Measurement of the top quark mass in the dileptonic tt decay channel using the mass observables M_(bℓ), M_(T2), and M_(bℓν) in pp collisions at s~(1/2) = 8 TeV

摘要

A measurement of the top quark mass (M_t) in the dileptonic tt 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 ± 0.5 fb~(−1). Events are selected with two oppositely charged leptons (ℓ = e, μ) 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 ofMt and an overall jet energy scale factor (JSF). A complementary approach is used to construct an invariant mass observable, M_(bℓν), 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)_(−0.93)~(+0.89) (syst) GeV.