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1. Search for $$ {\textrm{B}}_{\textrm{s}}^0 $$ → ℓ∓τ± with the semi-leptonic tagging method at Belle

   https://doi.org/10.1007/JHEP08(2023)178  

   Nayak, L; Nishida, S; Giri, A; Adachi, I; Aihara, H; Asner, D M; Atmacan, H; Aulchenko, V; Aushev, T; Ayad, R; et al (August 2023, Journal of High Energy Physics)

   A<sc>bstract</sc> We present a search for the lepton-flavor-violating decays$$ {B}_s^0 $$ $B_s^0$ →ℓ^∓τ^±, whereℓ=e, μ, using the full data sample of 121 fb⁻¹collected at the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energye⁺e⁻collider. We use$$ {B}_s^0{\overline{B}}_s^0 $$ $B_s^0{\overline{B}}_s^0$ events in which one$$ {B}_s^0 $$ $B_s^0$ meson is reconstructed in a semileptonic decay mode and the other in the signal mode. We find no evidence for$$ {B}_s^0 $$ $B_s^0$ → ℓ^∓τ^±decays and set upper limits on their branching fractions at 90% confidence level as$$ \mathcal{B} $$ $B$ ($$ {B}_s^0 $$ $B_s^0$ → e^∓τ^±)<14×10⁻⁴and$$ \mathcal{B} $$ $B$ ($$ {B}_s^0 $$ $B_s^0$ → μ^∓τ^±)<7.3×10⁻⁴. Our result represents the first upper limit on the$$ {B}_s^0 $$ $B_s^0$ → e^∓τ^±decay rate. 

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2. Search for lepton-flavor-violating tau decays to ℓα at Belle

   https://doi.org/10.1007/JHEP08(2025)155  

   Uno, K; Hayasaka, K; Inami, K; Aihara, H; Ayad, R; Banerjee, Sw; Belous, K; Bennett, J; Bessner, M; Biswas, D; et al (August 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> We report a search for the lepton-flavor-violating decaysτ^±→ℓ^±α(ℓ=e,μ), whereαis an undetected spin-0 particle, such as an axion-like particle using 736 × 10⁶tau lepton pairs collected by the Belle detector at the KEKB asymmetric-energye⁺e⁻collider. We find no evidence of signal and obtain the most stringent upper limits on the branching fractions at 95% confidence level:$$\mathcal{B}$$(τ^±→ e^±α) < (0.4–6.4)×10⁻⁴and$$\mathcal{B}$$(τ^±→ μ^±α) < (0.2–3.5)×10⁻⁴at 95% confidence level for anαmass in the range 0.0≤ m_α≤1.6 GeV/c². 

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3. Search for the lepton-flavour-violating decays B0 → K*0τ±e∓

   https://doi.org/10.1007/JHEP11(2025)172  

   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 (November 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> A first search at LHCb for the lepton-flavour-violating decaysB⁰→K^*0τ^±e^∓is presented. The analysis is performed using a sample of proton-proton collision data, collected with the LHCb detector at a centre-of-mass energy of 13 TeV between 2016 and 2018, corresponding to an integrated luminosity of 5.4 fb⁻¹. No significant signal is observed, and upper limits on the branching fractions are determined to be$$ \mathcal{B}\left({B}^0\to {K}^{\ast 0}{\tau}^{-}{e}^{+}\right)<5.9(7.1)\times {10}^{-6} $$ $B\left(B^0\to K^{\ast 0}{\tau }^{-}{e}^{+}\right)<5.9\left(7.1\right)\times {10}^{-6}$ and$$ \mathcal{B}\left({B}^0\to {K}^{\ast 0}{\tau}^{+}{e}^{-}\right)<4.9(5.9)\times {10}^{-6} $$ $B\left(B^0\to K^{\ast 0}{\tau }^{+}{e}^{-}\right)<4.9\left(5.9\right)\times {10}^{-6}$ at the 90% (95%) confidence level. These results correspond to the current most stringent upper limits forb→sτltransitions. 

