Search for CP Violation in the decays D+ -> K_S pi+ and D+ -> K_S K+

TL;DR

This study searches for direct CP violation in D+ meson decays using high-statistics data, finding asymmetry measurements consistent with no CP violation within uncertainties and providing precise branching ratio measurements.

Contribution

The paper presents the first high-statistics measurement of CP asymmetries and branching ratios in D+ decays to K_S pi+ and K_S K+ channels, with improved precision over previous results.

Findings

Measured CP asymmetries consistent with zero within errors.

Provided precise relative branching ratios for D+ decay modes.

Set limits on direct CP violation in charm decays.

Abstract

A high statistics sample of photo-produced charm from the FOCUS(E831) experiment at Fermilab has been used to search for direct CP violation in the decays D+->K_S pi+ and D+ -> K_S K+. We have measured the following asymmetry parameters relative to D+->K-pi+pi+: A_CP(K_S pi+) = (-1.6 +/- 1.5 +/- 0.9)%, A_CP(K_S K+) = (+6.9 +/- 6.0 +/- 1.5)% and A_CP(K_S K+) = (+7.1 +/- 6.1 +/- 1.2)% relative to D+->K_S pi+. The first errors quoted are statistical and the second are systematic. We also measure the relative branching ratios: \Gamma(D+->\bar{K0}pi+)/\Gamma(D+->K-pi+pi+) = (30.60 +/- 0.46 +/- 0.32)%, \Gamma(D+->\bar{K0}K+)/\Gamma(D+->K-pi+pi+) = (6.04 +/- 0.35 +/- 0.30)% and \Gamma(D+->\bar{K0}K+)/\Gamma(D+->\bar{K0}pi+) = (19.96 +/- 1.19 +/- 0.96)%.