The ντ-mass and the τ-decay modes

The behaviour of the different decay modes of the charged heavy lepton τ versus the neutrino ν_τ-mass is analyzed in detail. The τ→ν_τ A ₁ and τ→ν_τ K ^* decay rates have been evaluated using finite energy sum rules. The τ→ν_τ+ “Hadron Continuum” decay rate has been estimated within the framework of Quantum Chromodynamics (QCD). We find that the branching ratios of the semi-leptonic processes: τ→ν_τρ, τ→ν_τπ and τ→ν_τ+ “Hadron Continuum” are very sensitive to the value of the ν_τ-mass. Thus a more precise measurement of these branching ratios could provide an improved upper bound for the neutrino ν_τ-mass.     

Systematic Calculations of α-Decay Half-Lives of Well Deformed Nuclei

We perform an extensive investigation on the α decay of heavy deformed even-even and odd-A nuclei within the multichannel cluster model. The dynamics effects of core nuclei are taken into account in dealing with the interaction matrix and the α-cluster formation. Enough decay channels are considered for convergence in solving the coupled equations. Systematic calculations have been performed for 36 even-even nuclei and 32 odd-A nuclei. The calculated results show good agreement with the available experimental data concerning total α-decay half-lives and branching ratios, including the branching ratios for high-spin states.     

Predictions of 2ν and 0ν double beta decay rates for nuclei with A ⩾ 70

Microscopic calculations of double beta (ββ) decay matrix elements are presented for the first time for all potential ββ decaying nuclei with A ? 70. This replaces previous phase-space estimates for most of these nuclei. It is found that nuclear structure effects considerably influence the ββ decay rates. The best candidates for 2ν as well as 0νββ decay experiments are selected.     

The decay of 0.57 s114Cs

Fusion reactions between⁵⁸Ni projectiles and⁵⁸Ni target nuclei were used to produce¹¹⁴Cs activity, which was studied by on-line mass separation and decay spectroscopy. The obtained half-life of 0.57±0.02 s and the probability ratio of 44±3 between betadelayed proton and beta-delayed alpha emission represent data with improved precision. The absolute branching ratios for both particle decay modes were determined to be (7 ±2)×10^?2 and (1.6±0.6)×10^?3, respectively. These branching ratios and the shapes of particle spectra are discussed with reference to the statistical model calculations. Groundstate alpha decay of¹¹⁴Cs was observed with an alpha energy of 3,226±30 keV and a branching ratio of (1.8±0.6)×10^?4. An upper limit of the branching ratio for a possible ground-state proton decay was set at 5×10^?4. Fromγ-ray singles andγ-γ coincidence measurements, excited states in¹¹⁴Xe are proposed.     

πℓ2, Kℓ3and K0−K0 constraints on leptoquarks and supersymmetric particles

Mass bounds from different processes for charged Higgs particles, for pseudoscalar leptoquarks occurring in dynamically broken theories, for vector leptoquarks occurring in the Pati-Salam type of grand unified theories and for the exotic particles of supersymmetric theories are studied. The processes considered are the π → eν to π → μν branching ratio, the CP-violating K?3 decay parameters, and the CP-violating part of the K_L ? K_S mass difference. The π → eν to π → μν branching ratio sets the most stringent bounds, 0.5 TeV for charged Higgs particles, 1 TeV for pseudoscalar leptoquarks, 125 TeV for vector leptoquarks and 0.1–1 TeV for the supersymmetric partners of ordinary particles. The π?2 branching ratio should be sensitive at the present experimental accuracy to the effects of pseudoscalar leptoquarks.     

New limits on Primakoff production of hybrid mesons

I discuss constraints on properties of isoscalarJ ^PC =1^?+ exotic hybrid mesons, assuming their dominant decay mode is ηπ. This work expands on a similar study by the Rochester-Minnesota-Fermilab collaboration, which excluded ?π as the dominant decay channel for such hybrids. The experimental limits are based on Primakoff production of such states and on a VDM argument relating their radiative widths to their ?π decay modes. Using data on coherent production of ηπ⁺ systems in π⁺ collisions with nuclei, I obtain few percent limits on the ?π branching ratios for hybrid masses ?1.5 GeV.     

