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## First observation of $D^0-\bar D^0$ oscillations in $D^0\to K^+\pi^-\pi^+\pi^-$ decays and measurement of the associated coherence parameters

Physical Review Letters. 2016. Vol. 116. No. 24.
Borisyak M. A., Derkach D., Likhomanenko T., Ustyuzhanin A., Rogozhnikov A.

Charm meson oscillations are observed in a time-dependent analysis of the ratio of D0 → K+π −π +π − to D0 → K−π +π −π + decay rates, using data corresponding to an integrated luminosity of 3.0 fb−1 recorded by the LHCb experiment. The measurements presented are sensitive to the phase-space averaged ratio of doubly Cabibbo-suppressed to Cabibbo-favoured amplitudes r K3π D and the product of the co￾herence factor RK3π D and a charm mixing parameter y 0 K3π . The constraints measured are r K3π D = (5.67±0.12)×10−2 , which is the most precise determination to date, and RK3π D · y 0 K3π = (0.3 ± 1.8) × 10−3 , which provides useful input for determinations of the CP-violating phase γ in B±→ DK±, D→ K∓π ±π ∓π ± decays. The analysis also gives the most precise measurement of the D0 → K+π −π +π − branching fraction, and the first observation of D0–D0 oscillations in this decay mode, with a significance of 8.2 standard deviations.