Neutrinos, the miniscule, almost massless particles that are emitted from the sun and race through the Earth and our bodies every second of every day, are notoriously difficult to detect. Another layer of difficulty is added when scientists seek to observe the process of a neutrino changing from one type, or flavor, to another, which theoretically they do from time to time. But at long last, physicists working together at CERN in Switzerland and at Gran Sasso laboratory in Italy have succeeded in detecting such a change, as reported by Zoë Macintosh in a LiveScience article dated June 7, 2010.
The Mystery of Neutrinos
Neutrinos are tiny particles constantly being created not only inside the sun but also within radioactive decay reactions. They carry no electric charge and almost no mass, and they come in three flavors: electron neutrinos, muon neutrinos and tau neutrinos. It had long been known that neutrinos change their flavors as they rocket through space, but catching one in the act of transformation seemed an almost impossible task.
The OPERA Project
Three years ago, scientists working at the European Organization for Nuclear Research (CERN) in Geneva began a project called OPERA, which stood for Oscillation Project with Emulsion-tRacking Apparatus. They continually sent sprays of neutrinos from the Super Proton Synchrotron particle accelerator to an underground detector 450 miles away, in central Italy.
Over the course of the project, billions of neutrinos were blasted at the detector (taking about 2.4 milliseconds to travel the 450 miles). Of these, 5,000 neutrinos were actually picked up by the detector, and of those, only 1,000 were studied in depth. The chances of actually spotting a transformation taking place seemed very slim indeed.
From Muon to Tau
As they travel throughout space, rarely interacting with matter at all, neutrinos oscillate, changing back and forth from one flavor to another, as well as changing into other types of particles. Muon neutrinos, for example, can change to regular muons after interacting with the detector; muons have a much larger mass than muon neutrinos and can travel as much as a few meters before decaying.
In the single transformative oscillation captured by the detector, a muon-type neutrino changed into a tau-type neutrino. Physicists were thrilled by their good fortune, for the capture of even one transforming neutrino was an unbelievably lucky break when so few neutrinos were picked up by the detector at the Gran Sasso laboratory.
Contradiction to the Standard Model?
The theory of quantum mechanics allows that neutrinos can change flavors, but only if they have a mass. Running counter to this theory is the Standard Model, which demands that neutrinos have no mass. Physicists live with the contradiction for now, but clearly both models cannot be entirely correct.
Source:
Macintosh, Zoë. "Exotic Particle Caught After It Changes Flavor". LiveScience. June 8, 2010
Jenny Ashford - Jenny Ashford is a writer and graphic artist from central Florida. Her main area of interest in her Suite 101 articles is science, with a ...
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