Top Quark Physics at the Tevatron

Abstract

The discovery of the top quark in 1995, by the CDF and DØ collaborations at the Fermilab Tevatron, marked the dawn of a new era in particle physics. Since then, enormous efforts have been made to study the properties of this remarkable particle, especially its mass and production cross section. In this article, we review the status of top quark physics as studied by the two collaborations using the pp collider data at √ s = 1.8 TeV. The combined measurement of the top quark mass, m t = 173.8±5.0 GeV/c 2 , makes it known to a fractional precision better than any other quark mass. The production cross sections are measured as σ tt = 7.6 +1.8 −1.5 pb by CDF and σ tt = 5.5± 1.8 pb by DØ. Further investigations of tt decays and future prospects are briefly discussed.

Direct measurement of the top quark charge at hadron colliders

“…Therefore, the bounds which can be achieved at the Tevatron from analyzing the photon p T distribution in the phase space region defined by thettγ selection cuts are significantly weaker than those which can be obtained from either the p T (γ) or the ∆R(γ, b sf ) distribution in the combined radiative top decay regions. 3 At the LHC, most of thettγ cross section originates from gluon fusion, and the limits from the photon p T distribution forttγ selection cuts are similar to those which can be achieved in the phase space regions where radiative top decays dominate.…”

Measurement of the top - anti-top Production Cross Section at √s = 1.96-TeV in the e + jets Final State of proton anti-proton Collisions at the Tevatron

“…A significant fraction of the energy in a proton and antiproton is carried by a valance quark, and the qq channel therefore dominates the tt production mecha-nism. At the Tevatron, the relative contributions of these qq → tt and gg → tt are about 85% and 15%, respectively [9].…”

“…Because tt events correspond to the decay of heavy objects, whereas the jets from W+jet and multijet events contain much initial and final-state radiation [9], A is a good parameter for discrimination. Another topological variable is the Sphericity (S) of the event, defined as : 18) where λ 3 is the largest eigenvalue and λ 2 is the next largest eigenvalue of the momentum tensor in Eqs.…”

Advanced analysis methods in high energy physics

“…Two multivariate methods, (1) a modified loglikelihood technique (LB method) and (2) a feed forward neural network (NN method), were used to compute a signal probability ( ) [11].…”