila, Phys. Rev. D 98, 095023 (2018); L. Graf, F. F. Deppisch, F. Iachello and J. Kotila, to be published. [8] L. Graf, F. F. Deppisch, F. Iachello, J. Kotila and J. Ferretti, to be published. [9] J. Barea and F. Iachello, Phys. Rev. C 79, 044301 (2009); J. Barea, J. Kotila and F. Iachello, Phys. Rev. C 87, 014315 (2013); J. Barea, J. Kotila and F. Iachello, Phys. Rev. C 91, 034304 (2015). [10] J. Kotila and F. Iachello, Phys. Rev. C 85, 034316 (2012).

Speaker: Dr Jenni Kotila (University of Jyväskylä)

Slides medex19_kotila.pdf

10 Efficient QRPA calculation for two-neutrino double-beta decay nuclear matrix element

The quasiparticle random-phase approximation (QRPA) is used to evaluate the double-beta decay nuclear matrix element. In the QRPA, the isoscalar neutron-proton pairing is known to suppress the nuclear matrix element, and thus its strength has to be determined using available experimental data. The conventional solution of the QRPA equation is based on the diagonalization of the QRPA matrix in two-quasiparticle space. The method based on the mean field model can handle a very large single-particle model space, while the truncation of the model space may be necessary to perform the digonalization. In this presentation I will introduce the finite-amplitude method that is an efficient solution of the QRPA based on the linear response formalism for nuclear density functional theory, and discuss how the two-neutrino double-beta decay nuclear matrix element is derived. Numerical calculations for the double Gamow-Teller transition strength and two-neutrino NME for light pf shell nuclei are shown using Skyrme energy density functional.

Speaker: Dr Nobuo Hinohara (Center for Computational Sciences, University of Tsukuba)

Slides hinohara-medex19.pdf

11 Experimental studies of axial-vector weak couplings for double beta decays by nuclear and muon reactions

We report experimental studies of nuclear matrix elements (NME) for astro-neutrinos and double beta decays(DBDs) by nuclear and muon charge exchange reactions. The axial-vector NMEs for various multipolarities for both $\tau ^+$ and $\tau ^-$ sides in wide energy and momentum regions, which are relevant to sypernova and DBDs, are reduced with respect to pnQRPA MNEs. They are discussed in terms of the effective axial-vector coupling $g_A^{eff}$. [1] H. Ejiri 2000 Phys. Report 338 265. [2] H. Ejiri , J. Suhonen and K. Zuber 2019 Physics Report 797 1.

Speaker: Prof. Hiro Ejiri (RCNP Osaka University)

Slides ejiri

10:30 AM Coffee break

Session (Chair: F. Simkovic)

12 More than Exotic Neutrinoless Double Beta Decay with Majoron-like Emission

I present a novel mode of neutrinoless double beta decay with emission of a light Majoron-like scalar particle $\phi$. We assume it couples via an effective seven-dimensional operator with a $(V+A)$ lepton current and $(V\pm A)$ quark currents leading to a long-range contribution that is unsuppressed by the light neutrino mass. Calculating the total double beta decay rate and determine the fully differential shape for this mode, we find that future double beta decay searches are sensitive to scales of the order $\Lambda_{NP} \approx 1$ TeV for the effective operator and a light scalar $m_\phi < 0.2$ MeV, based on ordinary double beta decay Majoron searches. The angular and energy distributions can deviate considerably from that of two-neutrino double beta decay, which is the main background. I discuss possible ultraviolet completions where such an effective operator can emerge.

Speaker: Dr Frank Deppisch (UCL)

Slides FrankDeppisch_MEDEX19.pdf

13 Double beta decay beyond the mass mechanism

Neutrinoless double beta decay is usually considered a probe for Majorana neutrino masses. However, there are many other potential contributions to the total decay amplitude. In this talk, I will summarize a number of recent papers on such "exotic" contributions to double beta decay.

Speaker: Prof. Martin Hirsch (Instituto de Fisica Corpuscular, CSIC/University of Valencia)

Slides MH_Medex19.pdf

14 Investigation of Lorentz violation in double-beta decay

Observable effects of the Lorentz violation symmetry at low energy scale can also be investigated by comparing the theoretical calculations with precise analysis of the measured summed energy spectra of electrons emitted in two-neutrino double beta decay (DBD) mode. In this study we make a detailed comparison of the phase space factors (PSF) and their differentials computed with analytical (approximate) electron functions and with “exact” electron functions obtained by solving the Dirac equation in a realistic Coulomb-type potential with the inclusion of the finite nuclear size and screening effects. We found relevant differences between the electron spectra calculated by the two methods, which lead to revised constraints of the coefficient that governs the time-like component of Lorentz-violating operator a3of which appears in the Standard-Model Extension (SME) theory.

