Search for the top quark at D0 using multivariate methods Page: 7 of 14
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Layer 0 Layer 1 Layer 2
Input Layer Hidden Layer Output Layer
xk h O
FIG. 1. A feed-forward neural network with one hidden layer.
have examined the signal to background ratio with respect to WW -> e and
Z -> rr -> e (the dominant backgrounds).
We have used the PDE and neural network methods to analyze e+jets
data corresponding to an integrated luminosity of 47.9+5.7 pb-1. The domi-
nant background to the it -* e+jets channel is from the QCD production of
W+multi-jets where the signature is the same as that of the signal, viz. a
high PT electron, high $T, arising from the leptonic decay of the W boson,
and several jets. In addition, we have background from QCD multi-jet events
where one of the jets is mis-identified as an electron and the event also has a
high $r from mis-measurements as well as neutrinos from any heavy flavor
decays. We refer to this background as QCD fakes. The two backgrounds in
our data prior to the multivariate analyses are estimated directly from data.
The QCD fake background is estimated by the joint probability of multi-jet
events having $T larger than the cut applied and a jet being mis-identified
as an electron. The W+jets background is estimated using Berends' scaling
(14). The inclusive jet multiplicity data (after subtracting the QCD fakes
background) is fitted for this "jet-scaling" allowing for contribution from top
quark events. These background numbers are multiplied by the fraction of
events surviving the multivariate cuts to get the final background estimates.
H-matrix Analysis of e Data
We have chosen the following feature vector z=(ET, PT, ET' ,Eet2, ga1,
Hr, Meu, Aeu) to build the signal and background H-matrices, where $ca1
is the $r in the calorimeter, Meu is the invariant mass of the two leptons
and A4eu is the azimuthal angle between the two leptons. We have built
the signal H-matrix HroP using 180 GeV tt ISAJET Monte Carlo events
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Bhat, P.C. Search for the top quark at D0 using multivariate methods, article, July 1, 1995; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc621656/m1/7/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.