Looking for New Physics in Bd-Bd(bar) Mixing

TL;DR

This paper explores methods to detect new physics in b -> d flavor-changing neutral currents by analyzing weak phases in Bd-Bd(bar) mixing and related decay processes, highlighting the need for theoretical assumptions.

Contribution

It demonstrates the impossibility of measuring the t-quark penguin phase without assumptions and proposes a method to detect new physics using specific decay channels with a single hadronic assumption.

Findings

Measuring the t-quark penguin phase requires theoretical input.

Applying a hadronic assumption enables probing for new physics.

Decay channels Bd(t) -> K0 K0(bar) and Bs(t) -> φ Ks are useful for this purpose.

Abstract

There are variety of methods which directly test for the presence of new physics in the b -> s flavour-changing neutral current (FCNC), but none which cleanly probe new physics in the b -> d FCNC. One possible idea is to compare the weak phase of the t-quark contribution to the b -> d penguin, which is $-\beta$ in the SM, with that of Bd-Bd(bar) mixing ($-2\beta$ in the SM). In this talk I show that, in fact, it is impossible to measure the weak phase of the t-quark penguin, or indeed any penguin contribution, without theoretical input. However, if one makes a single assumption involving the hadronic parameters, it is possible to obtain the weak phase. I discuss how one can apply such an assumption to the time-dependent decays $Bd(t) -> K0 K0(bar)$ and $Bs(t) -> \phi K_s$ in order to detect new physics in the b -> d FCNC.