Abstract
The rare decay is expected to play an important role in searches for physics beyond the Standard Model at the near future -physics experiments. We investigate resonant and nonresonant backgrounds that arise beyond the narrow-width approximation for the . Nonresonant decays are analyzed in the region of low hadronic recoil, where form factors from the heavy-hadron-chiral-perturbation theory are available. In a Breit-Wigner–type model interference-induced effects in the signal region are found to be sizable, as large as 20% in the branching ratio. Corresponding effects in the longitudinal polarization fraction are smaller, at most around a few percent. Effects of the broad scalar states and are at the level of percent in the branching fraction in the signal region and negligible in . Since the backgrounds to are small, this observable constitutes a useful probe of form factor calculations or, alternatively, of right-handed currents in the entire region. The forward-backward asymmetry in the system, , with normalization to the longitudinal decay rate probes predominantly , -wave interference free of short-distance coefficients and can therefore be used to control the resonant and nonresonant backgrounds.
- Received 5 March 2017
DOI:https://doi.org/10.1103/PhysRevD.95.073001
© 2017 American Physical Society