Beta Decay Research Articles

Complementary LHC searches for UV resonances of the 0νββ decay operators

We investigate the quark-level effective operators related to the neutrinoless double beta (0νββ) decay process and their ultraviolet completions relevant to chiral enhancement effects at the hadronic level. We have classified several kinds of leptoquark models, matching to different standard model effective operators. Assuming weakly coupled new physics, we find the ongoing 0νββ decay experiments are sensitive to new physics scale at around 2–4 TeV, which is in the reach of LHC searches. We discuss the discovery potential of such resonances in the same-sign dilepton channels at the LHC. Therefore, the direct LHC searches and indirect 0νββ decay searches are complementary to each other in testing the UV completions of the effective operators for 0νββ decay. Published by the American Physical Society 2024

All orders factorization and the Coulomb problem

In the limit of large nuclear charge, Z≫1, or small lepton velocity, β≪1, Coulomb corrections to nuclear beta decay and related processes are enhanced as Zα/β and become large or even nonperturbative (with α the QED fine structure constant). We provide a constructive demonstration of factorization to all orders in perturbation theory for these processes and compute the all-orders hard and soft functions appearing in the factorization formula. We clarify the relationship between effective field theory amplitudes and historical treatments of beta decay in terms of a Fermi function. Published by the American Physical Society 2024

Neutrino mixing phenomenology: A4 discrete flavor symmetry with type-I seesaw mechanism

We study a neutrino mass model with [Formula: see text] discrete flavor symmetry using a type-I seesaw mechanism. The inclusion of extra flavons in our model leads to deviations from the exact tribimaximal mixing pattern resulting in a nonzero [Formula: see text] consistent with the recent experimental results and a sum rule for light neutrino masses is also obtained. In this framework, a connection is established among the neutrino mixing angles-reactor mixing angle ([Formula: see text]), solar mixing angle ([Formula: see text]), and atmospheric mixing angle ([Formula: see text]). This model also allows us a prediction of Dirac CP-phase and Jarlskog parameter [Formula: see text]. The octant of the atmospheric mixing angle [Formula: see text] occupies the lower octant. Our model prefers Normal Hierarchy (NH) than Inverted Hierarchy (IH). We use the parameter space of our model of neutrino masses to study the neutrinoless double beta decay parameter [Formula: see text].

Anomalies in global SMEFT analyses. A case study of first-row CKM unitarity

Recent developments in the Standard Model analysis of semileptonic charged-current processes involving light quarks have revealed ~ 3σ tensions in Cabibbo universality tests involving meson, neutron, and nuclear beta decays. In this paper, we explore beyond the Standard Model explanations of this so-called Cabibbo Angle Anomaly in the framework of the Standard Model Effective Field Theory (SMEFT), including not only low-energy charged current processes (‘L’), but also electroweak precision observables (‘EW’) and Drell-Yan collider processes (‘C’) that probe the same underlying physics across a broad range of energy scales. The resulting ‘CLEW’ framework not only allows one to test explanations of the Cabibbo Angle Anomaly, but is set up to provide near model-independent analyses with minimal assumptions on the flavor structure of the SMEFT operators. Besides the global analysis, we consider a large number of simpler scenarios, each with a subset of SMEFT operators, and investigate how much they improve upon the Standard Model fit. We find that the most favored scenarios, as judged by the Akaike Information Criterion, are those that involve right-handed charged currents. Additional interactions, namely oblique operators, terms modifying the Fermi constant, and operators involving right-handed neutral currents, play a role if the CDF determination of the W mass is included in the analysis.

