Belle II is an experiment operating at the intensity frontier. Over the next decades, it will record the decay of billions of bottom mesons, charm hadrons, and tau leptons produced in 10 GeV electron-positron collisions at the SuperKEKB high-luminosity collider at KEK. These data, collected in low-background and kinematically known conditions, will allow us to measure hundreds of parameters that test the standard model (SM) and probe for the existence of new particles, at mass scales orders of magnitudes higher than those studied at the energy frontier. We project our sensitivities for measurements that are of primary relevance and where Belle II will be unique or world leading for data corresponding to 1 to 50 ab$^{-1}$. Belle II will uniquely probe non-SM contributions in sensitive $b \to q\bar q s$ decays and charmless $b \to q\bar q d(u)$ decays, semileptonic $b \to s \nu \bar\nu$ and $s \tau^+ \tau^-$ decays, fully leptonic $b \to \ell \nu$ decays, and select $c \to u$ processes. Belle II will lead exploration of non-SM physics in $b \to c \tau \nu$ and $b \to s \gamma$ decays and will most precisely determine the quark-mixing parameters $|V_{ub}|$ and $|V_{cb}|$. Belle II will measure many parameters in $\tau$ physics to precisions that will be world leading for the foreseeable future, including the electric and magnetic dipole moments, branching fractions for charged-lepton-flavor-violating decays, and quantities that test lepton-flavor universality. Belle II will perform unique searches for dark-sector particles with masses in the MeV-GeV range. We will also pursue a broad spectroscopy program for conventional and multiquark $c \bar c$ and $b \bar b$ states and provide essential inputs to sharpen the interpretation of muon magnetic-anomaly results. Our exploration of uncharted regions of non-SM parameter space with high precision will reveal non-SM particles or set stringent constraints on their existence, guiding future endeavors.
These proceedings summarise recent work in which the Standard Model and New Physics form factors of $\Lambda_{b} \rightarrow \Lambda_{c} \ell^{-} \bar{\nu}_{\ell}$ decays were computed up to order $\mathcal{O}(\Lambda^{2}_{\rm QCD} / m^{2}_{c})$ using Heavy Quark Effective Theory (HQET). This allowed for a subsequent HQET-based determination of form factors of the decay using a fit, which combines recent theoretical predictions and experimental measurements. Consequently, the most precise value of $R(\Lambda_{c})$ to date was determined, $R(\Lambda_{c})=0.324 \pm 0.004$. Additionally, the sensitivity of $R(\Lambda_{c})$ to potential NP interactions was explored.
