Superallowed Beta Decay Research Articles

Superallowed beta-decay between isobaric analog states up to A=99\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ extbf {A}}}=\ extbf{99}$$\\end{document}

Isospin symmetry is used to fit the precisely known QEC\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Q_{EC}$$\\end{document}-values of lighter TZ=0,-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_Z=0,-1$$\\end{document} and TZ=-1/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_Z=-1/2$$\\end{document}β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta $$\\end{document}-emitters and to extrapolate them up to Z=50\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z=50$$\\end{document}. For the T=1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {T}=1$$\\end{document} emitters the half-lives of the pure 0+→0+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0^+\\rightarrow 0^+$$\\end{document} Fermi decays are calculated and compared with experimentally known values, even for the heaviest cases where the experimental uncertainties are still rather large. For the T=1/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {T} = 1/2$$\\end{document} emitters only the Fermi component of the transitions can be predicted, but with the experimental half-lives the ratio of Gamow–Teller to Fermi strength can be determined.

Model-Independent Determination of Nuclear Weak Form Factors and Implications for Standard Model Precision Tests.

We analyze the recoil corrections in superallowed beta decays of T=1, J^{P}=0^{+} nuclei by fixing the mean square charged weak radius model independently using the data of multiple charge radii across the nuclear isotriplet. By comparing to model estimations, we argue that the existing theory uncertainty in the statistical rate function f might have been substantially underestimated. We discuss the implications of our proposed strategy for precision tests of the standard model, including a potential alleviation of the first-row CKM unitarity deficit, and motivate new experiments for charge radii measurements.

Sterile neutrinos in light of the Cabibbo-angle anomaly

Based on recent developments in the lattice simulations and calculations of the radiative corrections to the charged-current interactions, the uncertainties for each component in the CKM matrix have been sophisticated. It is known that the first-row CKM unitarity is violated at about 3σ level, implying a 3σ level deviation from the standard model prediction. This new deviation is called Cabibbo-Angle Anomaly (CAA). These CKM components are mainly extracted from kaon, pion, and the superallowed beta decays. In this contribution, we point out that a MeV scale sterile neutrino can economically explain the CAA. We consistently investigate the sterile neutrino contributions to the kaon, pion, superallowed beta decays, and also the Fermi coupling constant.

Electroweak nuclear radii constrain the isospin breaking correction to Vud

We lay out a novel formalism to connect the isospin-symmetry breaking correction to the rates of superallowed nuclear beta decays, δC, to the isospin-breaking sensitive combinations of electroweak nuclear radii that can be accessed experimentally. We individuate transitions in the superallowed decay chart where a measurement of the neutron skin of a stable daughter even at a moderate precision could already help discriminating between models used to compute δC. We review the existing experimental situation and make connection to the existing and future experimental programs.

Commissioning of the St. Benedict RF carpet

The Superallowed Transition BEta NEutrino Decay Ion Coincidence Trap (St. Benedict) aims to measure the beta-neutrino angular correlation parameter for superallowed mixed beta decay transitions between mirror nuclei in order to conduct precision tests of the Standard Model. St. Benedict will include a gas catcher, a differentially pumped extraction system, a radio-frequency quadrupole (RFQ) cooler and buncher, and a Paul trap to utilize radioactive ion beams produced at the Nuclear Science Laboratory of the University of Notre Dame. The two-part differentially pumped extraction system contains a RF carpet at a helium gas pressure of around 3 mbar, and a radio-frequency quadrupole (RFQ) ion guide at a pressure of around 2×10−3 mbar. Transport efficiency of potassium ions in the first part of the extraction system using the RF carpet in the presence of gas flow was determined to be near 100% in the 0.75 to 5 mbar pressure range using the ion surfing transport method.

Coulomb corrections to Fermi beta decay in nuclei

We study the influence of the Coulomb force on the Fermi beta-decays in nuclei. This work is composed of two main parts. In the first part, we calculate the Coulomb corrections to super-allowed beta decay. We use the notion of the isovector monopole state and the self-consistent charge-exchange Random Phase Approximation to compute the correction. In the second part of this work, we examine the influence of the anti-analog state on isospin mixing in the isobaric analog state and the correction to the beta-decay Fermi transition.

