Why Big Bang produced more matter than antimatter

Scientists of the MINOS experiment at the Department of Energy’s Fermi National Accelerator Laboratory announced today (June 24) the results from a search for a rare phenomenon, the transformation of muon neutrinos into electron neutrinos. This could be the reason why the big bang produced more matter than antimatter, leading to the existence of the universe.

The result is consistent with and significantly constrains a measurement reported 10 days ago by the Japanese T2K experiment, which announced an indication of this type of transformation.

These two experiments could have implications for our understanding of the role that neutrinos may have played in the evolution of the universe. If muon neutrinos transform into electron neutrinos, neutrinos could be the reason that the big bang produced more matter than antimatter, leading to the universe as it exists today.

The Main Injector Neutrino Oscillation Search ( recorded a total of 62 electron neutrino-like events. If muon neutrinos do not transform into electron neutrinos, then MINOS should have seen only 49 events. The experiment should have seen 71 events if neutrinos transform as often as suggested by recent results from the Tokai-to-Kamioka (T2K) experiment in Japan. The two experiments use different methods and analysis techniques to look for this rare transformation.

To measure the transformation of muon neutrinos into other neutrinos, the MINOS experiment sends a muon neutrino beam 450 miles (735 kilometers) through the earth from the Main Injector accelerator at Fermilab to a 5,000-ton neutrino detector, located half a mile underground in the Soudan Underground Laboratory in northern Minnesota. The experiment uses two almost identical detectors: the detector at Fermilab is used to check the purity of the muon neutrino beam, and the detector at Soudan looks for electron and muon neutrinos. The neutrinos’ trip from Fermilab to Soudan takes about one four hundredths of a second, giving the neutrinos enough time to change their identities.

For more than a decade, scientists have seen evidence that the three known types of neutrinos can morph into each other. Experiments have found that muon neutrinos disappear, with some of the best measurements provided by the MINOS experiment. Scientists think that a large fraction of these muon neutrinos transform into tau neutrinos, which so far have been very hard to detect, and they suspect that a tiny fraction transform into electron neutrinos.