Ho Tso-hsiu

ON THE DETERMINATION OF NEUTRINO MASS - A CRITICAL STATUS-REPORT

Abstract The present situation in neutrino mass determination is summarized and critically analysed from various points of view. It is shown that from various kinds of experimental measurements and astrophysical observations combined with the relevant analysis, the non-zero mass of neutrino is plausible. However, model-independent or conclusive evidence for massive neutrino is still absent.

Operator expansion method and nuclear ββ decay

Abstract Recent developments in the theoretical description of double beta decay matrix elements are outlined. We present the formalism of the operator expansion method (OEM) and discuss its physical basis. The OEM has been combined with ground state wave functions obtained in a usual QRPA calculation and applied to the problem of evaluating nuclear matrix elements for double beta decay in the 2vββ as well as in the 0vββ decay mode. For 2vββ decay we have calculated that half-lives for all possible β − β − decay candidates with A ≥ 70. We confront our results with the existing experimental data and discuss the quality of the model. 0vββ decay matrix elements are then used to extract upper limits for the effective neutrino mass from published experimental lower half-life limits. The presently sharpest limits come from experiments using isotopically enriched 76 Ge. A short discussion is devoted to a recent measurement using 238 U in a radiochemical experiment. Our conclusion is that the experimental result should be interpreted as being due to 2vββ decay, and lepton number violation is not necessary to explain the experimental finding.

A New Mechanism for Low Energy Pion Induced Double Charge Exchange Reaction

Using a method developed in theory of double beta decay[1], we propose a new mechanism, namely the two-nucleon pion absorption-emission mechanism for pion double charge exchange reaction at low energies. The calculations are compared with the experimental data of the angular distribution at and the excitation functions of the DCX reactions on , with energies . It is found that the contribution of this new mechanism is very important at low energies.

Neutrinoless Double Beta Decay—A New Formalism*

A new method—the operator expansion method is used in neutrinoless double beta decay processes. Both the neutrino mass and mixing of right-handed leptonic current are included. It is shown that for nuclear neutrinoless double beta decay in 2n mechanism, there appear some new terms besides the terms given by the conventional treatment based on closure approximation. The with a Majoron emission is also discussed.

MATRIX-ELEMENTS FOR 0 NU-BETA-BETA DECAY CALCULATED WITH THE OPERATOR EXPANSION METHOD AND QRPA WAVE-FUNCTIONS

Matrix elements for 0νββ decay of76Ge,82Se,116Cd,128,130Te,136Xe and150Nd are calculated combining proton-neutron quasiparticle RPA wave functions with the operator expansion method (OEM). The differences between OEM and earlier QRPA calculations, using the closure approximation, are investigated in detail. Special emphasis is put on the discussion on the differences between the 2νββ and the 0νββ mode, since currently 0ν matrix elements can only indirectly be tested. By a comparison with experimental data upper limits on the effective neutrino mass are derived.

Contribution of highly excited intermediate states in the pion absorption-emission mechanism of double charge exchange

Abstract Within the framework of operator expansion approach for the pion absorption-emission mechanism of double charge exchange a summation over the leading terms of the infinite commutator series is performed. The contribution of highly excited states is estimated.

Contribution of the two-nucleon pion absorption-emission mechanism to the pion-nucleus double-charge-exchange reaction

Abstract The two-nucleon pion absorption-emission mechanism 1) and its contribution to the pioni-induced double-charge-exchange (DCX) reaction at energies T π ⩽ 300 MeV is studied. By combiing this new mechanism with the conventional sequential mechanism, the 0° excitation functions for the DCX reactions to the isobaric analog states on the 14 C, 18 O, 26 Mg, and 42 Ca are calculated and compared with the experimental data. We find that the theoretical results are much improved after considering the contribution of the new mechanism, especially at low energies.

On the Reaction Mechanism and the Selection Rule in the Double Charge Exchange Reaction of Pions on Nuclei (DCX)— A Study of the Connection Between the 2β–Decay and DCX on JP=0+ Nuclei

It is shown that in the pion induced double charge exchange reaction on nuclei, there exists a possible new reaction mechanism in so-called single step process, while that old speculative mechanism is forbidden by a well-known selection rule which has been indicated in the theory of the nuclear 2β–decay.

The Approximate B-S Wave Functions for (Σμ) Atom and the decay Rate for

In this paper, the Bethe-Salpeter equation for a Coulombic bound system consisting of a fermion (mass m1 and spin 1/2) and an anti-fermion (mass m2 and spin 1/2) is solved. The approximate B-S wave functions for (Σμ) atom are given. Utilizing the perturbative expansion of the quantum field theory of composite particles, the decay rate and branching ratio for are calculated with accuracy up to order 0(α) The results are and Similaraly, the process is also discussed.

A Possible Fireball Theory with Supersymmetry Between Quark and Antidiquark

A fireball theory in the quark level with supersymmetry between quark and antidiquark is suggested. A preliminary study of this model indicates that it can well describe all characteristic phenomena of multiproduction. In particular, the appearance of diquarks will enhance the baryon yield in multiproduction.