Combined constraints on first generation leptoquarks

In this article we perform a combined analysis of low energy precision constraints and LHC searches for leptoquarks which couple to first generation fermions. Considering all ten leptoquark representations, five scalar and five vector ones, we study at the precision frontier the constraints from $K\to\pi\nu\nu$, $K\to\pi e^+e^-$, $K^0-\bar K^0$ and $D^0-\bar D^0$ mixing, as well as from experiments searching for parity violation (APV and QWEAK). We include LHC searches for $s$-channel single resonant production, pair production and Drell-Yan-like signatures of leptoquarks. Interestingly, we find that the recent non-resonant di-lepton analysis of ATLAS provides stronger bounds than the resonant searches recasted so far to constrain $t$-channel production of leptoquarks. Taking into account all these bounds, we observe that none of the leptoquark representations can address the so-called "Cabibbo angle anomaly" via a direct contribution to super-allowed beta decays.

Branching ratio of the super-allowed $$\beta $$ decay of $$^{10}$$C

In an experiment performed at the ISOLDE facility of CERN, the super-allowed beta-decay branching ratio of 10C was determined with a high-precision single-crystal germanium detector. In order to evaluate the contribution of the pile-up of two 511 keV gamma quanta to one of the gamma-ray peaks of interest at 1021.7 keV, data were not only taken with 10C, but also with a 19Ne beam. The final result for the super-allowed decay branch is 1.4638(50)%, in agreement with the average from literature.

Constraints on sterile neutrinos in the MeV to GeV mass range

A detailed discussion is given of the analysis of recent data to obtain improved upper bounds on the couplings $|{U}_{e4}{|}^{2}$ and $|{U}_{\ensuremath{\mu}4}{|}^{2}$ for a mainly sterile neutrino mass eigenstate ${\ensuremath{\nu}}_{4}$. Using the excellent agreement among the $\mathcal{F}t$ values (products of kinematic rate factors times half-lives with radiative corrections included) for superallowed nuclear beta decays, an improved upper limit is derived for emission of a ${\ensuremath{\nu}}_{4}$. The agreement of the ratios of branching ratios ${R}_{e/\ensuremath{\mu}}^{(\ensuremath{\pi})}=\mathrm{BR}({\ensuremath{\pi}}^{+}\ensuremath{\rightarrow}{e}^{+}{\ensuremath{\nu}}_{e})/\mathrm{BR}({\ensuremath{\pi}}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\nu}}_{\ensuremath{\mu}})$, ${R}_{e/\ensuremath{\mu}}^{(K)}$, ${R}_{e/\ensuremath{\tau}}^{({D}_{s})}$, ${R}_{\ensuremath{\mu}/\ensuremath{\tau}}^{({D}_{s})}$, and ${R}_{e/\ensuremath{\tau}}^{(D)}$, and the branching ratios $\mathrm{BR}({B}^{+}\ensuremath{\rightarrow}{e}^{+}{\ensuremath{\nu}}_{e})$ and $\mathrm{BR}({B}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\nu}}_{\ensuremath{\mu}})$ decays with predictions of the Standard Model is utilized to derive new constraints on ${\ensuremath{\nu}}_{4}$ emission covering the ${\ensuremath{\nu}}_{4}$ mass range from MeV to GeV. We also discuss constraints from peak search experiments probing for emission of a ${\ensuremath{\nu}}_{4}$ via lepton mixing, as well as constraints from pion beta decay, CKM unitarity, $\ensuremath{\mu}$ decay, leptonic $\ensuremath{\tau}$ decay, and other experimental inputs.

