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1. Test of lepton flavor universality with a measurement of $R\left(D^{*}\right)$ using hadronic $B$ tagging at the Belle II experiment

   https://doi.org/10.1103/PhysRevD.110.072020  

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

   The ratio of branching fractions $R\left(D^{*}\right)=\mathcal{B}(\overline{B}\to D^{*}{\tau }^{-}{\overline{\nu }}_{\tau })/\mathcal{B}(\overline{B}\to D^{*}{\ell }^{-}{\overline{\nu }}_{\ell })$ , where $\ell$ is an electron or muon, is measured using a Belle II data sample with an integrated luminosity of $189{\mathrm{fb}}^{-1}$ at the SuperKEKB asymmetric-energy $e^{+}{e}^{-}$ collider. Data is collected at the $\mathrm{\Upsilon }\left(4\mathrm{S}\right)$ resonance, and one $B$ meson in the $\mathrm{\Upsilon }\left(4\mathrm{S}\right)\to B\overline{B}$ decay is fully reconstructed in hadronic decay modes. The accompanying signal $B$ meson is reconstructed as $\overline{B}\to D^{*}{\tau }^{-}{\overline{\nu }}_{\tau }$ using leptonic $\tau$ decays. The normalization decay, $\overline{B}\to D^{*}{\ell }^{-}{\overline{\nu }}_{\ell }$ , produces the same observable final-state particles. The ratio of branching fractions is extracted in a simultaneous fit to two signal-discriminating variables in both channels and yields $R\left(D^{*}\right)={0.262}_{-0.039}^{+0.041}\left(\mathrm{stat}{)}_{-0.032}^{+0.035}\right(\mathrm{syst})$ . This result is consistent with the current world average and with Standard Model predictions. Published by the American Physical Society2024 

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2. Measurement of $CP$ Violation Observables in $D^{+}\to K^{-}{K}^{+}{\pi }^{+}$ Decays

   https://doi.org/10.1103/PhysRevLett.133.251801  

   Aaij, R; Abdelmotteleb, A_S W; Abellan_Beteta, C; Abudinén, F; Ackernley, T; Adefisoye, A A; Adeva, B; Adinolfi, M; Adlarson, P; Agapopoulou, C; et al (December 2024, Physical Review Letters)

   A search for violation of the charge-parity ( $CP$ ) symmetry in the $D^{+}\to K^{-}{K}^{+}{\pi }^{+}$ decay is presented, with proton-proton collision data corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$ , collected at a center-of-mass energy of 13 TeV with the LHCb detector. A novel model-independent technique is used to compare the $D^{+}$ and $D^{-}$ phase-space distributions, with instrumental asymmetries subtracted using the $D_s^{+}\to K^{-}{K}^{+}{\pi }^{+}$ decay as a control channel. The $p$ value for the hypothesis of $CP$ conservation is 8.1%. The $CP$ asymmetry observables $A_{CP|S}^{\varphi {\pi }^{+}}=(0.95\pm 0.43_{\mathrm{stat}}\pm 0.26_{\mathrm{syst}})\times {10}^{-3}$ and $A_{CP|S}^{{\overline{K}}^{*0}{K}^{+}}=(-0.26\pm 0.56_{\mathrm{stat}}\pm 0.18_{\mathrm{syst}})\times {10}^{-3}$ are also measured. These results show no evidence of $CP$ violation and represent the most sensitive search performed through the phase space of a multibody decay. © 2024 CERN, for the LHCb Collaboration2024CERN 

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3. Evidence for $B^{-}\to D^{**0}{\tau }^{-}\overline{{\nu }_{\tau }}$ Decays

   https://doi.org/10.1103/rj9h-n4w1  

   Aaij, R; Abdelmotteleb, A_S W; Abellan_Beteta, C; Abudinén, F; Ackernley, T; Adefisoye, A A; Adeva, B; Adinolfi, M; Adlarson, P; Agapopoulou, C; et al (July 2025, Physical Review Letters)

