Saturday, June 18, 2011

Neutrinos Probe Antimatter in Japan

Neutrinos are nearly massless elementary particles that interact extremely weakly with matter. As you read this sentence, trillions of neutrinos are streaming through your body at nearly the speed of light, yet you don't feel a thing. It has been said that a neutrino could easily pass through light years of lead before disturbing even one atom - quite the feat for a particle that may hold the key to understanding the dearth of antimatter in our Universe! Not only are these subatomic speed ninjas extremely difficult to detect, but they actually possess a kind of quantum mechanical ADD as well. Neutrinos are known to spontaneously change between three distinct types, or flavors, during the course of their travels. Two of these so-called flavor oscillations have already been observed, leaving just one unaccounted for... until now.

Just a few days ago, scientists from the T2K experiment in Japan released data that suggests they may have witnessed the third flavor oscillation. At the T2K experiment, a beam of muon neutrinos is isolated from a proton stream at J-PARC in Tokai, and sent to the Super-Kamiokande detector in Kamioka, 295 kilometers away. The goal of the experiment is to see how many muon neutrinos change into electrons neutrinos along the way by detecting the number of electron events at the far detector. In an experiment of this nature, approximately 1.5 electron events that have nothing to do with neutrino flavor oscillations are to be expected. But when the background noise and other rogue neutrino events were filtered out of the data, 6 solid events remained: 6 events that suggest the appearance of electron neutrinos with 99.3% confidence, a 2.5 sigma result.

Due to the earthquake that struck Japan back in March, the T2K experiment has only been able to gather 2% of the total data it was designed to. So with 98% of the data still forthcoming, a 2.5 sigma is a pretty promising result. Physicists are hoping that understanding this last flavor oscillation will allow them to probe the differences between neutrinos and their anti-particles, anti-neutrinos. If the mechanism of flavor oscillation differs between the two sets, it may lead scientists to a better understanding of CP violation, the phenomenon believed to be responsible for the abundance of matter over anti-matter in our universe.

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