Abstract
The decay D rightarrow K^-pi ^+ is studied in a sample of quantum-correlated D{bar{D}} pairs, based on a data set corresponding to an integrated luminosity of 2.93 fb^{-1} collected at the psi (3770) resonance by the BESIII experiment. The asymmetry between C!P-odd and C!P-even eigenstate decays into K^-pi ^+ is determined to be {{mathcal {A}}}_{Kpi } = 0.132 pm 0.011 pm 0.007, where the first uncertainty is statistical and the second is systematic. This measurement is an update of an earlier study exploiting additional tagging modes, including several decay modes involving a K^0_L meson. The branching fractions of the K^0_L modes are determined as input to the analysis in a manner that is independent of any strong phase uncertainty. Using the predominantly C!P-even tag Drightarrow pi ^+pi ^-pi ^0 and the ensemble of C!P-odd eigenstate tags, the observable {{mathcal {A}}}_{Kpi }^{pi pi pi ^0} is measured to be 0.130 pm 0.012 pm 0.008. The two asymmetries are sensitive to r_D^{Kpi }cos delta _D^{Kpi }, where r_D^{Kpi } and delta _D^{Kpi } are the ratio of amplitudes and phase difference, respectively, between the doubly Cabibbo-suppressed and Cabibbo-favoured decays. In addition, events containing D rightarrow K^-pi ^+ tagged by D rightarrow K^0_{S,L} pi ^+pi ^- are studied in bins of phase space of the three-body decays. This analysis has sensitivity to both r_D^{Kpi }cos delta _D^{Kpi } and r_D^{Kpi }sin delta _D^{Kpi }. A fit to {{mathcal {A}}}_{Kpi }, {{mathcal {A}}}_{Kpi }^{pi pi pi ^0} and the phase-space distribution of the D rightarrow K^0_{S,L} pi ^+pi ^- tags yields delta _D^{Kpi }= left( 187.6 {^{+8.9}_{-9.7}}{^{+5.4}_{-6.4}} right) ^{circ }, where external constraints are applied for r_D^{Kpi } and other relevant parameters. This is the most precise measurement of delta _D^{Kpi } in quantum-correlated D{bar{D}} decays.
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