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1. Search for the baryon number and lepton number violating decays ${\tau }^{-}\to \mathrm{\Lambda }{\pi }^{-}$ and ${\tau }^{-}\to \overline{\mathrm{\Lambda }}{\pi }^{-}$ at Belle II

   https://doi.org/10.1103/PhysRevD.110.112003  

   Adachi, I; Aggarwal, L; Ahmed, H; Aihara, H; Akopov, N; Aloisio, A; Althubiti, N; Anh_Ky, N; Asner, D M; Atmacan, H; et al (December 2024, Physical Review D)

   We present a search for the baryon number $B$ and lepton number $L$ violating decays ${\tau }^{-}\to \mathrm{\Lambda }{\pi }^{-}$ and ${\tau }^{-}\to \overline{\mathrm{\Lambda }}{\pi }^{-}$ produced from the $e^{+}{e}^{-}\to {\tau }^{+}{\tau }^{-}$ process, using a $364{\mathrm{fb}}^{-1}$ data sample collected by the Belle II experiment at the SuperKEKB collider. No evidence of signal is found in either decay mode, which have $\left|\mathrm{\Delta }\right(B-L\left)\right|$ equal to 2 and 0, respectively. Upper limits at 90% credibility level on the branching fractions of ${\tau }^{-}\to \mathrm{\Lambda }{\pi }^{-}$ and ${\tau }^{-}\to \overline{\mathrm{\Lambda }}{\pi }^{-}$ are determined to be $4.7\times {10}^{-8}$ and $4.3\times {10}^{-8}$ , respectively. Published by the American Physical Society2024 

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2. Search for two-body $B$ meson decays to ${\mathrm{\Lambda }}^0$ and ${\mathrm{\Omega }}_c^{(*)0}$

   https://doi.org/10.1103/PhysRevD.110.L031102  

   Savinov, V; Adachi, I; Ahn, J K; Aihara, H; Asner, D M; Atmacan, H; Ayad, R; Banerjee, Sw; Bennett, J; Bessner, M; et al (August 2024, Physical Review D)

   We report the results of the first search for Standard Model and baryon-number-violating two-body decays of the neutral $B$ mesons to ${\mathrm{\Lambda }}^0$ and ${\mathrm{\Omega }}_c^{(*)0}$ using $711{\mathrm{fb}}^{-1}$ of data collected at the $\mathrm{\Upsilon }\left(4S\right)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We observe no evidence of signal from any such decays and set 95% confidence-level upper limits on the products of $B^0$ and ${\overline{B}}^0$ branching fractions for these two-body decays with $\mathcal{B}({\mathrm{\Omega }}_c^0\to {\pi }^{+}{\mathrm{\Omega }}^{-})$ in the range between $9.5\times {10}^{-8}$ and $31.2\times {10}^{-8}$ . Published by the American Physical Society2024 

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3. Evidence for $B^{+}\to K^{+}\nu \overline{\nu }$ decays

   https://doi.org/10.1103/PhysRevD.109.112006  

   Adachi, I; Adamczyk, K; Aggarwal, L; Ahmed, H; Aihara, H; Akopov, N; Aloisio, A; Anh_Ky, N; Asner, D M; Atmacan, H; et al (June 2024, Physical Review D)

   We search for the rare decay $B^{+}\to K^{+}\nu \overline{\nu }$ in a $362{\mathrm{fb}}^{-1}$ sample of electron-positron collisions at the $\mathrm{\Upsilon }\left(4S\right)$ resonance collected with the Belle II detector at the SuperKEKB collider. We use the inclusive properties of the accompanying $B$ meson in $\mathrm{\Upsilon }\left(4S\right)\to B\overline{B}$ events to suppress background from other decays of the signal $B$ candidate and light-quark pair production. We validate the measurement with an auxiliary analysis based on a conventional hadronic reconstruction of the accompanying $B$ meson. For background suppression, we exploit distinct signal features using machine learning methods tuned with simulated data. The signal-reconstruction efficiency and background suppression are validated through various control channels. The branching fraction is extracted in a maximum likelihood fit. Our inclusive and hadronic analyses yield consistent results for the $B^{+}\to K^{+}\nu \overline{\nu }$ branching fraction of $[2.7\pm 0.5(\mathrm{stat})\pm 0.5(\mathrm{syst}\left)\right]\times {10}^{-5}$ and $\left[{1.1}_{-0.8}^{+0.9}\right(\mathrm{stat}{)}_{-0.5}^{+0.8}\left(\mathrm{syst}\right)]\times {10}^{-5}$ , respectively. Combining the results, we determine the branching fraction of the decay $B^{+}\to K^{+}\nu \overline{\nu }$ to be $[2.3\pm 0.5(\mathrm{stat}{)}_{-0.4}^{+0.5}\left(\mathrm{syst}\right)]\times {10}^{-5}$ , providing the first evidence for this decay at 3.5 standard deviations. The combined result is 2.7 standard deviations above the standard model expectation. Published by the American Physical Society2024 

