T2K is a collaborative experiment between several countries which maintains the primary objective of investigating the neutrino, a particle postulated by Enrico Fermi as a “desperate measure” in order to reconcile the principle of energy conservation with nuclear decay.  It was not known until recently that the neutrino possesses mass, which stands at odds with the Standard Model devised by Glashow, Weinberg, and Salam.

Neutrinos are electrically neutral elementary particles which, due to their lack of charge, are able to pass through materials unimpeded.  The fact that  neutrinos exhibit an infinitesimal mass was confirmed through an understanding of flavor oscillation.  There are three types (“flavors”) of neutrinos, each of which can be associated with a corresponding heavier elementary particle: the electron, tau and muon.  These six particles form a group known as leptons, a subcategory of the fundamental building blocks in all matter.  The neutrinos associated with their heavier counterparts consist of a mixture of components which relate to the electron, muon, and tau particles.  These components are of slightly different masses, meaning that as the neutrino wave travels, the flavor can change, or oscillate.  It is through an understanding of quantum mechanics and these flavor oscillations that scientists are able to extrapolate the masses of the various neutrinos.  Specifically, in detecting neutrinos at a pre-calculated distance from their creation, it is possible to observe the change in flavor.  This would enable us to better extrapolate the mass of the three flavors of neutrinos.  The discovery that neutrinos possess mass implies a need to re-evaluate the current theory, known as the “Standard Theory”, which was thought to completely govern the laws of subatomic particles.

T2K public pages.