S. Jia, C. P. Shen , C. Z. Yuan, X. L. Wang, I. Adachi, H. Aihara, D. M. Asner, H. Atmacan, V. Aulchenko, R. Ayad, V. Babu, I. Badhrees, A. M. Bakich, P. Behera, B. Bhuyan, T. Bilka, J. Biswal, A. Bobrov, G. Bonvicini, A. Bozek, M. Bračko, T. E. Browder, M. Campajola, L. Cao, D. Červenkov, P. Chang, A. Chen, B. G. Cheon, K. Chilikin, H. E. Cho, K. Cho, S.-K. Choi, Y. Choi, D. Cinabro, S. Cunliffe, G. De Nardo, F. Di Capua, S. Di Carlo, Z. Doležal, T. V. Dong, S. Eidelman, D. Epifanov, J. E. Fast, T. Ferber, B. G. Fulsom, R. Garg, V. Gaur, N. Gabyshev, A. Garmash, A. Giri, P. Goldenzweig, B. Golob, K. Hayasaka, H. Hayashii, W.-S. Hou, C.-L. Hsu, T. Iijima, K. Inami, G. Inguglia, A. Ishikawa, R. Itoh, M. Iwasaki, Y. Iwasaki, W.W. Jacobs, Y. Jin, K. K. Joo, K. H. Kang, G. Karyan, H. Kichimi, B. H. Kim, C. H. Kim, D. Y. Kim, S. H. Kim, K. Kinoshita, P. Kodyš, S. Korpar, R. Kroeger, P. Krokovny, R. Kulasiri, A. Kuzmin, Y.-J. Kwon, K. Lalwani, J. S. Lange, I. S. Lee, S. C. Lee, P. Lewis, C. H. Li, L. K. Li, Y. B. Li, L. Li Gioi, J. Libby, K. Lieret, D. Liventsev, C. MacQueen, M. Masuda, T. Matsuda, D. Matvienko, M. Merola, K. Miyabayashi, H. Miyata, R. Mizuk, R. Mussa, K. J. Nath, M. Nayak, M. Niiyama, N. K. Nisar, S. Nishida, K. Nishimura, S. Ogawa, H. Ono, Y. Onuki, P. Oskin, P. Pakhlov, G. Pakhlova, T. Pang, S. Pardi, H. Park, S.-H. Park, S. Patra, S. Paul, T. K. Pedlar, R. Pestotnik, L. E. Piilonen, V. Popov, E. Prencipe, M. T. Prim, M. Röhrken, A. Rostomyan, N. Rout, G. Russo, D. Sahoo, Y. Sakai, S. Sandilya, L. Santelj, V. Savinov, O. Schneider, G. Schnell, C. Schwanda, Y. Seino, K. Senyo, M. E. Sevior, J.-G. Shiu, B. Shwartz, A. Sokolov, E. Solovieva, S. Stanič, M. Starič, Z. S. Stottler, T. Sumiyoshi, W. Sutcliffe, M. Takizawa, K. Tanida, F. Tenchini, K. Trabelsi, M. Uchida, T. Uglov, Y. Unno, S. Uno, Y. Usov, R. Van Tonder, G. Varner, A. Vinokurova, V. Vorobyev, C. H. Wang, M.-Z. Wang, M. Watanabe, E. Won, S. B. Yang, H. Ye, J. H. Yin, Z. P. Zhang, V. Zhilich, V. Zhukova, and V. Zhulanov
Y.-T. Lai, I. Adachi, H. Aihara, S. Al Said, D. M. Asner, H. Atmacan, V. Aulchenko, T. Aushev, V. Babu, I. Badhrees, A. M. Bakich, V. Bansal, P. Behera, C. Beleño, B. Bhuyan, T. Bilka, J. Biswal, A. Bobrov, A. Bozek, M. Bračko, L. Cao, D. Červenkov, P. Chang, V. Chekelian, A. Chen, B. G. Cheon, K. Chilikin, K. Cho, S.-K. Choi, Y. Choi, S. Choudhury, D. Cinabro, S. Cunliffe, N. Dash, S. Di Carlo, Z. Doležal, T. V. Dong, S. Eidelman, D. Epifanov, J. E. Fast, A. Frey, B. G. Fulsom, R. Garg, V. Gaur, N. Gabyshev, A. Garmash, M. Gelb, A. Giri, P. Goldenzweig, D. Greenwald, Y. Guan, J. Haba, T. Hara, K. Hayasaka, H. Hayashii, W.-S. Hou, C.-L. Hsu, K. Huang, T. Iijima, K. Inami, G. Inguglia, A. Ishikawa, R. Itoh, M. Iwasaki, Y. Iwasaki, S. Jia, Y. Jin, D. Joffe, A. B. Kaliyar, G. Karyan, T. Kawasaki, H. Kichimi, C. Kiesling, D. Y. Kim, H. J. Kim, J. B. Kim, S. H. Kim, K. Kinoshita, P. Kodyš, S. Korpar, D. Kotchetkov, P. Križan, R. Kroeger, P. Krokovny, T. Kuhr, R. Kulasiri, R. Kumar, A. Kuzmin, Y.-J. Kwon, K. Lalwani, J. S. Lange, I. S. Lee, J. K. Lee, J. Y. Lee, S. C. Lee, C. H. Li, L. K. Li, Y. B. Li, L. Li Gioi, J. Libby, Z. Liptak, D. Liventsev, P.