Speaker: Prof. Sabin Stoica (International Center for Advances Training and Research in Physics)

Slides SabinStoica_MEDEX'19.ppt

12:45 PM Lunch

www.avantgarderestaurant.cz/en

Session (Chair: A. Barabash)

15 Results of the CUPID-0 Phase I experiment

The search for neutrino-less double beta decay ($0\nu\beta\beta$) demands high energy resolution detectors, operated for long times in low background conditions. Scintillating cryogenic calorimeters are a viable strategy to fulfill these requirements, since they combine good energy resolution with background rejection capabilities. The CUPID-0 experiment is the first successful demonstrator for this technique. The detector has run 26 Zn$^{82}$Se crystals during two years of continuous operation, collecting 10 kg*y of exposure. The complete rejection of the alpha background was demonstrated, measuring the lowest counting rate in the region of interest ever reached with this technique. As a result, the most stringent limit on the $0\nu\beta\beta$ of $^{82}$Se was established. In this contribution we present the final results of CUPID-0, including a detailed model of the background and the measurement of the $2\nu\beta\beta$ decay half-life.

Speaker: Dr Lorenzo Pagnanini (Milano Bicocca University and INFN MiB)

Slides 20190526_Prague_CUPID0_MEDEX19_reduced.pdf

16 First forbidden transitions in the reactor antineutrino anomaly

Fueled by the reactor antineutrino anomaly and its link to possible sterile neutrinos, several very short baseline experiments have come online over the past few years. Despite high quality data, theoretical predictions have not able been able to line up with experimental results, requiring a reevaluated theoretical input. The central element in the latter is an accurate calculation of the antineutrino spectrum shape, for which up to now severe approximations have been employed. We report on the role of forbidden, (non-)unique transitions in the so-called summation approach. Using large-scale shell model calculations, we explicitly determine the shape factor for a large sample of dominant forbidden transitions. We show the influence on the cumulative spectral shape and its role in the so-called reactor 5 MeV bump. We discuss a proposed parametrisation of all non-unique forbidden transitions and a Monte Carlo analysis for a realistic uncertainty estimate.

Speaker: Dr Leendert Hayen (IKS, KU Leuven)

Slides Hayen_MEDEX_28_5_19.pdf

3:15 PM Coffee break

Round-Table discussion (Leader: O. Civitarese)

Wednesday, May 29

Session (Chair: J. Suhonen)

17 Reliability of QRPA approach to ββ and β decays

We have proposed in a series of previous papers a method to determine the effective axial-vector current coupling and the strength of the isoscalar proton-neutron pairing interaction for calculating the nuclear matrix elements of the neutrinoless ββ decay by the quasiparticle random-phase approximation. The combination of these two parameters have had an uncertainty in this approach, but now this uncertainty is removed. In this presentation, we show the result of applying our method to the neutrinoless ββ decays of $^{136}$Xe and $^{130}$Te and predict the nuclear matrix elements and reduced half-lives. Our calculation is tested first by a self-check method using the two-neutrino ββ decay, and this test ensures the application of our method to $^{136}$Xe. Comparison is made between the experimental data and our calculation for the spectrum of the intermediate nucleus, charge-change strength function, and a higher-order component of two-neutrino ββ decay recently proposed. Further test is made for our calculation of the β decay of $^{138}$Xe, and a satisfactory result is obtained.

Speaker: Dr Jun Terasaki (Czech Technical University in Prague)

Slides Terasaki_May2019.pptx

18 Matrix elements for the muon to electron conversion revisited

The muon to electron conversion process in nuclei is a lepton-flavor violation process whose theoretical interpretation requires the knowledge of both the nuclear structure of the participant nucleus as well as the details of the adopted extension of the standard electroweak Lagrangian. In the past a copious literature was produced concerning the calculation of nuclear matrix elements in the context of different nuclear models. Recently, more reliable results have been obtained using shell model codes. From the electroweak side, the structure of the Lagrangian was also re-analyzed. However, the analysis of the theoretical results is sometimes hampered by a not so clear distinction between the approximations controlling both sectors of the calculations. In order to allow for a more efficient model-building from the electroweak side, we have revisited the nuclear structure components in order to disentangle scalar, pseudo-scalar, vector, axial-vector, and tensor components of the electroweak current. We have started from the most general form of the Lagrangian, written at the quark-lepton level, and ended-up by casting it in the form of nucleon-lepton interactions.The formalism is illustrated for the case of muon to electron conversion in 208Pb.

