Time-dependent CP violation in charm mesons

Abstract

CP violation is a well established phenomenon for B and K mesons, but for D0 mesons, bound states made up of a quark-antiquark pair containing a charm quark, a conclusive answer to the question whether there is CP violation or not, has yet to be determined. I show here the phenomenology of time-dependent CP asymmetries in charm decays, and discuss the implications of experimental tests aimed at the measurement of CP violation in the interference between mixing and decays of charm mesons, in particular when studying the decay channels D0 ! h+hð€€€ (h = K; ). The decay channels considered can also be used to constrain quantities that are poorly measured or still to be investigated, such as MIX and c;eff , provided that the effects of penguin pollution are ignored. I considered correlated production of D0 mesons at the SuperB experiment and its planned asymmetric run at the charm threshold and performed a study of simulated events, finding that a boost factor = 0:28 would not be sufficient to produce competitive results; the desirable resolution on the decay vertex separation between two D mesons in an event can be obtained with = 0:9. Vertex detectors play the major role in this analysis and new vertex detectors with high granularity might help improving these studies. The reference pixels (25 25 m pixel sensors implementing a 4T architecture with a deep n-well implant) of the Cherwell sensor, studied within the ARACHNID Collaboration, might be a candidate as a vertexing/tracking system, in particular for the layers of an SVT which are just around the beam pipe. I show the results of a study performed with data collected during a test beam at CERN, where the Cherwell sensor has been irradiated with pion beams, in terms of the charge deposited in the pixels by the charged particles passing through it, and show that this is mostly collected by the eight pixels ring surrounding the pixel hit by the particle beam. This work culminates in the definition of the clustering algorithm used by ARACHNID.