Design and fabrication of low background, high energy resolution thermal bonding Micromegas detectors for the PandaX-III experiment

The high-pressure xenon time projection chamber (TPC) utilizing micro-pattern gaseous detector readout has emerged as a highly promising technical solution for the search of neutrino-less double beta decay events. This approach offers exceptional features, including high energy resolution, fine granularity, low background radioactivity, and scalability for large-scale experiments. In line with these advantages, the PandaX-III experiment aims to implement a 10 bar Xe136 TPC, employing a readout plane comprising 52 194 × 194 mm2 Micromegas detectors, within the China Jinping Underground Laboratory.To fulfill the stringent experimental requirements of PandaX-III, a low-background Micromegas detector with high energy resolution was proposed and developed using the thermal bonding method. The performance of the thermal bonding Micromegas prototypes was investigated using X-ray characterization under various gas mixtures with argon and isobutane from 1 bar to 10 bars. Remarkable results were presented at 1 bar gas pressure, where a maximum gas gain of ∼8 × 104 and the best energy resolution (FWHM @5.9 keV) of 13.6% is obtained, and at 10 bar pressure, where maximum gas gain exceeding 104, the best energy resolution of 19%, and excellent stability over a test duration exceeding 150 h is achieved.

Astatine-211 Radiopharmaceuticals; Status, Trends, and the Future.

The low range of alpha particles provides an opportunity to better target cancer cells theoretically leading to the introduction of interesting alpha emitter radiopharmaceuticals including 225Ac, 212Pb, etc. The combination of high energy and short range of alpha emitters differentiates targeted radiotherapy from other methods and reduces unwanted cytotoxicity of the cells around the tumoral tissue. Among interesting alpha emitters candidates for targeted therapy, 211At, one of the radioisotopes with the best optimal decay properties, shows great promise for targeted radiotherapy in some animal prostate cancer xenograft studies and bone micro tumors with significant effects compared to other beta and alpha emitters and also demonstrates interesting properties for clinical applications. However, production and application of this alpha emitter in the development of actinium-based radiopharmaceuticals is hampered by many obstacles. This mini-review demonstrates 211At production methods, chemical separation, radiolabeling procedures, 211At-radiopharmaceuticals and their clinical trials, transport, logistics, and costs and future trends in the field for ultimate clinical applications. This review showed that there are limited clinical trials on 211Ac-based radiopharmaceuticals, which is due to the low accessibility of this radioisotope and other limitations. However, the development programs of major industries indicate the development of 211Ac-based radiopharmaceuticals in the future.

Design and preliminary test results of the charge sensitive amplifier for gain-less charge readout in high-pressure TPC

This paper presents the design and electrical test results of a low-noise front-end chip (named Topmetal-S) in a High-pressure Time Projection Chamber (TPC) for searching the neutrinoless double beta decay. The Topmetal-S has been fabricated in a 130 nm CMOS technology. The proposed front-end chip consists of a charge collection electrode, a Charge Sensitive Amplifier (CSA) and peripheral circuits. The test results indicate that the CSA features an input linear dynamic range of approximately 6.64 fC, a charge-conversion gain of about 220 mV/fC and an Equivalent Noise Charge (ENC) of approximately 115 e - after a digital trapezoidal pulse shaper.

Shell-model study of [formula omitted] values for 139,140,141Ba → 139,140,141La transitions

In the present work, beta-decay properties such as log⁡ft values and half-lives have been systematically studied corresponding to Ba isotopes using large-scale shell-model calculations. An extensive comparison of beta decay results corresponding to 141Ba → 141La using shell-model calculations is made with the recently available experimental data. In addition, we have also calculated the nuclear and beta decay properties corresponding to 139Ba → 139La and 140Ba → 140La transitions. The model-space considered here is Z=50−82 and N=82−126 with 132Sn core, and the interaction employed here is jj56pnb interaction. The beta decay results using shell-model calculations for all the mentioned isotopes are compared with the available experimental data. This is the first theoretical interpretation corresponding to recent experimental data.

Revisiting Trimaximal TM2 mixing in two A4 modular symmetries

In this paper, we discuss a minimal lepton flavor model with two modular [Formula: see text] symmetries, one acting on neutrinos and the other acting on charged leptons. Two corresponding moduli fields are restricted at stabilizers. To avoid vanishing or degenerate lepton masses, the stabilizer in the charged lepton sector always preserves a [Formula: see text] symmetry, and that in the neutrino preserves a [Formula: see text] symmetry. By scanning all viable stabilizers, a unique Trimaximal TM2 mixing is predicted. However, the prediction of the lightest neutrino mass and the mass parameter in neutrinoless double beta decay, as well as two Majorana phases, are different and classified into three cases.