Neutrinoless double-beta decay and double-electron capture

The fundamental importance of searching for neutrinoless double-beta decay is widely recognized. Observation of the decay would tell us that the total lepton number is not conserved and that, consequently, neutrinos are massive Majorana fermions. The same statement could be made in the case of observing neutrinoless double-electron capture. We address the question of the sensitivity of the 0νεε decay to the effective mass of the Majorana neutrino. According to our estimates, in the case of ¹⁵²Gd and ¹⁶⁴Er the sensitivity can be comparable to the favored 0νββ decays of nuclei. The main uncertainty in the prediction of half-lives of the 0νεε decay stems from the lack of sufficient precision in measuring the mass difference between the parent and daughter atoms. More accurate measurements can be accomplished using the modern high-precision ion traps.     

New approaches to assign configurations using low-statistic γ-ray spectra

Analytical methods to deduce single particle configurations from g _K factors using branching ratios in rotational bands, especially in low-statistic cases for heavy nuclei, will be presented. Two methods utilising ??-ray branching ratios in rotational bands and also intensities in the K X-ray region of spectra are shown and results from these are given.     

Majorana neutrinos in rare meson decays

The rare meson decays K ⁺ → π ^??⁺?′⁺ and D ⁺ → K ^??⁺?′⁺ (?, ?′ = e, μ), which are induced by Majorana neutrino exchange and which are accompanied by lepton-number nonconservation, are considered. The effects of the meson structure are taken into account on the basis of the Gaussian model for the respective Bethe-Salpeter amplitudes. It is shown that existing direct experimental constraints on the decay branching ratios are overly lenient and therefore give no way to set realistic limits on effective Majorana masses. On the basis of the constraints on the lepton-mixing parameters and neutrino masses from precision measurements of electroweak processes, neutrino-oscillation experiments, searches for neutrinoless double-beta decay of nuclei, and cosmological data, indirect constraints on the branching ratios for the decays in question are obtained and found to be much more stringent than the above direct constraints.     

Tests for the pole model in exclusive and semi-inclusive decays of the D0-meson

The pole model for D⁰-nonleptonic decay implies that the final state has isospin $\text{1}\text{2}$. Experimental branching ratios are consistent with this selection rule, but the Dalitz plot for Kππ decay modes will have to show non-uniform structure in order to agree with it.     

Mass Spectrum and Decay Properties of D Meson

A comparative study of the spectroscopy and decay properties of the D meson is carried out within the framework of phenomenological quark-antiquark potential (Coulomb plus power) model using hydrogenic and Gaussian wave function. The spin-hyperfine, spin-orbit and tensor interactions are employed to obtain the pseudoscalar and vector meson masses incorporating the effect of mixing. The decay constants (f _P/V ) are computed with QCD correction using the wave function at the origin. The leptonic branching fractions and electromagnetic transition rates are also calculated in this scheme. Our predictions at potential index ν=1 are in good agreement with experimental results as well as lattice and other theoretical models.     

β delayed emission of a proton by a one-neutron halo nucleus

Some one-neutron halo nuclei can emit a proton in a β decay of the halo neutron. The branching ratio towards this rare decay mode is calculated within a two-body potential model of the initial core + neutron bound state and final core + proton scattering states. The decay probability per second is evaluated for the ¹¹Be, ¹⁹C and ³¹Ne one-neutron halo nuclei. It is very sensitive to the neutron separation energy.     

On the decay of the photo resonance in 14N and 14C nuclei

The decay of the photo resonances in ¹⁴N and ¹⁴C nuclei is analyzed in terms of the shell model with intermediate coupling. Cross sections and branching ratios of nucleon channels are compared with experimental data. Successive decay branches are estimated.     

