M1 Decay Research Articles

Angular correlations in the e+e− decay of excited states in Be8

Motivated by the recent observation of anomalous electron-positron angular correlations in the decay of the 18.15 MeV 1+ excited states in 8Be, we reexamine in detail the Standard Model expectations for these angular correlations. The 18.15 MeV state is above particle threshold, and several multipoles can contribute to its $e^+e^-$ decay. We present the general theoretical expressions for $e^+e^-$ angular distributions for nuclear decay by C0, C1, C2 M1, E1, and E2 multipoles, and we examine their relative contribution to the $e^+e^-$ decay of 8Be at 18.15 MeV. We find that this resonance is dominated by M1 and E1 decay, and that the ratio of M1 to E1 strength is a strong function of energy. This is in contract to the original analysis of the $e^+e^-$ angular distributions, where the M1/E1 ratio was assumed to be a constant over the energy region Ep = 0:8-1:2 MeV. We find that the existence of a `bump' in the measured angular distribution is strongly dependent on the assumed M1/E1 ratio, with the present analysis finding the measured large-angle contributions to the $e^+e^-$ angular distribution to be lower than expectation. Thus, in the current analysis we find no evidence for axion decay in the 18.15 MeV resonance region of 8Be.

Multiple SU(3) algebras in interacting boson model and shell model: Results for (β,γ) bands and scissors 1+ band

Shell model (SM) and interacting boson model (IBM) spaces admit multiple SU(α)(3) algebras generating the same rotational spectra but different E2 decay properties, depending on the phases α in the quadrupole generator. In the ground (g) K=0+ bands in nuclei this is demonstrated recently using systems with nucleons in a single oscillator shell (Kota et al. (2019) [23]; (2020) [25]). Going beyond these preliminary studies, results are presented here for E2 decay properties of β and γ bands members, as generated by multiple SU(3) algebras, using sdgIBM and sdgiIBM examples. Also, presented are some results for the γ band using a SM example with eight protons in sdg space. In addition, results are presented for the E2 and M1 decay properties of the levels of the scissors 1+ band in heavy nuclei using sdgIBM-2 and sdgiIBM-2. The scissors 1+ band properties are also studied using a SM example with six protons in (pf) shell and twelve neutrons in (sdg) shell. These results establish that: (i) with multiple SU(3) algebras, it is possible to have rotational bands with very weak E2 strengths among the levels where normally one expects strong strengths; (ii) E2 decay strengths of the levels of γ band (also β band) to the ground band levels are quite different for some of the SU(α)(3) algebras with strong dependence on (α); (iii) it is possible to have the scissors 1+ band with the E2 and M1 decay of the low-lying levels of this band to the g band levels are strong or weak depending on (α).

Properties of Charmonium States in a Phenomenological Approach

We investigate the spectrum and decay rates of charmonium states within the framework of the non relativistic quark model by employing a Coulomb like potential from the perturbative one gluon exchange and the linear confining potential along with the potential derived from instanton vacuum to account for the hyperfine mass splitting of charmonium states in variational approach. We predict radiative E1, M1, two-photon, lepton and two-gluon decay rates of low lying charmonium states. An overall agreement is obtained with the experimental masses and decay widths. We have estimated the branching ratio of two gluons decaying into light hadrons.

Cb¯ spectrum and decay properties with coupled channel effects

The mass spectrum of $c\bar{b}$ states has been obtained using the phenomenological relativistic quark model (RQM) with coupled channel effects. The Hamiltonian used in the investigation has confinement potential and confined one gluon exchange potential (COGEP). In the frame work of RQM a study of M1 and E1 radiative decays of $c\bar{b}$ states has been made. The weak decay widths in the spectator quark approximation have been estimated. An overall agreement is obtained with the experimental masses and decay widths.

Magnetic properties of ground-state mesons

Starting with the bag model a method for the study of the magnetic properties (magnetic moments, magnetic dipole transition widths) of ground-state mesons is developed. We calculate the M1 transition moments and use them subsequently to estimate the corresponding decay widths. These are compared with experimental data, where available, and with the results obtained in other approaches. Finally, we give the predictions for the static magnetic moments of all ground-state vector mesons including those containing heavy quarks. We have a good agreement with experimental data for the M1 decay rates of light as well as heavy mesons. Therefore, we expect our predictions for the static magnetic properties (usual magnetic moments) to be of sufficiently high quality, too.

Radiative M1 transitions of heavy baryons in the bag model

We study the M1 transitions of ground state heavy baryons within a framework of the modified bag model. Calculations of transition moments and corresponding M1 decay widths are performed. For the spin $\frac{1}{2}$ baryons containing three differently flavored quarks the hyperfine mixing effects are taken into account. Results are compared with estimates obtained using various other approaches.

