John Dominic Nicolini

Abstract: The Υ(2S) and Υ(3S) production cross-sections are measured relative to that of the Υ(1S) meson, as a function of charged-particle multiplicity in proton-proton collisions at a centre-of-mass energy of 13 TeV. The measurement uses data collected by the LHCb experiment in 2018 corresponding to an integrated luminosity of 2 fb−1. Both the Υ(2S)-to-Υ(1S) and Υ(3S)-to-Υ(1S) cross-section ratios are found to decrease significantly as a function of event multiplicity, with the Υ(3S)-to-Υ(1S) ratio showing a steeper decline towards high multiplicity. This hierarchy is qualitatively consistent with the comover model predictions, indicating that final-state interactions play an important role in bottomonia production in high-multiplicity events.

Abstract: Measurements of CP observables and the CKM angle γ are performed in B± → DK*(892)± decays, where D represents a superposition of D0 and D¯0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\overline{D}}^0 $$\end{document} states, using the LHCb dataset collected during Run 1 (2011–2012) and Run 2 (2015–2018). A study of this channel is presented with the D meson reconstructed in two-body final states K±π∓, K+K− and π+π−; four-body final states K±π∓π±π∓ and π+π−π+π−; and three-body final states KS0π+π−\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {K}_{\textrm{S}}^0{\pi}^{+}{\pi}^{-} $$\end{document} and KS0K+K−\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {K}_{\textrm{S}}^0{K}^{+}{K}^{-} $$\end{document}. This analysis includes the first observation of the suppressed B±→ [π±K∓]DK*± and B±→ [π±K∓π±π∓]DK*± decays. The combined result gives γ = (63 ± 13)°.

TL;DR: Helium identification at LHCb is achieved using measurements of ionisation losses and timing measurements. A total of 105 helium and antihelium candidates are identified with negligible background contamination.