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1. Photoproduction of $K^{+}{K}^{-}$ Pairs in Ultraperipheral Collisions

   https://doi.org/10.1103/PhysRevLett.132.222303  

   Acharya, S; Adamová, D; Aglieri_Rinella, G; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; Ahuja, I; Akindinov, A; et al (May 2024, Physical Review Letters)

   $K^{+}{K}^{-}$ pairs may be produced in photonuclear collisions, either from the decays of photoproduced $\varphi \left(1020\right)$ mesons or directly as nonresonant $K^{+}{K}^{-}$ pairs. Measurements of $K^{+}{K}^{-}$ photoproduction probe the couplings between the $\varphi \left(1020\right)$ and charged kaons with photons and nuclear targets. The kaon-proton scattering occurs at energies far above those available elsewhere. We present the first measurement of coherent photoproduction of $K^{+}{K}^{-}$ pairs on lead ions in ultraperipheral collisions using the ALICE detector, including the first investigation of direct $K^{+}{K}^{-}$ production. There is significant $K^{+}{K}^{-}$ production at low transverse momentum, consistent with coherent photoproduction on lead targets. In the mass range $1.1<M_{KK}<1.4\mathrm{GeV}/c^2$ above the $\varphi \left(1020\right)$ resonance, for rapidity $\left|y_{KK}\right|<0.8$ and $p_{T,KK}<0.1\mathrm{GeV}/c$ , the measured coherent photoproduction cross section is $\mathrm{d}\sigma /\mathrm{d}y=3.37\pm 0.61\left(\text{stat}\right)\pm 0.15\left(\mathrm{syst}\right)\mathrm{mb}$ . The center-of-mass energy per nucleon of the photon-nucleus (Pb) system $W_{\gamma \mathrm{Pb},n}$ ranges from 33 to 188 GeV, far higher than previous measurements on heavy-nucleus targets. The cross section is larger than expected for $\varphi \left(1020\right)$ photoproduction alone. The mass spectrum is fit to a cocktail consisting of $\varphi \left(1020\right)$ decays, direct $K^{+}{K}^{-}$ photoproduction, and interference between the two. The confidence regions for the amplitude and relative phase angle for direct $K^{+}{K}^{-}$ photoproduction are presented. © 2024 CERN, for the ALICE Collaboration2024CERN 

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2. Measurement of the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{\pi }^0$ cross section in the energy range 0.62–3.50 GeV at Belle II

   https://doi.org/10.1103/PhysRevD.110.112005  

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

   We report a measurement of the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{\pi }^0$ cross section in the energy range from 0.62 to 3.50 GeV using an initial-state radiation technique. We use an $e^{+}{e}^{-}$ data sample corresponding to $191{\mathrm{fb}}^{-1}$ of integrated luminosity, collected at a center-of-mass energy at or near the $\mathrm{\Upsilon }\left(4S\right)$ resonance with the Belle II detector at the SuperKEKB collider. Signal yields are extracted by fitting the two-photon mass distribution in $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{\pi }^0\gamma$ events, which involve a ${\pi }^0\to \gamma \gamma$ decay and an energetic photon radiated from the initial state. Signal efficiency corrections with an accuracy of 1.6% are obtained from several control data samples. The uncertainty on the cross section at the $\omega$ and $\varphi$ resonances is dominated by the systematic uncertainty of 2.2%. The resulting cross sections in the 0.62–1.80 GeV energy range yield $a_{\mu }^{3\pi }=[48.91\pm 0.23(\mathrm{stat})\pm 1.07(\mathrm{syst}\left)\right]\times {10}^{-10}$ for the leading-order hadronic vacuum polarization contribution to the muon anomalous magnetic moment. This result differs by 2.5 standard deviations from the most precise current determination. Published by the American Physical Society2024 

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3. Study of $e^{+}{e}^{-}\to h^{+}{h}^{-}J/\psi$ ( $h=\pi$ , $K$ , $p$ ) via initial-state radiation at Belle II

   https://doi.org/10.1103/f8qf-b284  

   Abumusabh, M; Adachi, I; Aggarwal, A; Aggarwal, L; Ahmed, H; Ahn, Y; Aihara, H; Akopov, N; Alghamdi, S; Alhakami, M; et al (June 2026, Physical Review D)

   Using a data sample of $427.9{\mathrm{fb}}^{-1}$ collected by the Belle II detector at or near the $\mathrm{\Upsilon }\left(4S\right)$ and $\mathrm{\Upsilon }\left(10753\right)$ resonances, the cross sections for $e^{+}{e}^{-}\to h^{+}{h}^{-}J/\psi (h=\pi /K/p)$ at center-of-mass energies ranging from 3.8 GeV or the production threshold to $5.5/6.0/7.0\mathrm{GeV}$ have been measured via initial-state radiation. The cross sections for the processes $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$ and $e^{+}{e}^{-}\to K^{+}{K}^{-}J/\psi$ are consistent with previously published results. The cross sections for these channels obtained by combining with previous Belle results are also given. The process $e^{+}{e}^{-}\to p\overline{p}J/\psi$ is investigated for the first time. The yields are small and no significant structure is observed in the cross section versus energy. Searches for vector charmoniumlike states in the $h^{+}{h}^{-}J/\psi$ systems, and for associated intermediate states in the $h^{\pm }J/\psi$ systems, are also presented. 

