of Birmingham Observation of CP violation in charm decays

A search for charge-parity ( CP ) violation in D 0 → K − K þ and D 0 → π − π þ decays is reported, using pp 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 (cid:2) ð 2010 Þ þ → D 0 π þ decays or from the charge of the muon in ¯ B → D 0 μ − ¯ ν μ X decays. The difference between the CP asymmetries in D 0 → K − K þ and D 0 → π − π þ decays is measured to be Δ A CP ¼ ½ − 18 . 2 (cid:3) 3 . 2 ð stat Þ (cid:3) 0 . 9 ð syst Þ(cid:4) × 10 − 4 for π -tagged and Δ A CP ¼ ½ − 9 (cid:3) 8 ð stat Þ (cid:3) 5 ð syst Þ(cid:4) × 10 − 4 for μ tagged D 0 mesons. Combining these with previous LHCb results leads to Δ A CP ¼ ð − 15 . 4 (cid:3) 2 . 9 Þ × 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 CP violation in the decay of charm hadrons.