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Register a new userFirst observation of $D^0-bar D^0$ oscillations in $D^0to K^+pi^-pi^+pi^-$ decays and measurement of the associated coherence parameters
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Charm meson oscillations are observed in a time-dependent analysis of the ratio of $D^0to K^+pi^-pi^+pi^-$ to $D^0to K^-pi^+pi^-pi^+$ decay rates, using data corresponding to an integrated luminosity of $3.0,{rm fb}^{-1}$ recorded by the LHCb experiment. The measurements presented are sensitive to the phase-space averaged ratio of doubly Cabibbo-suppressed to Cabibbo-favoured amplitudes $r_{D}^{K3pi}$ and the product of the coherence factor $R_{D}^{K3pi}$ and a charm mixing parameter $y^{}_{K3pi}$. The constraints measured are $r_{D}^{K3pi}=(5.67 pm 0.12)times10^{-2}$, which is the most precise determination to date, and $R_{D}^{K3pi} cdot y^{}_{K3pi} = (0.3 pm 1.8)times 10^{-3}$, which provides useful input for determinations of the CP-violating phase $gamma$ in $B^pm to D K^pm, D to K^mppi^pmpi^mppi^pm$ decays. The analysis also gives the most precise measurement of the $D^0to K^+pi^-pi^+pi^-$ branching fraction, and the first observation of $D^0-bar D^0$ oscillations in this decay mode, with a significance of 8.2 standard deviations.
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Time-integrated $CP$ asymmetries in $D^0$ decays to the final states $K^- K^+$ and $pi^- pi^+$ are measured using proton-proton collisions corresponding to $3mathrm{,fb}^{-1}$ of integrated luminosity collected at centre-of-mass energies of $7mathrm{,Tekern -0.1em V}$ and $8mathrm{,Tekern -0.1em V}$. The $D^0$ mesons are produced in semileptonic $b$-hadron decays, where the charge of the accompanying muon is used to determine the initial flavour of the charm meson. The difference in $CP$ asymmetries between the two final states is measured to be begin{align} Delta A_{CP} = A_{CP}(K^-K^+)-A_{CP}(pi^-pi^+) = (+0.14 pm 0.16mathrm{,(stat)} pm 0.08mathrm{,(syst)})% . onumber end{align} A measurement of $A_{CP}(K^-K^+)$ is obtained assuming negligible $CP$ violation in charm mixing and in Cabibbo-favoured $D$ decays. It is found to be begin{align} A_{CP}(K^-K^+) = (-0.06 pm 0.15mathrm{,(stat)} pm 0.10mathrm{,(syst)}) % , onumber end{align} where the correlation coefficient between $Delta A_{CP}$ and $A_{CP}(K^-K^+)$ is $rho=0.28$. By combining these results, the $CP$ asymmetry in the $D^0rightarrowpi^-pi^+$ channel is $A_{CP}(pi^-pi^+)=(-0.20pm0.19mathrm{,(stat)}pm0.10mathrm{,(syst)})%$.
We report measurements of charm-mixing parameters based on the decay-time-dependent ratio of $D^0to K^+pi^-$ to $D^0to K^-pi^+$ rates. The analysis uses a data sample of proton-proton collisions corresponding to an integrated luminosity of $5.0$ fb$^{-1}$ recorded by the LHCb experiment from 2011 through 2016. Assuming charge-parity (CP) symmetry, the mixing parameters are determined to be $x^2=(3.9 pm 2.7) times10^{-5}$, $y=(5.28 pm 0.52) times 10^{-3}$, and $R_D=(3.454 pm 0.031)times10^{-3}$. Without this assumption, the measurement is performed separately for $D^0$ and $overline{D}{}^0$ mesons, yielding a direct CP-violating asymmetry $A_D =(-0.1pm9.1)times10^{-3}$, and magnitude of the ratio of mixing parameters $1.00< |q/p| <1.35$ at the $68.3%$ confidence level. All results include statistical and systematic uncertainties and improve significantly upon previous single-measurement determinations. No evidence for CP violation in charm mixing is observed.
Using a data sample corresponding to 13.7 fb^-1 collected with the CLEO II and II.V detectors, we report new branching fraction measurements for two Cabibbo-suppressed decay modes of the D^+ meson: Br(D^+ to pi^+ pi^0) = (1.3 +/- 0.2) x 10^-3 and Br(D^+ to bar{K}^0 K^+) = (5.2 +/- 0.6) x 10^-3 which are significant improvements over past measurements. The errors include statistical and systematical uncertainties as well as the uncertainty in the absolute D^+ branching fraction scale. We also set the first 90% confidence level upper limit on the branching fraction of the doubly Cabibbo-suppressed decay mode Br(D^+ to K^+ pi^0) < 4.2 x 10^-4.
The decays $Dto K^-pi^+pi^+pi^-$ and $D to K^-pi^+pi^0$ are studied in a sample of quantum-correlated $Dbar{D}$ pairs produced through the process $e^+e^- to psi(3770) to Dbar{D}$, exploiting a data set collected by the BESIII experiment that corresponds to an integrated luminosity of 2.93 fb$^{-1}$. Here $D$ indicates a quantum superposition of a $D^0$ and a $bar{D}^0$ meson. By reconstructing one neutral charm meson in a signal decay, and the other in the same or a different final state, observables are measured that contain information on the coherence factors and average strong-phase differences of each of the signal modes. These parameters are critical inputs in the measurement of the angle $gamma$ of the Unitarity Triangle in $B^- to DK^-$ decays at the LHCb and Belle II experiments. The coherence factors are determined to be $R_{K3pi}=0.52^{+0.12}_{-0.10}$ and $R_{Kpipi^0}=0.78 pm 0.04$, with values for the average strong-phase differences that are $delta_D^{K3pi}=left(167^{+31}_{-19}right)^circ$ and $delta_D^{Kpipi^0}=left(196^{+14}_{-15}right)^circ$, where the uncertainties include both statistical and systematic contributions. The analysis is re-performed in four bins of the phase-space of the $D to K^-pi^+pi^+pi^-$ to yield results that will allow for a more sensitive measurement of $gamma$ with this mode, to which the BESIII inputs will contribute an uncertainty of around 6$^circ$.
We present an observation and rate measurement of the decay D0 -> K+pi-pi0 produced in 9/fb of e+e- collisions near the Upsilon(4S) resonance. The signal is inconsistent with an upward fluctuation of the background by 4.9 standard deviations. We measured the rate of D0 -> K+pi-pi0 normalized to the rate of D0bar -> K+pi-pi0 to be 0.0043 +0.0011 -0.0010 (stat) +/- 0.0007 (syst). This decay can be produced by doubly-Cabibbo-suppressed decays or by the D0 evolving into a D0bar through mixing, followed by a Cabibbo-favored decay to K+pi-pi0. We also found the CP asymmetry A=(8 +25 -22)% to be consistent with zero.
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