Observation of the Top Quark

TL;DR

The D0 collaboration reports on a search for the Standard Model top quark in p{bar p} collisions at {radical}s = 1.8 TeV at the Fermilab Tevatron, with an integrated luminosity of approximately 50 pb{sup {minus}1}.

Abstract

The DO collaboration reports on a search for the Standard Model top quark in pbar-p collisions at Sqrt(s)=1.8TeV at the Fermilab Tevatron, with an integrated luminosity of approximately 50pb-1. We have searched for t-tbar production in the dilepton and single-lepton decay channels, with and without tagging of b-quark jets. We observed 17 events with an expected background of 3.8+/-0.6 events. The probability for an upward fluctuation of the background to produce the observed signal is 2.0E-6 (equivalent to 4.6 standard deviations). The kinematic properties of the excess events are consistent with top quark decay. We conclude that we have observed the top quark and measure its mass to be 199^+19_21 (stat.)+/- 22 (syst.)GeV/c**2 and its production cross section to be 6.4 +/- 2.2 pb.

Figures (5)

• Figure 1: Shape of $H_T$ distributions expected for the principal backgrounds (dashed line) and 200 GeV/c$^2$ top quarks (solid line) for (a) $e\mu + \rm jets$ and (b) untagged single-lepton + jets.
• Figure 2: Observed $H_T$ distributions (points) compared to the distributions expected from background (line) for $\hbox{/}E_T > 25$ GeV/c and (a) $e~+ \ge 2$ jets and (b) $e~+ \ge 3$ jets.
• Figure 3: DØ measured $t\bar{t}$ production cross section (solid line with one standard deviation error band) as a function of assumed top quark mass. Also shown is the theoretical cross section curve (dashed line) laenen.
• Figure 4: Single-lepton + jets two-jet vs. three-jet invariant mass distribution for (a) background, (b) 200 GeV/c$^2$ top Monte Carlo ( isajet), and (c) data.
• Figure 5: Fitted mass distribution for candidate events (histogram) with the expected mass distribution for 199 GeV/c$^2$ top quark events (dotted curve), background (dashed curve), and the sum of top and background (solid curve) for (a) standard and (b) loose event selection.