B-Decay CP Asymmetries, Discrete Ambiguities and New Physics

TL;DR

This paper discusses how CP violation measurements in B meson decays can be used to detect new physics, addressing the challenges posed by discrete ambiguities and exploring methods to resolve them even with potential new physics contributions.

Contribution

It systematically analyzes methods to resolve discrete ambiguities in CP measurements and demonstrates their effectiveness in uncovering new physics despite these challenges.

Findings

Discrete ambiguities can be resolved with existing methods even with new physics.

Certain parameter choices can mimic or hide new physics effects.

Relaxing positivity assumptions on bag parameters complicates new physics detection.

Abstract

The first measurements of CP violation in the $B$ system will likely probe $\sin 2\alpha$, $\sin 2\beta$ and $\cos 2\gamma$. Assuming that the CP angles $\alpha$, $\beta$ and $\gamma$ are the interior angles of the unitarity triangle, these measurements determine the angle set $(\alpha,\beta,\gamma)$ except for a twofold discrete ambiguity. If one allows for the possibility of new physics, the presence of this discrete ambiguity can make its discovery difficult: if only one of the two candidate solutions is consistent with constraints from other measurements in the $B$ and $K$ systems, one is not sure whether new physics is present or not. We review the methods used to resolve the discrete ambiguity and show that, even in the presence of new physics, they can usually be used to uncover this new physics. There are some exceptions, which we describe in detail. We systematically scan the parameter space and present examples of values of $(\alpha,\beta,\gamma)$ and the new-physics parameters which correspond to all possibilities. Finally, we show that if one relaxes the assumption that the bag parameters $\BBd$ and $\BK$ are positive, one can no longer definitively establish the presence of new physics.