Study on pure annihilation type B to V gamma decays

Abstract

We investigate the pure annihilation type radiative B meson decays B 0 → φγ and B s → ρ 0 (ω)γ in the soft-collinear effective theory. We consider three types of contributions to the decay amplitudes, including the direct annihilation topology, the contribution from the electro-magnetic penguin operator and the contribution of the neutral vector meson mixings. The numerical analysis shows that the decay amplitudes are dominated by the ω − φ mixing effect in the B 0 → φγ and B s → ωγ modes. The corresponding decay branching ratios are enhanced about three orders of magnitudes relative to the pure annihilation type contribution in these two decay channels. The decay rate of B s → ρ 0 γ is much smaller than that of B s → ωγ because of the smaller ρ 0 −φ mixing. The predicted branching ratios B(B 0 → φγ) = (3.99 +1.67 −1.46 ) × 10 −9 , B(B s → ωγ) = (2.01 +0.81 −0.71 ) × 10 −7 are to be tested by the Belle-II and LHC-b experiments.

Search for the decay B0 → ϕμ+μ−

“…The decay B 0 → φγ has not yet been observed, and the current upper limit on the branching fraction is 1.0 × 10 −7 at a 90% confidence level set by the Belle collaboration [7]. Assuming a dominant ω − φ contribution [6] and scaling the B 0 → ρ 0 µ + µ − branching fraction measured by the LHCb experiment [8], the B 0 → φµ + µ − branching fraction is predicted to be between 10 −11 and 10 −10 . The decay B 0 → φµ + µ − has not yet been observed, but may be accessible at high luminosity flavour physics experiments such as the LHCb experiment and its upgrade, where it can be reconstructed with high efficiency.…”

“…There is no theoretical study of these effects in the literature. Some clues can be found in the reported studies of the decay B 0 → φγ [2][3][4][5][6][7], which has similar quark-level transitions as the B 0 → φµ + µ − decay. The annihilation contributions to the B 0 → φγ branching fraction have been found to be of the order of 10 −12 to 10 −11 [2][3][4], depending on the factorization techniques.…”

“…Contributions by new particles such as a Z boson in the annihilation diagrams could be of the order of 10 −9 -10 −8 [2,5], large enough to be observed by the LHCb detector. A recent study with soft-collinear effective theory indicates that the contribution from ω −φ mixing could be three orders of magnitude larger than the pure annihilation contribution in the SM, increasing the branching fraction of the decay B 0 → φγ to O(10 −9 ) [6]. The decay B 0 → φγ has not yet been observed, and the current upper limit on the branching fraction is 1.0 × 10 −7 at a 90% confidence level set by the Belle collaboration [7].…”