Searching for the Origin of CP violation in Cabibbo Suppressed D-meson   Decays
  The recent evidence of large direct CP violation in D0 decay at LHCb suggests that such CP studies may become an important avenue for understanding CP. In this paper, we make several suggestions to try to clarify the role of new physics in these results. We propose that the enhancement needed in the Standard Model to attribute the observed CP violation in D to two pseudoscalar modes may not operate for inclusive final states where asymmetries will likely approximate the quark level expectation. Experimentally testing this principle requires a search for CP asymmetries in final states containing K and K-bar with a total energy of less than M_D. We also propose that CP asymmetries may be enhanced in modes where the tree is color suppressed. In particular, the final state rho0 rho0 is of special interest; similarly Ds-> rho0 K+ and rho0 K*+ likewise appear interesting. We discuss how isospin symmetry yields observables sensitive to certain classes of new physics and suppressed in the Standard Model. Some modes considered in this context are D-> pi pi, rho pi, rho rho as well as Ds-> K* pi. We also consider how such analysis may eventually be supplemented by information about the weak phases in D0 decay. In order to obtain this information experimentally, we consider various methods for preparing an initial state which is a quantum mechanical mixture of D0 and D0-bar. This may be done through the use of natural D0 D0-bar oscillations; observing D0-mesons which arise from Bd or Bs mesons which themselves are oscillating or from quantum correlations in D0 pairs which arise from either psi" decay or B-meson decay. Observing CP violation in the magnitudes of decay amplitudes should be within the capability of experiments in the near future however obtaining the weak phases through the methods we discuss will likely require future generations of machines. 
David Atwood and Amarjit Soni
hep-ph hep-ex