Measurement of the direct CP-violating parameter A_CP in the decay D+ -> K- pi+ pi+

TL;DR

This paper reports the most precise measurement to date of the direct CP-violating parameter A_CP in D+ -> K- pi+ pi+ decays, using a large dataset from the Fermilab Tevatron, finding results consistent with CP conservation.

Contribution

First measurement of A_CP in D+ -> K- pi+ pi+ decays with unprecedented precision using Tevatron data.

Findings

A_CP measured as -0.16% with uncertainties

Results consistent with standard model CP conservation

Most precise measurement of this parameter to date

Abstract

We measure the direct CP-violating parameter A_CP for the decay of the charged charm meson, D+ -> K-pi+pi+ (and charge conjugate), using the full 10.4 fb-1 sample of ppbar collisions at sqrt(s) = 1.96 TeV collected by the D0 detector at the Fermilab Tevatron collider. We extract the raw reconstructed charge asymmetry by fitting the invariant mass distributions for the sum and difference of charge-specific samples. This quantity is then corrected for detector-related asymmetries using data-driven methods and for possible physics asymmetries (from B -> D processes) using input from Monte Carlo simulation. We measure A_CP = [-0.16 +- 0.15 (stat.) +- 0.09 (syst.)]%, which is consistent with zero, as expected from the standard model prediction of CP conservation, and is the most precise measurement of this quantity to date