By Dr David Whitehouse
BBC News Online science editor
Particle physicists have seen a rare happening that may force a rethink of current theories of sub-atomic matter.
The K-meson's track through the detector was unusual
After watching more than seven trillion disintegrations of the kaon particle they have seen three peculiar events when they expected to see just one.
At present physicists at the Brookhaven National Laboratory in the US do not know if this is a fluke or points the way to a deeper theory of matter.
The research has been submitted to the Journal Physical Review Letters.
Fluke or breakthrough
The experiment looked at the disintegration of a sub-atomic particle called the K-meson or kaon.
It can decay in a number of ways. One involves it turning into a charged pion particle, a neutrino, and an anti-neutrino.
Physicists regard this decay pattern as especially interesting because it may reveal new effects not accounted for in the so-called Standard Model.
So far they have constructed a theory around 16 particles that make up all matter called the Standard Model of fundamental particles and interactions.
The Standard Model predicts that this particular event should occur only once in every 13 billion decays.
Issue to resolve
The new result now suggests the rare event could occur once in every 7 billion decays - almost twice the rate predicted by the Standard Model. The data is not yet conclusive, however.
"It is very important to establish whether these first few events represent a statistical fluke or an important breakthrough," says Douglas Bryman, of the University of British Columbia, Canada.
"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.
"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."