Continuum effects in excited states of light hypernuclei

The spectra of the hypernuclei ⁶_ΛLi, ⁷_ΛLi and ⁹_ΛBe are calculated in the lambda particle - neutron hole basis using the Green's function method. The model includes the effects of the Λ continuum. As a result the Λ escape widths are calculated. for the various hypernuclear states. A comparison with the recently measured strangeness exchange (K⁻, π⁻) reaction results is made.     

Baryon decays and gamma-spectroscopy of hypernuclei

The applicability of (K ^–,^–) - and (K ^–,^– N)-reactions on^13,14C and^14,15N nuclei to the study of -transitions in primary and daughter -hypernuclei is discussed. The intensity of -deexcitation of ¹³C state |S ¹²C(15·11 MeV; 1⁺1): 1/2⁺ has been shown to be comparable with the intensity of baryon decay. Isospin selection rules are used to distinguish excitation energy ranges of primary hypernuclei, where the identification of the secondary -lines is probable.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

Pionic decay of hypernuclei

The mass number dependence of the total pionic decay rate of hypernuclei is evaluated under the closure approximation by using DDHF single-particle wave functions and taking into account the pion distortion and absorption. The effect ofNN andN correlations are then incorporated and found to give a drastic enhancement especially in heavy hypernuclei. More detailed features are discussed for partial and total decay rates of typical light hypernuclei.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

Two-neutrino double beta decay to excited states

Both doubleβ ⁻ and doubleβ ⁺/EC decay transitions to excited final states in the two-neutrino mode are discussed, their gross properties reviewed and a compilation of recent calculations presented. A brief presentation of the involved nuclear models is given. The close connection between the single and double beta decays is discussed. Presented at Workshop on calculation of double-beta-decay matrix elements (MEDEX’97), Prague, May 27–31, 1997.     

Excited states of hypernuclei

A two-body model of a hypernucleus with realistic N potentials is used to calculate the energies of the excited states of the particle in heavy hypernuclei. The positions of the levels are investigated as functions of: a) the form of the N potential, b) the size of the core nucleus and the form of the nucleon density, and c) the mass number A.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 33–37, April, 1980.     

Double-beta decay to the excited states (Experiment)

The brief review on the decay to excited states of daughter nuclei is performed. New positive result of experiments with ¹⁰⁰Mo for transition to 0⁺ excited state in ¹⁰⁰Ru are presented.     

Asymmetric weak decay of polarized hypernuclei

We measured the asymmetric weak decay of the polarized _Λ⁵He hypernuclei. The polarization was derived by the observed asymmetry of the mesonic decay pions for the first time. The asymmetry parameter of the nonmesonic decay has been evaluated using the obtained polarization and the asymmetry of the decay protons. The positive asymmetry parameter contradicts theoretical prediction based on meson exchange model. The present data indicates the limitation of the model in ΛN weak interaction, in particular short range phenomena such the nonmesonic decay of hypernuclei.     

Baryon number violating nuclear decay

The expressions for baryon number violating nuclear partial decay widths are derived from the interactions as predicted by grand unified theories. Theory predicts that the baryon number violating proton decay inside the nucleus is hindered relative to the free proton decay rate. In the case of closed shell nuclei, the meson spin-isospin dependence of the partial width is the same as that for the nucleon decay. The branching ratios of decay amplitudes depend on the nuclear binding energies. Nuclear structure introduces lepton energy spread of ±49.5 MeV for light closed shell nuclei, while it does not affect the back to back emission of lepton-meson pair.     

Gamma decay of the lowly excited states of 189Re

189W activities were produced via the 192Os(n, α) reaction using irradiation of isotopically enriched 192Os metallic powder of ～100 mg/cm2 with 14 MeV neutrons. The X-γ and γ-γ coincidence measurements were made so as to obtain γ rays from 189W decay and its coincidence relations. A new simple decay scheme of 189W including three γ rays of 210.2, 229.6 and 260.2 keV is proposed. Two new levels of 189Re at 470.4 and 489.8 keV are assigned.     

Spontaneous decay of excited atomic states near a carbon nanotube

The spontaneous decay process of an excited atom placed inside or outside a carbon nanotube is analyzed. Calculations have been performed for various achiral nanotubes. The effect of the nanotube surface is shown to increase the atomic spontaneous decay rate by up to 6 orders of magnitude compared with that of the same atom in vacuum. This increase is associated with nonradiative decay via surface excitations in the nanotube.     