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4. Search for a pentaquark state decaying into pJ/ψ in Υ(1, 2S) inclusive decays at Belle

   https://doi.org/10.1007/JHEP09(2025)048  

   Dong, X; Zou, S M; Zhang, H Y; Wang, X L; Adachi, I; Ahn, J K; Aihara, H; Al_Said, S; Asner, D M; Atmacan, H; et al (September 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> Using the data samples of 102 million Υ(1S) and 158 million Υ(2S) events collected by the Belle detector, we search for a pentaquark state in thepJ/ψfinal state from Υ(1,2S) inclusive decays. Here, the charge-conjugate$$\overline{p }J/\psi $$is included. We observe clearpJ/ψproduction in Υ(1,2S) decays and measure the branching fractions to be$$\mathcal{B}[\Upsilon (1S)\to pJ/\psi +anything]=[8.1\pm 0.6(stat.)\pm 0.5(syst.)]\times {10}^{-5}$$and$$\mathcal{B}[\Upsilon (2S)\to pJ/\psi +anything]=[4.3\pm 0.5(stat.)\pm 0.4(syst.)]\times {10}^{-5}$$. We also measure the cross section of inclusivepJ/ψproduction ine⁺e⁻annihilation to beσ(e⁺e⁻→pJ/ψ+anything) = [108 ± 11(stat.) ± 6(syst.)] fb at$$\sqrt{s}=10.52$$GeV using an 89.5 fb⁻¹continuum data sample. There is no significantP_c(4312)⁺,P_c(4440)⁺orP_c(4457)⁺signal found in thepJ/ψfinal states in Υ(1,2S) inclusive decays. We determine the upper limits of$$\mathcal{B}\left[\Upsilon \left({1},{2}S\right)\to {P}_{c}^{+}+anything\right]\cdot \mathcal{B}\left({P}_{c}^{+}\to pJ/\psi \right)$$to be at the 10⁻⁶level. 

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5. A case study of SMEFT $$ \mathcal{O}\left(1/{\Lambda}^4\right) $$ effects in diboson processes: pp → W±(ℓ±ν)γ

   https://doi.org/10.1007/JHEP05(2024)223  

   Martin, Adam (May 2024, Journal of High Energy Physics)

   A<sc>bstract</sc> In this paper we explorepp→W^±(ℓ^±ν)γto$$ \mathcal{O}\left(1/{\Lambda}^4\right) $$ $O\left(1/{\Lambda }^4\right)$ in the SMEFT expansion. Calculations to this order are necessary to properly capture SMEFT contributions that grow with energy, as the interference between energy-enhanced SMEFT effects at$$ \mathcal{O}\left(1/{\Lambda}^2\right) $$ $O\left(1/{\Lambda }^2\right)$ and the Standard Model is suppressed. We find that there are several dimension eight operators that interfere with the Standard Model and lead to the same energy growth, ~$$ \mathcal{O}\left({E}^4/{\Lambda}^4\right) $$ $O\left(E^4/{\Lambda }^4\right)$ , as dimension six squared. While energy-enhanced SMEFT contributions are a main focus, our calculation includes the complete set of$$ \mathcal{O}\left(1/{\Lambda}^4\right) $$ $O\left(1/{\Lambda }^4\right)$ SMEFT effects consistent with U(3)⁵flavor symmetry. Additionally, we include the decay of theW^±→ ℓ^±ν, making the calculation actually$$ \overline{q}{q}^{\prime}\to {\ell}^{\pm}\nu \gamma $$ $\overline{q}{q}^{\prime }\to {\ell }^{\pm }\mathrm{\nu \gamma }$ . As such, we are able to study the impact of non-resonant SMEFT operators, such as$$ \left({L}^{\dagger }{\overline{\sigma}}^{\mu }{\tau}^IL\right)\left({Q}^{\dagger }{\overline{\sigma}}^{\nu }{\tau}^IQ\right) $$ $\left(L^{†}{\overline{\sigma }}^{\mu }{\tau }^{I}L\right)\left(Q^{†}{\overline{\sigma }}^{\nu }{\tau }^{I}Q\right)$ B_μν, which contribute to$$ \overline{q}{q}^{\prime}\to {\ell}^{\pm}\nu \gamma $$ $\overline{q}{q}^{\prime }\to {\ell }^{\pm }\mathrm{\nu \gamma }$ directly and not to$$ \overline{q}{q}^{\prime}\to {W}^{\pm}\gamma $$ $\overline{q}{q}^{\prime }\to W^{\pm }\gamma$ . We show several distributions to illustrate the shape differences of the different contributions. 

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