Lecturer: Dr. Kosuke Nomura (University of Zagreb)
Abstract:
Neutrino-less double-beta decay is a fundamental process in which two
neutrons decay to two protons and two electrons, and the observation
of it would imply the neutrino is a Majorana particle and provide
information about neutrino masses. Experiments to measure this process
have been planned worldwide. In nuclear physics, precise calculation
of the double-beta matrix element with a reasonable accuracy is
essential to better understanding the process. In particular, the
interacting boson model has been extensively used to calculate the
nuclear matrix element. The model, however, lacks isospin and
neutron-proton pairing, which are known to be important in the
double-beta decay from several theoretical approaches.
In this work, we introduce the interacting boson model (IBM) that
conserves isospin symmetry, constructed by mapping a realistic
shell-model operator in the nucleon-pair basis to the corresponding
boson image. The model is applied to calculate nuclear matrix elements
of some medium-mass nuclei to identify the importance of
neutron-proton pair, in particular the isoscalar one, in the IBM
double-beta calculation. It is shown that in the IBM the isoscalar
pair is not important for energy spectra but improves the accuracy for
the calculation of double-beta matrix elements.
Ref: P. Van Isacker, J. Engel, and K. Nomura, accepted for publication in
Phys. Rev. C, arXiv:1708.05925