Measurement of the jet mass distribution in boosted top quark decays

The production of top quarks with very high transverse momenta results in collimated decays, where all decay products merge into a single jet. The distribution of the jet mass is important for jet substructure applications (top tagging) and shows sensitivity to the top quark mass. Studies for a measurement of the jet mass distribution unfolded to the particle level are presented, using data recorded by the CMS detector at a centre of mass energy of 13 TeV. The measurement is performed in the lepton+jets channel, which offers a good suppression of non-t anti t backgrounds while retaining a high selection efficiency. The choice of a suitable jet algorithm is essential to reduce pile up effects but ensure that all decay products are merged into a single jet. Performance studies using different jet algorithms, especially the XCone jet algorithm, are presented.