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

Slides civitarese.pdf

19 Double beta decay nuclear matrix elements from deformed QRPA calculations with realistic forces

With the partially restored isopsin symmetry, we calculate double beta decay nuclear matrix elements for five nuclei: $^{76}$Ge, $^{82}$Se, $^{130}$Te, $^{136}$Xe and $^{150}$Nd with deformed QRPA method with realistic forces. We observe the reductions of NME compared to spherical calculations and have also obtained good agreements with results from large scale shell model calcualtions especially for light neutrino mechanism. Meanwhile, suppression of NME for $^{136}$Xe is observed, we find that this is due to a small overlap factor between the initial and final nuclei.

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

Slides MEDEX_Fang.pdf

10:30 AM Coffee break

Session (Chair: J. Suhonen)

20 Ordinary muon capture studies as an opportunity for DBD calculations

In the talk we would like to suggest the ideas about application of the ordinary muon capture studies to the DBD investigations. The series of measurements performed since 2002 at SμS/PSI muon facility (Switzerland) and MUSIC/RCNP (Japan) is described, namely high precision gamma-spectroscopy with negative slow muons by means of HPGe – detectors. The targets were used in solid and gaseous form. The parameters of the beams allowed us to measure isotopically enriched targets of a small mass. OMC could be a good supplementary tool for DBD matrix elements calculations since it represents quite well one branch of this decay. Also, with the huge transferred momentum (up 100 MeV) these reactions could excite high-lying level states of the intermediate nuclei. We also plan to discuss the possibilities to continue such investigations during the future experiments and the research of G_a suppression in the nuclei.

Speaker: Mr Mark Shirchenko (Joint Institute for Nuclear Research)

Slides MEDEX_19_Shirchenko.pptx

21 Muon capture in Mo-100/Mo-nat and Ru-nat

The ordinary muon capture (OMC) on the enriched $^{100}$Mo, as well as natural $^{nat}$Mo and $^{nat}$Ru were investigated at MuSIC (RCNP, Osaka) in order to study neutrino nuclear responses for neutrinoless double beta decay ($0\nu\beta\beta$) and supernova neutrino nuclear reactions. The considered experiment aimed to study the muon absolute lifetime and radioactive production rate of OMC on $^{100}$Mo, $^{nat}$Mo and $^{nat}$Ru.

Speaker: Mrs Daniya Zinatulina (JINR)

Slides MEDEX_19_Zinatulina.pdf

22 Nuclear responses for double beta decay and muon capture

To describe the double beta decay processes reliably one needs a possibility to test the involved virtual transitions against experimental data. Unfortunately, traditional EC or $\beta^-$ -decay experiments only allow probing the lowest transitions. However, the available data on charge-exchange or OMC allows the examining of higher states. In this work we manifest how to utilise the charge-exchange and OMC data in the study of $0\nu\beta\beta$ decay. We compute the nuclear matrix elements (NMEs)for the light Majorana-neutrino mode of $0\nu\beta\beta$ decay by exploiting the available data on isovector spin-dipole (IVSD) $J^{\pi}=2^-$ giant resonances. We calculate the OMC giant resonance in $^{100}$Nb and compare it with the experimental value, and compare the computed total capture rate value with the Primakoff estimate. We also compute the OMC rates to the daughter nuclei of some $0\nu\beta\beta$ decay triplets of immediate experimental interest. In order to correctly describe the IVSD and OMC up to and beyond the giant-resonance region, we perform the present computations in extended no-core single-particle model spaces using the proton-neutron quasiparticle random-phase approximation (pnQRPA) with two-nucleon interactions based on the Bonn one-boson-exchange G matrix. We include the appropriate short-range correlations, nucleon form factors, higher-order nucleonic weak currents, and partial restoration of the isospin symmetry in the calculations. Exploiting the IVSD $J=2^-$ data offers a new way of fitting the $g_{ph}$ value of pnQRPA which leads to improved reliability of the $0\nu\beta\beta$ matrix elements. The calculated first OMC giant resonance in $^{100}$Nb is in agreement with the experimental value. However, the total capture rate is higher than the Primakoff estimate which refers to quenched $g_A$ value. Eventually, the OMC process can be used to probe the structure of the intermediate states appearing in the double-beta-decay process. Future experiments can help fine-tune the nuclear-structure parameters for the double-beta-decay calculations.

