Measurement of branching fractions, CP asymmetry, and isospin asymmetry for $\boldsymbol{B\rightarrow\rho\gamma}$ decays using Belle and Belle II data

• Main Authors: Adachi, I, Aloisio, A, Asner, D. M, Aushev, V, Ayad, R, Bae, H, Bahinipati, S, Bambade, P, Becker, J, Bennett, J. V, Bertacchi, V, Bianchi, F, Bilka, T, Bondar, A, Bračko, M, Branchini, P, Bussino, S, Campajola, M, Chang, M. -C, Cheon, B. G, Chilikin, K, Cho, H. -E, De La Motte, S. A, Dong, T. V, Dorigo, M, Dreyer, S, Eliachevitch, M, Finck, C, Gaudino, G, Gellrich, A, Ghevondyan, G, Gobbo, B, Goldenzweig, P, Greenwald, D, Gudkova, K, Halder, S, Hoek, M, Horak, P, Iijima, T, Ipsita, N, Joo, K. K, Kalita, D, Kaliyar, A. B, Kandra, J, Kim, K. -H, Kim, Y. -K, Kinoshita, K, Kodyš, P, Kuhr, T, Kunigo, T, Lai, Y. -T, Liu, Q. Y, Maity, S, Manfredi, R, Marcello, S, Massaccesi, L, Masuda, M, Maurya, S. K, Meier, F, Miyake, H, Nakamura, I, Nakamura, K. R, Nakazawa, Y, Charan, A. Narimani, Narwal, D, Natochii, A, Niebuhr, C, Onishchuk, Y, Oskin, P, Pakhlov, P, Pardi, S, Park, H, Podesta-Lerma, P. L. M, Prim, M. T, Rados, P, Raeuber, G, Roney, J. M, Rout, N, Russo, G, Savinov, V, Schwartz, A. J, Schwickardi, M, Shen, C. P, Shi, X. D, Shiu, J. -G, Simon, F, Singh, J. B, Sumisawa, K, Tamponi, U, Tittel, O, Tiwary, R, Urquijo, P, Veronesi, M, Vinokurova, A, Wach, B, Warburton, A, Wiechczynski, J, Yamada, S, Yang, S. B, Zhou, X. Y
• Format: Journal Article
• Language: English
• Published: 12.07.2024
• Subjects: Physics - High Energy Physics - Experiment
• DOI: 10.48550/arxiv.2407.08984

We present measurements of $B^{+}\rightarrow\rho^{+}\gamma$ and $B^{0}\rightarrow\rho^{0}\gamma$ decays using a combined data sample of $772 \times 10^6$ $B\overline{B}$ pairs collected by the Belle experiment and $387\times 10^6$ $B\overline{B}$ pairs collected by the Belle II experiment in $e^{+}e^{-}$ collisions at the $\Upsilon (4S)$ resonance. After an optimized selection, a simultaneous fit to the Belle and Belle II data sets yields $114\pm 12$ $B^{+}\rightarrow\rho^{+}\gamma$ and $99\pm 12$ $B^{0}\rightarrow\rho^{0}\gamma$ decays. The measured branching fractions are $(13.1^{+2.0 +1.3}_{-1.9 -1.2})\times 10^{-7}$ and $(7.5\pm 1.3^{+1.0}_{-0.8})\times 10^{-7}$ for $B^{+}\rightarrow\rho^{+}\gamma$ and $B^{0}\rightarrow\rho^{0}\gamma$ decays, respectively, where the first uncertainty is statistical and the second is systematic. We also measure the isospin asymmetry $A_{\rm I}(B\rightarrow\rho\gamma)=(10.9^{+11.2 +7.8}_{-11.7 -7.3})\%$ and the direct CP asymmetry $A_{CP}(B^{+}\rightarrow\rho^{+}\gamma)=(-8.2\pm 15.2^{+1.6}_{-1.2})\%$.