# How large can the SM contribution to CP violation in $D^0-ar D^0$ mixing be - High Energy Physics - Phenomenology

How large can the SM contribution to CP violation in $D^0-ar D^0$ mixing be - High Energy Physics - Phenomenology - Download this document for free, or read online. Document in PDF available to download.

Abstract: We investigate the maximum size of CP violating effects in $D$-mixing withinthe Standard Model SM, using Heavy Quark Expansion HQE as theoreticalworking tool. For this purpose we determine the leading HQE contributions andalso $\alpha s$ corrections as well as subleading $1-m c$ corrections to theabsorptive part of the mixing amplitude of neutral $D$ mesons. It turns outthat these contributions to $\Gamma {12}$ do not vanish in the exactSU$3 \mathrm{F}$ limit. Moreover, while the leading HQE terms give a resultfor $\Gamma {12}$ orders of magnitude lower than the current experimentalvalue, we do find a sizeable phase. In the literature it was suggested thathigher order terms in the HQE might be much less affected by the severe GIMcancellations of the leading terms; it is even not excluded that these higherorder terms can reproduce the experimental value of $y$. If such an enhancementis realized in nature, the phase discovered in the leading HQE terms can have asizeable effect. Therefore, we think that statements like: {\it -CP violatingeffects in $D$-mixing of the order of $10^{-3}$ to $10^{-2}$ are an unambigoussign of new physics-}-given our limited knowlegde of the SM prediction-arepremature. Finally, we give an example of a new physics model that can enhancethe leading HQE terms to $\Gamma {12}$ by one to two orders of magnitude.

Author: ** M. Bobrowski, A. Lenz, J. Riedl, J. Rohrwild**

Source: https://arxiv.org/