Isospin effects upon the decay of highly excited nuclear states

It is proposed that T_< states which strongly mix with analog states to give states of mixed isospin results in the enhancement of the probability of proton decay from highly excited nuclear states. Such considerations are shown to explain the anomalies observed in the ($\text{p, n}\text{p}$) reactions.     

pi-Mesonic decay of hypernuclei and pion wavefunction

The pi-mesonic decay of hypernuclei is studied by using the pion distorted waves which are the solutions of the Klein-Gordon equation with the optical potential. The distortions of the pion waves give rise to significant enhancement of theπ-decay rate compared with the pion free-wave case. Theπ-decay rates are very sensitive to the behavior of the pion wave deep inside the nucleus and therefore to the chosen pion optical potentials. There is a tendency that the enhancement is larger for theπ ^?-decay than for theπ ⁰-decay due to the combined effects of the Coulomb and optical potentials.     

Baryon poles in proton decay amplitudes

The decay rate of the p→π⁰e⁺ mode is calculated in SU(5) grand unified theory using a pole model with proton and $\text{1}\text{2}{}^{\mathrm{?}}$ baryon poles. Baryon-to-vacuum amplitudes are calculated in the framework of the MIT bag model. It is found that the partial decay rate [～(5×10³¹ yr)^?)] is close to the partial decay rates calculated by different methods.     

Baryon wave functions and nucleon decay

We apply to nucleon decay the knowledge about the short-distance structure of baryon wave functions gleaned from QCD form factor calculations nd the $\text{J}\text{gY →}\text{p}\text{?}\text{p}$ decay rate. We review the uncertainties arising when current algebra and PCAC are used to relate $\text{N}\text{→}\text{?}\text{+}$ meson decay rates to 〈0|qqq|N〉 matrix elements. We show that the relevant matrix elements are not directly related to those of the leading twist operators “measured” in conventional high momentum transfer physics, but argue for an indirect based on models that fit both form factor and $\text{J}\text{Ψ}$ decay data. We use these inputs to calculate the p → e⁺π⁰ decay rate in minimal SU(5) and other grand unified theories (GUTs) for a specified value of the heavy vector boson mass m_X. Our results combined with the recent experimental lower limit on this mode indicate that m_X > 2 × 10¹⁵ GeV in the minimal SU(5) GUT, and we derive analogous bounds for supersymmetric GUTs. Our calculated lifetime for a given value of m_X is considerably shorter than previous estimates made using non-relativistic SU(6) or the bag model, a difference traceable to the different normalizations of 2 and 3 quark wave functions at short distances.     

The light 1P-shell nuclei

The binding energies and other characteristics of the light 1P-shell nuclei (N, Z8) are calculated. We use the method denoted as modified oscillator shell model (MOSM), proposed by one of the authors (Nguyen tien Nguyen: Czech. J. Phys. B31 (1981) 16). We succeed in choosing the parameter set of the Skyrme-type force, which gives satisfactory and interesting results.On leave fromFaculty of Physics, Hanoi University, Vietnam.The authors would like to thank I. Wilhelm for the useful discussion.     

Investigation of the gamma decay of excited states in25Al

The gamma decay of the low-lying energy levels (E _x <4MeV) in²⁵Al has been studied through the²⁴Mg(p, γ)²⁵Al reaction using seven resonances in the proton energy rangeE _p +200?1700 keV. Ge(Li) detectors and isotopically separated targets have been used. Energies and branching ratios of several excited states have been measured. TheQ-value of the reaction was determined to be 2271.3±0.8 keV. Lifetimes, investigated by the Doppler-shift attenuation method and γ-ray angular distributions have been determined using theE _p +823, 1201, 1490 and 1660 keV resonances of the²⁴Mg(p, γ)²⁵Al reaction.     

Production of excited double hypernuclei via Fermi breakup of excited strange systems

Precise spectroscopy of multi-strange hypernuclei provides a unique chance to explore the hyperon–hyperon interaction. In the present work we explore the production of excited states in double hypernuclei following the micro-canonical break-up of an initially excited double hypernucleus which is created by the absorption and conversion of a stopped Ξ⁻${\Xi }^{-}$ hyperon. Rather independent on the spectrum of possible excited states in the produced double hypernuclei the formation of excited states dominates in our model. For different initial target nuclei which absorb the Ξ⁻${\Xi }^{-}$, different double hypernuclei nuclei dominate. Thus the ability to assign the various observable γ-transitions in a unique way to a specific double hypernuclei by exploring various light targets as proposed by the Panda Collaboration seems possible. We also confront our predictions with the correlated pion spectra measured by the E906 Collaboration.