BaBar experiment team has announced that their latest data suggest possible flaws in the Standard Model of particle physics, the reigning description of how the Universe works on subatomic scales.
The latest results from the BaBar experiment may suggest a surplus over Standard Model predictions of a type of particle decay called “B to D-star-tau-nu.” 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 (Greg Stewart / SLAC National Accelerator Laboratory)
Submitted for publication in the journal Physical Review Letters, the analysis of the data from BaBar, a high-energy physics experiment based at the SLAC National Accelerator Laboratory in Menlo Park, shows that a particular type of particle decay called “B to D-star-tau-nu” happens more often than the Standard Model says it should.
In this type of decay, a particle called the B-bar meson decays into a D meson, an antineutrino and a tau lepton. While the level of certainty of the 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, including those attempting to deduce the properties of Higgs bosons.
“The excess over the Standard Model prediction is exciting,” said Michael Roney, a professor at the University of Victoria in Canada, and BaBar spokesperson. “The results are significantly more sensitive than previously published studies of these decays. 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.”
The BaBar experiment, which collected particle collision data from 1999 to 2008, was designed to explore various mysteries of particle physics, including why the universe contains matter, but no antimatter. The collaboration’s data helped confirm a matter-antimatter theory for which two researchers won the 2008 Nobel Prize in Physics.
Researchers continue to apply BaBar data to a variety of questions in particle physics. The data, for instance, has raised more questions about Higgs bosons, which arise from the mechanism thought to give fundamental particles their mass. Higgs bosons are predicted to interact more strongly with heavier particles – such as the B mesons, D mesons and tau leptons in the BaBar study – than with lighter ones, but the Higgs posited by the Standard Model can’t be involved in this decay.
“If the excess decays shown are confirmed, it will be exciting to figure out what is causing it,” said BaBar physics coordinator Dr 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,” Dr Soffer concluded.
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Bibliographic information: Lees J.P. et al. 2012. Evidence for an excess of B -> D(*) Tau Nu decays. Manuscript submitted to Phys. Rev. Lett.; arXiv:1205.5442v1
