The Canadian astrophysicist born in 1943 won the 2015 Nobel prize in physics for his discovery of what phenomenon? 
Massless particle:  The discovery of this phenomenon, known as neutrino oscillation, led to Canadian scientist Arthur B. McDonald and Japanese scientist Takaaki Kajita sharing the 2015 Nobel prize in physics. Arthur B. McDonald: Arthur Bruce McDonald, {'1': ", '2': ", '3': ", '4': "} (born August 29, 1943) is a Canadian astrophysicist.
neutrino oscillation