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Search for time-dependent $CP$ violation in $D^0 to K^+ K^-$ and $D^0 to pi^+ pi^-$ decays

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 Added by Tommaso Pajero
 Publication date 2021
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and research's language is English




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A search for time-dependent violation of the charge-parity symmetry in $D^0 to K^+ K^-$ and $D^0 to pi^+ pi^-$ decays is performed at the LHCb experiment using proton-proton collision data recorded from 2015 to 2018 at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb$^{-1}$. The $D^0$ meson is required to originate from a $D^*(2010)^+ to D^0 pi^+$ decay, such that its flavour at production is identified by the charge of the accompanying pion. The slope of the time-dependent asymmetry of the decay rates of $D^0$ and $bar{D}^0$ mesons into the final states under consideration is measured to be $Delta Y_{K^+ K^-} = (-2.3 pm 1.5 pm 0.3) times 10^{-4}$, $Delta Y_{pi^+ pi^-} = (-4.0 pm 2.8 pm 0.4)times 10^{-4}$, where the first uncertainties are statistical and the second are systematic. These results are compatible with the conservation of the $CP$ symmetry at the level of 2 standard deviations and improve the precision by nearly a factor of two.



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A search for decay-time-dependent charge-parity ($CP$) asymmetry in $D^0 to K^+K^-$ and $D^0 to pi^+pi^-$ decays is performed at the LHCb experiment using proton-proton collision data recorded at a center-of-mass energy of 13TeV, and corresponding to an integrated luminosity of 5.4fb$^{-1}$. The $D^0$ mesons are required to originate from semileptonic decays of $b$ hadrons, such that the charge of the muon identifies the flavor of the neutral $D$ meson at production. The asymmetries in the effective decay widths of $D^0$ and $overline{D}^0$ mesons are determined to be $A_{Gamma}(K^+K^-) = ( -4.3 pm 3.6 pm 0.5 )times 10^{-4}$ and $A_{Gamma}(pi^+pi^-) = ( 2.2 pm 7.0 pm 0.8)times 10^{-4}$, where the uncertainties are statistical and systematic, respectively. The results are consistent with $CP$ symmetry and, when combined with previous LHCb results, yield $A_{Gamma}(K^+K^-) = ( -4.4 pm 2.3 pm 0.6 )times 10^{-4}$ and $A_{Gamma}(pi^+pi^-) = ( 2.5 pm 4.3 pm 0.7)times 10^{-4}$.
A search for charge-parity ($CP$) violation in Cabibbo-suppressed $D_s^+to K_S^0 pi^+$, $D^+to K_S^0 K^+$ and $D^+to phi pi^+$ decays is reported using proton-proton collision data, corresponding to an integrated luminosity of 3.8 fb$^{-1}$, collected at a center-of-mass energy of 13 TeV with the LHCb detector. High-yield samples of kinematically and topologically similar Cabibbo-favored $D_{(s)}^+$ decays are analyzed to subtract nuisance asymmetries due to production and detection effects, including those induced by $CP$ violation in the neutral kaon system. The results are begin{align*} mathcal{A}_{CP}(D_s^+to K_S^0 pi^+) &=left(phantom{-}1.3phantom{0}pm1.9phantom{0}pm0.5phantom{0}right)times10^{-3}, mathcal{A}_{CP}(D^+to K_S^0 K^+) &=left(-0.09pm0.65pm0.48right)times10^{-3}, mathcal{A}_{CP}(D^+to phi pi^+) &=left(phantom{-}0.05pm0.42pm0.29right)times10^{-3}, end{align*} where the first uncertainties are statistical and the second systematic. They are the most precise measurements of these quantities to date, and are consistent with $CP$ symmetry.
A search for $CP$ violation using $T$-odd correlations is performed using the four-body $D^0 to K^+K^-pi^+pi^-$ decay, selected from semileptonic $B$ decays. The data sample corresponds to integrated luminosities of $1.0,text{fb}^{-1}$ and $2.0,text{fb}^{-1}$ recorded at the centre-of-mass energies of 7 TeV and 8 TeV, respectively. The $CP$-violating asymmetry $a_{CP}^{Ttext{-odd}}$ is measured to be $(0.18pm 0.29text{(stat)}pm 0.04text{(syst)})%$. Searches for $CP$ violation in different regions of phase space of the four-body decay, and as a function of the $D^0$ decay time, are also presented. No significant deviation from the $CP$ conservation hypothesis is found.
We search for CP violation in neutral charm meson decays using a data sample with an integrated luminosity of 966 fb^-1 collected with the Belle detector at the KEKB e+e- asymmetric-energy collider. The asymmetry obtained in the rate of D^0 and D^0-bar decays to the pi^0 pi^0 final state, [-0.03+-0.64(stat)+-0.10(syst)]%, is consistent with no CP violation. This constitutes an order of magnitude improvement over the existing result. We also present an updated measurement of the CP asymmetry in the D^0 -> K_S pi^0 decay: A_{CP}(D^0 -> K_S pi^0) = [-0.21+-0.16(stat)+-0.07(syst)]%.
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.
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