Speaker: Ms Lotta Jokiniemi (University of Jyväskylä)

Slides MEDEX19-LottaJokiniemi.pdf

12:45 PM Lunch

www.avantgarderestaurant.cz/en

Session (Chair: F. Danevych)

23 Investigation of Mo-100 two-neutrino double beta decay in NEMO-3

The full data set of the NEMO-3 experiment has been used to measure the half-life of the two-neutrino double beta decay of $^{100}$Mo to the ground state of $^{100}$Ru, $T_{1/2} = \left[ 6.81 \pm 0.01\,\left(\mbox{stat}\right) ^{+0.38}_{-0.40}\,\left(\mbox{syst}\right) \right] \times10^{18}$ y. Clear evidence for the Single State Dominance model is found for this nuclear transition. Limits on Majoron emitting neutrinoless double beta decay modes with spectral indices of n = 2, 3, 7, as well as constraints on Lorentz invariance violation and on the bosonic neutrino contribution to the two-neutrino double beta decay mode are obtained.

Speaker: Dr Victor Tretyak (JINR)

Slides nemo3-medex19-talk.pdf

24 Various aspects and results on beta decay, DBD, COBRA and LFV

The status of the COBRA double beta decay experiment based on CZT detectors. One of the major results is the quenching of g_A . New developments will be presented. Further interesting results on long-living nuclides and flavour violation will be presented.

Speaker: Prof. Kai Zuber (TU Dresden)

Slides MEDEX-2019-v2.pptx

3:15 PM Coffee break

Session (Chair: F. Danevych)

25 Recent results on heavy-ion induced reactions of interest for neutrinoless double beta decay at INFN-LNS

In order to get quantitative information on neutrino absolute mass scale from the possible measurement of the 0νββ decay half-lives, the knowledge of the Nuclear Matrix Elements (NME) involved in such transitions is mandatory. In addition, NME are important also to compare limits on half-lives made with different isotopes, which is a crucial information to design present and future experiments for 0νββ decay. The use heavy-ion induced double charge exchange (DCE) reactions as a tool to extract information on the NME is one of the goals of the NUMEN [1] project in Italy. The basic point is that there are a number of similarities between the two processes, mainly that the initial and final state wave functions are the same and the transition operators are similar, including in both cases a superposition of Fermi, Gamow-Teller and rank-two tensor components [2]. The availability of the MAGNEX magnetic spectrometer [3] for high resolution measurements of the very suppressed DCE reaction channels is essential to obtain high resolution energy spectra and accurate cross sections at very forward angles including zero degree. The measurement of the competing multi-nucleon transfer processes allows to study their contribution and constrain the theoretical calculations. An experimental campaign is ongoing at INFN-Laboratori Nazionali del Sud (Italy) to explore medium-heavy ion induced reactions on target of interest for 0νββ decay. Recent preliminary results from the ($^{20}$Ne,$^{20}$O) DCE reaction and competing channels, measured for the first time using a $^{20}$Ne cyclotron beam at 15 MeV/u, on $^{116}$Cd, $^{130}$Te and $^{20}$Ge targets will be presented at the Conference. [1] F.Cappuzzello et al., Eur. Phys. J. A 54:72 (2018)
[2] F.Cappuzzello et al., Eur. Phys. J. A 51:145 (2015)
[3] F.Cappuzzello et al., Eur. Phys J. A 52:167 (2016)

Speaker: Prof. Francesco Cappuzzello (University of Catania and INFN-LNS laboratory, Catania, Italy)

Slides 26-MEDEX_2019_red.pptx

Round-Table discussion (Leader: H. Ejiri)

7:00 PM BANQUET

www.nebozizek.cz/en

Thursday, May 30

Session (Chair: M. Hirsch)

26 Particle Physics of Non-Standard Neutrinoless Double Beta Decay

The talk will focus on the effective description of exotic neutrinoless double beta decay and the implications of its hypothetical observation. Particular attention will be paid to the short-range mechanisms, which, being represented at low energies by 9-dimensional effective operators, implicitly assume the existence of some underlying new heavy degrees of freedom. The microscopic description of neutrinoless double beta decay including a thorough calculation of relevant nuclear matrix elements and phase-space factors allows for the estimation of the corresponding effective couplings and it can also help to pinpoint the dominant mechanism. Moreover, as the low-energy neutrinoless-double-beta-decay-contributing operators can be encoded in terms of the Standard Model effective operators violating lepton number by two units, it is possible to study the interplay between lepton number violation at high and low energy scales. Specifically, the contribution of the SM effective operators to the rate of neutrinoless double beta decay can be correlated with the washout of lepton number induced by the same operators in the early universe, and thus potentially constrain mechanisms of high-scale baryogenesis.

