Abstract
A novel technique for measuring the mass of the top quark that uses only the kinematic properties of its charged decay products is presented. Top quark pair events with final states with one or two charged leptons and hadronic jets are selected from the data set of 8 TeV proton-proton collisions, corresponding to an integrated luminosity of 19.7 inverse femtobarns. By reconstructing secondary vertices inside the selected jets and computing the invariant mass of the system formed by the secondary vertex and an isolated lepton, an observable is constructed that is sensitive to the top quark mass that is expected to be robust against the energy scale of hadronic jets. The main theoretical systematic uncertainties, concerning the modeling of the fragmentation and hadronization of b quarks and the reconstruction of secondary vertices from the decays of b hadrons, are studied. A top quark mass of 173.68 +/- 0.20 (stat) +1.58 -0.97 (syst) GeV is measured. The overall systematic uncertainty is dominated by the uncertainty in the b quark fragmentation and the modeling of kinematic properties of the top quark.
Highlights
The top quark is the heaviest known elementary particle and as such has a privileged interaction with the Higgs boson
This paper describes a measurement performed with the CMS experiment at the CERN LHC that minimizes the sensitivity to experimental systematic uncertainties such as jet energy scale
: Effects arising from mismodeling of the overall kinematic properties of the event are canceled, to first approximation, by studying the ratio of the two momenta, in which the secondary vertex serves as a proxy for the b hadron and the charged particles represent the full momentum of the initial b quark
Summary
The top quark is the heaviest known elementary particle and as such has a privileged interaction with the Higgs boson. This paper describes a measurement performed with the CMS experiment at the CERN LHC that minimizes the sensitivity to experimental systematic uncertainties such as jet energy scale. This is achieved by constructing a massdependent observable that uses only the individually measured momenta of charged decay products (tracks) of the top quark. The paper is organized as follows: Sec. II describes the experiment, the collected and simulated data, and the event reconstruction and selection; Sec. III describes control region studies of b quark fragmentation and secondary vertex reconstruction; Sec. IV describes the measurement of the top quark mass and the assigned systematic uncertainties; and Sec. V concludes and gives an outlook of prospects in the ongoing LHC run
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