Anatomy of $B_s \to VV $ decays and effects of next-to-leading order contributions in the perturbative QCD factorization approach
By employing the perturbative QCD (PQCD) factorization approach, we calculated the branching ratios, CP-violating asymmetries, the longitudinal and transverse polarization fractions and other physical observables of the thirteen charmless hadronic $\bar{B}^0_s \to V V $ decays with the inclusion of all currently known next-to-leading order (NLO) contributions. We focused on the examination of the effects of all those currently known NLO contributions and found that: (a) for the measured decays $\bar{ B}_s^0 \to \phi \phi, K^{*0} \phi,\bar K^{*0} K^{*0}$ and $\rho^0 \phi$, the NLO contributions can provide $\sim 20\%$ to $\sim 40\%$ enhancements to the leading order (LO) PQCD predictions of their CP-averaged branching ratios, and consequently the agreement between the PQCD predictions and the measured values are improved effectively after the inclusion of the NLO contributions; (b) for the measured decays, the NLO corrections to the LO PQCD predictions for $(f_L,f_\perp)$ and $(\phi_{\|},\phi_{\bot})$ are generally small in size, but the weak penguin annihilation contributions play an important role in understanding the data about their decay rates, $f_L$ and $f_\perp$; (c) the NLO PQCD predictions for above mentioned physical observables do agree with the measured ones and the theoretical predictions from the QCDF, SCET and FAT approaches; (d) for other considered $B_s^0 \to VV$ decays, the NLO PQCD predictions for their decay rates and other physical observables are also basically consistent with the theoretical predictions from other popular approaches, future precision measurements could help us to test or examine these predictions.