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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. 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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3. Angular analysis of $B\to K^{*}{e}^{+}{e}^{-}$ in the low- $q^2$ region with new electron identification at Belle

   https://doi.org/10.1103/PhysRevD.110.072005  

   Ferlewicz, D; Urquijo, P; Adachi, I; Adamczyk, K; Aihara, H; Asner, D M; Atmacan, H; Ayad, R; Babu, V; Banerjee, Sw; et al (October 2024, Physical Review D)

   We perform an angular analysis of the $B\to K^{*}{e}^{+}{e}^{-}$decay for the dielectron mass squared, $q^2$, range of $0.0008–1.1200{\mathrm{GeV}}^2/c^4$using the full Belle dataset in the $K^{*0}\to K^{+}{\pi }^{-}$and $K^{*+}\to K_S^0{\pi }^{+}$channels, incorporating new methods of electron identification to improve the statistical power of the dataset. This analysis is sensitive to contributions from right-handed currents from physics beyond the Standard Model by constraining the Wilson coefficients ${\mathcal{C}}_7^{(\prime )}$. We perform a fit to the $B\to K^{*}{e}^{+}{e}^{-}$differential decay rate and measure the imaginary component of the transversality amplitude to be $A_T^{\mathrm{Im}}=-1.27\pm 0.52\pm 0.12$, and the $K^{*}$transverse asymmetry to be $A_T^{\left(2\right)}=0.52\pm 0.53\pm 0.11$, with $F_L$and $A_T^{\mathrm{Re}}$fixed to the Standard Model values. The resulting constraints on the value of ${\mathcal{C}}_7^{\prime }$are consistent with the Standard Model within a $2\sigma$confidence interval. Published by the American Physical Society2024 

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4. Search for proton decay via $p\to e^{+}\eta$ and $p\to {\mu }^{+}\eta$ with a 0.37 Mton-year exposure of Super-Kamiokande

   https://doi.org/10.1103/PhysRevD.110.112011  

   Taniuchi, N; Abe, K; Abe, S; Asaoka, Y; Bronner, C; Harada, M; Hayato, Y; Hiraide, K; Hosokawa, K; Ieki, K; et al (December 2024, Physical Review D)

   A search for proton decay into $e^{+}/{\mu }^{+}$and a $\eta$meson has been performed using data from a $0.373\mathrm{Mton}·\mathrm{year}$exposure (6050.3 live days) of Super-Kamiokande. Compared to previous searches this work introduces an improved model of the intranuclear $\eta$interaction cross section, resulting in a factor of 2 reduction in uncertainties from this source and $\sim 10\%$increase in signal efficiency. No significant data excess was found above the expected number of atmospheric neutrino background events resulting in no indication of proton decay into either mode. Lower limits on the proton partial lifetime of $1.4\times {10}^{34}\mathrm{years}$for $p\to e^{+}\eta$and $7.3\times {10}^{33}\mathrm{years}$for $p\to {\mu }^{+}\eta$at the 90% CL were set. These limits are around 1.5 times longer than our previous study and are the most stringent to date. Published by the American Physical Society2024 

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5. 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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