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4. Observation of $e^{+}{e}^{-}\to \eta \mathrm{\Upsilon }\left(2S\right)$ and search for $e^{+}{e}^{-}\to \eta \mathrm{\Upsilon }\left(1S\right)$ , $\gamma X_b$ at $\sqrt{s}$ near 10.75 GeV

   https://doi.org/10.1103/9f61-rmvx  

   Adachi, I; Aggarwal, L; Ahmed, H; Ahn, Y; Aihara, H; Akopov, N; Alghamdi, S; Alhakami, M; Aloisio, A; Althubiti, N; et al (March 2026, Physical Review D)

   We present an analysis of the processes $e^{+}{e}^{-}\to \eta \mathrm{\Upsilon }\left(1S\right)$ , $\eta \mathrm{\Upsilon }\left(2S\right)$ , and $\gamma X_b$ with $X_b\to {\pi }^{+}{\pi }^{-}{\chi }_{bJ},{\chi }_{bJ}\to \gamma \mathrm{\Upsilon }\left(1S\right)$ ( $J=1$ , 2) reconstructed from $\gamma \gamma {\pi }^{+}{\pi }^{-}{\ell }^{+}{\ell }^{-}$ $(\ell =e,\mu )$ final states in $19.6{\mathrm{fb}}^{-1}$ of Belle II data collected at four energy points near the peak of the $\mathrm{\Upsilon }\left(10753\right)$ resonance. Here, $X_b$ is a hypothetical bottomonium-sector partner of the $X\left(3872\right)$ . In the process $e^{+}{e}^{-}\to \eta \mathrm{\Upsilon }\left(2S\right)$ , we observe a signal with a significance that exceeds $6.0\sigma$ when all energy points are combined. A signal with a significance of $4.2\sigma$ is observed at a center-of-mass energy of 10.653 GeV, close to the $B^{*}{\overline{B}}^{*}$ threshold. At this energy, we measure $\sigma \left(\eta \mathrm{\Upsilon }\right(2S\left)\right)/\sigma \left({\pi }^{+}{\pi }^{-}\mathrm{\Upsilon }\right(2S\left)\right)>23$ at the 90% confidence level, indicating a strong violation of heavy-quark spin symmetry. No significant signal is observed for $e^{+}{e}^{-}\to \eta \mathrm{\Upsilon }\left(1S\right)$ or $\gamma X_b$ . Upper limits on the Born cross sections for the processes $e^{+}{e}^{-}\to \eta \mathrm{\Upsilon }\left(1S\right)$ and $e^{+}{e}^{-}\to \gamma X_b$ with $X_b\to {\pi }^{+}{\pi }^{-}{\chi }_{bJ}$ are determined. 

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5. First Observation of $CP$ Violation and Measurement of Polarization in $B^{+}\to \rho \left(770{)}^0{K}^{*}\right(892{)}^{+}$ Decays

   https://doi.org/10.1103/9zhl-kkwg  

   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 (January 2026, Physical Review Letters)

   An amplitude analysis of the $B^{+}\to \left({\pi }^{+}{\pi }^{-}\right)\left(K_{\mathrm{S}}^0{\pi }^{+}\right)$ decay is performed in the mass regions $0.30<m_{{\pi }^{+}{\pi }^{-}}<1.10\mathrm{GeV}/c^2$ and $0.75<m_{K_{\mathrm{S}}^0{\pi }^{+}}<1.20\mathrm{GeV}/c^2$ , using $pp$ collision data recorded with the LHCb detector corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$ . The polarization fractions and $CP$ asymmetries for $B^{+}\to \rho \left(770{)}^0{K}^{*}\right(892{)}^{+}$ decays are measured. Violation of the $CP$ symmetry in the decay $B^{+}\to \rho \left(770{)}^0{K}^{*}\right(892{)}^{+}$ is observed for the first time, with a significance exceeding 9 standard deviations. The $CP$ asymmetry is measured to be ${\mathcal{A}}_{CP}=0.507\pm 0.062\left(\mathrm{stat}\right)\pm 0.024\left(\mathrm{syst}\right)$ and the $CP$ -averaged longitudinal polarization fraction of $f_L=0.720\pm 0.028\left(\mathrm{stat}\right)\pm 0.009\left(\mathrm{syst}\right)$ . The measurements help to shed light on the polarization puzzle of $B$ mesons decaying to two vector mesons. 

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