Using a data set corresponding to an integrated luminosity of 3 fb−1den">de">, collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 TeV, the effective lifetime in the den">de"> decay mode, τeffden">de">, is measured to be
dea72ac1e161f0d70fbb4a" title="Click to view the MathML source">τeff=1.479±0.034 (stat)±0.011 (syst) ps.den">de">
Assuming CP conservation, τeffden">de"> corresponds to the lifetime of the light den">de"> mass eigenstate. This is the first measurement of the effective lifetime in this decay mode.