Measurement of $CP$ asymmetry in $D^0 \to K^0_S K^0_S$ decays

TL;DR

This paper reports the most precise measurement of the $CP$ asymmetry in $D^0 o K^0_S K^0_S$ decays using LHCb data from 2015-2018, providing insights into matter-antimatter asymmetry in charm mesons.

Contribution

It presents the first high-precision measurement of $CP$ asymmetry in $D^0 o K^0_S K^0_S$ decays, improving upon previous results with a large data sample and refined analysis techniques.

Findings

Measured $A^{CP}(D^0 o K^0_S K^0_S) = (-3.1 \pm 1.2 ext{(stat)} \pm 0.4 ext{(syst)} \pm 0.2)\%$

Achieved the most precise determination of this $CP$ asymmetry to date.

Used $D^{*\pm}$ charge to determine $D^0$ flavor and calibration with $D^0 o K^+ K^-$ decay.

Abstract

A measurement of the $CP$ asymmetry in $D^0 \to K^0_S K^0_S$ decays is reported, based on a data sample of proton-proton collisions collected by the LHCb experiment from 2015 to 2018, corresponding to an integrated luminosity of 6 fb$^{-1}$. The flavor of the $D^0$ candidate is determined using the charge of the $D^{*\pm}$ meson, from which the decay is required to originate. The $D^0 \to K^+ K^-$ decay is used as a calibration channel. The time-integrated $CP$ asymmetry for the $D^0 \to K^0_S K^0_S$ mode is measured to be: $$A^{CP}(D^0 \to K^0_S K^0_S) = (-3.1\pm 1.2\pm 0.4 \pm 0.2)\%, $$ where the first uncertainty is statistical, the second is systematic, and the third is due to the uncertainty on the $CP$ asymmetry of the calibration channel. This is the most precise determination of this quantity to date.