Scalar resonance effects on the B_s - bar B_s mixing angle

The $B_s^0 \to J/\psi \phi$ and $B_s^0 \to J/\psi f_0(980)$ decays are analyzed within generalized QCD factorization including all leading-order corrections in $\alphas$. We point out that the ratio of our calculated widths, $\Gamma (B_s^0\to J/\psi f_0(980), f_0(980)\to \pi^+\pi^-)/ \Gamma(B_s^0 \to J/\psi \phi,\phi\to K^+K^-)$, strongly indicates that $S$-wave effects in the $f_0(980)$'s daughter pions or kaons cannot be ignored in the extraction of the $B_s-\bar{B}_s$ mixing angle, $-2\beta_s$, from the $B_s^0 \to \phi J/\psi$ decay amplitudes.