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Register a new userMeasurements of indirect CP asymmetries in $D^0to K^-K^+$ and $D^0topi^-pi^+$ decays
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A study of indirect CP violation in $D^0$ mesons through the determination of the parameter $A_Gamma$ is presented using a data sample of $pp$ collisions, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected with the LHCb detector and recorded at the centre-of-mass energy of 7 TeV at the LHC. The parameter $A_Gamma$ is the asymmetry of the effective lifetimes measured in decays of $D^0$ and $bar{D}^0$ mesons to the CP eigenstates $K^-K^+$ and $pi^-pi^+$. Fits to the data sample yield $A_Gamma(KK)=(-0.35pm0.62pm0.12)times 10^{-3}$ and $A_Gamma(pipi)=(0.33pm1.06pm0.14)times 10^{-3}$, where the first uncertainties are statistical and the second systematic. The results represent the worlds best measurements of these quantities. They show no difference in $A_Gamma$ between the two final states and no indication of CP violation.
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We report a measurement of the indirect CP-violating asymmetries ($A_{Gamma}$) between effective lifetimes of anticharm and charm mesons reconstructed in $D^0to K^+ K^-$ and $D^0to pi^+pi^-$ decays. We use the full data set of proton-antiproton collisions collected by the Collider Detector at Fermilab experiment and corresponding to $9.7$~fb$^{-1}$ of integrated luminosity. The strong-interaction decay $D^{*+}to D^0pi^+$ is used to identify the meson at production as $D^0$ or $overline{D}^0$. We statistically subtract $D^0$ and $overline{D}^0$ mesons originating from $b$-hadron decays and measure the yield asymmetry between anticharm and charm decays as a function of decay time. We measure $A_Gamma (K^+K^-) = (-0.19 pm 0.15 (stat) pm 0.04 (syst))%$ and $A_Gamma (pi^+pi^-)= (-0.01 pm 0.18 (stat) pm 0.03 (syst))%$. The results are consistent with the hypothesis of CP symmetry and their combination yields $A_Gamma = (-0.12 pm 0.12)%$.
The first measurements of the forward-backward asymmetry of the dimuon pair ($A_{FB}$), the triple-product asymmetry ($A_{2phi}$), and the charge-parity-conjugation asymmetry ($A_{CP}$), in $D^0topi^+pi^-mu^+mu^-$ and $D^0to K^+K^-mu^+mu^-$ decays are reported. They are performed using data from proton-proton collisions collected with the LHCb experiment from 2011 to 2016, corresponding to a total integrated luminosity of 5 fb$^{-1}$. The asymmetries are measured to be begin{align*} A_{FB}(D^0topi^+pi^-mu^+mu^-) &= (phantom{-}3.3pm3.7pm0.6)%, A_{2phi}(D^0topi^+pi^-mu^+mu^-)&= (-0.6pm3.7pm0.6)%, A_{CP}(D^0topi^+pi^-mu^+mu^-) &= (phantom{-}4.9pm3.8pm0.7)%, A_{FB}(D^0to K^+K^-mu^+mu^-) &= (0pm11pm2)%, A_{2phi}(D^0to K^+K^-mu^+mu^-)&= (9pm11pm1)%, A_{CP}(D^0to K^+K^-mu^+mu^-) &= (0pm11pm2)%, end{align*} where the first uncertainty is statistical and the second systematic. The asymmetries are also measured as a function of the dimuon invariant mass. The results are consistent with the Standard Model predictions.
Time-dependent $CP$ asymmetries in the decay rates of the singly Cabibbo-suppressed decays $D^0rightarrow K^-K^+$ and $D^0rightarrow pi^-pi^+$ are measured in $pp$ collision data corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected by the LHCb experiment. The $D^0$ mesons are produced in semileptonic $b$-hadron decays, where the charge of the accompanying muon is used to determine the initial state as $D^0$ or $bar{D}^0$. The asymmetries in effective lifetimes between $D^0$ and $bar{D}^0$ decays, which are sensitive to indirect $CP$ violation, are determined to be begin{align*} A_{Gamma}(K^-K^+) = (-0.134 pm 0.077 ; {}^{+0.026}_{-0.034})% , A_{Gamma}(pi^-pi^+) = (-0.092pm 0.145 ; {}^{+0.025}_{-0.033})% , end{align*} where the first uncertainties are statistical and the second systematic. This result is in agreement with previous measurements and with the hypothesis of no indirect $CP$ violation in $D^0$ decays.
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 flavour-tagged decay-time-dependent amplitude analysis of $B_s^0to(K^+pi^-)(K^-pi^+)$ decays is presented in the $K^{pm}pi^{mp}$ mass range from 750 to 1600 MeV$/c^2$. The analysis uses $pp$ collision data collected with the LHCb detector at centre-of-mass energies of $7$ and $8$ TeV, corresponding to an integrated luminosity of $3.0$ fb$^{-1}$. Several quasi-two-body decay modes are considered, corresponding to $K^{pm}pi^{mp}$ combinations with spin 0, 1 and 2, which are dominated by the $K_0^*(800)^0$ and $K_0^*(1430)^0$, the $K^*(892)^0$ and the $K_2^*(1430)^0$ resonances, respectively. The longitudinal polarisation fraction for the $B_s^0to K^*(892)^0overline{K}^*(892)^0$ decay is measured as $f_L=0.208 pm 0.032 pm 0.046$, where the first uncertainty is statistical and the second is systematic. The first measurement of the mixing-induced $CP$-violating phase, $phi_s^{doverline{d}}$, in $bto doverline{d}s$ transitions is performed, yielding a value of $phi_s^{doverline{d}}=-0.10$ $pm$ $0.13$ (stat) $pm$ $0.14$ (syst) rad.
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