S-waves and the Measurement of CP Violating Phases in Bs Decays

TL;DR

This paper discusses how S-wave contributions affect measurements of CP violating phases in Bs decays, proposing alternative methods and analyzing potential systematic issues to improve accuracy in detecting new physics.

Contribution

It highlights the significance of S-wave contamination in Bs decay analyses and suggests using Bs -> J/psi f0 as a cleaner alternative for measuring eta_s.

Findings

S-wave contamination can bias CP violation measurements.

Using Bs -> J/psi f0 avoids angular analysis complexities.

Estimated event rates for alternative decay modes are 4-5 times fewer.

Abstract

Heavy, as yet undiscovered particles, can affect measurements of CP violation in the B system. Measuring CP violation in the Bs system provides an excellent place to observe such effects since Standard Model sources are predicted to produce very small effects. The angle -2beta_s, the "phase of Bs-\bar{B}s mixing," thought to be best measured in Bs -> J/psi\phi decays is of order -0.04, while the CP violating asymmetry in Bs -> \phi\phi is predicted to be zero, due to the cancellation of the mixing phase with the decay phase. Recent measurements of \beta_s in J/psi\phi, while not definitive, are much larger than the Standard Model predictions. Measurements in the B^o and Ds+ systems of analogous modes point toward a 5-10% contamination of S-wave K+K- under the \phi peak. This S-wave was not taken into account in these recent analyses. Furthermore this S-wave can also materialize as a f0(980) meson that decays to \pi+\pi-, making the final state J/psi f0 useful for measuring \beta_s with the added advantage of not requiring an angular analysis. Rate estimates, while not precise, predict four to five times fewer such events than those in the J/psi\phi mode. The error on \beta_s, however, may be similar. We also remark on S-wave problems with the Bs -> \phi\phi mode, and possible systematic checks using Bs -> \phi f0.