Adachi, I.Aggarwal, L.Aihara, H.Akopov, N.Aloisio, A.Althubiti, N.Anh Ky, N.Asner, D.M.Atmacan, H.Aushev, T.Aushev, V.Aversano, M.Ayad, R.Babu, V.Bae, H.Bahinipati, S.Bambade, P.Banerjee, S.Bansal, S.Barrett, M.et al.2025-11-092025-11-092025Physical Review D, 2025; 111(11):112009-1-112009-202470-00102470-0029https://hdl.handle.net/2440/148106We present a measurement of |𝑉𝑢⁢𝑏| from a simultaneous study of the charmless semileptonic decays 𝐵⁰→𝜋⁻⁢ℓ⁺⁢𝜈ℓ and 𝐵⁺→𝜌⁰⁢ℓ⁺⁢𝜈ℓ, where ℓ =𝑒, 𝜇. This measurement uses a data sample of 387 million 𝐵⁢¯𝐵 meson pairs recorded by the Belle II detector at the SuperKEKB electron-positron collider between 2019 and 2022. The two decays are reconstructed without identifying the partner 𝐵 mesons. We simultaneously measure the differential branching fractions of 𝐵⁰ →𝜋⁻⁢ℓ⁺⁢𝜈ℓ and 𝐵⁺ →𝜌⁰⁢ℓ⁺⁢𝜈ℓ decays as functions of 𝑞² (momentum transfer squared). From these, we obtain total branching fractions ℬ⁡(𝐵⁰→𝜋⁻⁢ℓ⁺𝜈ℓ) = (1.516 ± 0.042⁢(stat) ± 0.059⁢(syst)) ×10⁻⁴ and ℬ⁡(𝐵⁺→𝜌⁰⁢ℓ⁺⁢𝜈ℓ) = (1.625 ± 0.079⁢(stat) ± 0.180⁢(syst)) ×10⁻⁴. By fitting the measured 𝐵⁰ →𝜋⁻⁢ℓ⁺⁢𝜈ℓ partial branching fractions as functions of 𝑞², together with constraints on the nonperturbative hadronic contribution from lattice QCD calculations, we obtain |𝑉𝑢⁢𝑏| =(3.93 ± 0.09 ± 0.13 ± 0.19) × 10⁻³. Here, the first uncertainty is statistical, the second is systematic, and the third is theoretical.enPublished 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 SCOAP3Cabibbo–Kobayashi–Maskawa matrix; Form factors; Leptonic, semileptonic & radiative decaysJournal article10.1103/jnwn-ts6q743769De La Motte, S.A. [0000-0003-3905-6805]Harris, C. [0000-0003-0448-4244]Jackson, P. [0000-0002-0847-402X]