Observation of CP Violation in Charm Decays

Abstract

A search for charge-parity ( C P ) violation in D 0 → K − K + and D 0 → π − π + decays is reported, using p p collision data corresponding to an integrated luminosity of 5.9 fb − 1 collected at a center-of-mass energy of 13 TeV with the LHCb detector. The flavor of the charm meson is inferred from the charge of the pion in D ∗ ( 2010 ) + → D 0 π + decays or from the charge of the muon in ¯ B → D 0 μ − ¯ ν μ X decays. The difference between the C P asymmetries in D 0 → K − K + and D 0 → π − π + decays is measured to be Δ A C P = [ − 18.2 ± 3.2 ( stat ) ± 0.9 ( syst ) ] × 10 − 4 for π -tagged and Δ A C P = [ − 9 ± 8 ( stat ) ± 5 ( syst ) ] × 10 − 4 for μ -tagged D 0 mesons. Combining these with previous LHCb results leads to Δ A C P = ( − 15.4 ± 2.9 ) × 10 − 4 , where the uncertainty includes both statistical and systematic contributions. The measured value differs from zero by more than 5 standard deviations. This is the first observation of C P violation in the decay of charm hadrons.