Measurement of the charm mixing parameter $y_{CP} - y_{CP}^{K\pi}$ using two-body $D^0$ meson decays

TL;DR

This paper reports a precise measurement of charm mixing parameters using $D^0$ meson decays at LHCb, significantly improving the accuracy over previous results and enhancing understanding of charm quark behavior.

Contribution

The study provides the most precise measurement to date of the charm mixing parameter difference $y_{CP} - y_{CP}^{K o ext{pi}}$, using proton-proton collision data at 13 TeV.

Findings

Measured $y_{CP}^{ ext{pi pi}} - y_{CP}^{K o ext{pi}}$ as (6.57 ± 0.53 ± 0.16)×10^{-3}

Measured $y_{CP}^{KK} - y_{CP}^{K o ext{pi}}$ as (7.08 ± 0.30 ± 0.14)×10^{-3}

Combined $y_{CP} - y_{CP}^{K o ext{pi}}$ as (6.96 ± 0.26 ± 0.13)×10^{-3}

Abstract

A measurement of the ratios of the effective decay widths of $D^0 \to \pi^-\pi^+$ and $D^0 \to K^-K^+$ decays over that of $D^0 \to K^-\pi^+$ decays is performed with the LHCb experiment using proton-proton collisions at a centre-of-mass energy of $13 \, \mathrm{TeV}$, corresponding to an integrated luminosity of $6 \, \mathrm{fb^{-1}}$. These observables give access to the charm mixing parameters $y_{CP}^{\pi\pi} - y_{CP}^{K\pi}$ and $y_{CP}^{KK} - y_{CP}^{K\pi}$, and are measured as $y_{CP}^{\pi\pi} - y_{CP}^{K\pi} = (6.57 \pm 0.53 \pm 0.16) \times 10^{-3}$, $y_{CP}^{KK} - y_{CP}^{K\pi} = (7.08 \pm 0.30 \pm 0.14) \times 10^{-3}$, where the first uncertainties are statistical and the second systematic. The combination of the two measurements is $y_{CP} - y_{CP}^{K\pi} = (6.96 \pm 0.26 \pm 0.13) \times 10^{-3}$, which is four times more precise than the previous world average.