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