T2K experiment gives insight into role of neutrinos in shaping our Universe

By April 16, 2020IFAE

Researchers from the Institute for High Energy Physics (IFAE), a BIST centre, are part of the T2K Collaboration which announced this week that they are one step closer to understanding how neutrinos may have helped create the Universe we live in today. The results were published on April 15th as the cover story of Nature.

Moments after the Big Bang, during the birth of our Universe, an immense number of particles was swirling in a so-called particle soup. Both matter and antimatter particles were present, and should have been created as counterparts, that is, in equal numbers. These particles are identical in every way except for some opposite physical properties like electric charge, which should cause them to cancel each other out. If equal amounts of both were truly present, they should have cancelled out completely, leaving nothing but dark matter and photons in our Universe. Instead we have life, planets, stars, and galaxies, all of which are composed of matter, not antimatter. Why there is more matter than antimatter in the Universe is an unsolved mystery, and has been the motivation for massive international experiments. 

Now, the T2K (Tokai to Kamioka) Collaboration which involves 12 countries and over 500 physicists, including researchers from the Institute for High Energy Physics (a BIST centre) in Barcelona, ​​the Corpuscular Physics Institute (IFIC) in Valencia and the Autonomous University of Madrid, has presented results that give new insight into whether neutrinos, tiny neutral elusive particles that can transition into various different “flavours”, and antineutrinos (their counterparts) behave slightly differently. This difference might have caused more matter particles than antimatter particles to remain after the cooling period that succeeded the Big Bang.

Using beams of muon neutrinos and muon antineutrinos, T2K has studied the probability of these particles and antiparticles transitioning into another flavour, “electron neutrinos” and “electron antineutrinos”, respectively. They have found a slight difference in the probabilities, which is indicative of the particles not being exactly identical.

This is an important step on the way to knowing whether or not neutrinos and antineutrinos behave differently. These results, using data collected through to 2018, have been published in Nature on April 15th.

More information can be found on the IFAE website.