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Register a new userObservation of $D^0to rho^0gamma$ and search for $CP$ violation in radiative charm decays
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We report the first observation of the radiative charm decay $D^0 to rho^0 gamma$ and the first search for $CP$ violation in decays $D^0 to rho^0 gamma$, $phigamma$, and $overline{K}{}^{*0} gamma$, using a data sample of 943 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The branching fraction is measured to be $mathcal{B}(D^0 to rho^0 gamma)=(1.77 pm 0.30 pm 0.07) times 10^{-5}$, where the first uncertainty is statistical and the second is systematic. The obtained $CP$ asymmetries, $mathcal{A}_{CP}(D^0 to rho^0 gamma)=+0.056 pm 0.152 pm 0.006$, $mathcal{A}_{CP}(D^0 to phi gamma)=-0.094 pm 0.066 pm 0.001$, and $mathcal{A}_{CP}(D^0 to overline{K}{}^{*0} gamma)=-0.003 pm 0.020 pm 0.000$, are consistent with no $CP$ violation. We also present an improved measurement of the branching fractions $mathcal{B}(D^0 to phi gamma)=(2.76 pm 0.19 pm 0.10) times 10^{-5}$ and $mathcal{B}(D^0 to overline{K}{}^{*0} gamma)=(4.66 pm 0.21 pm 0.21) times 10^{-4}$.
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The decay-time-dependent $CP$ asymmetry in $B^0 to D^{*pm}D^{mp}$ decays is measured using a data set corresponding to an integrated luminosity of $9$fb$^{-1}$ recorded by the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The $CP$ parameters are measured as $ S_{D^*D} = -0.861 pm 0.077,text{(stat)} pm 0.019 ,text{(syst)},, $ $ Delta S_{D^*D} = 0.019 pm 0.075 ,text{(stat)} pm 0.012 ,text{(syst)} ,, $ $ C_{D^*D} = -0.059 pm 0.092 ,text{(stat)} pm 0.020 ,text{(syst)} ,, $ $ Delta C_{D^*D} = -0.031 pm 0.092 ,text{(stat)} pm 0.016 ,text{(syst)} ,, $ $ {cal A}_{D^*D} = 0.008 pm 0.014 ,text{(stat)} pm 0.006 ,text{(syst)},. $ The analysis provides the most precise single measurement of $CP$ violation in this decay channel to date. All parameters are consistent with their current world average values.
We report a measurement of ${D^{0}}$-${overline{D}{}^{0}}$ mixing parameters and a search for indirect $CP$ violation through a time-dependent amplitude analysis of ${D^0to K_S^0pi^+pi^-}$ decays. The results are based on 921~fb$^{-1}$ of data accumulated with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. Assuming $CP$ conservation, we measure the mixing parameters $x=(0.56pm0.19^{+0.03}_{-0.09}{^{+0.06}_{-0.09}})%$ and $y=(0.30pm0.15^{+0.04}_{-0.05}{^{+0.03}_{-0.06})}%$, where the errors are statistical, experimental systematic, and systematic due to the amplitude model, respectively. With $CP$ violation allowed, the parameters $|q/p|=0.90^{+0.16}_{-0.15}{^{+0.05}_{-0.04}}{^{+0.06}_{-0.05}}$ and $arg(q/p)=(-6pm11{pm3}{^{+3}_{-4}})^{circ}$ are found to be consistent with conservation of $CP$ symmetry in mixing and in the interference between mixing and decay, respectively.
The phenomenon of mixing in neutral meson systems has now been observed in all flavours, but only in the past year in the D0 system. The standard model anticipated that, for the charm sector, the mixing rate would be small, and also that CP violation, either in mixing or in direct decay, would be below the present levels of observability. It is hoped that further study of these phenomena might reveal signs of new physics. A review of recently available, experimental results is given.
A model-independent search for direct CP violation in the Cabibbo suppressed decay $D^+ to K^- K^+pi^+$ in a sample of approximately 370,000 decays is carried out. The data were collected by the LHCb experiment in 2010 and correspond to an integrated luminosity of 35 pb$^{-1}$. The normalized Dalitz plot distributions for $D^+$ and $D^-$ are compared using four different binning schemes that are sensitive to different manifestations of CP violation. No evidence for CP asymmetry is found.
By analyzing an $e^+e^-$ annihilation data sample corresponding to an integrated luminosity of $2.93~mathrm{fb}^{-1}$ collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we measure the branching fraction of the $D^0to rho^- mu^+ u_mu$ decay for the first time. We obtain ${mathcal B}_{D^0to rho^- mu^+ u_mu}=(1.35pm0.09_{rm stat}pm0.09_{rm syst})times 10^{-3}$. Combining with theoretical predictions, we extract the CKM matrix element $|V_{cd}|=0.204pm0.007_{rm stat}pm0.007_{rm syst}pm0.014_{rm theory}$. Using the world average of ${mathcal B}_{D^0to rho^- e^+ u_e}$, we find a branching fraction ratio of ${mathcal B}_{D^0to rho^- mu^+ u_mu}/{mathcal B}_{D^0to rho^- e^+ u_e}=0.90pm0.11$, which agrees with the theoretical expectation of lepton flavor universality within the uncertainty. Combining the world average of ${mathcal B}_{D^+to rho^0 mu^+ u_mu}$ and the lifetimes of $D^{0(+)}$, we obtain a partial decay width ratio of ${Gamma}_{D^0to rho^- mu^+ u_{mu}}/(2{Gamma}_{D^+to rho^0 mu^+ u_{mu}}) = 0.71pm0.14$, which is consistent with the isospin symmetry expectation of one within $2.1sigma$. For the reported values of ${mathcal B}_{D^0to rho^- mu^+ u_mu}/{mathcal B}_{D^0to rho^- e^+ u_e}$ and ${Gamma}_{D^0to rho^- mu^+ u_{mu}}/2{Gamma}_{D^+to rho^0 mu^+ u_{mu}}$, the uncertainty is the quadratic sum of the statistical and systematic uncertainties.
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