  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.