Selection and purification of Li2CO3 precursor for bolometric double beta decay experiments

This paper describes the preparation of radiopure lithium carbonate powder for the needs of low-background research, in particular, AMoRE-II, the second phase of a search for the neutrinoless double-beta decay (0νDBD) of the 100Mo isotope using over 100 kg of 100Mo contained in 200 kg of ultra-pure Li2100MoO4 bolometric crystals. About 150 kg of pure Li2CO3 powder is required to synthesize the crystals. The desired radiopurity for the lithium powder is 40K below 100 mBq/kg, and Th/U and Ra are at a few mBq/kg. Several commercially available powders were tested with ICP-MS and HPGe detectors at the Center for Underground Physics (CUP) of the Institute for Basic Science in Korea. The lowest purity of the tested products was 99.99%. The results of the powders’ radioassay at CUP showed that none of the tested products were suited for the 0νDBD search application. A special purification technology had to be developed to remove the original contamination of the powder with potassium (K), thorium (Th), uranium (U), and radium (Ra). Lithium carbonate crystallization via carbonization technique was inefficient in removing radiochemical impurities. Lithium formate fractional recrystallization effectively removed Ra, K, and Th, but the synthesis of the final lithium carbonate product had a low yield and required the introduction of additional chemicals. The analysis results of raw and purified powders, the decontamination efficiency, and plans are described in the article.

Bell inequality is violated in B0→J/ψK*(892)0 decays

The violation of the Bell inequality is one of the hallmarks of quantum mechanics and can be used to rule out local deterministic alternative descriptions. We utilize the data analysis published by the LHCb Collaboration on the helicity amplitudes for the decay B0→J/ψK*(892)0 to compute the entanglement among the polarizations of the final vector mesons and the violation of the Bell inequality that it entails. We find that quantum entanglement can be detected with a significance well above 5σ (nominally 84σ) and Bell inequality is violated with a significance well above 5σ (nominally 36σ)—thereby firmly establishing these distinguishing feature of quantum mechanics at high energies in a collider setting and in the presence of strong and weak interactions. Entanglement is also present and the Bell inequality is violated in other decays of the B mesons into vector mesons, but with lesser significance. Published by the American Physical Society 2024

Neutrino mass sum rules from modular A4 symmetry

Modular symmetries offer a dynamic approach to understanding the flavor structure of leptonic mixing. Using the modular A4 flavor symmetry integrated in a type-II seesaw, we propose a simple and minimalistic model that restricts the neutrino oscillation parameter space and, most importantly, introduces a sum rule in the physical neutrino masses. When combined with the mass squared differences observed in neutrino oscillations, this sum rule determines the absolute neutrino mass scale. This has significant implications for cosmology, neutrinoless double beta decay experiments, and direct neutrino mass measurements. In particular, the model predicts ∑imi≈0.1 eV for both normal and inverted ordering, and thus can be fully probed by the current generation of cosmological probes in the upcoming years. Published by the American Physical Society 2024

Toward distinguishing Dirac from Majorana neutrino mass with gravitational waves

We propose a new method toward distinguishing the Dirac versus Majorana nature of neutrino masses from the spectrum of gravitational waves (GWs) associated with neutrino mass genesis. Motivated by the principle of generating small neutrino masses without tiny Yukawa couplings, we assume generic seesaw mechanisms for both Majorana and Dirac neutrino masses. For Majorana neutrinos, we further assume a spontaneously broken gauged U(1)B−L symmetry, independently of the type of Majorana seesaw mechanism, which gives a cosmic string induced GW signal flat over a wide range of frequencies. For Dirac neutrinos, we assume the spontaneous breaking of a Z2 symmetry, the minimal symmetry choice associated with all Dirac seesaw mechanisms, which is softly broken, generating a peaked GW spectrum from the annihilation of the resulting domain walls. In fact, the GW spectra for all types of Dirac seesaws with such a broken Z2 symmetry are identical, subject to a mild caveat. As an illustrative example, we study the simplest respective type-I seesaw mechanisms, and show that the striking difference in the shapes of the GW spectra can help differentiate between these Dirac and Majorana seesaws, complementing results of neutrinoless double beta decay experiments. We also discuss detailed implications of the recent NANOGrav data for Majorana and Dirac seesaw models. Published by the American Physical Society 2024