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

Slides MEDEX2019.pdf

27 Low-scale seesaw from neutrino condensation

Knowledge of the mechanism of neutrino mass generation would help understand a lot more about Lepton Number Violation (LNV), the cosmological evolution of the Universe, or the evolu tion of astronomical objects. Here we propose a verifiable and viable extension of the Standard model for neutrino mass generation, with a low-scale seesaw mechanism via LNV condensation in the sector of sterile neutrinos. To prove the concept, we analyze a simplified model of just one single family of elementary particles and check it against a set of phenomenological constraints coming from electroweak symmetry breaking, neutrino masses, leptogenesis and dark matter. The model predicts (i) TeV scale quasi-degenerate heavy sterile neutrinos, suitable for leptogenesis with resonant enhancement of the CP asymmetry, (ii) a set of additional heavy Higgs bosons whose existence can be challenged at the LHC, (iii) an additional light and sterile Higgs scalar which is a candidate for decaying warm dark matter, and (iv) a majoron. Since the model is based on simple and robust principles of dynamical mass generation, its parameters are very restricted, but remarkably it is still within current phenomenological limits.

Speaker: Dr Adam Smetana (IEAP CTU in Prague)

Slides 28-smetana_MEDEX19.pdf

28 GERDA searches for 0νββ and other ββ decay modes of 76Ge

The GERDA collaboration searches for the 0νββ decay of 76Ge by operating bare germanium detectors in an active liquid argon shield. GERDA is the first experiment that surpasses a sensitivity for the 0νββ decay half-life of T1/2 > 10^26 yr (90% C.L.) and that operates in a background-free regime such that the expected number of background events is less than 1 in the energy region of interest at the final exposure of 100 kg*yr. The present status of GERDA and the results obtained in searching for 0νββ and other ββ decay modes such as 2νββ decay to the ground and exited states of 76Se and Majoron emitting 0νββχ0 decay modes will be presented. A combination of the GERDA 0νββ results with the results of the other searches using different isotopes with respect to upper limits on the effective Majorana electron neutrino mass will be given too. Some aspects of the analysis and results interpretation of searching for several exotic ββ mechanisms associated with bosonic neutrinos, Lorentz invariance violation, and others, using calorimetric type detectors like GERDA are going to be discussed.

Speakers: Dr Anatoly Smolnikov (MPIK Heidelberg), Prof. Kai Zuber (TU Dresden)

Slides Smolnikov_GERDA.pdf

10:30 AM Coffee break

Session (Chair: M. Hirsch)

29 Ab initio theory for electroweak properties of nuclei

In this talk I will discuss recent advances which expand the scope of ab initio calculations to essentially all properties of light, medium-mass nuclei and beyon. When based on consistently derived two- and three-nucleon forces, as well as two-body currents, these powerful approaches allow first predictions of the limits of nuclear existence and the evolution of magic numbers far from stability. In particular I will focus on recent extensions to fundamental problems in nuclear-weak physics, including a proposed solution of the long- standing gA-quenching puzzle in beta decays, calculations of neutrinoless double-beta decay nuclear matrix elements, and WIMP-nucleus scattering cross sections relevant for dark matter direct detection searches.

Speaker: Dr Jason Holt (TRIUMF)

Slides Holt_MEDEX.pptx

30 Quantifying uncertainties in nuclear matrix elements for dark matter searches

In this contribution I will report on quantification of theoretical uncertainties in nuclear matrix elements relevant for dark matter and electro-weak interactions with nuclei. Recently we have developed a novel ab initio framework for computations of nuclear matrix elements [1] and applied it in calculations of reaction rates for dark matter particles scattering off selected nuclear targets relevant for dark matter direct detection experiments. To evaluate the nuclear matrix elements we used nuclear wave functions computed within an ab initio many-body framework employing state-of-the-art nuclear Hamiltonians derived from chiral effective field theory. For the first time, we have quantified the uncertainties of nuclear matrix elements that result from the remaining freedom in the construction of realistic nuclear interactions and the impact of such nuclear-physics uncertainties on physical observables. In particular, we found significant uncertainties especially for certain spin-dependent nuclear matrix elements. While our nuclear structure calculations have been performed with the no-core shell model and applied in the context of dark matter searches, the approach can be generalized to other ab initio methods and extended to other sectors, such as to study the electro-weak interactions in nuclei. [1] D. Gazda, R. Catena, C. Forssén, Ab initio nuclear response functions for dark matter searches, Phys. Rev. D 95, 103011 (2017).

