Pion decay in magnetic fields

The leptonic decay of the charged pion in the presence of background magnetic fields is investigated using quenched Wilson fermions. It is demonstrated that the magnetic field opens up a new channel for this decay. The magnetic field-dependence of the decay constants for both the ordinary and the new channel is determined. Using these inputs from QCD, we calculate the total decay rate perturbatively.

FLAVOR CONSERVATION, MICRO-CAUSALITY AND GSI ANOMALY

The GSI anomaly brings the theoretical controversy whether the total amplitude of the electron capture (EC) decay is the coherent sum of the amplitude of the different massive neutrino channel. According to the coherent interpretation, the oscillation of the EC decay rate is the result of the flavor state of the neutrino and the time scale of order 10–100 s. We find that the introduction of the flavor state and that of the nonzero time scale in the frame of the time-dependent perturbation theory would bring the considerable flavor violation in the total decay rate, which is in contradiction with the micro-causality. Employing the correct time scale t(t≪1 s ), the right EC decay rate is obtained which is the result of the incoherent sum of the component probability with the mass eigenstates. Accordingly, there is no oscillation term in the total decay rate.

NONMESONIC DECAY OF Λ AND ΛΛ HYPERNUCLEI

Nonmesonic weak decays of single and double hypernuclei are studied on the basis of two-body baryon-baryon interactions, ΛN → NN and ΛΛ → YN transitions. The two-body weak transition is described by the combination of two processes, i.e., meson exchange and direct quark processes. The result indicates the importance of the direct quark(DQ) contribution. It largely enhances both the total decay rate and Γnn/Γpn ratio, and its property is different from the heavy meson exchanges (i.e. η, ρ, ω, and K*). The quark-meson hybrid picture, such as π+K+ DQ , reproduces the current experimental data except for the asymmetry parameter for light hypernuclei. The ΛΛ → YN transition in ΛΛ hypernucleus is complement of the ΛN → NN transition because it occurs only in the J = 0 channel which is hidden by J = 1 transition in the ΛN → NN case.

Rotational Dependence of the Unimolecular Decay Rate: Benzene Cation Dissociation

We present the first example of unimolecular decay rates of a polyatomic system in which reactants are rotational state selected. Highly excited, but internal energy selected and J rotational quantum number selected benzene cations are produced in a two laser pump-pump experiment. Slow reactive decay of these ions is observed in a reflectron time-of-flight mass spectrometer and the total decay rate constant k(E, J ) is measured as a function of J. At constant internal energy E, k(E, J) decreases with increasing J.