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Session I (13:00-14:50)
Chair:---- (----) |
| 13:00 | Two-neutrino double beta decay within the mapped IBM (13:00-13:30)
Abstract:
Two-neutrino double beta decay is studied using the framework of the interacting boson model that is based on the nuclear density functional theory. The interacting boson and boson-fermion Hamiltonians for describing the even-even parent and odd-odd intermediate nuclei, and the Gamow-Teller and Fermi transition operators of the considered double beta decay are constructed by using the results of the self-consistent mean-field calculations with a universal energy density functional. The mapped IBM framework provides a simultaneous description of excitation spectra and electromagnetic transition properties of each nucleus, and double beta decay matrix elements without the closure approximation. The calculated NMEs are compares with experiment and earlier theoretical predictions.
| Kosuke Nomura (Hokkaido University) |
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| 13:30 | Modeling neutrinoless double-beta decay with operators from chiral effective field theory (13:30-14:00)
Abstract:
We report the first comprehensive ab initio uncertainty quantification of the $0\nu\beta\beta$-decay NME, in the key nucleus 76Ge. Our method employs nuclear strong and weak interactions derived within chiral effective field theory and recently developed many-body emulators. Our result, with a conservative treatment of uncertainty, is an NME of
$2.60^{+1.28}_{-1.36}$, which, together with the best-existing half-life sensitivity and phase-space factor, sets an upper limit for effective neutrino mass of $187^{+205}_{-62}$ meV. The result is important for designing next-generation germanium detectors aiming to cover the entire inverted hierarchy region of neutrino masses.
| Jiangming Yao (Sun Yat-sen University) |
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| 14:00 | The PIKACHU experiment - Challenge to discover 2nbb of 160Gd - (14:00-14:30)
Abstract:
Double beta decay rates need to be measured for various nuclides due to the theoretical uncertainty of the nuclear matrix elements. We have launched the PIKACHU(Pure Inorganic scintillator experiment in KAmioka for CHallenging Underground sciences) project and developed a large high-purity Ce:Gd3(Ga,Al)5O12 (GAGG) crystal to study the double beta decay of 160Gd. Two nuclear matrix element calculations for the 2nbb of 160Gd predict half-lives that differ by about an order of magnitude.
The aim is to increase the sensitivity by just over an order of magnitude over previous studies using 160Gd, with the aim of discovering 2nbb. In this talk, the current status of the PIKACHU experiment will be reported.
| Takashi Iida (University of Tsukuba) |
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| 14:30 | Break(14:30-14:50) |
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Session II (14:50-16:50)
Chair:--- (---) |
| 14:50 | Impact of isovector pairing fluctuations on neutrinoless double-βdecay in MR-CDFT (14:50-15:20)
Abstract:
We extend the multi reference covariant density-functional theory(MR-CDFT) by including fluctuations in quadrupole deformations and average isovector pairing gaps simultaneously for the nuclear matrix elements (NMEs) of neutrinoless double-beta (0νββ) decay assuming the exchange of either light or heavy neutrinos. We calculate the NMEs and give a comparison with the results from various nuclear many-body methods.
| Chenrong Ding (Sun Yat-sen University) |
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| 15:00 |
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Improvement of reliability of nuclear matrix element of double-beta decay (15:20-15:50)
Abstract:
My talk consists of three parts. The first part is a hybrid improvement of the nuclear matrix element (NME) of the neutrinoless double-beta decay using the NMEs of the shell model and the quasiparticle random-phase approximation.
The second part is the solution of the discrepancy problem of the running sum of the NMEs of the two-neutrino double-beta decay for 136Xe.
The third part is the discussion on the vertex correction of the NME of the double-beta decay to improve the effective axial-vector current coupling.
| Jun Terasaki (Czech Technical University in Prague) |
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| 15:30 |
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Neutrinoless double-beta decay from valence-space in-medium similarity renormalization group (15:50-16:20)
Abstract:
Neutrinoless double-beta decay is a key process that could explore new physics beyond the standard model of particle physics. A major challenge in theoretical nuclear physics is to compute the nuclear matrix element (NME) of the process. With the recent advancement in nuclear ab initio calculation techniques, it is becoming possible to calculate the NME for realistic candidate nuclei. In this talk, I will present the recent results computed with the in-medium similarity renormalization group approach for valence-space problems.
