Measurement of the Top Quark Mass at D0 Run II with the Matrix Element Method in the Lepton+Jets Final State

The mass of the top quark is a fundamental parameter of the
Standard Model. Its precise knowledge yields valuable insights into
unresolved phenomena in and beyond the Standard Model. A
measurement of the top quark mass with the matrix element method in
the lepton+jets final state in D0 Run II is presented. Events are
selected requiring an isolated energetic charged lepton (electron
or muon), significant missing transverse energy, and exactly four
calorimeter jets. For each event, the probabilities to originate
from the signal and background processes are calculated based on
the measured kinematics, the object resolutions and the respective
matrix elements. The jet energy scale is known to be the dominant
source of systematic uncertainty. The reference scale for the mass
measurement is derived from Monte Carlo events. The matrix element
likelihood is defined as a function of both, mtop and jet energy
scale JES, where the latter represents a scale factor with respect
to the reference scale. The top mass is obtained from a
two-dimensional correlated fit, and the likelihood yields both the
statistical and jet energy scale uncertainty. Using a dataset of
320 pb-1 of D0 Run II data, the mass of the top quark is measured
to be mtop (ljets) = 169.5 +/- 4.4(stat.+JES) +1.7-1.6(syst.) GeV
mtop (ejets) = 168.8 +/- 6.0(stat.+JES) +1.9-1.9(syst.) GeV mtop
(mujets)= 172.3 +/- 9.6(stat.+JES) +3.4-3.3(syst.) GeV The jet
energy scale measurement in the lepton+jets sample yields JES=1.034
+/- 0.034, suggesting good consistency of the data with the
simulation. The measurement forecasts significant improvements to
the total top mass uncertainty during Run II before the startup of
the LHC, as the data sample will grow by a factor of ten and D0's
tracking capabilities will be employed in jet energy reconstruction
and flavor identification.