Measurement of the t anti-t production cross section in p anti-p collisions at s**(1/2) = 1.96 = TeV using kinematic characteristics of lepton + jets events Page: 4 of 7
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quark. The top quark pair production cross section
oJi was measured by the CDF  and DO  collabo-
rations at a center-of-mass energy of 1.8 TeV. Recent
measurements  of oUt at i = 1.96 TeV have focused
on the selection of candidates via the reconstruction of
displaced vertices signaling the presence of b quarks in
the final state. These measurements assume that the
branching ratio of the top quark B(t -> Wb) 1,
thus making an implicit use of the SM prediction that
Vt1 =0.9990 0.9992 (at 90% C.L.) . This prediction
is based on the requirements that there are three fermion
families and the CKM matrix is unitary. If these assump-
tions are relaxed, IVtbI is essentially unconstrained, which
allows for large deviations of B (t -> Wb) from unity .
Such deviations would be an indication of physics beyond
the SM. Our analysis exploits only the kinematic prop-
erties of the events to separate signal from background,
with no assumptions about the multiplicity of final-state
b quarks, thus providing a less model-dependent deter-
mination of the top quark production cross section.
In this Letter, we report a new measurement of ot
using data collected with the DO detector from August
2002 through March 2004 at the Fermilab Tevatron pp
collider at Vs 1.96 TeV. The decay channel used in
this analysis is tt -> W+W--q, with the subsequent de-
cay of one W boson into two quarks, and the other W
boson into a charged lepton and a neutrino. We re-
fer to this decay mode of tt events as the lepton+jets
(f+jets) channel. These events are characterized by the
presence of one high-PT isolated electron (e+jets chan-
nel) or muon (p+jets channel), large transverse energy
imbalance due to the undetected neutrino (KT), and at
least four hadronic jets.
The three main subsystems of the DO Run II de-
tector  used in this analysis are the central tracking
system, the liquid-argon/uranium calorimeters, and the
muon spectrometer. The central tracking system is lo-
cated within a 2 Tesla superconducting solenoidal mag-
net, and consists of a silicon microstrip tracker (SMT)
and a central fiber tracker (CFT) that provide tracking
and vertexing in the pseudorapidity  range lyj < 3.0.
The primary interaction vertex of the events was required
to be within 60 cm of the center of the detector along the
direction of the beam. Electrons and jets were detected
in hermetic calorimeters [8, 9] with transverse granularity
An x A = 0.1 x 0.1, where 0 is the azimuthal angle. The
third layer of the electromagnetic (EM) calorimeter, in
which the maximum energy deposition of EM showers is
expected, has a finer granularity An x A = 0.05 x 0.05.
The calorimeters consist of a central section (CC) cover-
ing the region Iyj < 1.1, and two end calorimeters (EC)
extending coverage to 4nj , 4.2. Muons were detected
as tracks reconstructed from hits recorded in three layers
of tracking detectors and two layers of scintillators ,
both located outside the calorimeter. A 1.8 Tesla iron
toroidal magnet is located outside the innermost layer
of the muon detector. The luminosity was calculated by
measuring the rate for pp inelastic collisions using two
hodoscopes of scintillation counters mounted close to the
beam pipe on the front surfaces of the EC calorimeters.
Jets were defined using a cone algorithm  with
radius AR (Ay)2 + (Ap)2= 0.5. To improve
calorimeter performance we use an algorithm that su-
presses cells with negative energy as well as cells with
energies significantly below the average electronics noise
(unless they neighbor a cell of high positive energy).
Identified jets were required to be confirmed by the in-
dependent trigger readout.
In the e+jets channel, we accepted electrons with
ynj < 1.1 and jets with rapidity yJ < 2.5 . At the
trigger level, we required a single electron with trans-
verse momentum (PT) greater than 15 GeV, and a jet
with PT > 15 GeV (20 GeV) for the first (second) half of
the data. The total integrated luminosity for this sam-
ple is 226 15 pb-1. The offline electron identification
requirements consisted of the following: i) the electron
had to deposit at least 90% of its energy in the electro-
magnetic calorimeter within a cone of radius AR 0.2
relative to the shower axis; ii) the electron had to be
isolated, i.e., the ratio of the energy in the hollow cone
0.2 < AR < 0.4 to the reconstructed electron energy
could not exceed 15%; iii) the transverse and longitudi-
nal shower shapes had to be consistent with those ex-
pected for an electron (based on a detailed Monte Carlo
simulation); and iv) a good spatial match had to exist be-
tween a reconstructed track in the tracking system and
the shower position in the calorimeter. Electrons satis-
fying the above requirements are referred to as "loose."
For a "tight" electron, we required in addition, that a dis-
criminant formed by combining the above variables with
the information about impact parameter of the matched
track relative to the primary interaction vertex, and the
number and PT of other tracks around the electron can-
didate, be consistent with the expectations for a high-PT
In the p+jets channel, we accepted muons with
4nj < 2.0 and jets with yJ < 2.5. At the trigger level,
we required a single muon detected outside the toroidal
magnet (which corresponds to an effective minimum mo-
mentum of , 3 GeV), and a jet with PT > 20 GeV
(25 GeV) for the first (second) half of the data. The
total integrated luminosity for this sample is 229 15
pb--1. The offline muon identification requirements con-
sisted of the following: i) a muon track segment on the
inside of the toroid had to be matched to a muon track
segment on the outside of the toroid; ii) the timing of the
muon, based on information from associated scintillator
hits, had to be inconsistent with that of a cosmic ray; iii)
a track reconstructed in the tracking system and point-
ing to the event vertex was required to be matched to
the muon candidate found in the muon system; iv) the
reconstructed muon was required to be separated from
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Abazov, V. M.; Abbott, B.; Abolins, M.; Acharya, B. S.; Adams, M.; Adams, T. et al. Measurement of the t anti-t production cross section in p anti-p collisions at s**(1/2) = 1.96 = TeV using kinematic characteristics of lepton + jets events, article, April 1, 2005; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc1415679/m1/4/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.