| Abstract: | A search for charge-parity ($C!P$) violation in $D^0 o K^- K^+$ and $D^0
o pi^- pi^+$ 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 $D^*(2010)^+ o D^0 pi^+$ decays or
from the charge of the muon in $overline{B} o D^0 mu^-ar{
u}_mu X$
decays. The difference between the $C!P$ asymmetries in $D^0 o K^- K^+$ and
$D^0 o pi^- pi^+$ decays is measured to be $Delta A_{C!P} = [ -18.2 pm
3.2,(
m stat.) pm 0.9,(
m syst.) ] imes 10^{-4}$ for $pi$-tagged and
$Delta A_{C!P} = [ -9 pm 8,(
m stat.) pm 5,(
m syst.) ] imes 10^{-4}
$ for $mu$-tagged $D^0$ mesons. Combining these with previous LHCb results
leads to $$Delta A_{C!P} = ( -15.4 pm 2.9) imes 10^{-4},$$ 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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