Abstract
A measurement of the top quark mass (M[t]) in the dileptonic t t-bar decay channel is performed using data from proton-proton collisions at a center-of-mass energy of 8 TeV. The data was recorded by the CMS experiment at the LHC and corresponding to an integrated luminosity of 19.7 +/- 0.5 inverse femtobarns. Events are selected with two oppositely charged leptons (l = e, mu) and two jets identified as originating from b quarks. The analysis is based on three kinematic observables whose distributions are sensitive to the value of M[t]. An invariant mass observable, M[bl], and a `stransverse mass' observable, M[T2], are employed in a simultaneous fit to determine the value of M[t] and an overall jet energy scale factor (JSF). A complementary approach is used to construct an invariant mass observable, M[blnu], that is combined with M[T2] to measure M[t]. The shapes of the observables, along with their evolutions in M[t] and JSF, are modeled by a nonparametric Gaussian process regression technique. The sensitivity of the observables to the value of M[t] is investigated using a Fisher information density method. The top quark mass is measured to be 172.22 +/- 0.18 (stat) +0.89/-0.93 (syst) GeV.
Highlights
The top quark mass is a fundamental parameter of the standard model (SM), and an important component in global electroweak fits evaluating the self-consistency of the SM [1]
To address the JES uncertainty, we introduce a technique that uses the Mbl and MbTb2 observables to determine an overall jet energy scale factor (JSF) simultaneously with the top quark mass, where the JSF is defined as a multiplicative factor scaling the four-vectors of all jets in the event
Pairings in which the b jet and lepton emerge from different top quarks do not necessarily obey the upper bound described in Eq (2), and do not have a clean kinematic end point in Mbl
Summary
The top quark mass is a fundamental parameter of the standard model (SM), and an important component in global electroweak fits evaluating the self-consistency of the SM [1]. To address the JES uncertainty, we introduce a technique that uses the Mbl and MbTb2 observables to determine an overall jet energy scale factor (JSF) simultaneously with the top quark mass, where the JSF is defined as a multiplicative factor scaling the four-vectors of all jets in the event. It achieves sensitivity to the JSF through the kinematic differences between b jets, which are subject to JSF scaling, and leptons, which are not Because it does not use light quarks from a hadronic W boson decay, this approach is insensitive to flavor-dependent JES uncertainties. The distribution shapes can conveniently be modeled as functions of multiple variables In this analysis, three variables are used: the value of the relevant observable (Mbl, MbTb2, or Mblν), Mt, and the JSF.
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