LHCb

Abstract:

This paper presents a study of the charmless three-body decays Bs0→KS0h+h′−$$ {B}_{(s)}^0\to {K}_{\mathrm{S}}^0{h}^{+}h{\prime}^{-} $$ (where h(′) = π, K), using a sample of pp collision data collected by the LHCb experiment during Runs 1 and 2 of the LHC, corresponding to an integrated luminosity of 9 fb−1. The decay Bs0→KS0K+K−$$ {B}_s^0\to {K}_{\mathrm{S}}^0{K}^{+}{K}^{-} $$ is observed for the first time, and the following ratios of branching fractions are measured:BB0→KS0K+K−BB0→KS0π+π−=0.578±0.007±0.017,BB0→KS0K±K∓BB0→KS0π+π−=0.1363±0.0035±0.051,BBs0→KS0π+π−BB0→KS0π+π−=0.269±0.011±0.015±0.008,BBs0→KS0K+K−BB0→KS0π+π−=0.0303±0.0041±0.0025±0.0009,BBs0→KS0K±π∓BB0→KS0π+π−=1.818±0.021±0.031±0.056,$$ {\displaystyle \begin{array}{l}\frac{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{K}^{+}{K}^{-}\right)}{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}=0.578\pm 0.007\pm 0.017,\\ {}\frac{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{K}^{\pm }{K}^{\mp}\right)}{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}=0.1363\pm 0.0035\pm 0.051,\\ {}\begin{array}{l}\frac{\mathcal{B}\left({B}_s^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}=0.269\pm 0.011\pm 0.015\pm 0.008,\\ {}\frac{\mathcal{B}\left({B}_s^0\to {K}_{\mathrm{S}}^0{K}^{+}{K}^{-}\right)}{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}=0.0303\pm 0.0041\pm 0.0025\pm 0.0009,\\ {}\frac{\mathcal{B}\left({B}_s^0\to {K}_{\mathrm{S}}^0{K}^{\pm }{\pi}^{\mp}\right)}{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}=1.818\pm 0.021\pm 0.031\pm 0.056,\end{array}\end{array}} $$where the uncertainties are statistical, systematic, and due to knowledge of the ratio of hadronisation fractions of the Bs0$$ {B}_s^0 $$ and B0 mesons, respectively.

Abstract:

Particle Identification is a key requirement for future Higgs factories such as FCC-ee at Future Circular Collider. The ARC (Array of RICH Cells) detector is a compact and modular Ring Imaging Cherenkov (RICH) concept designed for π/K separation in the 1–40 GeV/c momentum range. It combines gas and aerogel radiators in independent cells equipped with mirrors and SiPM-based photon detectors. Simulation studies, including inverse ray-tracing reconstruction, confirm the expected photon yield and PID performance. A key challenge for SiPM-based RICH systems is noise reduction. We present the development of a compact and scalable SiPM housing module integrating mechanical support, front-end compatibility, and active cooling. The design builds on the Elementary Cell concept of the LHCb RICH Upgrade and extends it with embedded thermal management at sensor level. Thermal modelling and prototype measurements demonstrate stable and uniform operation at temperatures down to -80°C. This approach provides a viable solution for low-noise SiPM modules for next-generation RICH detectors.

Abstract:

A flavor-tagged time-dependent analysis of $B^0\to K_{\mathrm{S}}^0{\mu }^{+}{\mu }^{-}$ decays is performed across the full dimuon mass range excluding the $J/\psi$ and $\psi (2S)$ resonance regions. The analysis uses proton-proton collision data collected by the LHCb experiment in 2011–2018 at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$ . The $CP$ violation parameters are determined to be $C=-0.13\pm 0.32\pm 0.04$ , $S=+0.82\pm 0.29\pm 0.05$ , where the first uncertainties are statistical and the second are systematic. The results are consistent with the standard model prediction. This is the first experimental study of time-dependent $CP$ violation in $b\to s{\ell }^{+}{\ell }^{-}$ processes.