Testing $CPT$ invariance with the neutral-$D$ system

Abstract

We investigate the issue of testing $CPT$ invariance in the neutral-$D$ system, using $D$ events obtained either from fixed-target experiments or from a $\tau$-charm factory. For both types of experiments we show that the expected suppression of mixing in the $D$ system, normally viewed as a disadvantage for $CP$ tests, allows unsuppressed measurement of certain parameters describing $CPT$ violation. Asymmetries are presented that permit the extraction of parameters for direct $CPT$ violation in the $D$ system and for indirect $CPT$ violation in the $K$ system. We also show that experiments on the neutral-$D$ system provide an alternative means for measuring conventional indirect $T$ violation in the kaon system.