Determination of the strong coupling constant αs

We demonstrate the feasibility of determining the strong coupling constant, α s , from the inclusive semileptonic decay width of B mesons. We express the semileptonic B decay width as a function of α s ( 5 GeV ) , the Cabibbo-Kobayashi-Maskawa matrix element | V c b | , and b - and c -quark masses in the MS ¯ scheme. We fit α s ( 5 GeV ) to current world averages of the B ± and B 0 semileptonic decay widths. This yields α s ( 5 GeV ) = 0.245 ± 0.009 , corresponding to a five-flavor extrapolation of α s ( m Z ) = 0.1266 ± 0.0023 . The primary uncertainty contributions arise from the uncertainty on the perturbative expansion and the value of | V c b | . Future advancements, including higher-order perturbative calculations and precise measurements of | V c b | and B decay widths from upcoming B and Z factories, could enable this method to determine α s ( m Z ) with a competitive precision of Δ α s ( m Z ) ∼ 0.0018 . This precision is comparable to the current accuracy of α s ( m Z ) measurements from τ -lepton decays, which is regarded as the most precise experimental approach.