Measurement of the jet mass in highly boosted [Formula: see text] events from pp collisions at [Formula: see text][Formula: see text].

ABSTRACT

The first measurement of the jet mass [Formula see text] of top quark jets produced in [Formula see text] events from pp collisions at [Formula see text] [Formula see text] is reported for the jet with the largest transverse momentum [Formula see text] in highly boosted hadronic top quark decays. The data sample, collected with the CMS detector, corresponds to an integrated luminosity of 19.7[Formula see text]. The measurement is performed in the lepton+jets channel in which the products of the semileptonic decay [Formula see text] with [Formula see text] where [Formula see text] is an electron or muon, are used to select [Formula see text] events with large Lorentz boosts. The products of the fully hadronic decay [Formula see text] with [Formula see text] are reconstructed using a single Cambridge-Aachen jet with distance parameter [Formula see text], and [Formula see text] [Formula see text]. The [Formula see text] cross section as a function of [Formula see text] is unfolded at the particle level and is used to test the modelling of highly boosted top quark production. The peak position of the [Formula see text] distribution is sensitive to the top quark mass [Formula see text], and the data are used to extract a value of [Formula see text] to assess this sensitivity.