Measurement of the top quark mass in the dileptonic tt¯ decay channel using the mass observables Mbℓ, MT2, and Mbℓν in pp collisions at s=8 TeV

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Abstract

A measurement of the top quark mass (${M}_{t}$) in the dileptonic $t\overline{t}$ 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 corresponds to an integrated luminosity of $19.7\ifmmode\pm\else\textpm\fi{}0.5\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. Events are selected with two oppositely charged leptons ($\ensuremath{\ell}=e$, $\ensuremath{\mu}$) 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, ${M}_{b\ensuremath{\ell}}$, and a ``stransverse mass'' observable, ${M}_{\mathrm{T}2}$, 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, ${M}_{b\ensuremath{\ell}\ensuremath{\nu}}$, that is combined with ${M}_{\mathrm{T}2}$ 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 $172.22\ifmmode\pm\else\textpm\fi{}0.18(\mathrm{stat}){\text{ }}_{\ensuremath{-}0.93}^{+0.89}(\mathrm{syst})\text{ }\text{ }\mathrm{GeV}$.

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