Determination of $|V_{ub}|$ from simultaneous measurements of untagged $B^0\to\pi^- \ell^+ \nu_{\ell}$ and $B^+\to\rho^0 \ell^+\nu_{\ell}$ decays

• Main Authors: Adachi, I, Aloisio, A, Asner, D. M, Aushev, V, Bae, H, Bahinipati, S, Bambade, P, Becherer, F, Bertemes, M, Briere, R. A, Chang, P, Cho, S. -J, Choi, S. -K, Choudhury, S, Jiménez, I. Domínguez, Dubey, S, Dugic, K, Ecker, P, Feichtinger, P, Ferber, T, Gabrielli, A, Garg, R, Gaudino, G, Gaz, A, Giakoustidis, G, Giri, A, Granderath, S, Halder, S, Hedges, M. T, Villanueva, M. Hernández, Higuchi, T, Hohmann, M, Inami, K, Iwasaki, M, Jang, E. -J, Jia, S, Kiesling, C, Kim, C. -H, Kohani, S, Korpar, S, Kowalewski, R, Križan, P, Kulii, Y, Kumar, M, Kuzmin, A, Kwon, Y. -J, Lee, M. J, Levit, D, Lewis, P. M, Masuda, M, Metzner, F, Miller, C, Mirra, M, Mondal, S, Moneta, S, Mussa, R, Natochii, A, Nayak, L, Neu, M, Ogawa, S, Passeri, A, Pedlar, T. K, Peschke, R, Angioni, G. Pinna, Prell, S, Prudiiev, I, Raeuber, G, Raiz, S, Reuter, L, Robertson, S. H, Rostomyan, A, Sanders, D. A, Sandilya, S, Sato, Y, Schwanda, C, Seino, Y, Selce, A, Senyo, K, Shan, W, Sharma, C, Shtol, D, Soffer, A, Starič, M, Stroili, R, Sutcliffe, W, Tittel, O, Ushiroda, Y, Vismaya, V. S, Vitale, L, Vobbilisetti, V, Vossen, A, Wallner, S, Wang, E, Wang, M. -Z, Wessel, C, Xu, X. P, Yamada, S, Yook, Y. M, Zhang, B, Zhilich, V
• Format: Journal Article
• Language: English
• Published: 24.07.2024
• Subjects: Physics - High Energy Physics - Experiment
• DOI: 10.48550/arxiv.2407.17403

We present a measurement of $|V_{ub}|$ from a simultaneous study of the charmless semileptonic decays $B^0\to\pi^- \ell^+ \nu_{\ell}$ and $B^+\to\rho^0 \ell^+\nu_{\ell}$, where $\ell = e, \mu$. This measurement uses a data sample of 387 million $B\overline{B}$ 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 $B^0\to\pi^- \ell^+ \nu_{\ell}$ and $B^+\to\rho^0 \ell^+\nu_{\ell}$ decays as functions of $q^2$ (momentum transfer squared). From these, we obtain total branching fractions $B(B^0\to\pi^- \ell^+ \nu_{\ell}) = (1.516 \pm 0.042 (\mathrm{stat}) \pm 0.059 (\mathrm{syst})) \times 10^{-4}$ and $B(B^+\to\rho^0 \ell^+\nu_{\ell}) = (1.625 \pm 0.079 (\mathrm{stat}) \pm 0.180 (\mathrm{syst})) \times 10^{-4}$. By fitting the measured $B^0\to\pi^- \ell^+ \nu_{\ell}$ partial branching fractions as functions of $q^2$, together with constraints on the non-perturbative hadronic contribution from lattice QCD calculations, we obtain $|V_{ub}|$ = $(3.93 \pm 0.09 \pm 0.13 \pm 0.19) \times 10^{-3}$. Here, the first uncertainty is statistical, the second is systematic, and the third is theoretical.