The Impact of a 4th Generation on Mixing and CP Violation in the Charm System
Abstract
We study D0-D0 mixing in the presence of a fourth generation of quarks. In particular, we calculate the size of the allowed CP violation which is found at the observable level well beyond anything possible with CKM dynamics. We calculate the semileptonic asymmetry aSL and the mixing induced CP asymmetry etafSf which are correlated with each other. We also investigate the correlation of etafSf with a number of prominent observables in other mesonic systems like epsilon'/epsilon, Br(KL -> pi0 nu nu), Br(K+ -> pi+ nu nu), Br(Bs ->mu+ mu-), Br(Bd -> mu+ mu-) and finally Spsi phi in the Bs system. We identify a clear pattern of flavour and CP violation predicted by the SM4 model: While simultaneous large 4G effects in the K and D systems are possible, accompanying large NP effects in the Bd system are disfavoured. However this behaviour is not as pronounced as found for the LHT and RSc models. In contrast to this, sizeable CP violating effects in the Bs system are possible unless extreme effects in etafSf are found, and Br(Bs ->mu+ mu-) can be strongly enhanced regardless of the situation in the D system. We find that, on the other hand, Spsi phi > 0.2 combined with the measured epsilon'/epsilon significantly diminishes 4G effects within the D system.