THE MYSTERY OF VUS FROM TAU DECAYS

The BaBar experiment at the SLAC B-factory operating at a centre-of-mass energy of 10.58 GeV
provides one of the largest data samples of e+e- -> tau+tau- events. This high statistics tau
dataset, together with BaBar's high precision pion vs kaon separation capability, makes it a
very interesting laboratory to study strange decays of the tau lepton. Tau decays into strange
mesons provide an interesting probe of Vus, the largest off-diagonal element of the CKM quark 
mixing matrix.

A curious discrepency shows up when Vus is measured from the strange partial width vs when Vus
is measured from ratio of (tau->K nu)/(tau->pi nu) decays: while the former measurement is ~ 3
sigma lower, the latter is consistent with unitarity prediction. I will present these 2
measurements, and discuss possible interpretations.