An international team of physicists examining an extremely rare form of subatomic particle decay -- a veritable golden needle in a micro-cosmic haystack of 7.8 trillion candidates -- has discovered evidence for the highly sought process, which could be an indication of new forces beyond those incorporated in the Standard Model of particle physics. That long-standing theory of all particle physics precisely predicts the rate of such decays to be half that observed by the experimenters although it is still too soon to say if a deviation has occurred. The innovative experiment, which uses the most comprehensive particle detector ever built, is located at the U.S. Department of Energys Brookhaven National Laboratory. The result is being presented at a colloquium at Brookhaven Lab today and has been submitted to Physical Review Letters.
The experiment detects the disintegration of an unstable subatomic particle called a K meson, which can decay, or break apart, in a variety of ways. One particular decay -- in which the K meson turns into other particles, a positively charged pion, a neutrino, and an antineutrino -- is extremely important due to the internal subatomic processes involved and its sensitivity to new physical effects not accounted for in the Standard Model. The decay is so rare that it was predicted to happen only once in all the decays ever observed by all of the experiments that have searched for it since the 1960s.
The latest evidence of the long-sought process was found in just-analyzed data. It followed two earlier sightings at Brookhaven in 1997 and 2002 (see: http://www.bnl.gov/bnlweb/pubaf/pr/2002/bnlpr011002.htm). The new data were obtained using improved apparatus that exploited higher beam intensities and achieved greater efficiency of detection than any previous experimental setup.
Karen McNulty Walsh | BNL
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