-C. Lu, M. Lubej, T. Luo, J. MacNaughton, M. Masuda, T. Matsuda, D. Matvienko, M. Merola, K. Miyabayashi, R. Mizuk, G. B. Mohanty, T. Mori, M. Mrvar, R. Mussa, E. Nakano, M. Nakao, K. J. Nath, M. Nayak, N. K. Nisar, S. Nishida, S. Ogawa, G. Pakhlova, B. Pal, S. Pardi, H. Park, S. Paul, T. K. Pedlar, R. Pestotnik, L. E. Piilonen, V. Popov, E. Prencipe, A. Rabusov, M. Ritter, A. Rostomyan, G. Russo, Y. Sakai, M. Salehi, S. Sandilya, L. Santelj, T. Sanuki, V. Savinov, O. Schneider, G. Schnell, C. Schwanda, Y. Seino, K. Senyo, O. Seon, M. E. Sevior, C. P. Shen, T.-A. Shibata, J.-G. Shiu, E. Solovieva, M. Starič, M. Sumihama, T. Sumiyoshi, W. Sutcliffe, M. Takizawa, K. Tanida, Y. Tao, F. Tenchini, M. Uchida, T. Uglov, Y. Unno, S. Uno, P. Urquijo, Y. Usov, R. Van Tonder, G. Varner, K. E. Varvell, V. Vorobyev, B. Wang, C. H. Wang, M.-Z. Wang, P. Wang, X. L. Wang, E. Widmann, E. Won, H. Yamamoto, S. B. Yang, H. Ye, C. Z. Yuan, Y. Yusa, Z. P. Zhang, V. Zhilich, V. Zhukova, and V. Zhulanov
The Full Event Interpretation is presented: a new exclusive tagging algorithm used by the high-energy physics experiment Belle II. The experimental setup of Belle II allows the precise measurement of otherwise inaccessible $B$ meson decay-modes. The Full Event Interpretation algorithm enables many of these measurements. The algorithm relies on machine learning to automatically identify plausible $B$ meson decay chains based on the data recorded by the detector. Compared to similar algorithms employed by previous experiments, the Full Event Interpretation provides a greater efficiency, yielding a larger effective sample size usable in the measurement.
Y. Li, Y. B. Li, C. P. Shen , I. Adachi, H. Aihara, D. M. Asner, H. Atmacan, V. Aulchenko, R. Ayad, V. Babu, I. Badhrees, A. M. Bakich, P. Behera, T. Bilka, J. Biswal, A. Bobrov, G. Bonvicini, A. Bozek, M. Bračko, T. E. Browder, M. Campajola, L. Cao, D. Červenkov, P. Chang, A. Chen, B. G. Cheon, K. Chilikin, H. E. Cho, K. Cho, S.-K. Choi, Y. Choi, D. Cinabro, S. Cunliffe, G. De Nardo, F. Di Capua, S. Di Carlo, Z. Doležal, T. V. Dong, S. Eidelman, J. E. Fast, T. Ferber, D. Ferlewicz, B. G. Fulsom, R. Garg, V. Gaur, N. Gabyshev, A. Garmash, A. Giri, P. Goldenzweig, B. Golob, B. Grube, T. Hara, K. Hayasaka, H. Hayashii, W.-S. Hou, C.-L. Hsu, T. Iijima, K. Inami, G. Inguglia, A. Ishikawa, R. Itoh, M. Iwasaki, Y. Iwasaki, W.W. Jacobs, S. Jia, Y. Jin, K. K. Joo, K. H. Kang, G. Karyan, H. Kichimi, C. H. Kim, D. Y. Kim, S. H. Kim, K. Kinoshita, P. Kodyš, S. Korpar, R. Kroeger, P. Krokovny, T. Kuhr, R. Kulasiri, A. Kuzmin, Y.-J. Kwon, K. Lalwani, J. S. Lange, I. S. Lee, S. C. Lee, P. Lewis, C. H. Li, L. K. Li, L. Li Gioi, J. Libby, K. Lieret, D. Liventsev, C. MacQueen, M. Masuda, T. Matsuda, D. Matvienko, M. Merola, H. Miyata, R. Mizuk, R. Mussa, M. Nakao, K. J. Nath, M. Nayak, M. Niiyama, N. K. Nisar, S. Nishida, K. Nishimura, S. Ogawa, H. Ono, Y. Onuki, P. Oskin, P. Pakhlov, G. Pakhlova, T. Pang, S. Pardi, H. Park, S.-H. Park, S. Patra, S. Paul, T. K. Pedlar, R. Pestotnik, L. E. Piilonen, T. Podobnik, V. Popov, E. Prencipe, M. T. Prim, M. Röhrken, A. Rostomyan, N. Rout, G. Russo, D. Sahoo, Y. Sakai, S. Sandilya, L. Santelj, V. Savinov, O. Schneider, G. Schnell, C. Schwanda, Y. Seino, K. Senyo, M. E. Sevior, J.