LHCb

Abstract:

A search is presented for the two-body charmed baryonic decays, ${\overline{B}}_{(s)}^0\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-}$ , using a data sample collected by the LHCb experiment during 2011–2012 and 2015–2018, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$ . The first observation of the ${\overline{B}}_s^0\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-}$ decay is reported with $6.2\sigma$ significance along with $4.3\sigma$ evidence for the ${\overline{B}}^0\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-}$ decay. The branching fractions are measured to be $\mathcal{B}({\overline{B}}^0\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-})=(1.01_{-0.28}^{+0.27}\pm 0.08\pm 0.15)\times {10}^{-5}$ and $\mathcal{B}({\overline{B}}_s^0\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-})=(5.0\pm 1.3\pm 0.5\pm 0.8)\times {10}^{-5}$ , where the first uncertainty is statistical, the second systematic, and the third due to external inputs. These results provide novel experimental inputs for the theoretical framework describing two-body baryonic decays of $B$ mesons via $W$ -emission and $W$ -exchange mechanisms.

Abstract:

The first observation of the decay $B^{+}\to p\overline{\mathrm{\Lambda }}$ is presented using proton-proton collision data collected by the LHCb experiment between 2016 and 2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$ . The signal significance exceeds seven standard deviations. Using the $B^{+}\to K_{\mathrm{S}}^0{\pi }^{+}$ decay as a normalization channel, the branching fraction is measured and combined with previous LHCb results based on data collected at 7 and 8 TeV in 2011 and 2012, yielding $\mathcal{B}(B^{+}\to p\overline{\mathrm{\Lambda }})=(1.24\pm 0.17\pm 0.05\pm 0.03)\times {10}^{-7},$ where the first uncertainty is statistical, the second is systematic, and the third comes from the uncertainty on the branching fraction of the normalization channel. The $B^{+}\to p\overline{\mathrm{\Lambda }}$ weak decay parameter is measured to be ${\alpha }_B=0.87_{-0.29}^{+0.26}\pm 0.09$ , indicating the presence of comparable S-wave and P-wave decay amplitudes.

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.