On the detectability of57Fe axion-photon mode conversion in the Sun

The purpose of this paper is to assess the feasibility of axion detection by X-ray spectroscopy of the sun. We review the theory of axion-photon mode conversion with special attention to axions emitted in the 14.4 keV M1 decay of 57Fe at the solar center. These then mode convert to photons in the outer layers of the solar envelope, and may in principle be detected subsequently as X-rays. For axion masses above about 10^-4 eV, resonant mode conversion at a layer where the axion mass matches the local electron plasma frequency is necessary. For axion masses above about 10^-2 eV, this mode conversion occurs too deep in the solar atmosphere for the resulting photon to escape the solar surface and be detected before Compton scattering obscures the line. At the (detectable) axion masses below this, the flux of mode converted photons predicted by axion models appears to be too low for detection to be feasible with current instrumentation. Nonresonant mode conversion for axion masses below 10^-4 eV is also plausible, but with still lower predicted fluxes, since the axion coupling constant is related to it mass. Prospects for meaningful constraints on massive axion parameters from X-ray observations of this transition from the Sun do not appear to be promising. However parameters for massless counterparts (e.g. the "arion") may still result from such observations. It may mode convert in the outer layers of the solar atmosphere, but is not restricted by this to have a small coupling constant.

Charmonium Spectrum and Their Transitions in Relativistic Quark Models

Using the phenomenological relativistic harmonic model (RHM) for quarks, we have obtained the masses of S wave charmonium states. The full Hamiltonian used in the investigation has Lorentz scalar plus vector confinement potential, along with the confined one gluon exchange potential (COGEP). A good agreement with the experimental masses for the ground state and the radially excited states is obtained for both the triplet and singlet S wave mesons. The calculated charge radii, meson decay constants, leptonic decay width, two photon decay width, and the radiative M1 decay width are in good agreement with the experimental results.

M1, M2 and hyperfine-induced decay rates in Mg-like ions of Co, Ni and Cu measured at a heavy-ion storage ring

The optical decay rates of the 3s3p 3Po2 level in Mg-like ions of 59Co, 58Ni and 63, 65Cu have been measured at a heavy-ion storage ring. The measurement is sensitive to M1, M2 and hyperfine-induced decay rates. The measurement precision is just about high enough to detect the difference in the isotope effect on the level lifetime in the ions 63, 65Cu17+. We also discuss our findings when trying to measure the hyperfine-induced decay of the lowest triplet level, 3s3p 3Po0, in the two Cu isotopes.

Dark-matter detection by elastic and inelastic LSP scattering on 129Xe and 131Xe

We calculate the nuclear matrix elements involved in the elastic and inelastic scattering of the lightest supersymmetric particle (LSP) on the 129Xe and 131Xe dark-matter detector nuclei. This is the first time when both channels are addressed within the same unified microscopic nuclear framework, namely we perform large-scale shell-model calculations with a realistic two-body interaction to produce the participant nuclear wave functions. These wave functions successfully reproduce the spectroscopic data on the relevant magnetic moments and M1 decays. The tested wave functions are used to produce annual average detection rates for both the elastic and inelastic channels. It is found that the inelastic channel has great detection potential for 129Xe if the LSP is heavy and stems from a SUSY model that enhances the spin-dependent scattering.

Inclusion of Electric Octupole Contributions Explains the Fast Radiative Decays of Two Metastable States inAr+

A laser probing investigation has yielded the lifetimes of the 3s(2)3p(4)(1D)3d (2)G(7/2,9/2) metastable doublet states of Ar+. The results, obtained with the CRYRING ion storage ring of Stockholm, are 3.0+/-0.4 and 2.1+/-0.1 s, respectively. Comparisons with theoretical values calculated with two independent theoretical approaches, i.e., the pseudorelativistic Hartree-Fock method and the multiconfiguration Breit-Pauli approach, have allowed us to establish the unexpected and extraordinary strong contribution of an electric octupole (E3) transition to the ground state, in addition to the M1 decay channels to the 3d ;{2,4}F states and the E2 contributions to the 4s 2P, 2D states.

On the unusual properties of the 282 keV state in 135Sb

Recently the first excited state in 135Sb has been observed at the unexpectedly low excitation energy of only 282keV and interpreted as mainly d 5/2 proton coupled to the 134Sn core. Based on theoretical considerations it was suggested that its low excitation energy is related to a relative shift of the proton d 5/2 and g 7/2 orbits induced by the neutron excess. We have measured the lifetime of the 282keV state by the advanced time-delayed βγγ(t) method. The measured half-life, T 1/2 = 6.1(4)ns, yields exceptionally low limits of B(M1;5/21 +→7/21 +)≤3.0×10-4 μ 2 N and B(E2;5/21 +→7/21 +)≤54e 2 fm 4. These strongly hindered M1 and slow E2 transition rates are similar to those for the transition de-populating the first excited state at 405keV in 211Bi. Results of shell model calculations with realistic interactions are presented. The M1 decay rate was found to be extremely sensistive both to the wave function and to the M1 effective operator.

