S-waves and the extraction of beta_s

Abstract

The CP Violating asymmetry in Bs mixing (beta_s) is one of the most promising measurements where physics beyond the Standard Model could be revealed. As such, analyses need to be subjected to great scrutiny. The mode Bs -> J/psi\phi has been used, and the mode Bs -> \phi \phi proposed for future measurements. These modes both have two vector particles in the final state and thus angular analyses must be used to disentangle the contributions from CP+ and CP- configurations. The angular distributions, however, could be distorted by the presence of S-waves masquerading as low mass K+K- pairs, that could result in erroneous values of beta_s. The S-waves could well be the result of a final state formed from an s-quark anti-s-quark pair in a 0+ spin-parity state, such as the f0(980) meson. Data driven and theoretical estimates of the Bs decay rate into the CP+ final state J/psi f0(980) are given, when f0 -> pi+pi-. The S-wave contribution in J\psi\phi should be taken into account when determining beta_s by including a K+K- S-wave amplitude in the fit. This may change the central value of current results and will also increase the statistical uncertainty. Importantly, the J/psi f0(980) mode has been suggested as an alternative channel for measuring beta_s.