Search for CP Violation in D0 → KS π+ π-

Primary Authors: Michael Feindt, Michal Kreps, Thomas Kuhr, Felix Wick

Introduction

While CP violation is well established for B mesons and kaons, this is not the case for charm mesons. First evidence for CP violation in D0 → π+ π- and D0 → K+ K- was recently reported by LHCb. Whether this is a hint for new physics is not yet clear. Therefore it is important to search for and measure CP violation in further charm meson decays.

In a data sample corresponding to an integrated luminosity of 6.0 fb-1 we search for time integrated CP asymmetries in the resonant substructure of the three-body decay D0 → KS π+ π- decays. As the standard model expectation of these CP asymmetries is of the order 10-6 and thus well below the experimantal sensitivity, an observation of CP violation would be a clear hint for new physics. The production flavor of the D0 is determined by the charge of the pion from the strong decay D*(2010)+ → D0 π+. For the first time at a hadron collider, the Dalitz plot technique is applied for the description of the dynamic decay structure. Two complementary approaches are used, namely a full Dalitz fit employing the Isobar model for the involved resonances and a model-independent bin-by-bin comparison of the D0 and D0bar Dalitz plots.

Results

No hints for any CP violating effects are found. The measured CP violating amplitudes, phases (eps) (png), and fit fractions (eps) (png) are consistent with zero and upper limits on the CP asymmetries of the individual resonances (eps) (png) are calculated. The value

ACP = -0.0005 ± 0.0057 (stat.) ± 0.0054 (syst.)

is measured for the overall integrated CP asymmetry. Assuming no direct CP violation one can derive from this value an indirect CP asymmetry of aCPind = -0.0002 ± 0.0025 (stat.) ± 0.0024 (syst.).

List of Figures