Revisiting renormalization group equations of the SMEFT dimension-seven operators

In this work, we revisit the renormalization group equations (RGEs) of dimension-seven (dim-7) operators in the Standard Model effective field theory (SMEFT) resulting from mixing among dim-7 operators themselves by means of the background field method. Adopting a recently proposed physical basis for dim-7 operators, we achieve the explicit RGEs of all non-redundant dim-7 operators in the SMEFT for the first time. Together with those originating from the dim-5 and dim-6 operators, these results constitute the complete RGEs of dim-7 operators, and hence can be exploited to study full RG-running effects on some lepton- or baryon-number-violating processes involving dim-7 operators in the SMEFT, such as neutrino masses, neutrinoless double beta decay, meson and nucleon decays. We perform an analysis of the structure and perturbative power counting of the obtained one-loop anomalous dimension matrix, which is consistent with a non-renormalization theorem and the naive dimension analysis. Additionally, a partial check on some results is carried out by means of different tools and quantum field gauges.

Development of samarium-doped phosphate glass microspheres for internal radiotheranostic applications

Internal radiotherapy delivers radioactive sources inside the body, near to or into malignant tumours, which may be particularly effective when malignancies are not responding to external beam radiotherapy. A pure beta emitter, 90Y, is currently used for internal radiotherapy. However, theranostic radionuclide-doped microspheres can be developed by incorporating 153Sm, which emits therapeutic beta and diagnostic gamma energies. This study investigated the production of high concentrations of samarium-content doped phosphate-based glass microspheres. The glass P60 (i.e. 60P2O5-25CaO-15Na2O) was mixed with Sm2O3 at ratios of 75:25 (G75:Sm25), 50:50 (G50:Sm50) and 25:75 (G25:Sm75) and processed via flame spheroidisation. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) confirmed the microsphere uniformity with significantly high samarium content up to 44 % in G25:Sm75. Via X-ray diffraction (XRD) analysis, samarium-doped microspheres appeared to be glass–ceramic in nature. Mass-loss, size and pH changes were performed over 28 days, revealing a significant increase in samarium microsphere stability. After 15 min of neutron activation (neutron flux 3.01 × 1013 n.cm−2.s−1), the specific activity of the microspheres (G75:Sm25, G50:Sm50 and G25:Sm75) was 0.28, 0.54 and 0.58 GBq.g−1, respectively. Therefore, the samarium microspheres produced in this study provide great potential for improving internal radiotherapy treatment for liver cancer by avoiding complex procedures and using less microspheres with shorter irradiation time.

Search for the decay Bs0→J/ψπ0 at Belle experiment

We have analyzed 121.4 fb−1 of data collected at the ϒ(5S) resonance by the Belle experiment using the KEKB asymmetric-energy e+e− collider to search for the decay Bs0→J/ψπ0. We observe no signal and report an upper limit on the branching fraction B(Bs0→J/ψπ0) of 1.21×10−5 at 90% confidence level. This result is the most stringent, improving the previous bound by 2 orders of magnitude. Published by the American Physical Society 2024

First Study of the PIKACHU Project: Development and Evaluation of High-Purity Gd3Ga3Al2O12:Ce Crystals for 160Gd Double Beta Decay Search

Abstract Uncovering neutrinoless double beta decay (0ν2β) is crucial for confirming neutrinos’ Majorana characteristics. The decay rate of 0νββ is theoretically uncertain, influenced by nuclear matrix elements that vary across nuclides. To reduce this uncertainty, precise measurement of the half-life of neutrino-emitting double beta decay (2ν2β) in different nuclides is essential. We have launched the PIKACHU (Pure Inorganic scintillator experiment in KAmioka for CHallenging Underground sciences) project to fabricate high-purity Ce-doped Gd3Ga3Al2O12 (GAGG) single crystals and use them to study the double beta decay of 160Gd. Predictions from two theoretical models on nuclear matrix element calculations for 2ν2β in 160Gd show a significant discrepancy in estimated half-lives, differing by approximately an order of magnitude. If the lower half-life estimation holds true, detecting 2ν2β in 160Gd could be achievable with a sensitivity enhancement slightly more than an order of magnitude compared to prior investigations using Ce-doped Gd2SiO5 (GSO) crystal. We have successfully developed GAGG crystals with purity levels surpassing previous standards through refined purification and selection of raw materials. Our experiments with these crystals indicate the feasibility of reaching sensitivities exceeding those of earlier studies. This paper discusses the ongoing development and scintillator performance evaluation of High-purity GAGG crystals, along with the anticipated future prospects of the PIKACHU experiment.

