Measurements of the CKM Angle beta

TL;DR

This paper reports on precise measurements of the CKM angle beta using data from BaBar and Belle, highlighting potential hints of new physics in penguin decay modes and emphasizing the need for further data to clarify these observations.

Contribution

It provides the most recent combined measurements of sin(2beta) from B factories, including both tree-level and penguin decay modes, and discusses possible indications of physics beyond the Standard Model.

Findings

Measured sin(2beta) = 0.685 ± 0.032 from charmonium modes

Penguin decay modes show slightly lower sin(2beta) values

Hints of potential new physics contributions in loop diagrams

Abstract

In this article I report on new and updated measurements of the CP-violating parameter beta (phi_1), which is related to the phase of the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix of the electroweak interaction. Over the past few years, beta has become the most precisely known parameter of the CKM unitarity triangle that governs the B system. The results presented here were produced by the two B factories, BaBar and Belle, based on their most recent datasets of over 600 million BB events combined. The new world average for sin(2beta), measured in the theoretically and experimentally cleanest charmonium modes, such as B -> J/psi K0s, is sin(2beta) = 0.685 +- 0.032. In addition to these tree-level dominated decays, independent measurements of sin(2beta) are obtained from gluonic b --> s penguin decays, including B --> phi K0s, B --> eta' K0s and others. There are hints, albeit somewhat weaker than earlier this year, that these measurements tend to come out low compared to the charmonium average, giving rise to the tantalizing possibility that New Physics amplitudes could be contributing to the corresponding loop diagrams. Clearly, more data from both experiments are needed to elucidate these intriguing differences.