Measurement of $C\!P$ observables in $B^\pm \to D^{(*)} K^\pm$ and $B^\pm \to D^{(*)} \pi^\pm$ decays using two-body $D$ final states

TL;DR

This paper reports precise measurements of $CP$ observables in various $B^\pm$ decays involving $D^{(*)}$ mesons, including first observations of certain decay modes, to improve constraints on the CKM angle $\gamma$.

Contribution

It presents the first measurements of partially reconstructed $B^\pm o D^* K^\pm$ and $B^\pm o D^* \pi^\pm$ decays, and observes the $B^\pm o (D \pi^0)_{D^*} \pi^\pm$ decay with high significance.

Findings

First measurements of partially reconstructed $B^\pm o D^* K^\pm$ and $B^\pm o D^* \pi^\pm$ with $D o K^\mp \pi^\pm$

Observation of $B^\pm o (D \pi^0)_{D^*} \pi^\pm$ decay with 6.1 sigma significance

All $CP$ observables measured with world-best precision

Abstract

Measurements of $C\!P$ observables in $B^\pm \rightarrow D^{(*)} K^\pm$ and $B^\pm \rightarrow D^{(*)} \pi^\pm$ decays are presented, where $D^{(*)}$ indicates a neutral $D$ or $D^*$ meson that is an admixture of meson and anti-meson states. Decays of the $D^*$ meson to the $D\pi^0$ and $D\gamma$ final states are partially reconstructed without inclusion of the neutral pion or photon. Decays of the $D$ meson are reconstructed in the $K^\pm \pi^\mp$, $K^+K^-$, and $\pi^+\pi^-$ final states. The analysis uses a sample of charged $B$ mesons produced in proton-proton collisions and collected with the LHCb experiment, corresponding to integrated luminosities of 2.0, 1.0, and 5.7 fb$^{-1}$ taken at centre-of-mass energies of 7, 8, and 13 TeV, respectively. The measurements of partially reconstructed $B^\pm \to D^* K^\pm$ and $B^\pm \to D^* \pi^\pm$ with $D \to K^\mp \pi^\pm$ decays are the first of their kind, and a first observation of the $B^\pm \to (D \pi^0)_{D^*} \pi^\pm$ decay is made with a significance of 6.1 standard deviations. All $C\!P$ observables are measured with world-best precision, and in combination with other LHCb results will provide strong constraints on the CKM angle $\gamma$.