Takaaki Kajita and Arthur MacDonald have won the 2015 Nobel Physics prize for their discovery of neutrino oscillations, which show that neutrinos — the second-most abundant particles in the universe, next to photons — have mass.

The Nobel Committee said in a statement that the research done by Kajita, of the University of Tokyo, and MacDonald, of Queen’s University, Canada, has changed the world’s understanding of the innermost workings of matter.

On Monday, the Nobel Committee announced the prize winners for medicine: scientists from Ireland, Japan and China.

William Campbell from Ireland and Satoshi Omura from Japan shared the prize for their discovery of a new therapy for infections caused by roundworm parasites.