Speaker: Dr Daniel Gazda (Nuclear Physics Institute Řež/Prague)

Slides gazda-MEDEX2019.pdf

31 Implications of new theoretical calculations on reactor antineutrino and gallium anomalies

The reactor antineutrino and gallium anomalies have been long unexplained. Possible explanations for both of these anomalies include new physics, such as the existence of one or more eV-scale sterile neutrino [1]. However, the previous theoretical calculations, which do not replicate the experimental results, rely on many simplifying approximations [2,3]. In the reactor-antineutrino analysis the beta decays contributing to the cumulative electron spectrum are usually assumed to have allowed spectral shapes. However, many of these decays are actually first-forbidden. Moreover, these decays dominate the experimentally observable region. In some cases, like in the case of the ground-state-to-ground-state decay of 140Cs (see figure), this is found to be a rather poor approximation. Based on the recent results, the use of this allowed approximation can at least partially explain the so called reactor antineurtino anomaly. Our new large-scale shell model calculations regarding the neutrinonucleus scattering cross section of 71Ga shows no statistical difference to the experimental results of GALLEX and SAGE experiments. Conflict between charge-exchange BGTs and the neutrino-nucleus cross sections can to some extent be explained by destructive interference between Gamow-Teller and tensor contributions. ![Electron spectrum of $^{140}\rm Cs$ for $g_{\rm A}=0.8-1.2$.][1] References [1] S. Gariazzo, C. Giunti, M. Laveder, Y. F. Li, and E. M. Zavanin, J. Phys. G: Nucl. Part. Phys. 43, 033001 (2015). [2] J. N. Bahcall Phys. Rev. C **56**, 3391 (1997). [3] L. Hayen, J. Kostensalo, N. Severijns, and J. Suhonen Phys. Rev. C **99**, 031301(R) (2019). [1]: https://drive.google.com/open?id=1nkCRlqoX6Qz0OhionWd9jVZPLvi_TsqD

Speaker: Mr Joel Kostensalo (University of Jyväskylä)

Slides slides-MEDEX19.pdf

12:45 PM Lunch

www.avantgarderestaurant.cz/en

Session (Chair: H. Ejiri)

32 Recent Results of the Majorana Demonstrator Experiment

Neutrinoless double beta (0$\nu\beta\beta$) decay, forbidden for Dirac neutrinos, is one of the most promising approaches to answer the question of whether neutrinos are Majorana particles. If discovered, it can also shed light on the neutrino mass ordering, since the half-life of this process is related to the effective Majorana mass for the electron neutrino, m$_{bb}$, by the two-body space factor and the nuclear matrix element. Probing the inverted-ordering neutrino mass is a reasonable target for a ton-scale experiment to reach. Achieving the required sensitivity requires not only a large detector, but also ultra-low background. High purity germanium detectors (HPGe) present one of the best choices to perform this measurement due to their excellent energy resolution and background rejection capabilities. The Majorana Demonstrator, located at the 4850’ level of the Sanford Underground Research Facility in South Dakota, is demonstrating that a ton-scale germanium experiment is capable of probing the 0$\nu\beta\beta$ decay in the inverted ordering mass region. The experiment uses two modular arrays of HPGe detectors, 44 kg total in mass, of which 30 kg is enriched to 88% in $^{76}$Ge. The detectors are surrounded by active and passive shielding with the most sensitive parts constructed from ultrapure materials to reduce the background. I will discuss the recent results obtained by the Majorana Demonstrator, including both the low background present in the detector and the unprecedented energy resolution achieved.

Speaker: José Mariano López Castaño (University of South Dakota)

Slides 20190530_MEDEX2019_Mariano.pdf

33 Final results of the Aurora experiment to study double beta decay of 116Cd with enriched 116CdWO4 crystal scintillators

The double beta decay of 116Cd has been investigated with the help of radiopure enriched 116CdWO4 crystal scintillators (1.162 kg) at the Gran Sasso underground laboratory. The half-life of 116Cd relative to the two neutrino double beta decay to the ground state of 116Sn was measured with the highest up-to-date accuracy as T1/2=(2.63+-0.11)e19 yr. A new improved limit on the neutrinoless double beta decay of 116Cd to the ground state of 116Sn was set as T12 > 2.2e23 yr at 90% C.L., which is the most stringent known restriction for this isotope (corresponds to the effective Majorana neutrino mass limit in the range of 1.0 - 1.7 eV, depending on the nuclear matrix elements used in the estimations). New improved half-life limits for double beta decay with majoron(s) emission, Lorentz-violating decay, and transitions to excited states of 116Sn were set at the level of > 1e20 – 1e22 yr. New limits for the hypothetical lepton-number violating parameters (right-handed current admixtures in weak interaction, the effective majoron-neutrino coupling constants, R-parity violating parameter, Lorentz-violating parameter, heavy neutrino mass) were set.

