K mesons or kaons are unstable and can decay in a number of ways. In one important but very rare decay, a positive kaon – a bound state of an up quark and a strange antiquark -- decays into a positive pion plus a neutrino and an antineutrino. The Standard Model predicts that this particular decay should occur only once in every 13 billion decays. However, the decay rate might be influenced by particles and processes that are not included in the model. Therefore, any discrepancies between the predictions of the model and experiment could be evidence for these new particles and processes.

The E949 team uses the AGS accelerator at Brookhaven to produce an intense beam of kaons and a detector that is capable of examining 1.6 million decays every second. In particular, the detector can filter the pion-neutrino-antineutrino event from all the other possible decays that the kaon can undergo.

The new result suggests that the rare event could occur once in every 7 billion decays – almost twice the rate predicted by the Standard Model. It follows two earlier sightings of the decay at Brookhaven in 2002 and 1997.

“It is very important to establish whether these first few events represent a statistical fluke or an important breakthrough,” said Douglas Bryman of the University of British Columbia and a spokesperson for the experiment. “Additional running of the experiment would resolve the issue and firmly establish whether we are seeing an extremely significant departure from standard theory,” he added.

“If our findings continue at the current pace, 20 or more events would be observed,” according to a press release issue by Brookhaven. “Such a result could profoundly alter our current picture of particle physics, forcing an expanded view of the fundamental constituents of the universe and their interactions.” The E949 collaboration includes physicists from Canada, Russia, Japan and the US.