Top Mass Determination in Leptonic Final States with J/psi

Taking advantage of large ttbar production cross-section at the LHC the leptonic final states with J/psi are explored for a precise determination of the top quark mass. The top is partially reconstructed by combining the isolated lepton from the W with the J/psi from the decays of the corresponding $b$-quark. The method essentially relies on the Monte-Carlo description of the top production and decay. The main emphasis is put on the systematics studies. Expected mass measurement accuracy is dominated by the current understanding of theoretical uncertainties which result to a systematic error of ~ 1 GeV.