Malcolm John

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:

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 $B^{+}\to ({\pi }^{+}{\pi }^{-})(K_{\mathrm{S}}^0{\pi }^{+})$ 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 $B^{+}\to \rho (770{)}^0{K}^{*}(892{)}^{+}$ decays are measured. Violation of the $CP$ symmetry in the decay $B^{+}\to \rho (770{)}^0{K}^{*}(892{)}^{+}$ is observed for the first time, with a significance exceeding 9 standard deviations. The $CP$ asymmetry is measured to be ${\mathcal{A}}_{CP}=0.507\pm 0.062(\mathrm{stat})\pm 0.024(\mathrm{syst})$ and the $CP$ -averaged longitudinal polarization fraction of $f_L=0.720\pm 0.028(\mathrm{stat})\pm 0.009(\mathrm{syst})$ . The measurements help to shed light on the polarization puzzle of $B$ mesons decaying to two vector mesons.

Abstract:

Searches are presented for $B_c^{+}\to D{h}^{+}{h}^{-}$ decays, where $D$ is a charmed meson and $h^{\pm }$ 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 $B_c^{+}\to D^{+}{K}^{+}{\pi }^{-}$ , $B_c^{+}\to D^{*+}{K}^{+}{\pi }^{-}$ , and $B_c^{+}\to D_s^{+}{K}^{+}{K}^{-}$ are observed for the first time. Their branching fractions, expressed as ratios relative to that of the $B_c^{+}\to B_s^0{\pi }^{+}$ decay, are determined to be $\mathcal{R}(B_c^{+}\to D^{+}{K}^{+}{\pi }^{-})=(1.96\pm 0.23\pm 0.08\pm 0.10)\times {10}^{-3}$ , $\mathcal{R}(B_c^{+}\to D^{*+}{K}^{+}{\pi }^{-})=(3.67\pm 0.55\pm 0.24\pm 0.20)\times {10}^{-3}$ , $\mathcal{R}(B_c^{+}\to D_s^{+}{K}^{+}{K}^{-})=(1.61\pm 0.35\pm 0.13\pm 0.07)\times {10}^{-3}$ , 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 $\varphi$ mesons, and open a new avenue for studies of charge-parity violation in beauty mesons.