Observation of the decay B¯s0→χc2K+ K− in the ϕ mass region

Abstract

Studies of two-body b-hadron decays to final states containing a hidden charm meson such as a χcJ state (J = 0, 1, 2) provide powerful probes of the strong interaction. These decays proceed predominantly via a colour-suppressed b → ccs¯ transition. Theoretically, such decays are often studied in the factorization approach [1,2]. It is predicted, in the absence of final-state interactions, that decays to spin-0 and 2 charmonium states are highly suppressed compared to decays to spin-1 states [1]. Experimentally, factorization has been observed to hold for B+ → χc1,c2K+ decays,1 for which the Belle collaboration reported B(B+ → χc2K+)/B(B+ → χc1K+) = (2.25+0.73 −0.69 (stat) ± 0.17 (syst)) × 10−2 [3]. In other modes, less suppression is observed. For example, the LHCb collaboration has measured B(B0 → χc2K∗ (892)0 )/B(B0 → χc1K∗ (892)0 ) = (17.1 ± 5.0 (stat) ± 1.7 (syst) ± 1.1 (B)) × 10−2 [4], where the third uncertainty is due to the knowledge of external branching fractions, and the Belle collaboration has measured B(B+ → χc2K+π +π −)/B(B+ → χc1K+π +π −) = 0.36 ± 0.05 [5], where the total uncertainty is quoted. Even more strikingly, the LHCb collaboration reported [6] B(Λ 0 b → χc2pK−)/B(Λ 0 b → χc1pK−) = 1.02 ± 0.10 (stat) ± 0.02 (syst) ± 0.05 (B). These observations are difficult to reconcile with the factorization hypothesis. It is thus interesting to probe this ratio with other exclusive decay modes.