S-waves and the extraction of betaₛ

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The CP Violating asymmetry in Bs mixing (betaₛ) 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/psiϕhas been used, and the mode Bs -> ϕϕproposed 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 betaₛ. 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 Jψϕshould be taken into account when determining betaₛ 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 betaₛ.