Measurements of the branching fractions B(B¯0→D*+π−) and B(B¯0→D*+K−) and tests of QCD factorization

Abstract

Using (771.6±10.6)×106 BB¯ meson pairs recorded by the Belle experiment at the KEKB e+e− collider, we report the branching fractions B(B¯0→D*+π−)=(2.62±0.02±0.09)×10−3 and B(B¯0→D*+K−)=(2.22±0.06±0.08)×10−4; the quoted uncertainties are statistical and systematic, respectively. A measurement of the ratio of these branching fractions is also presented, RK/π=B(B¯→D*+K−)/B(B¯→D*+π−)=(8.41±0.24±0.13)×10−2, where systematic uncertainties due to the D*+ meson reconstruction cancel out. Furthermore, we report a new QCD factorization test based on the measured ratios for B¯→D*+h− and B¯→D*+ℓ−ν decays at squared momentum transfer values equivalent to the mass of the h=π or K hadron. The parameters |a1(h)| are measured to be |a1(π)|=0.884±0.004±0.003±0.016 and |a1(K)|=0.913±0.019±0.008±0.013, where the last uncertainties account for all external inputs. These values are approximately 15% lower than those expected from theoretical predictions. Subsequently, flavor SU(3) symmetry is tested by measuring the ratios for pions and kaons, |a1(K)|2/|a1(π)|2=1.066±0.042±0.018±0.023, as well as for different particle species. The ratio is consistent with unity and therefore no evidence for SU(3) symmetry breaking effects is found at the 5% precision level.Received 3 July 2022Accepted 10 October 2022DOI:https://doi.org/10.1103/PhysRevD.107.012003Published 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 fractionPhysical SystemsBottom mesonsParticles & Fields