Nuclear Particle Astrophysics (NPA) Seminar: Jenni Kotila, Yale University, “Double Beta Decay and Neutrino Mass”

Thursday May 7, 2015, 3:30 PM → 4:30 PM US/Eastern

WLC 108

The question of whether neutrinos are Majorana or Dirac particles and what are their average masses remains one of the most fundamental problems in physics today. Observation of neutrinoless double-β decay (0νββ) would verify the Majorana nature of the neutrino and constrain the absolute scale of the neutrino mass spectrum. The inverse half-life for 0νββ-decay is given by the product of a phase space factor and a nuclear matrix element, which both rely on theoretical description, and a function f containing the physics beyond the standard model.

In this talk, recent calculations of phase space factors and nuclear matrix elements for 0νββ -decay proceeding through mass mechanism will be presented together with comparison to other available calculations. The question of renormalization of gA is also addressed. These calculations serve the purpose of extracting the average neutrino mass if 0νββ is observed, and of guiding searches if 0νββ is not observed. The current situation is then analyzed by combining the theoretical results with experimental limits on the half-life of neutrinoless double beta decay. The extracted limits on the average neutrino mass will be discussed.

A second, somewhat exotic mechanism for 0νββ- decay involves the emission of one or two additional bosons called Majorons. This decay has different electron spectrum and, therefore, also a different phase space factors depending on the spectral index n. Calculations with different n will be discussed as well as the half-life predictions for the ordinary Majoron decay (spectral index n=1). Furthermore, comparing theoretical predictions with the obtained experimental lower bounds for this decay mode we are able to set some limits on the effective Majoron-neutrino coupling constant

Kotila_NPA_Seminar_05072015.pdf