| Takayuki Miyagi (TU Darmstadt) |
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| 16:00 |
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Beta spectral shapes - A versatile tool for probing weak interactions (16:20-16:50)
Abstract:
In beta minus/plus decays an energy distribution of electrons/positrons can be observed. This distribution can be coined beta spectral shape. This shape is universal and simple for allowed (Fermi and Gamow-Teller) and forbidden unique beta transitions, whereas the spectral shape for forbidden non-unique (FNU) beta transitions depends on the structure of the wave function of the involved initial and final state through nuclear matrix elements (NME). This NME dependence of the FNU transitions can be exploited in determination of the effective value of the weak axial coupling g_A, relevant for analyses of the rates of the double beta decays, in particular the neutrinoless mode. Further applications include reactor antineutrinos and background characterization of rare-events experiments.
| Jouni Suhonen (University of Jyväskylä) |
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| 16:30 |
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| Time | Title | Speaker |
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Session I (09:00-15:30)
Chair:---- (----) |
| 09:00 | Neutrinoless double-beta decay nuclear matrix elements: overview and future directions (09:00-10:00)
Abstract:
In this talk I will present an overview of the recent developments in the nuclear structure calculations of the neutrinoless double-beta decay (0nbb).
There has been a very significant progress in the past few years. First, several calculations now include the short-range contribution to 0nbb, neglected until very recently but which contributes sizably to the total nuclear matrix element.
Second, novel 0nbb calculations using several ab initio methods are now available for most double-beta emitters, and they are complemented by calculations using more phenomenological approaches with emphasis in estimating the theoretical uncertainty of each many-body method.
Altogether, I will review the best knowledge of the values of the nuclear matrix elements, and their theoretical uncertainty.
| Javier Menendez (University of Barcelona) |
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| 09:30 |
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| 10:00 | implication of ab initio no-core Monte Carlo Shell Model to double beta dacay (10:00-10:30)
Abstract:
TBA
| Takaharu Otsuka (Univ Tokyo / RIKEN) |
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| 10:30 | Break(10:30-10:50) |
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Session III (10:50-12:20)
Chair:---- (----) |
| 10:50 | Improved neutrinoless double-beta-decay matrix elements in the pnQRPA (10:50-11:20)
Abstract:
The proton-neutron quasiparticle random-phase approximation (pnQRPA) is one of the most widely used nuclear many-body methods to study the nuclear matrix elements of neutrinoless double-beta decay of medium-heavy to heavy nuclei. Currently the matrix elements are not well constrained and there are sizeable disagreements between different many-body methods. In my talk, I will discuss complementary ways to constrain the nuclear matrix elements in the pnQRPA by using data on other nuclear observables. I will also discuss recent corrections to the matrix elements, such as the new leading-order contact term.
| Lotta Jokiniemi (TRIUMF) |
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| 11:00 |
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Experimental approaches to DBD NMEs by studying CER IAS EM transitions (11:20-11:50)
Abstract:
Experimental studies of DBD NMEs are crucial since theoretical NMEs are very sensitive to the models and the parameters such as the weak couplings used for the models. It is shown for the first time that electric diploe (E1) and magnetic dipole (M1) gamma transitions fron IAS of the DBD nucleus provide the analogous vector dipole and axial-vector dipole weak NMEs associated with the DBD NME and the vector and axial-vector couplings. They are used to hepl theoretical evaluations for the DBD NME.
Ref. H, Ejiri, Phys. Rev. C Letters, 108 L011302 2023.
| Hiroyasu Ejiri (RCNP Osaka Univ.) |
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| 11:30 |
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Anti-Neutrino Nuclear Responses by Ordinary Muon Capture: Status and Review (11:50-12:20)
Abstract:
This is a brief review of anti-neutrino nuclear responses by ordinary muon capture (OMC)
experiments, which are relevant for the study of double beta decays (DBDs). OMC involves a
charge exchange reaction mediated by the charged weak boson, resulting in reactions with
muons (μ) and muon neutrinos (vμ). In OMC on nuclei, the nucleus typically becomes highly
excited and unbound, subsequently returning to its ground state by emitting various particles
such as neutrons, protons, alphas, deuterons, and others, accompanied by delayed gamma rays.
