Experiment raises doubt over Standard Model of physics

The Standard Model of particle physics – the accepted view of how the universe works at a sub-atomic scale – may need a re-think.

Recently-analyzed data from BaBar, a high-energy physics experiment based at the US Department of Energy’s SLAC National Accelerator Laboratory, show 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 – means the finding isn’t definitive, it’s likely to have an effect on existing theories all the same.

“The excess over the Standard Model prediction is exciting,” says BaBar spokesperson Michael Roney, professor at the University of Victoria in Canada.

“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, explored various aspects of particle physics, including why the universe contains matter, but no antimatter.

The latest findings could have implications for the properties of Higgs bosons. These 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. However, 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,” says BaBar physics coordinator Abner Soffer, associate professor at Tel Aviv University.

“We hope our results will stimulate theoretical discussion about just what the data are telling us about new physics.” added Soffer.

The results could be confirmed by the Belle collaboration, which studies similar particle collisions.

“If they do, the combined significance could be compelling enough to suggest how we can finally move beyond the Standard Model,” he says.