Hot Topics from the BABAR Experiment

TL;DR

This paper reports on searches for rare B meson decays and performs an amplitude analysis using data from the BABAR experiment, providing new measurements and hints of potential new physics effects.

Contribution

It presents the first measurement of the B+ -> tau nu branching fraction and an amplitude analysis of B+ -> phi(1020)K*(892)+, revealing possible contributions from unknown sources.

Findings

Evidence for B+ -> tau nu decay with 2.6 sigma significance

Measured polarization fractions in B+ -> phi K* decays

Indications of a substantial helicity-plus amplitude

Abstract

With a sample of about 384 million BBbar pairs recorded with the BABAR detector, we search for the flavor-changing charged current transition B+ -> \tau\nu and perform an amplitude analysis of the effective flavor-changing neutral current transition B+ -> \phi(1020)K*(892)+. We also extend our search for other K* final states in the decay B0 -> phi(1020)K*0 with a large K*0 -> K+pi- invariant mass. Two samples of events with one reconstructed hadronic B decay or one reconstructed semileptonic B decay are selected, and in the recoil a search for B+ -> \tau\nu is performed. We find a 2.6 sigma (3.2 sigma not including expected background uncertainty) excess in data which can be converted to a preliminary branching fraction central value of BR(B+ -> \tau\nu ) = (1.20 +0.40-0.38 +0.29-0.30 +-0.22) 10^-4. With the decay B+- -> \phi(1020)K*(892)+-, twelve parameters are measured, where our measurements of f_L=0.49+-0.05+-0.03, f_perp=0.21+-0.05+-0.02, and the strong phases point to the presence of a substantial helicity-plus amplitude from a presently unknown source.