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Abstract:

Particle Identification (PID) is a key requirement for future Higgs factories such as FCC-ee, in particular for heavy-flavour physics and jet flavour tagging. The ARC (Array of RICH Cells) detector is a novel compact and modular RICH (Ring Imaging Cherenkov) concept designed to provide charged hadron separation over a momentum range 1 − 40 GeV/c . ARC combines gas and aerogel radiators within independent cells, each equipped with spherical mirrors and SiPM-based photodetectors. A detailed simulation and reconstruction framework has been developed, including inverse ray-tracing algorithms for Cherenkov angle reconstruction. Simulation studies demonstrate excellent photon yield and π / K separation performance across the target momentum range.

Abstract:

This paper describes a measurement of the Λb0→J/ψΛ branching fraction using data collected with the LHCb experiment in proton-proton collisions from 2016 to 2018. The dataset corresponds to an integrated luminosity of 5.4 fb−1. The branching fraction is determined relative to that of B0→J/ψKS0 decays,BΛb0→J/ψΛBB0→J/ψKS0=0.750±0.005±0.022±0.005±0.062, yielding BΛb0→J/ψΛ=3.34±0.02±0.10±0.08±0.28×10−4, where the first uncertainty is statistical, the second systematic, the third due to external inputs on branching fractions and the fourth due to the ratio of Λb0 baryon and B0 meson hadronisation fractions. In addition, the isospin asymmetry between the rates of B0→J/ψKS0 and B+→ J/ψK+ decays is measured to beAI=−0.0135±0.0004±0.0133, where the first uncertainty is statistical and the second systematic.

Abstract:

An amplitude analysis of the $B^{+}→({\mathrm{Ï€}}^{+}{\mathrm{Ï€}}^{−})(K_{\mathrm{S}}^0{\mathrm{Ï€}}^{+})$ decay is performed in the mass regions $0.30<m_{{\mathrm{Ï€}}^{+}{\mathrm{Ï€}}^{−}}<1.10\mathrm{GeV}/c^2$ and $0.75<m_{K_{\mathrm{S}}^0{\mathrm{Ï€}}^{+}}<1.20\mathrm{GeV}/c^2$ , 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 $B^{+}→\mathrm{ÒÏ}(770{)}^0{K}^{*}(892{)}^{+}$ decays are measured. Violation of the $CP$ symmetry in the decay $B^{+}→\mathrm{ÒÏ}(770{)}^0{K}^{*}(892{)}^{+}$ is observed for the first time, with a significance exceeding 9 standard deviations. The $CP$ asymmetry is measured to be ${\mathcal{A}}_{CP}=0.507Â\pm 0.062(\mathrm{stat})Â\pm 0.024(\mathrm{syst})$ and the $CP$ -averaged longitudinal polarization fraction of $f_L=0.720Â\pm 0.028(\mathrm{stat})Â\pm 0.009(\mathrm{syst})$ . The measurements help to shed light on the polarization puzzle of $B$ mesons decaying to two vector mesons.

Abstract:

Searches are presented for $B_c^{+}→D{h}^{+}{h}^{−}$ decays, where $D$ is a charmed meson and $h^{Â\pm }$ is a charged pion or kaon, using $pp$ collision data collected by the LHCb experiment corresponding to an integrated luminosity of $9{\mathrm{fb}}^{−1}$ . The decays $B_c^{+}→D^{+}{K}^{+}{\mathrm{Ï€}}^{−}$ , $B_c^{+}→D^{*+}{K}^{+}{\mathrm{Ï€}}^{−}$ , and $B_c^{+}→D_s^{+}{K}^{+}{K}^{−}$ are observed for the first time. Their branching fractions, expressed as ratios relative to that of the $B_c^{+}→B_s^0{\mathrm{Ï€}}^{+}$ decay, are determined to be $\mathcal{R}(B_c^{+}→D^{+}{K}^{+}{\mathrm{Ï€}}^{−})=(1.96Â\pm 0.23Â\pm 0.08Â\pm 0.10)×{10}^{−3}$ , $\mathcal{R}(B_c^{+}→D^{*+}{K}^{+}{\mathrm{Ï€}}^{−})=(3.67Â\pm 0.55Â\pm 0.24Â\pm 0.20)×{10}^{−3}$ , $\mathcal{R}(B_c^{+}→D_s^{+}{K}^{+}{K}^{−})=(1.61Â\pm 0.35Â\pm 0.13Â\pm 0.07)×{10}^{−3}$ , where the first uncertainty is statistical, the second is systematic, and the third is due to the limited precision on the $D$ -meson branching fractions. The decay channels proceed primarily through excited $K^0$ or $D^0$ resonances or $\mathrm{Ï•}$ mesons, and open a new avenue for studies of charge-parity violation in beauty mesons.