Time-resolved soft-x-ray spectroscopy of a magnetic octupole transition in nickel-like xenon, cesium, and barium ions

A microcalorimeter with event mode capability for time-resolved soft-x-ray spectroscopy, and a high-resolution flat-field extreme ultraviolet spectrometer have been employed at the Livermore EBIT-I electron beam ion trap for observations and wavelength measurements of M1, E2, and M3 decays of long-lived levels in the Ni-like ions Xe{sup 26+}, Cs{sup 27+}, and Ba{sup 28+}. Of particular interest is the lowest excited level, 3d{sup 9}4s {sup 3}D{sub 3}, which can only decay via a magnetic octupole (M3) transition. For this level in Xe, an excitation energy of (590.40{+-}0.03 eV) and a level lifetime of (11.5{+-}0.5 ms) have been determined.

N II Electric Quadrupole Transition Rate Measured at a Heavy-Ion Storage Ring

The decay rate of the 2s2 2p21S0 level in N II has been measured optically (λ = 575 nm) at a heavy-ion storage ring. The result of (1.10 ± 0.27) s-1 agrees with the theoretical predictions. The new data complement an earlier study of the same level decay in O III and F IV. Over this short range of ions, the role of the E2 and M1 decay modes changes dramatically.

Relativistic many-body perturbation calculations on extreme ultraviolet and soft-x-ray transition energies in siliconlike iron

Relativistic multireference many-body perturbation theory is generalized to calculate the energies of highly excited levels in multivalence-electron ions of iron group elements responsible for soft-x-ray emission lines. Term energies of the highly excited $n=4$ states arising from the $3{s}^{2}3p4l\phantom{\rule{0.3em}{0ex}}(l=0--3)$ and $3s3{p}^{2}4l\phantom{\rule{0.3em}{0ex}}(l=0--3)$ configurations in $\mathrm{Fe}\phantom{\rule{0.3em}{0ex}}\text{XIII}$ are computed to high accuracy. Theoretical electric dipole transition probabilities and wavelengths of the transitions to low-lying $n=3$ levels are compared with solar and laboratory lines to identify hitherto unidentified $\text{and}∕\text{or}$ poorly characterized extreme ultraviolet and soft-x-ray spectral lines. $E1$, $E2$, and $M1$ decay rates and lifetimes of lower excited levels of the $n=3$ manifold are evaluated as a benchmark for future experiments.

Radiative corrections to one-photon decays of hydrogenic ions

Radiative corrections to the decay rate of n=2 states of hydrogenic ions are calculated. The transitions considered are the M1 decay of the 2s state to the ground state and the E1(M2) decays of the $2p_{1/2}$ and $2p_{3/2}$ states to the ground state. The radiative corrections start in order $\alpha (Z \alpha)^2$, but the method used sums all orders of $Z\alpha$. The leading $\alpha (Z\alpha)^2$ correction for the E1 decays is calculated and compared with the exact result. The extension of the calculational method to parity nonconserving transitions in neutral atoms is discussed.

Spectra and M1 decay widths of heavy–light mesons

The M1 decay widths of charm and bottom mesons and their excited states are sensitive to the relativistic aspect of the quark current operators and obtain a significant contribution from the interaction current that is associated with the scalar confining interaction between heavy quarks (Q) and light antiquarks ( q̄ ). Consequently they provide direct evidence on the latter. The spectra and the M1 transition widths of the D , D s and B , B s mesons and their orbital excitations are calculated here within the framework of the Blankenbecler–Sugar equation, which allows a covariant treatment, while retaining a formal similarity to the nonrelativistic approach. The hyperfine interaction in the Q q̄ mesons is modeled by screened gluon exchange, which shares many features with the instanton induced interaction. The quality of the model is tested by calculation of the spectra and M1 decay widths of charmonium.

The confining interaction and the M1 decay rates of heavy quarkonia

The confining interaction and the M1 decay rates of heavy quarkonia

Higher Order Photon Transitions in H-like and He-like Ions

Higher order photon transitions such as M1, M2 and two-photon decay are conveniently studied using highly-charged few electron ions. Here we discuss two examples from recent experiments which were done using the ATLAS facility at Argonne National Laboratory. The first is a test of Relativistic Quantum Mechanics involving a precision measurement of the spectral shape of the two-photon decay of the 1s2s1S0 state in He-like nickel and the second is a test of the theory of damping in quantum mechanics involving observation of E1–M1 interference in the electric field quenching of metastable H-like ions.

Heavy quarkonia in a covariant Salpeter model

The heavy quarkonia (charmonium c c and bottomonium b b ) are investigated in a covariant formulation of the Salpeter equation. We parameterize confinement alternatively by a linearly rising scalar or a vector interaction kernel and take into account the one-gluon-exchange (OGE) interaction in the instantaneous approximation. Mass spectra as well as leptonic, two-photon, E1 and M1 decay widths are calculated. Our results show that a reasonable description of the experimental data can be obtained with both spin structures for the confining kernel. The relativistic treatment leads to an improved description compared to nonrelativistic results for the two-photon width of the η c and to some extent for the E1-transition widths. However, characteristic deviations indicate that within a relativistic framework confinement is not described adequately by a simple potential in coordinate space.