Search for $CP$ violation in D$^0$ $\to$ K$^0_\mathrm{S}$K$^0_\mathrm{S}$ decays in proton-proton collisions at $\sqrt{s}$ = 13 TeV

TL;DR

This paper reports a search for $CP$ violation in D$^0$ decays to $K^0_ ext{S}K^0_ ext{S}$ using 13 TeV proton-proton collision data from CMS, measuring asymmetry with unprecedented data volume and methodology.

Contribution

First CMS measurement of $CP$ asymmetry in charm sector using a fully hadronic final state with 41.6 fb$^{-1}$ of data.

Findings

Measured $A_{CP}$ = (6.2 ± 3.0 ± 0.2 ± 0.8)% in D$^0$ → $K^0_ ext{S}K^0_ ext{S}$ decays.

First $CP$ asymmetry measurement in charm by CMS.

Utilized a large dataset of about 10 billion events.

Abstract

A search is reported for charge-parity $CP$ violation in D$^0$ $\to$ K$^0_\mathrm{S}$K$^0_\mathrm{S}$ decays, using data collected in proton-proton collisions at $\sqrt{s}$ = 13 TeV recorded by the CMS experiment in 2018. The analysis uses a dedicated data set that corresponds to an integrated luminosity of 41.6 fb$^{-1}$, which consists of about 10 billion events containing a pair of b hadrons, nearly all of which decay to charm hadrons. The flavor of the neutral D meson is determined by the pion charge in the reconstructed decays D$^{*+}$ $\to$ D$^0\pi^+$ and D$^{*-}$ $\to$ D$^0\pi^-$. The $CP$ asymmetry in D$^0$ $\to$ K$^0_\mathrm{S}$K$^0_\mathrm{S}$ is measured to be $A_{CP}$(K$^0_\mathrm{S}$K$^0_\mathrm{S}$) = (6.2 $\pm$ 3.0 $\pm$ 0.2 $\pm$ 0.8)%, where the three uncertainties represent the statistical uncertainty, the systematic uncertainty, and the uncertainty in the measurement of the $CP$ asymmetry in the D$^0$ $\to$ K$^0_\mathrm{S}\pi^+\pi^-$ decay. This is the first $CP$ asymmetry measurement by CMS in the charm sector as well as the first to utilize a fully hadronic final state.