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Babar data hint at cracks in the standard model
(NCYT/STFC) The data refers to a particle called the B-bar meson that decays into a D meson, an anti-neutrino and a tau lepton (³B to D-star-tau-nu²). This particular decay of a B meson should, theoretically, only happen in one in every 100 cases, but the new results from BaBar show it is happening too often. While the level of certainty of the difference, or excess, (3.4 sigma in statistical language) is not enough to claim a break from the Standard Model, the results are a potential sign of something amiss and are likely to impact existing theories.
"The excess over the Standard Model prediction is exciting", said BaBar spokesperson Michael Roney, Professor at the University of Victoria in Canada. "The results are significantly more sensitive than previously published studies of these decays", said Roney. "But before we can claim an actual discovery, other experiments have to replicate it and rule out the possibility this isn't just an unlikely statistical fluctuation".
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| In this conceptual art, an electron and positron collide, resulting in a B meson (not shown) and an antimatter B-bar meson, which then decays into a D meson and a tau lepton as well as a smaller antineutrino. (Photo: Greg Stewart, SLAC National Accelerator Laboratory) |
Fergus Wilson, one of the analysers of data from Babar who is from STFC's Rutherford Appleton Laboratory, added: "Our current theory about the fundamental forces of the Universe, which has been around for nearly 40 years, is beginning to show signs of failure. Just as exciting, our new measurement indicates that any replacement theory will need to be more exotic and complex than we could have hoped or imagined. Although we must not jump to conclusions based on just one measurement, this new result is one of the most compelling yet. It follows on from previous indications recently reported by us, all of which point in the same direction".
The BaBar experiment, which collected data from 1999 to 2008, was designed to explore various mysteries of particle physics, including why the universe contains matter, but no antimatter. Data from the collaboration which includes 75 institutions from Canada, France, Germany Italy, Norway, Russia, Spain, the UK and the US helped confirm a matter-antimatter theory for which two researchers won the 2008 Nobel Prize in Physics. At its peak, some 90 British particle physicists and engineers from eleven institutions took part in the experiment. Researchers continue to apply BaBar data to a variety of questions in particle physics. Adrian Bevan said: "This result will help guide teams of researchers looking for potentially related new physics effects at the Large Hadron Collider and at other particle physics labs around the world".
"If the excess decays shown are confirmed, it will be exciting to figure out what is causing it," said BaBar physics coordinator Abner Soffer, associate professor at Tel Aviv University. "Other theories involving new physics are waiting in the wings, but the BaBar results already rule out one important model called the Two Higgs Doublet Model. We hope our results will stimulate theoretical discussion about just what the data are telling us about new physics", added Soffer. The researchers also hope their colleagues in the Belle collaboration, which studies the same types of particle collisions, see something similar. "If they do, the combined significance could be compelling enough to suggest how we can finally move beyond the Standard Model", said Professor Roney.
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