Existence of neutrinoless double beta decay

Determine whether neutrinoless double beta decay occurs in nature, namely whether the nuclear process in which two neutrons within a nucleus transform into two protons and two electrons with no neutrino emission takes place, as allowed by Majorana’s neutrino theory that predicts the transformation rate proportional to the square of the electron-flavor neutrino mass.

Background

The essay explains that Majorana’s symmetric treatment of electrons and positrons eliminates the need for the Dirac sea and naturally permits the possibility that neutral fermions, such as neutrinos, coincide with their antiparticles. Given modern evidence that neutrinos have nonzero mass, this raises the prospect that certain processes forbidden for strictly Dirac neutrinos become allowed.

Specifically, the author highlights the neutrinoless double beta decay process—two neutrons transforming into two protons plus two electrons without neutrino emission—which would directly indicate that neutrinos are Majorana particles. The text notes that the transformation rate in Majorana’s framework is proportional to the square of the electron-associated neutrino mass. Despite intense experimental searches worldwide (e.g., Gran Sasso), the existence of this process remains unresolved; the author states it would be very rare if it exists.