An improved upper limit on the ντ-mass from the decay π−→π−π−π−π+π+ντ

Using the ARGUS detector at the e⁺e⁻ storage ring DORIS II, we have observed the decay τ⁻→π⁻π⁻π⁻π⁺π⁺ν_τ in tau-pair events produced at center-or-mass energies between 9.4 and 10.6 GeV. From the 5π invariant mass distribution we derive an upper limit of m(ν_τ)<35 MeV/c² at the 95% confidence level. The branching ratio for this decay channel is found to be (0.064±0.023±0.01)%.     

Bounds on a top quark with charged Higgs decay

If the top quark decays to a charged Higgs boson t→bH⁺, semileptonic decay signatures are suppressed and the mass bounds set by the UA1 top search are evaded. However the charged Higgs decay mode H⁺→τ⁺ν_τ gives a missing-ϱ_T signature; depending on the decay branching fraction and using the UA1 limits on new physics contributions to missing-ϱ_T, we set bounds on the top mass in this scenario. We also evaluate the feasibility of seeking visible-τ-jet signals for top at a pp̄ collider.     

Manifestation of a singlet heavy up-type quark in the branching ratios of rare decays K → πν \bar \nu , B → πν \bar \nu , and B → Kν \bar \nu

The implications of the model with a SU(2)-singlet up-type quark, heavy enough not to be produced at the LHC, namely, the contribution of the new quark to the branching ratios of the K → πν $ \bar \nu $ , B → πν $ \bar \nu $ , and B → Kν $ \bar \nu $ decays are investigated. It is shown that the deviation from the Standard Model can be up to 10% in the case of a 5-TeV quark. Precise measurements of these branching ratios in future experiments will allow for the observation of the contributions of the new quark or to impose stronger constraints on its mass.     

Search for decay modes of heavy and superheavy nuclei

Spontaneous fission(SF) with a new formula based on a liquid drop model is proposed and used in the calculation of the SF half-lives of heavy and superheavy nuclei(Z = 90–120). The predicted half-lives are in agreement with the experimental SF half-lives. The half-lives of decay(AD) for the same nuclei are obtained by using the Wentzel-Kramers-Brillouin(WKB) method together with Bohr-Sommerfeld(BS) quantization condition considering the isospin-dependent effects for the cosh potential. The decay modes and branching ratios of superheavy nuclei(Z =104-118) with experimental decay modes are obtained, and the modes are compared with the experimental ones and with the predictions found in the literature. Although some nuclei have predicted decay modes that are different from their experimental decay modes, decay modes same as the experimental ones are predicted for many nuclei. The SF and AD half-lives, branching ratios, and decay modes are obtained for superheavy nuclei(Z = 119–120) with unknown decay modes and compared with the predictions obtained in a previous study. The present results provide useful information for future experimental studies performed on both the AD and SF of superheavy nuclei.     

Calculated properties of superheavy nuclei

Ground-state properties of the heaviest nuclei are analyzed within a macroscopic-microscopic approach. The main attention is paid to such properties as deformation, deformation energy, energy of the first rotational state 2⁺ of a nucleus, and the branching ratio of α decay to this 2⁺ state with respect to the decay to the ground state 0⁺. The analysis concerns the problem of experimental confirmation of theoretically predicted deformed shapes of superheavy nuclei situated in the region around the nucleus ²⁷⁰Hs. A large region of even-even nuclei with proton, Z=82–128, and neutron, N=126–190, numbers is considered.     

Nuclear matrix elements for rare decays

Neutrinoless double electron capture (0νECEC) is being vigorously investigated because of the possibility of it telling us something about the absolute mass scale of the neutrino. The resonant 0νECEC is particularly interesting due to the potentially huge enhancement of its decay rate by a resonance condition. Recently the mass differences of two atom pairs were measured in order to study the enhancement of the 0νECEC rates of ⁷⁴Se and ¹¹²Sn. The associated nuclear matrix elements were also evaluated. The neutrino mass can also be detected by using beta decays with low Q values. Related to this we have investigated the second-forbidden decay branch of ¹¹⁵In with its ultra-low Q value. Open questions about nuclear and atomic contributions to the associated decay rate emerge.