Visualisation of CP-violation effects in decay-time-dependent analyses of multibody B-meson decays

• Andrew MORRIS (CPPM)

Historically, in measurements of decay-time-dependent CP violation using two-body decays - in particular the angle β from the CKM unitarity triangle - a visualisation of the result has been possible by plotting the time-dependent CP-asymmetry of the data. This shows the oscillations of B↔B̄  with an amplitude given by sin(2β). The 'golden mode' of these decays has historically been B->J/Ψ KS. By contrast, multibody decays allow for sensitivity to both sin(2β) and cos(2β) - removing ambiguity in the measured value of 2β. However, the visualisation using the CP-asymmetry is lost if multibody decays are used in the same way. Therefore an approach has been formulated where by weighting events based on their position in the phase space, the CP-asymmetry may be recovered with amplitudes once again given in terms of sin(2β) and cos(2β). This presentation will give a pedagogical approach to the subject, using B→ DCPππ decays to illustrate the methodology. It will also contain an introduction to time-dependent CP violation - assuming no prior knowledge beyond the existence of the CKM matrix in the Standard Model.