Two research teams have found new evidence of transformations in elusive elementary particles called neutrinos. The findings may finally help explain why the universe didn’t vanish shortly after its birth.
“These results are just the beginning of the story for neutrinos,” said physicist Robert Plunkett of Fermilab in Chicago. “They could lead to clues and tell us why there’s now far more matter than antimatter.”
Most neutrinos are emitted by the sun, and are so small and ghostly that billions pass through our bodies every second. Most go right through Earth without hitting anything. But some human-built devices—slabs of iron and plastic, big chambers of oil or water lined with photon detectors, or detector arrays plunged into seawater or Antarctic ice—can record the blip of light when a neutrino occasionally slams into an atom.
Using these detection events, physicists have identified three types of neutrino, called muon, tau and electron neutrinos. Further discoveries suggested that each type can transform into another, with muon-to-tau and tau-to-electron neutrino transformations being dominant, at least in particle-accelerator-powered experiments. Researchers proposed a third and weaker change, that of muon-to-electron neutrinos, but until now lacked evidence for its existence.
On June 14, the Japanese Tokai-to-Kamioka experiment reported the significant detection of muon-to-electron neutrino changes. On June 24, the Main Injector Neutrino Oscillation Search (MINOS) experiment at Fermilab reported the same. While the ranges of their data varied, the basic claims were the same.
“[The values] differ because we used different techniques and distances, but they overlap at one part. They’re complementary,” said Plunkett, a co-spokesperson of MINOS.
With a more complete understanding of neutrino transformation in hand, Plunkett said physicists can now design experiments to investigate larger questions about the universe. The largest among them: why there’s far more matter than antimatter.
Matter and antimatter particles annihilate when they meet. Each type is thought to have appeared in equal proportions shortly after the Big Bang, yet the matter-rich universe as we know it still exists. As a result, physicists are seeking evidence of “asymmetries,” in which matter-antimatter encounters end up emitting more matter particles.
Some matter-favoring asymmetry shows up in the annihilation of quarks, though the effect is relatively meager. But physicists say a muon-to-electron neutrino transformation supports the possibility of more significant asymmetries.
“We now have a good enough handle on neutrinos to design experiments and try to address such a big mystery,” Plunkett said.