Measurement of the CP asymmetry in $D^+ \to \pi^+ \pi^0$ decays at Belle II

TL;DR

This paper reports the most precise measurement to date of CP asymmetry in $D^+ o \pi^+ \pi^0$ decays at Belle II, confirming Standard Model predictions and previous results.

Contribution

First precise measurement of CP asymmetry in $D^+ o \pi^+ \\pi^0$ decays at Belle II, using control samples to correct for detection and production asymmetries.

Findings

Measured $A_{CP} = (-1.8 \\pm 0.9 \\pm 0.1)\%$

Results agree with Standard Model predictions

Most precise to date

Abstract

We measure the CP asymmetry in $D^+ \to \pi^+ \pi^0$ decays reconstructed in $e^+ e^-$ collisions at the Belle II experiment using a data set corresponding to an integrated luminosity of 428 fb$^{-1}$. A control sample of $D^+ \to \pi^+ K_{S}$ decays is used to correct for detection and production asymmetries. The result, $A_{CP}(D^+ \to \pi^+\pi^0) =(-1.8 \pm 0.9 \pm 0.1)\%$, where the first uncertainty is statistical and the second systematic, is the most precise determination to date. It agrees with the prediction of CP symmetry from the standard model, and with results of previous measurements.