Speaker: Dr Volodymyr Tretyak (Institute for Nuclear Research of the National Academy of Sciences of Ukraine)

Slides 34-2019-medex-tretyak-116cd.pdf

3:15 PM Coffee break

Session (Chair: H. Ejiri)

34 SEARCH FOR β+EC AND ECEC PROCESSES IN 74Se

Search for double beta decay processes (β+EC, EC/EC) of 74Se was performed at the Modane underground laboratory (LSM, France, 4800 m w.e.) using an ultra low-background HPGe detector OBELIX with sensitive volume of 600 cm3 and a sample of natural selenium. The sample of natural selenium was powder with a total mass of 1.6 kg containing ~0.89% (~14.24 g) of 74Se. Selenium was filled in a circular Teflon box and placed on the end cap of HPGe detector. The measurement of selenium sample was lasted during 3040 h. The efficiency of measurement was obtained by using Monte Carlo simulations performed on the base of GEANT 4 and GEANT 3 and then tested by measurement of. low active samples placed on the end cap of Obelix detector. Low active samples were prepared on the base of La2O3 powder containing ~0.09% of 138La (T1/2≈1.02×10^11 yr) and had activities of −19.3 and 61.8 Bq. . The main goals of present investigation were searches for radiative 0νECEC decay of 74Se into the ground 0+ state of 74Ge, 2νECEC decay of 74Se into 2+1, 596 keV and 2+2,1204 keV exited states of 74Ge, and β+EC decay into 2+1, 596 keV excited state of 74Ge. Based on preliminary calculations of experimental data new limits on β+EC and ECEC decays of 74Se into ground 0+, 2+1, 596 keV and 2+2,1204 keV exited states of 74Ge was obtained. They are ranged from T1/2 ~1×10^19 yr (90% CL) to T1/2 ~ 5 ×10^19 yr (90% CL) and significantly improved previous experimental limits.

Speaker: Dr Nikolay Rukhadze (Joint Institute for Nuclear Research,)

Slides rukhadze

Round-Table discussion (Leader: A.Barabash)

Friday, May 31

Session (Chair: J.Suhonen)

35 Heavy-ion double-charge-exchange and its relation to neutrinoless double-𝛽 decay

Recent theoretical results on the relation between Heavy-ion double-charge-exchange and neutrinoless double-𝛽 decays will be presented and discussed.

Speaker: Elena Santopinto (INFN)

Slides MEDEX_Elena_LASTLAST.pdf

36 Neutrino Mass and High-Precision Penning-Trap Mass Spectrometry

The neutrino mass is still unknown. Currently a few experiments, namely KATRIN, HOLMES and ECHo, are built with the ultimate goal to reach a sub-eV/c2 uncertainty in the neutrino-mass determination from the analysis of two nuclear beta-decays: beta-decay of tritium and electron capture in 163Ho. All these experiments demand directly and independently determined Q-values of these beta-processes. High-precision Penning-trap mass spectrometry is the most suitable tool to deliver these Q-values. This contribution will give a brief overview of PENTATRAP – the most advanced Penning-trap mass spectrometer in the world. The focus will be put on our present activity at PENTATRAP within the framework of the ECHo project. First, the results of our first, “proof-of-principle”, measurements, namely the mass differences of various stable xenon isotopes, will be presented. Then, the current measurement of the beta-decay of 187Re and its preliminary results will be reported. Finally, the planned measurement of the Q-value of the electron capture in 163Ho with PENTATRAP with a sub-eV uncertainty and its impact on the determination of the neutrino mass will be discussed.

Speaker: Dr Sergey Eliseev (Max-Planck Institut für Kernphysik)

Slides MEDEX_2019_talk_Sergey_Eliseev.pdf

37 Precise measurement of two-neutrino double-beta decay of 100Mo with lithium molybdate low temperature detectors

The two-neutrino double-beta decay of 100Mo was investigated with the help of enriched in 100Mo lithium molybdate scintillating bolometers. The measurements were performed in the EDELWEISS-III low background set-up in the Modane underground laboratory with a total exposure of 42.235 kg x d. Preliminary, the half-life of 100Mo with respect to the two-neutrino double-beta decay to the ground state of 100Ru is measured to be T1/2 = (6.99 \pm 0.17) 10^18 yr. This is the most accurate determination of the 100Mo half-life to date. Moreover, the half-life value (the relative uncertainty ~ 2.4 %) is the most accurate among the most precise double beta decay measurements. An effective nuclear matrix element for the two-neutrino double-beta decay of 100Mo to the ground state of 100Ru, assuming the single-state dominance mechanism of the decay, is calculated as 0.1860 \pm 0.0023.

