An international team of scientists, including a York University professor, has released new findings on neutrinos, which may help unlock the mysteries behind their behaviour and provide insights into how the universe was formed.
Researchers in the Tokai-to-Kamioka (T2K) experiment reported yesterday that neutrinos travelling over a long distance transformed into other types of neutrino particles in greater numbers than expected.
A neutrino is a subatomic particle similar to an electron but with no electric charge and a mass about a million times smaller. Although elusive, neutrinos are among the most numerous particles in the universe, with the ability to pass through matter without stopping. At any given moment, billions of neutrinos are streaming out of the sun and passing through our bodies.
Researchers theorize that as the only surviving particles left over from the moments just after the Big Bang, they could help explain one of the great mysteries of science: What happened to the antimatter that was produced at the birth of the universe?
“Neutrinos are the ‘spooky’ particles – in a way they’re like ghosts of the Big Bang,” says Sampa Bhadra (right), professor in York’s Department of Physics & Astronomy, Faculty of Science & Engineering, who is part of the Canadian T2K team. “In order to understand our universe and how it was created, we need to comprehend the properties of the fundamental particles that make up everything. This result signals that a conclusive understanding [of neutrinos] is within reach.”
T2K data indicates that muon neutrinos are able to transform into electron neutrinos over a distance of nearly 300 km through a phenomenon known as neutrino flavour oscillations. During the experiment, scientists observed six candidate electron neutrino events; the average number of events is 1.5. According to T2K scientists, the chance of seeing six or more events is less than one percent.
“This spike [in electron neutrino events] likely means that some of the muon neutrinos are changing into electron neutrinos,” Bhadra says. However, she cautions that more research is needed to confirm the statistical significance of the findings.
The experiment uses a beam of muon neutrinos produced at the J-PARC accelerator laboratory in eastern Japan. These neutrinos are beamed from J-PARC through Japan’s Honshu Island to the Super-Kamiokande neutrino detector 295 km away. A neutrino detector at J-PARC measures the beam at its production point to allow a before-and-after comparison for measurements at Super-Kamiokande.
Previous experiments have shown that muon neutrinos with similar energies can transform into other kinds of neutrinos while in transit. However, the low rate at which they turn into electron neutrinos is an outstanding puzzle in particle physics.
The experiment collected about two percent of its original “events” goal before the Japanese earthquake hit on March 11, 2011. Once J-PARC resumes producing muon neutrinos, the T2K experiment will strive to accumulate the target number of events to confirm electron neutrino appearance. Researchers then plan to combine neutrino measurements with measurements using anti-neutrinos, in order to shed light on how neutrinos differ from their antimatter counterparts.
Mark Hartz, a research associate at York University and the University of Toronto, will present T2K’s current findings at the Canadian Association of Physicists’ annual meeting on June 17 in St. John’s, Newfoundland. T2K researchers have submitted a publication describing the new results to the journal Physical Review Letters.
The T2K collaboration consists of approximately 500 people from 12 countries and 59 different institutions. Canada is one of the largest contributors to the experiment, with over forty scientists contributing from the University of Victoria; the University of British Columbia; TRIUMF, Canada’s national lab for particle physics; the University of Alberta; the University of Regina; York University, and the University of Toronto. T2K is supported in Canada by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canada Foundation for Innovation (CFI).
Bhadra is also associate dean, academic affairs in York’s Faculty of Graduate Studies.