The subjects discussed in this review include: 1) Unique features of anti-neutrino nuclear
responses by OMC for studying DBDs. 2)The measurement of delayed gamma rays for studying
DBDs and anti-neutrino nuclear responses. 3) N-Z dependence of OMC rates. Finally, remarks and
perspectives on OMC experiments for studying anti-neutrino nuclear responses are briefly
described.
| IZYAN HASHIM (Universiti Teknologi Malaysia) |
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| 12:00 |
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| Break(12:20-13:40) |
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| 12:30 |
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| 13:00 |
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| 13:30 |
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Session IV (13:40-15:10)
Chair:---- (----) |
| 13:40 | Recent progress in the nuclear matrix element calculation using the finite-amplitude method for QRPA (13:40-14:10)
Abstract:
The finite-amplitude method (FAM) allows us to perform the quasiparticle random-phase approximation (QRPA) in an efficient way. In this talk I will show the application of the finite-amplitude method to the nuclear matrix element of the 2\nu\beta\beta decay. I will also report the status of the application of the FAM to the 0\nu\beta\beta decay using the emulator technique based on the reduced basis method.
| Nobuo Hinohara (University of Tsukuba) |
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| 14:00 |
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High precision description of two neutrino double beta decay spectra (14:10-14:40)
Abstract:
With recent measurements of the two neutrino double beta decay high precision electron spectra, combining with charge exchange or beta-decay experimental data, we give severe constraints over the current nuclear many body calculations. Our calculation shows that Quasi-particle Random Phase Approximation (QRPA) approach can well reproduce the measured spectra for the two open shell nuclei, Se82 and Mo100. For the closed shell nucleus Xe136, QRPA can also reproduce the spectra with proper treatments.
| DongLiang Fang (Institute of Modern Physics, China Academy of Sciences) |
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| 14:30 |
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Study of Neutrinoless Double Beta Decay in Nuclear Shell Model (14:40-15:10)
Abstract:
Recent topics on calculating nuclear matrix element are discussed in terms of nuclear shell model calculations.
| Yoritaka Iwata (Osaka University of Economics and Law) |
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| 15:00 |
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| Break(15:10-15:30) |
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Session V (15:30-17:00)
Chair:---- (----) |
| 15:30 | Impact from nuclear structure aspects on the neutrinoless double-beta decay (15:30-16:00)
Abstract:
In this talk, I will outline recent works on 0νββ nuclear matrix elements by using the Hamiltonian-based generator coordinate method, which enables the treatment of collective and non-collective correlations on the same footing. I will demonstrate the impact from nuclear structural aspects on the 0νββ matrix element calculations. In addition, I will discuss some strengths and weaknesses and give a prospectus for future improvements.
| Changfeng Jiao (Sun Yat-sen University) |
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| 16:00 | Measurement of two-neutrino double-electron capture in the XENON experiments (16:00-16:30)
Abstract:
In recent years xenon-based dark matter direct detection experiments have reached large enough target masses and low enough background levels to additionally probe rare double-weak decays. Among these decays is the two-neutrino double-electron capture of Xe-124. While it is a Standard Model process, it was only detected by XENON1T in 2018. The decay provides nuclear structure information from the proton-rich side of the nuclide chart that can be used as a benchmark for nuclear models. Such models are required to interpret results from searches for the hypothetical neutrinoless double-beta decay. This contribution will present results from XENON1T and discuss prospects for measurements in XENONnT with its three times larger active xenon mass and five times lower background.
| Christian Wittweg (Physik-Institut, University of Zurich) |
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| 16:30 | Uncertainties of nuclear matrix elements of neutrinoless double beta decay based on Skyrme QRPA model and beyond (16:30-17:00)
Abstract:
The uncertainty in the nuclear matrix elements (NMEs) of 0νββ decay in the self-consistent quasiparticle random phase approximation (QRPA) method is investigated by using eighteen Skyrme interactions supplemented with either a volume- or surface-type of pairing interactions. The NMEs for the isotopes concerned (except 136Xe) are less sensitive to the particle-hole (ph) interactions, while strongly dependent on the employed isovector particle-particle (pp) pairing interactions even though the pairing strengths are optimized to the same pairing gap. The higher-order many-body correlation effects on NME of 0νββ decay are also investigated by implementing quasiparticle vibration coupling model.
| Yifei Niu (Lanzhou University) |
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