-G. Shiu, B. Shwartz, A. Sokolov, E. Solovieva, S. Stanič, M. Starič, Z. S. Stottler, M. Sumihama, T. Sumiyoshi, W. Sutcliffe, M. Takizawa, K. Tanida, F. Tenchini, K. Trabelsi, M. Uchida, T. Uglov, Y. Unno, S. Uno, R. Van Tonder, G. Varner, A. Vinokurova, C. H. Wang, M.-Z. Wang, X. L. Wang, M. Watanabe, E. Won, S. B. Yang, H. Ye, J. Yelton, J. H. Yin, C. Z. Yuan, Z. P. Zhang, V. Zhilich, V. Zhukova, and V. Zhulanov
The ratio of branching fractions ${\cal{R}}(D^{*-})\equiv {\cal{B}}(B^0 \to D^{*-} \tau^+ \nu_{\tau})/{\cal{B}}(B^0 \to D^{*-} \mu^+\nu_{\mu})$ is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3$~$fb$^{-1}$. The $\tau$ lepton is reconstructed with three charged pions in the final state. A novel method is used that exploits the different vertex topologies of signal and backgrounds to isolate samples of semitauonic decays of $b$ hadrons with high purity. Using the $B^0 \to D^{*-}\pi^+\pi^-\pi^+$ decay as the normalization channel, the ratio ${\cal{B}}(B^0 \to D^{*-} \tau^+ \nu_{\tau})/{\cal{B}}(B^0 \to D^{*-}\pi^+\pi^-\pi^+)$ is measured to be $1.93 \pm 0.13 \pm 0.18$, where the first uncertainty is statistical and the second systematic. The LHCb measurement of the branching fraction for the normalization channel is used to derive ${\cal{B}}(B^0 \to D^{*-} \tau^+ \nu_{\tau}) = (1.40 \pm 0.09 \pm 0.12 \pm 0.10) \%$, where the third uncertainty is due to the limited knowledge of ${\cal{B}}(B^0\to D^{*-}\pi^+\pi^-\pi^+)$. A test of lepton flavor universality is performed using the well-measured branching fraction ${\cal{B}}(B^0 \to D^{*-} \mu^+\nu_{\mu})$ to compute ${\cal{R}}(D^{*-}) = 0.286 \pm 0.019 \pm 0.025 \pm 0.021$, where the third uncertainty originates from the uncertainties on ${\cal{B}}(B^0 \to D^{*-}\pi^+\pi^-\pi^+)$ and ${\cal{B}}(B^0 \to D^{*-} \mu^+\nu_{\mu})$. This measurement is in agreement with the Standard Model prediction and with previous measurements.
The decay $Z \rightarrow b \bar{b}$ is reconstructed in $pp$ collision data, corresponding to 2 fb$^{-1}$ of integrated luminosity, collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}=8$ TeV. The product of the $Z$ production cross-section and the $Z \rightarrow b \bar{b}$ branching fraction is measured for candidates in the fiducial region defined by two particle-level $b$-quark jets with pseudorapidities in the range $2.2 20$ GeV and dijet invariant mass in the range $45 < m_{jj} < 165$ GeV. From a signal yield of $5462 \pm 763$ $Z \rightarrow b \bar{b}$ events, where the uncertainty is statistical, a production cross-section times branching fraction of $332 \pm 46 \pm 59$ pb is obtained, where the first uncertainty is statistical and the second systematic. The measured significance of the signal yield is 6.0 standard deviations. This measurement represents the first observation of the $Z \rightarrow b \bar{b}$ production in the forward region of $pp$ collisions.