Can One Measure the Weak Phase of a Penguin Diagram?

TL;DR

This paper discusses the challenges in measuring the weak phase of penguin diagrams in B meson decays, highlighting the need for assumptions and the potential to detect new physics through phase comparisons.

Contribution

It demonstrates the impossibility of measuring the weak phase without assumptions and proposes a method to test for new physics using a single hadronic parameter assumption.

Findings

Measuring the weak phase of penguin contributions requires theoretical input.

A single assumption can enable the extraction of the weak phase.

Comparison of phases can reveal new physics in b -> d transitions.

Abstract

The b -> d penguin amplitude receives contributions from internal u, c and t-quarks. We show that it is impossible to measure the weak phase of any of these penguin contributions without theoretical input. However, it is possible to obtain the weak phase if one makes a single assumption involving the hadronic parameters. With such an assumption, one can test for the presence of new physics in the b -> d flavour-changing neutral current by comparing the weak phase of B_d^0-{\bar B}_d^0 mixing with that of the t-quark contribution to the b -> d penguin.