Search for lepton flavor violating decays tau(+/-) --> l(+/-)pi0, l(+/-)eta, l(+/-)eta'

Area of Science:

• Particle Physics
• High Energy Physics
• Lepton Flavor Violation

Background:

• The Standard Model of particle physics allows lepton flavor conservation.
• Extensions to the Standard Model predict lepton flavor violating (LFV) decays.
• Tau leptons offer a unique probe for LFV due to their large mass.

Purpose of the Study:

• To search for lepton flavor violating decays of the tau lepton.
• Specifically, to investigate decays of the form tau -> l + pseudoscalar meson, where l is a lighter lepton (electron or muon).
• To set stringent upper limits on the branching fractions of these decays.

Main Methods:

• Utilized a large dataset of 339 fb^{-1} from e^{+}e^{-} collisions at a center-of-mass energy of 10.58 GeV.
• Data collected by the BABAR detector at the SLAC PEP-II storage ring.
• Analysis involved searching for specific signatures of tau lepton decays into a lighter lepton and a pseudoscalar meson.

Main Results:

• No statistically significant signal was observed for any of the searched-for lepton flavor violating tau decays.
• Upper limits on the branching fractions for these decays were established at the 10^{-7} level.
• These results constrain new physics models beyond the Standard Model.

Conclusions:

• The absence of a signal in this search places important constraints on theories predicting lepton flavor violation.
• The achieved sensitivity pushes the boundaries for exploring new physics phenomena at the intensity frontier.
• Further searches with increased datasets or improved techniques may be needed to probe even smaller branching ratios.