October 11, 2011
Neutrinos are perhaps the most mysterious and intriguing fundamental particles known to exist in nature. It took 40 years to determine that they have tiny, non-zero masses, and even today neutrino mass properties can only be inferred indirectly through quantum mechanical interference effects. So why should nature give us a particle which is so extraordinarily light, and yet not exactly massless? Our best hope to unravel this puzzle is to address a closely related question: does the neutrino act as its own anti-particle? Unfortunately, there has been little direct experimental progress on these issues in the last ten years, but now several ambitious new experiments are promising to significantly advance the frontier in relatively short order. The first such experiment to come online is the EXO-200 experiment, which was designed, constructed, and operated by a collaboration which includes the University of Maryland. An order of magnitude larger than all previous efforts, EXO-200 has already made the first observation of the ultra-rare two-neutrino double beta decay of the Xenon-136 nucleus. The half-life of this decay, at 2.11x10^21 years, ranks it as the longest half-life ever directly observed in nature, and yet it was seen and accurately measured by EXO-200 with only six weeks of data. Due to this demonstrated and unprecedented sensitivity, we expect to shed some welcome light on the critical questions of neutrino mass in the near future.
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Colloquia are held Tuesdays in Room 1410 at 4:00 pm (preceded by light refreshments at 3:30). If you have additional questions, please call 301-405-5946.
