The Golden Modes B^0 -> J/psi K_{S,L} in the Era of Precision Flavour Physics

TL;DR

This paper analyzes the B^0 -> J/psi K_{S,L} decays as probes of CP violation, addressing Standard-Model uncertainties, and proposes a method to improve the precision of CP violation measurements relevant for new physics searches.

Contribution

It introduces a strategy to account for doubly Cabibbo-suppressed penguin effects using related decay measurements, enhancing the accuracy of CP violation studies.

Findings

Identified that penguin contributions can be unambiguously constrained.

Found a negative shift in the extracted value of beta from recent data.

Proposed a method to constrain new-physics phases in B^0-ar B^0 mixing.

Abstract

The B^0 -> J/\psi K_{S,L} channels are outstanding probes of CP violation. We have a detailed look at the associated Standard-Model uncertainties, which are related to doubly Cabibbo-suppressed penguin contributions, and point out that these usually neglected effects can actually be taken into account unambiguously through the CP asymmetries and the branching ratio of the B^0 -> J/\psi pi^0 decay. Using the most recent B-factory measurements, we find a negative shift of the extracted value of beta, which softens the tension in the fits of the unitarity triangle. In addition, this strategy can be used to constrain a possible new-physics phase in B^0-\bar B^0 mixing. The proposed strategy is crucial to fully exploit the tremendous accuracies for the search for this kind of new physics that can be achieved at the LHC and future super-flavour factories.