Top Quark Production and Decay at the Tevatron Page: 4 of 10
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1 Overview of Top Quark Production
Since the observation of the top quark in 1995 by the CDF and DO collaborations,
the Tevatron experiments have moved rapidly into a program of detailed studies of the top
quark. In this paper I describe recent measurements of the top quark production cross
section[3, 4] by CDF and DO using a number of final state topologies. I also describe a
recent CDF measurement of BR(t -> Wb)/BR(t -> Wq), where q is any quark. Recent
measurements of the top quark mass are described in Ref. .
At the Tevatron energy of Vs/ = 1.8 TeV, most top quarks are produced in pairs via the
annihilation processes qq -> tt (90%) and gg -> tt (10%). Top quarks can also be produced
singly by electroweak processes such as W-gluon fusion. While no signal has been isolated
for the single-top process yet, it is included as a "background" when studying tt production.
For the remainder of this paper we consider only the pair production of top quarks.
In the Standard Model each top quark decays nearly 100% of the time into Wb. Each
W in turn can decay into a charged lepton plus neutrino, with a branching ratio of 1/9 to
each lepton family, or into a qq' pair ("jets"), with a branching ratio of 2/3. Top quark
candidate events are characterized by the decay modes of the two W's. Most analyses done
by the Tevatron experiments focus on final states containing at least one W decay to ev or
" Dilepton final states (5% of tt decays) contain two isolated, high-PT leptons (e+e-,
y+A--, or e [T), significant missing transverse energy (4T) from the undetected neu-
trinos, and two jets from b quarks.
" Lepton + jets final states (30% of ti decays) contain one isolated, high-PT electron
or muon, significant 4T, and typically three or more jets, two of which are from b's.
While this paper will emphasize these two final state topologies, top decays to all-hadronic
final states have been observed by CDF, and a handful of suggestive events have also
been observed in the r dilepton channel.
2 tt Production Cross Section
The top quark production cross section, otE, is of interest for several reasons. First, it is
a test of QCD calculations[8, 9, 10]. Second, departures from the theoretical expectation
could indicate new physics, such as production through a high-mass intermediate state or
decays to final states other than Wb. By measuring otE in as many channels as possible, we
hope to gain a consistent picture of top as a Standard Model object or to identify the places
where the theory may be in error. Finally, ota is an important "engineering number" for
estimating top yields in future experiments at the Tevatron and LHC. The tt production
cross section has been measured in the dilepton, lepton + jets, and all-hadronic final states
using the full Run I datasets with integrated luminosities of approximately 110 pb-1.
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Gerdes, D.W. Top Quark Production and Decay at the Tevatron, article, May 1, 1997; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc702138/m1/4/: accessed October 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.