FIRST EVIDENCE FOR B s → φφ AND PENGUIN B DECAYS AT CDF

We present the first evidence of the decay mode Bs → φφ and a measurement of partial width and direct CP asymmetry for the B + → φK + decay using 180 pb −1 of data collected by the CDF II experiment at the Fermilab Tevatron collider. We measure: BR(Bs → φφ) = (1.4 ± 0.6(stat.) ± 0.2(syst.) ± 0.5(BR)) · 10 −5 , where the last error is due to the uncertainty on the Bs → J/ψφ branching ratio used as normalization, BR(B + → φK +) = (7.2 ± 1.3(stat.) ± 0.7(syst.)) · 10 −6 and A CP (B + → φK +) = −0.07 ± 0.17(stat.) +0.06 −0.05 (syst.). We also briefly discuss prospects for studying other charmless B → V V decays at CDF Several precision measurements on B u,d meson decays are available, yet many crucial theory predictions on B s mesons, including mixing, CP violation and the decay width difference, ∆Γ s , are still to be tested. B s → V V decays offer insights to both CP violation and ∆Γ s thank to the presence of CP-odd and CP-even components in the decay amplitude. B s → φφ decays are the first charmless B s → V V to be observed. This channel has been considered extensively in the literature 1 , even as a probe for New Physics along with other B s modes. A recent calculation 2 predicts a branching ratio of 3.7 · 10 −5. In the Standard Model (SM) the decay is mediated by b→s¯ ss penguin amplitudes which have shown discrepancies with the SM predictions, confirmed by recent data, for certain CP asymmetry measurements 3. B ± →φK ± decays are mediated by the same quark-level transition and have been already studied at B-factories 4. Measuring precisely rates and CP violation parameters in as many such decays as possible may help in determining the source of the above discrepancies. We report the first evidence of the B s → φφ decay and the first measurement , at hadron colliders, of CP-averaged BR and direct CP asymmetry (A CP) for B + → φK + (charge conjugate modes are implied here unless otherwise stated). In order to cancel the production cross section uncertainty as well as to reduce the systematic uncertainty on detector efficien-cies, the branching ratios are extracted from ratios of decay rates of signals and well …