Recent D-Zero results on the top quark Page: 3 of 8
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Recent DO Results on the Top Quark
Qizhong Lia
aFermi National Accelerator Laboratory,
P.O.Box 500, Batavia, IL 60510, U.S.A.
(for the DO collaboration)
Recent results on top quark physics with the DO experiment in pp collisions at ,fs = 1.8 TeV for an integrated
luminosity of 125 pb-- are reported. The direct measurement of the top quark mass uses single lepton events,
giving the result mt., = 173.3 + 5.6(stat.) + 6.2(syst.) GeV/c2. The measurement of the tt production cross
section includes analyses from 8 top decay channels: dilepton (ti -> eg, ee, and ), electron and neutrino (ti
-> ev), and single leptons (ti -> e + jets and ti -> g + jets) with and without b tagging. We measure the ti
production cross section to be 5.5 + 1.8 pb at mtop = 173.3 GeV/c2.1. Introduction
Since the top quark was discovered [1,2] by the
DO and CDF experiments at the Fermilab Teva-
tron collider in 1995, much of the current effort
has been focused on measuring the it production
cross section and the top quark mass.
In the Tevatron pp collider at a center of mass
energy of 1.8 TeV top quarks are predominantly
produced in pairs through qq annihilation (~
90%) or gluon fusion (~ 10%). According to the
standard model a top quark decays almost 100%
of the time into a W and a b quark. Each W
boson decays either into a charged lepton and a
neutrino or into a pair of quarks. Our analysis
channels are classified on the basis of the W boson
decay. The cleanest channel is dilepton channel,
it -> 2 leptons + 2 neutrinos + 2 jets, where both
W bosons decay into leptons. There is a branch-
ing ratio of for it decays into e , ee, and p
channels. The single lepton decay channel, where
one W boson decays leptonically and other W bo-
son decays hadronically, has a branching ratio of
81, but it has a sizable background from W+jets
production.
This paper reports the recent DO results on
the it production cross section using the dilep-
ton and single lepton decay channels, and on the
direct measurement of the top quark mass using
the single lepton channel.
The results reported in this paper use the entiredata sample, which has an integrated luminosity
of about 125 pb-1, and which was collected dur-
ing the 1992-1996 collider run. Since our report
on the discovery of the top quark [1], our data
sample has doubled. DO has optimized the anal-
ysis to maximize the expected precision of the
tt production cross section measurement and im-
proved the techniques on the measurement of the
top quark mass.
2. Measurement of it Production Cross
Section
The triggers and the particle identification al-
gorithms used in these analyses are described in
detail in DO publications [1,3].
2.1. Dilepton Decay Channels
The signature of it events in the dilepton decay
channels is two high pT isolated leptons, two or
more jets and large missing ET ($T ) due to the
presence of the two neutrinos.
The offline event selection requires that the iso-
lated electrons have ET > 20 GeV with 4qJ < 2.5
and that the isolated muons have pT > 15 GeV
with 4I < 1.7. At least two jets are required to
be reconstructed with a transverse energy above
20 GeV with 4qJ < 2.5. All jets are reconstructed
using a cone algorithm with radius 0.5 in q-4
space. The $T is required to be above 25 GeV
for the ce channel and to be above 20 GeV for
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Li, Q. Recent D-Zero results on the top quark, article, July 1, 1997; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc690419/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.