Search for time-dependent CP violation in D0 → K+K– and D0 → π+π– decays

A search for time-dependent violation of the charge-parity (CP) symmetry in D0→ K+K− and D0→ π+π− decays is performed at the LHCb experiment using proton–proton collision data recorded in 2015–2018 at a centre-of-mass energy of 13TeV, corresponding to an integrated luminosity of 5.7 fb−1. The D0 meson is required to originate from D∗(2010)+→ D0π+ decays, such that its flavour at production is identified by the charge of the pion meson. The slope of the time-dependent asymmetry of the decay rates of D0 and D0 mesons, ΔY, into the final states under consideration is measured to be ΔYK+K− = (−2.3 ± 1.5 ± 0.3) × 10−4, ΔYπ+π− = (−4.0 ± 2.8 ± 0.4) × 10−4, where the first uncertainties are statistical and the second are systematic. Neglecting possible final-state dependent contributions, these results are combined yielding ΔY = (−2.7 ± 1.3 ± 0.3) × 10−4, which is compatible with the CP-invariance hypothesis at the level of 2σ. This result improves by nearly a factor of two on the precision of the world average of the parameter A, which is approximately equal to the negative of ΔY. Thus, it sets the strongest bound on the value of the phase φM2 , which parametrises dispersive CP-violating contributions to D0-meson mixing.