   The first evidence for the decay $B^{-}\to D^{**0}{\tau }^{-}{\overline{\nu }}_{\tau }$ is obtained using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$ , at centre-of-mass energies of 7, 8, and 13 TeV. Here, the $D^{**0}$ meson represents any of the three excited charm mesons $D_1(2420{)}^0$ , $D_2^{*}(2460{)}^0$ , and $D_1^{\prime }(2400{)}^0$ . The $B^{-}\to D^{**0}{\tau }^{-}{\overline{\nu }}_{\tau }$ signal is measured with a significance of $3.5\sigma$ , including systematic uncertainties. The combined branching fraction $\mathcal{B}(B^{-}\to D_{1,2}^{**0}{\tau }^{-}{\overline{\nu }}_{\tau })\times \mathcal{B}(D_{1,2}^{**0}\to D^{*+}{\pi }^{-})$ , where $D_{1,2}^{**0}$ denotes both $D_1(2420{)}^0$ and $D_2^{*}(2460{)}^0$ contributions, is measured to be $[0.051\pm 0.013\left(\mathrm{stat}\right)\pm 0.006\left(\mathrm{syst}\right)\pm 0.009(\mathrm{ext}\left)\right]\%$ , where the last uncertainty reflects that of the branching fraction of the normalization channel $B^{-}\to D_{1,2}^{**0}{D_s^{-}}^{(*)}$ . The ratio between the tauonic and muonic semileptonic $B$ decays, with the latter taken from world average values, is also determined and found to be $\mathcal{R}\left(D_{1,2}^{**0}\right)=0.13\pm 0.03\left(\mathrm{stat}\right)\pm 0.01\left(\mathrm{syst}\right)\pm 0.02\left(\mathrm{ext}\right)$ . 

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4. Search for the decay $B^0\to \gamma \gamma$ using Belle and Belle II data

   https://doi.org/10.1103/PhysRevD.110.L031106  

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

   We report the result of a search for the rare decay $B^0\to \gamma \gamma$ using a combined dataset of $753\times {10}^{6}B\overline{B}$ pairs collected by the Belle experiment and $387\times {10}^{6}B\overline{B}$ pairs collected by the Belle II experiment from decays of the $\mathrm{\Upsilon }\left(4\mathrm{S}\right)$ resonance produced in $e^{+}{e}^{-}$ collisions. A simultaneous fit to the Belle and Belle II data sets yields ${11.0}_{-5.5}^{+6.5}$ signal events, corresponding to a $2.5\sigma$ significance. We determine the branching fraction $\mathcal{B}(B^0\to \gamma \gamma )=\left({3.7}_{-1.8}^{+2.2}\right(\text{stat})\pm 0.5(\text{syst}\left)\right)\times {10}^{-8}$ and set a 90% credibility level upper limit of $\mathcal{B}(B^0\to \gamma \gamma )<6.4\times {10}^{-8}$ . Published by the American Physical Society2024 

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5. Evidence for the Rare Decay $B^{+}\to \overline{\mathrm{\Lambda }}p{\mu }^{+}{\mu }^{-}$

   https://doi.org/10.1103/pl88-4435  

   Aaij, R; Abdelmotteleb, A_S W; Abellan_Beteta, C; Abudinén, F; Ackernley, T; Adefisoye, A A; Adeva, B; Adinolfi, M; Adlarson, P; Agapopoulou, C; et al (July 2026, Physical Review Letters)

   A search for the rare decay $B^{+}\to \overline{\mathrm{\Lambda }}p{\mu }^{+}{\mu }^{-}$ is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of $\sqrt{s}=13\mathrm{TeV}$ , corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$ . An excess of events is found with respect to the background-only expectation, with a signal significance of 3.5 standard deviations, in the low invariant-mass region of $m\left(\overline{\mathrm{\Lambda }}p\right)<2.8\mathrm{GeV}/c^2$ . The branching fraction is measured to be ${\mathcal{B}}_{\mathrm{low}}(B^{+}\to \overline{\mathrm{\Lambda }}p{\mu }^{+}{\mu }^{-})=\left(1.70_{-0.56}^{+0.65}\right(\mathrm{stat})\pm 0.17(\mathrm{syst})\pm 0.14(\mathrm{ext}\left)\right)\times {10}^{-8}$ , where the last uncertainty is due to external inputs on $\mathcal{B}(B^{+}\to J/\psi \overline{\mathrm{\Lambda }}p)\times \mathcal{B}(J/\psi \to {\mu }^{+}{\mu }^{-})$ . With no significant signal observed in the high $m\left(\overline{\mathrm{\Lambda }}p\right)$ region above $2.8\mathrm{GeV}/c^2$ , an upper limit is set to be ${\mathcal{B}}_{\mathrm{high}}(B^{+}\to \overline{\mathrm{\Lambda }}p{\mu }^{+}{\mu }^{-})<2.8\left(3.7\right)\times {10}^{-9}$ at the 90% (95%) confidence level. 

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