Measurement of the Lifetime of the Doubly Charmed Baryon <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msubsup><mml:mi mathvariant="normal">Ξ</mml:mi><mml:mrow><mml:mi>c</mml:mi><mml:mi>c</mml:mi></mml:mrow><mml:mrow><mml:mo form="prefix">+</mml:mo><mml:mo form="prefix">+</mml:mo></mml:mrow></mml:msubsup></mml:math>

The first measurement of the lifetime of the doubly charmed baryon Ξ_{cc}^{++} is presented, with the signal reconstructed in the final state Λ_{c}^{+}K^{-}π^{+}π^{+}. The data sample used corresponds to an integrated luminosity of 1.7 fb^{-1}, collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV. The Ξ_{cc}^{++} lifetime is measured to be 0.256_{-0.022}^{+0.024}(stat)±0.014(syst) ps.