Radiative corrections to neutron and nuclear beta decays revisited

The universal radiative corrections common to neutron and super-allowed nuclear beta decays (also known as ``inner'' corrections) are revisited in light of a recent dispersion relation study that found $+2.467(22)\%$, i.e.~about $2.4\sigma$ larger than the previous evaluation. For comparison, we consider several alternative computational methods. All employ an updated perturbative QCD four-loop Bjorken sum rule (BjSR) defined QCD coupling supplemented with a nucleon form factor based Born amplitude to estimate axial-vector induced hadronic contributions. In addition, we now include hadronic contributions from low $Q^2$ loop effects based on duality considerations and vector meson resonance interpolators. Our primary result, $2.426(32)\%$ corresponds to an average of a Light Front Holomorphic QCD approach and a three resonance interpolator fit. It reduces the dispersion relation discrepancy to approximately $1.1\sigma$ and thereby provides a consistency check. Consequences of our new radiative correction estimate, along with that of the dispersion relation result, for CKM unitarity are discussed. The neutron lifetime-$g_A$ connection is updated and shown to suggest a shorter neutron lifetime $< 879$ s. We also find an improved bound on exotic, non-Standard Model, neutron decays or oscillations of the type conjectured as solutions to the neutron lifetime problem, $\text{BR}(n\to \text{exotics}) < 0.16 \%$.

Gamow-Teller response in the configuration space of a density-functional-theory–rooted no-core configuration-interaction model

The atomic nucleus is a unique laboratory to study fundamental aspects of the electroweak interaction. This includes a question concerning in medium renormalization of the axial-vector current, which still lacks satisfactory explanation. Study of spin-isospin or Gamow-Teller (GT) response may provide valuable information on both the quenching of the axial-vector coupling constant as well as on nuclear structure and nuclear astrophysics. We have performed a seminal calculation of the GT response by using the no-core-configuration-interaction approach rooted on multi-reference density functional theory (DFT-NCCI). The model treats properly isospin and rotational symmetries and can be applied to calculate both the nuclear spectra and transition rates in atomic nuclei, irrespectively of their mass and particle-number parity. The method is applied to compute the GT strength distribution in selected $N\approx Z$ nuclei including the $p$-shell $^8$Li and $^8$Be nuclei and the $sd$-shell well-deformed nucleus $^{24}$Mg. In order to demonstrate a flexibility of the approach we present also a calculation of the superallowed GT beta decay in doubly-magic spherical $^{100}$Sn and the low-spin spectrum in $^{100}$In. It is demonstrated that the DFT-NCCI model is capable to capture the GT response satisfactorily well by using relatively small configuration space exhausting simultaneously the GT sum rule. The model, due to its flexibility and broad range of applicability, may either serve as a complement or even as an alternative to other theoretical approaches including the conventional nuclear shell model.

Testing CVC and CKM Unitarity via superallowed nuclear beta decay

Currently, the most restrictive test of the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix is anchored by nuclear beta decay. Precise measurements of the ft-values for superallowed beta transitions between analog 0+ states are used to determine GV, the vector coupling constant; this, in turn, yields Vud, the up-down quark-mixing element of the CKM matrix. The determination of a transition’s ft-value requires the measurement of three quantities: its Q value, branching ratio and parent half-life. To achieve 0.1% precision on the final result, each of these quantities must be measured to substantially better precision, for which special techniques have had to be developed. A new survey and analysis of world data reveals that there are now fourteen such transitions with ft-values known to ∼ 0.1% precision or better, and that they span a wide range of nuclear masses, from 10C, the lightest parent, to 74Rb, the heaviest. Of particular interest is the recent completion of the first mirror pair of 0+ → 0+ transitions, 38Ca → 38mK and 38mK → 38Ar, which provides a valuable constraint on the calculated isospin-symmetry-breaking corrections needed to derive GV from the experimental data. As anticipated by the Conserved Vector Current hypothesis, CVC, all fourteen transitions yield consistent values for GV. The value of Vud derived from their average makes it by far the most precisely known element of the CKM matrix, which, when combined with the other top-row elements, Vus and Vub, leads to the most demanding test available of the unitarity of that matrix. Since CKM unitarity is a key pillar of the Electroweak Standard Model, this test is of fundamental significance.

Isospin corrections to super-allowed beta decays in nuclei

Isospin corrections to the super-allowed beta decay matrix elements are evaluated in perturbation theory using the notion of the giant isovector monopole state. The calculation avoids the separation into different contributions and therefore presents a consistent, systematic and more transparent approach. Explicit expressions for δc as a function of the mass number A are derived. These corrections affect the values of the Vud matrix element in the Cabbibo-Maskawa-Kobayashi matrix. Also, it is pointed out that in some nuclei with a low number of excess neutrons (protons) Coulomb mixing with the anti-analog state can introduce significant isospin impurities in the isobaric analog state.

