S-waves and the measurement of β_s in B_s decays

The CP Violating asymmetry in B_s mixing (β_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 B_s → J/ψφ has been used, and the mode B_s → φφ 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 β_s. The S-waves could well be the result of a final state formed from an s-quark s-quark pair in a 0⁺ spin-parity state, such as the f₀(980) meson. Data driven and theoretical estimates of the B_s decay rate into the CP+ final state J/ψ f₀(980) are given, when f₀ → π⁺π⁻. The S-wave contribution in J/ψφ should be taken into account when determining β_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/ψ f₀(980) mode has been suggested as an alternative channel for measuring β_s. An expanded version of this paper is available at arXiv:1009.4939 [hep-ph].