Measurement of the CKM angle $\gamma$ using $B^0 \rightarrow D K^{*0}$ with $D \rightarrow K^0_S \pi^+ \pi^-$ decays

TL;DR

This paper presents a model-dependent amplitude analysis of B0 decays to measure the CKM angle gamma, achieving the most precise CP violation observable measurements to date using LHCb data.

Contribution

The study provides the first precise measurement of the CKM angle gamma using B0 to D K*0 decays with D to K0_S pi+ pi- in a model-dependent amplitude analysis.

Findings

Measured CP violation observables x±, y± with unprecedented precision.

Estimated gamma as (80+21-22) degrees, the most accurate to date.

Determined the ratio of decay amplitudes r_B0 as 0.39 ± 0.13.

Abstract

A model-dependent amplitude analysis of the decay $B^0\rightarrow D(K^0_S\pi^+\pi^-) K^{*0}$ is performed using proton-proton collision data corresponding to an integrated luminosity of 3.0fb$^{-1}$, recorded at $\sqrt{s}=7$ and $8 TeV$ by the LHCb experiment. The CP violation observables $x_{\pm}$ and $y_{\pm}$, sensitive to the CKM angle $\gamma$, are measured to be \begin{eqnarray*} x_- &=& -0.15 \pm 0.14 \pm 0.03 \pm 0.01, y_- &=& 0.25 \pm 0.15 \pm 0.06 \pm 0.01, x_+ &=& 0.05 \pm 0.24 \pm 0.04 \pm 0.01, y_+ &=& -0.65^{+0.24}_{-0.23} \pm 0.08 \pm 0.01, \end{eqnarray*} where the first uncertainties are statistical, the second systematic and the third arise from the uncertainty on the $D\rightarrow K^0_S \pi^+\pi^-$ amplitude model. These are the most precise measurements of these observables. They correspond to $\gamma=(80^{+21}_{-22})^{\circ}$ and $r_{B^0}=0.39\pm0.13$, where $r_{B^0}$ is the magnitude of the ratio of the suppressed and favoured $B^0\rightarrow D K^+ \pi^-$ decay amplitudes, in a $K\pi$ mass region of $\pm50 MeV$ around the $K^*(892)^0$ mass and for an absolute value of the cosine of the $K^{*0}$ decay angle larger than $0.4$.