# $\Delta A_{CP}$ within the Standard Model and beyond

## TL;DR

This paper reviews the Standard Model predictions for CP violation in charm decays, compares them with recent experimental results, and explores how a new flavor-violating Z' boson could resolve observed discrepancies.

## Contribution

It provides an updated SM upper bound on $A_{CP}$ and proposes a Z' extension to explain the experimental tension.

## Key findings

- SM predicts $|A_{CP}| \u2264 3.6 imes 10^{-4}$
- LHCb measures A_{CP}  (-15.4 1 2.9) imes 10^{-4}
- A light Z' boson can reconcile theory and experiment without conflicting with existing constraints.

## Abstract

In light of the recent LHCb observation of CP violation in the charm sector, we review standard model (SM) predictions in the charm sector and in particular for $\Delta A_{CP}$. We get as an upper bound in the SM $| \Delta A_{CP} ^{\rm SM}| \leq 3.6 \times 10^{-4}$, which can be compared to the measurement of $\Delta A_{CP} ^{\rm LHCb2019} = (-15.4 \pm 2.9) \times 10^{-4}$. We discuss resolving this tension within an extension of the SM that includes a flavour violating $Z'$ that couples only to $\bar{s}s$ and $\bar{c}u$. We show that for masses below 80 GeV and flavour violating coupling of the order of $10^{-4}$, this model can successfully resolve the tension and avoid constraints from dijet searches, $D^0-\overline{D}^0$ mixing and measurements of the $Z$ width.