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4. Observation of the ${\mathrm{\Xi }}_b^{-}\to \psi \left(2S\right){\mathrm{\Xi }}^{-}$ decay and studies of the ${\mathrm{\Xi }}_b(5945{)}^0$ baryon in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$

   https://doi.org/10.1103/PhysRevD.110.012002  

   Hayrapetyan, A; Tumasyan, A; Adam, W; Andrejkovic, J W; Bergauer, T; Chatterjee, S; Damanakis, K; Dragicevic, M; Hussain, P S; Jeitler, M; et al (July 2024, Physical review)

   The first observation of the decay ${\mathrm{\Xi }}_b^{-}\to \psi \left(2S\right){\mathrm{\Xi }}^{-}$ and measurement of the branching ratio of ${\mathrm{\Xi }}_b^{-}\to \psi \left(2S\right){\mathrm{\Xi }}^{-}$ to ${\mathrm{\Xi }}_b^{-}\to J/\psi {\mathrm{\Xi }}^{-}$ are presented. The $J/\psi$ and $\psi \left(2S\right)$ mesons are reconstructed using their dimuon decay modes. The results are based on proton-proton colliding beam data from the LHC collected by the CMS experiment at $\sqrt{s}=13\mathrm{TeV}$ in 2016–2018, corresponding to an integrated luminosity of $140{\mathrm{fb}}^{-1}$ . The branching fraction ratio is measured to be $\mathcal{B}\left({\mathrm{\Xi }}_b^{-}\to \psi \left(2S\right){\mathrm{\Xi }}^{-}\right)/\mathcal{B}\left({\mathrm{\Xi }}_b^{-}\to J/\psi {\mathrm{\Xi }}^{-}\right)=0.84_{-0.19}^{+0.21}\left(\mathrm{stat}\right)\pm 0.10\left(\mathrm{syst}\right)\pm 0.02\left(\mathcal{B}\right)$ , where the last uncertainty comes from the uncertainties in the branching fractions of the charmonium states. New measurements of the ${\mathrm{\Xi }}_b(5945{)}^0$ baryon mass and natural width are also presented, using the ${\mathrm{\Xi }}_b^{-}{\pi }^{+}$ final state, where the ${\mathrm{\Xi }}_b^{-}$ baryon is reconstructed through the decays $J/\psi {\mathrm{\Xi }}^{-}$ , $\psi \left(2S\right){\mathrm{\Xi }}^{-}$ , $J/\psi \mathrm{\Lambda }{K}^{-}$ , and $J/\psi {\mathrm{\Sigma }}^0{K}^{-}$ . Finally, the fraction of ${\mathrm{\Xi }}_b^{-}$ baryons produced from ${\mathrm{\Xi }}_b(5945{)}^0$ decays is determined. © 2024 CERN, for the CMS Collaboration2024CERN 

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5. Search for Rare $b\to d{\ell }^{+}{\ell }^{-}$ Transitions at Belle

   https://doi.org/10.1103/PhysRevLett.133.101804  

   Adachi, I; Aggarwal, L; Aihara, H; Akopov, N; Aloisio, A; Al_Said, S; Asner, D M; Atmacan, H; Aushev, V; Aversano, M; et al (September 2024, Physical Review Letters)

   We present the results of a search for the $b\to d{\ell }^{+}{\ell }^{-}$ flavor-changing neutral-current rare decays $B^{+,0}\to (\eta ,\omega ,{\pi }^{+,0},{\rho }^{+,0})e^{+}{e}^{-}$ and $B^{+,0}\to (\eta ,\omega ,{\pi }^0,{\rho }^{+}){\mu }^{+}{\mu }^{-}$ using a $711{\mathrm{fb}}^{-1}$ data sample that contains $772\times {10}^{6}B\overline{B}$ events. The data were collected at the $\mathrm{\Upsilon }\left(4S\right)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We find no evidence for signal and set upper limits on branching fractions at the 90% confidence level in the range $\left(3.8–47\right)\times {10}^{-8}$ depending on the decay channel. The obtained limits are the world’s best results. This is the first search for the channels $B^{+,0}\to (\omega ,{\rho }^{+,0})e^{+}{e}^{-}$ and $B^{+,0}\to (\omega ,{\rho }^{+}){\mu }^{+}{\mu }^{-}$ . Published by the American Physical Society2024 

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