βDecay ofCa38: Sensitive test of Isospin Symmetry-Breaking Corrections from Mirror Superallowed0+→0+Transitions

We report the first branching-ratio measurement of the superallowed 0+→0+β transition from Ca38. The result, 0.7728(16), leads to an ft value of 3062.3(68)s with a relative precision of ±0.2%. This makes possible a high-precision comparison of the ft values for the mirror superallowed transitions, Ca38→38mK and K38m→Ar38, which sensitively tests the isospin symmetry-breaking corrections required to extract Vud, the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, from superallowed β decay. The result supports the corrections currently used and points the way to even tighter constraints on CKM unitarity.

Relation between isospin-symmetry-breaking correction to superallowedβdecay and the energy of the charge-exchange giant monopole resonance

After application of an analytical transformation, a new exact representation for the nuclear isospin-symmetry breaking correction $\delta_C$ to superallowed beta decay is obtained. The correction is shown to be essentially the reciprocal of the square of an energy parameter $\Omega_M$ which characterizes the charge-exchange monopole strength distribution. The proportionality coefficient in this relation is determined by basic properties of the ground state of the even-even parent nucleus, and should be reliably calculable in any realistic nuclear model. Therefore, the single parameter $\Omega_M$ contains all the information about the properties of excited $0^+$ states needed to describe $\delta_C$. This parameter can possibly be determined experimentally by charge-exchange reactions. Basic quantities of interest are calculated within the isospin-consistent continuum random phase approximation, and the values of $\delta_C$ are compared with the corresponding results from other approaches.

The influence of pairing correlations on the isospin symmetry breaking corrections of superallowed Fermi beta decays

Within the framework of quasi-particle random phase approximation, the isospin breaking correction of superallowed 0+ → 0+ beta decay and unitarity of Cabibbo-Kobayashi-Maskawa mixing matrix have been investigated. The broken isotopic symmetry of nuclear part of Hamiltonian has been restored by Pyatov’s method. The isospin symmetry breaking correction with pairing correlations has been compared with the previous results without pairing. The effect of pairing interactions has been examined for nine superallowed Fermi beta decays; their parent nuclei are 26Al, 34Cl, 38K, 42Sc, 46V, 50Mn, 54Co, 62Ga, 74Rb.

The ft values of the superallowed Fermi beta decays

In this work, the ft values of the 0+→0+ superallowed Fermi beta decays have been investigated. In the calculations, the shell model has been modified by Pyatov’s restoration method because of the isospin breaking and the transition matrix elements have been found by means of the quasi-particle random phase approximation (QRPA).

The isospin mixing and the superallowed Fermi beta decay

In the present work, the isospin admixtures in the nuclear ground states of the parent nuclei and isospin structure of the isobar analog resonance (IAR) states have been investigated by studying the 0 + →0 + superallowed Fermi β decays using Pyatov’s restoration method. Within the random phase approximation (RPA), in this method, the effect of isospin breaking due to the Coulomb forces has been evaluated, taking into account the effect of pairing correlations between nucleons.

Microscopic Calculations of Isospin-Breaking Corrections to Superallowed Beta Decay

The superallowed β-decay rates that provide stringent constraints on physics beyond the standard model of particle physics are affected by nuclear structure effects through isospin-breaking corrections. The self-consistent isospin- and angular-momentum-projected nuclear density functional theory is used for the first time to compute those corrections for a number of Fermi transitions in nuclei from A=10 to A=74. The resulting leading element of the Cabibbo-Kobayashi-Maskawa matrix, |V(ud)|=0.97447(23), agrees well with the recent result of Towner and Hardy [Phys. Rev. C 77, 025501 (2008)].

QECValues of the SuperallowedβEmittersCl34andKm38

The superallowed beta-decay Q(EC) values of (34)Cl and (38)K(m) have been measured with an online Penning trap to be 5491.662(47) keV and 6044.223(41) keV, respectively. The new values are more precise than the previous high-precision reaction-based values but are consistent with them and establish that there are no significant systematic differences between the two types of measurements.