Speaker: Prof. Fedir Danevych (Institute for Nuclear Research, Kyiv, Ukraine)

Slides danevich_T12-100Mo_01g.pdf

10:30 AM Coffee break

Session (Chair: J.Suhonen)

38 New limit on two neutrino electron capture with positron emission in 106Cd

By comparing decay rates of neutrinolessdouble electron capture and electron capture with positron emission one could distinguish mechanism (due to light neutrino exchange or right-handed currents admixture in the weak interaction) of the neutrinoless double beta “minus” decay if observed. However, even the allowed two-neutrino mode of electron capture with positron emission is not observed yet. The nuclide 106Cd is a promising candidate fortheexperimental investigations of the double beta “plus”decays due to its high energy release 2775.39(10) keV andrelatively high isotopic abundance 1.245(22)%. An experiment to search for double beta processes in 106Cd is in progress with the help of 106CdWO4 crystal scintillator (enriched in 106Cd to 66%) in coincidence with two large volume CdWO4 scintillation detectors in close geometry at the Gran Sasso Underground Laboratory. The time resolution of the set-up was analysed,andthe methods of pulse-shape discrimination of alphaand gamma(beta) events was applied to estimate theradioactive contamination of the crystal and to reduce the background counting rate.The possible double beta decay processes and the background components have been simulated by a Monte Carlo procedure. The sensitivity of the experiment is approaching the theoretical predictions for the two-neutrino electron capture with positron emission in 106Cd: lim T1/2 ~ 4×10^21 yr (the best previous limit was established in the previous stage of the experiment as T1/2 >1.1×10^21 yr, while the theoretical predictions are in the region of half-lives 10^20-10^22 yr).

Speaker: Dr Oksana Polishchuk (Kyiv Institute for Nuclear Research)

Slides 39.Polishchuk_Medex2019.pdf

39 Study of double beta decay of 150Nd to the first 0+ excited level of 150Sm

The nuclide 150Nd is one of the most promising to search for double beta decay among 35 naturally occurring double beta isotopes due to the high energy release 3371.38(20) keV and comparatively high isotopic abundance ~5.6 %. The double beta transition to the first 0+ 740.5 keV excited level of 150Sm was observed in few experiments with the half-lives in a wide range (7 – 14) x 10^19 yr. Investigations of the decay process is carried out at the Gran Sasso Underground Laboratory (Italy) by using a highly purified 2.381-kg sample of neodymium oxide. Gamma quanta emitted in the decay are measured with the help of four ultra-low-background HP Ge detectors with volume 225 cm3 each, mounted in one cryostat. Two gamma-quanta with energies 334.0 keV and 406.5 keV emitted after deexcitation of the 0+ 740.5 keV excited level of 150Sm are observed in the coincidence spectra accumulated over 25947 h. Preliminary, the half-life of 150Nd relatively to the two-neutrino double-beta decay to the first 0+ excited level of 150Sm is estimated as T1/2 = [7.0 +5.8 -2.6] x 10^19 yr (the errors are mainly due to low statistics of the observed peaks). The experiment is in progress to improve the half-life value accuracy.

Speaker: Mr Dmytro Kasperovych (Institute for Nuclear Research, Kyiv, Ukraine)

Slides 40._D.Kasperovych_medex19.pdf

40 Gamow-Teller Resonances in the solar neutrino capture cross-section and charge-exchange strength function for 76Ge nuclei.

The effect of the GT-resonance structure of charge-exchange strength function in the ${^{76}Ge(^{3}He,t)^{76}As}$ reaction on the solar neutrino capture cross section was examined. It is shown that accounting of GT-resonances increase solar neutrino capture rate more then 20%. Theoretical strength functions for $^{76}Ge$ and $^{74}Ge$ were calculated in accordance with the framework of the self-consistent theory of finite Fermi systems. This results could help to decompose experimental strength function and itemize some low-lying excitation states and pygmy resonances. Also we demonstrate significant role of quenching effect for cross section calculations. Accurate counting of neutrino capture rate could change estimations on background events index in experiments on double beta decay search (like LEGEND).

Speaker: Grigory Koroteev (MIPT)

Slides MEDEX_Koroteev_31.05.pdf

12:45 PM Lunch

www.avantgarderestaurant.cz/en