A joint Fermilab/SLAC publication

BaBar data may hint at new physics


A technician works on the BaBar detector, which collected data at SLAC National Accelerator Laboratory until 2008. (Image: SLAC)

A new crack in the Standard Model may be starting to form.

Recently analyzed data from the BaBar experiment show that one type of particle decay happens more often than predicted by the Standard Model.  This excess, seen with a “3.4 sigma” level of certainty, is not enough to claim a definitive break from the accepted theory, but it is a sign that something could well be amiss.

If the Belle experiment at the Japanese high-energy physics laboratory KEK replicates this finding, “the combined significance could be compelling enough to suggest how we can finally move beyond the Standard Model,” BaBar spokesman Michael Roney said in a SLAC press release.

The particle decays in question, B to D-tau-nu and B to D-star-tau-nu, involve an anti-B meson decaying into a D or D* meson, a tau lepton, and an anti-neutrino.

The finding, if confirmed, may impact a range of theories, including those that seek to determine the properties of Higgs bosons. Thought to be related to the mechanism that gives elementary particles mass, Higgs bosons are predicted to interact more strongly with heavier particles—such as B mesons, D mesons and tau leptons—than lighter ones.  But the Standard Model posits an electrically neutral Higgs, while the decays observed by BaBar are sensitive to the existence of a charged Higgs, such as is posited in a variety of new-physics models.

“If the excess is confirmed, it will be exciting to figure out what’s causing it,” said BaBar physics coordinator Abner Soffer, associate professor at Tel Aviv University.

For more information, see the SLAC press release.

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