Constraints on subleading interactions in beta decay Lagrangian

We discuss the effective field theory (EFT) for nuclear beta decay. The general quark-level EFT describing charged-current interactions between quarks and leptons is matched to the nucleon-level non-relativistic EFT at the OMeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O}\\left(\ extrm{MeV}\\right) $$\\end{document} momentum scale characteristic for beta transitions. The matching takes into account, for the first time, the effect of all possible beyond-the-Standard-Model interactions at the subleading order in the recoil momentum. We calculate the impact of all the Wilson coefficients of the leading and subleading EFT Lagrangian on the differential decay width in allowed beta transitions. As an example application, we show how the existing experimental data constrain the subleading Wilson coefficients corresponding to pseudoscalar, weak magnetism, and induced tensor interactions. The data display a 3.5 sigma evidence for nucleon weak magnetism, in agreement with the theory prediction based on isospin symmetry.

Solar neutrino background in high-pressure gaseous 82SeF6 TPC neutrinoless double beta decay experiments* *Supported in part by the National Natural Science Foundation of China (12105110) and National Key Research and Development Program of China (2022YFA1604703)

In this study, the possibility of observing a solar neutrino background in a future neutrinoless double beta decay experiment using a high-pressure gaseous 82SeF6 TPC is investigated. Various contributions are simulated, and possible features that could be used for event classification are discussed; two types of backgrounds are identified. The rate of multi-site background events is approximately 0.63 events/(ton·yr) in a 30 keV ROI window. This background could be effectively reduced to less than 0.0001 events/(ton·yr) (95% C.L.) while maintaining a high signal efficiency of 93% by applying a selection based on the number of clusters and energy of the leading cluster. The rate of the single-electron background events is approximately 0.01 events/(ton·yr) in the ROI. Assuming a reduction factor of 10 for the single-electron background events obtained via the algorithms developed for radioactive background rejection, the total background induced by the solar neutrino would be 0.001 events/(ton·yr), which is sufficiently small for conducting ton-level experiments.

How long do neutrinos live and how much do they weigh?

The next-generation water Cherenkov Hyper-Kamiokande detector will be able to detect thousands of neutrino events from a galactic Supernova explosion via Inverse Beta Decay processes followed by neutron capture on Gadolinium. This superb statistics provides a unique window to set bounds on neutrino properties, as its mass and lifetime. We shall explore the capabilities of such a future detector, constraining the former two properties via the time delay and the flux suppression induced in the Supernovae neutrino time and energy spectra. Special attention will be devoted to the statistically sub-dominant elastic scattering induced events, normally neglected, which can substantially improve the neutrino mass bound via time delays. When allowing for a invisible decaying scenario, the 95% CL lower bound on τ/m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ au /m$$\\end{document} is almost one order of magnitude better than the one found with SN1987A neutrino events. Simultaneous limits can be set on both mν\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$m_\ u $$\\end{document} and τν\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ au _{\ u }$$\\end{document}, combining the neutrino flux suppression with the time-delay signature: the best constrained lifetime is that of ν1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ u _1$$\\end{document}, which has the richest electronic component. We find τν1≳4×105\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ au _{\ u _1}\\gtrsim 4\ imes 10^5$$\\end{document} s at 95% CL. The tightest 95% CL bound on the neutrino mass we find is 0.34 eV, which is not only competitive with the tightest neutrino mass limits nowadays, but also comparable to future laboratory direct mass searches. Both mass and lifetime limits are independent on the mass ordering, which makes our results very robust and relevant.