  A study of mixing and indirect CP violation in D0 mesons through the
determination of the parameters y_CP and A_\Gamma\ is presented. The parameter
y_CP is the deviation from unity of the ratio of effective lifetimes measured
in D0 decays to the CP eigenstate K+K- with respect to decays to the Cabibbo
favoured mode K-\pi+. The result measured using data collected by LHCb in 2010,
corresponding to an integrated luminosity of 29 pb^-1, is y_CP =
(5.5+/-6.3_{stat}+/-4.1_{syst}) x 10^-3. The parameter A_\Gamma\ is the
asymmetry of effective lifetimes measured in decays of D0 and anti-D0 mesons to
K+K-. The result is A_\Gamma\ = (-5.9+/-5.9_{stat}+/-2.1_{syst}) x 10^-3. A
data-driven technique is used to correct for lifetime-biasing effects.
