Ereditato is the former leader of the 160 physicists from 13 countries that compose the OPERA collaboration, whose goal is to study neutrino physics. It was first proposed in 2000, and Ereditato led it from 2008 to 2012. Then in late winter of 2011, the impossible seemed to happen. “The guy who is looking at the data calls me,” Ereditato tells me from my computer screen. “He says, ‘I see something strange.’ ” What he saw was evidence that neutrinos traveled through 454 miles of Earth’s crust, from Switzerland to Italy—which they are supposed to do—at such a high speed that they arrived 60.7 nanoseconds faster than light could travel that distance in outer space—which should have been impossible.
Over the last century, Einstein’s observation that no massive object can travel faster than the speed of light in a vacuum, enshrined in his theory of special relativity, has become a keystone of how we understand the universe. If the OPERA measurement was correct, it would mark the first-ever violation of that theory: An atom bomb in the heart of our understanding of the universe.
I ask Ereditato if he thought it must have been a mistake. “I don’t think it’s fair to say this,” Ereditato tells me. “If we say that, we bias our analysis. So when we got this indication that something was so astonishing, the first reaction was, well, let’s find why this is so.”
Wolfgang Pauli postulated the existence of neutrinos in 1930 to solve a simple problem. When nuclei undergo beta decay through the emission of an electron or a positron, the electron’s antimatter equivalent, something is missing. Either something invisible is emitted along with the electron or positron, or energy must disappear. Since no repeatable experiment of anything flying, falling, moving, colliding, decaying, or staying put had ever seen energy disappear, Pauli proposed the neutrino, an invisible particle with all the properties necessary to bring beta decay into accord with the first law of thermodynamics. By invisible, I mean that when neutrinos pass through matter they rarely leave a trace. So rarely that it took almost 30 years before an experiment (by Frederick Reines and Clyde Cowan) found physical evidence of them.
Today, neutrinos are an integral part of the Standard Model’s periodic table of particle physics. Here you’ll find the particles that make up matter listed in pairs separated into three categories: electron neutrinos are paired with electrons, muon neutrinos with muons, and tau neutrinos with, you guessed it, taus. Neutrinos can morph from one flavor into another. For example, an electron neutrino can oscillate into a muon neutrino, and a muon neutrino can flip into a tau neutrino. “Neutrino oscillations are the first indication of physics beyond the Standard Model,” Ereditato tells me. Laughing, he adds, “That’s the reason why I like neutrinos.”
posted by f. sheikh