Abstract
A search for the decays B+→hcK+ and B0→hcKS0 is performed. Evidence for the decay B+→hcK+ is found; its significance is 4.8σ. No evidence is found for B0→hcKS0. The branching fraction for B+→hcK+ is measured to be (3.7−0.9+1.0 −0.8+0.8)×10−5; the upper limit for the B0→hcKS0 branching fraction is 1.4×10−5 at 90% C.L. In addition, a study of the pp¯π+π− invariant mass distribution in the channel B+→(pp¯π+π−)K+ results in the first observation of the decay ηc(2S)→pp¯π+π− with 12.1σ significance. The analysis is based on the 711 fb−1 data sample collected by the Belle detector at the asymmetric-energy e+e− collider KEKB at the ϒ(4S) resonance.Received 15 March 2019DOI:https://doi.org/10.1103/PhysRevD.100.012001Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBranching fractionHadronic decaysPhysical SystemsBottom mesonsQuarkoniaParticles & Fields
Highlights
The decays Bþ → χc0Kþ, Bþ → χc2Kþ, and Bþ → hcKþ are suppressed by factorization [1,2]
The Belle detector is a large-solid-angle magnetic spectrometer that consists of a silicon vertex detector (SVD), a 50-layer central drift chamber (CDC), an array of aerogel threshold Cherenkov counters (ACC), 012001-3
A barrel-like arrangement of time-of-flight scintillation counters (TOF), and an electromagnetic calorimeter (ECL) composed of CsI(Tl) crystals located inside a superconducting solenoid coil that provides a 1.5 T magnetic field
Summary
The decays Bþ → χc0Kþ, Bþ → χc2Kþ, and Bþ → hcKþ are suppressed by factorization [1,2]. Before the first experimental searches, this resulted in an assumption that the process Bþ → hcKþ may have a large branching fraction BðBþ → hcKþÞ ≈ BðBþ → χc0KþÞ [2]. The LHCb Collaboration searched for the process Bþ → hcð→ pp ÞKþ [6] and set the upper limit on the branching fraction product BðBþ → hcKþÞ × Bðhc → pp Þ < 6.4 × 10−8 (95% C.L.). All the results mentioned above are close to each other, and the theoretical values of BðBþ → hcKþÞ are slightly below the current experimental upper limit. This motivates an updated study of the decays Bþ → hcKþ, which may be able to find them. The discrimination of the signal and background events is improved by performing a multivariate analysis
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