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Register a new userObservation of $C!P$ violation in charm decays
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A search for charge-parity ($C!P$) violation in $D^0 to K^- K^+$ and $D^0 to pi^- pi^+$ decays is reported, using $pp$ collision data corresponding to an integrated luminosity of 6 $mathrm{fb}^{-1}$ collected at a center-of-mass energy of 13 TeV with the LHCb detector. The flavor of the charm meson is inferred from the charge of the pion in $D^*(2010)^+ to D^0 pi^+$ decays or from the charge of the muon in $overline{B} to D^0 mu^-bar{ u}_mu X$ decays. The difference between the $C!P$ asymmetries in $D^0 to K^- K^+$ and $D^0 to pi^- pi^+$ decays is measured to be $Delta A_{C!P} = [ -18.2 pm 3.2,(rm stat.) pm 0.9,(rm syst.) ] times 10^{-4}$ for $pi$-tagged and $Delta A_{C!P} = [ -9 pm 8,(rm stat.) pm 5,(rm syst.) ] times 10^{-4} $ for $mu$-tagged $D^0$ mesons. Combining these with previous LHCb results leads to $$Delta A_{C!P} = ( -15.4 pm 2.9) times 10^{-4},$$ where the uncertainty includes both statistical and systematic contributions. The measured value differs from zero by more than five standard deviations. This is the first observation of $C!P$ violation in the decay of charm hadrons.
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A search for $C!P$ violation in the $Lambda_b^0 to p pi^- pi^+ pi^-$ decay is performed using LHCb data corresponding to an integrated luminosity of 6.6$,fb^{-1}$ collected in $pp$ collisions at centre-of-mass energies of 7, 8 and 13$,Tekern -0.1em V$. The analysis uses both triple product asymmetries and the unbinned energy test method. The highest significances of $C!P$ asymmetry are 2.9 standard deviations from triple product asymmetries and 3.0 standard deviations for the energy test method. Once the global $p$-value is considered, all results are consistent with no $C!P$ violation. Parity violation is observed at a significance of $5.5$ standard deviations for the triple product asymmetry method and $5.3$ standard deviations for the energy test method.
Measurements of charm mixing and $C!P$ violation parameters from the decay-time-dependent ratio of $ D^0 to K^+ pi^- $ to $ D^0 to K^- pi^+ $ decay rates and the charge-conjugate ratio are reported. The analysis uses $overline{B}to D^{*+} mu^- X$, and charge-conjugate decays, where $D^{*+}to D^0 pi^+$, and $D^0to K^{mp} pi^{pm}$. The $pp$ collision data are recorded by the LHCb experiment at center-of-mass energies $sqrt{s}$ = 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$. The data are analyzed under three hypotheses: (i) mixing assuming $C!P$ symmetry, (ii) mixing assuming no direct $C!P$ violation in the Cabibbo-favored or doubly Cabibbo-suppressed decay amplitudes, and (iii) mixing allowing either direct $C!P$ violation and/or $C!P$ violation in the superpositions of flavor eigenstates defining the mass eigenstates. The data are also combined with those from a previous LHCb study of $D^0to K pi$ decays from a disjoint set of $ D^{*+} $ candidates produced directly in $pp$ collisions. In all cases, the data are consistent with the hypothesis of $C!P$ symmetry.
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 $mathcal{B}(D^0 to overline{K}{}^{*0} gamma)=(4.66 pm 0.21 pm 0.21) times 10^{-4}$.
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.
Since the discovery of CP violation more than 5 decades ago, this phenomenon is still attracting a lot of interest. Among the many fascinating aspects of this subject, this review is dedicated to direct CP violation in non-leptonic decays. The advances within the last decade have been enormous, driven by the increasingly large samples of b- and c-hadron decays, and have led to very interesting results such as large CP asymmetries in charmless B decays and the observation of direct CP violation in the charm sector. We address the quest for understanding the origin of strong phases, the importance of final state interactions and the relation with CPT symmetry, and different approaches to measure direct CP violation in these decays. The main experimental results and their implications are then discussed.
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