WHERE IS TOP?

Abstract

Possibilities are discussed for determining the top-quark mass mt from observations on the decay processes for top-antitop pairs produced in antiproton-proton collisions at Tevatron energies, assuming that the t→bW+ decay channel is dominant and much faster than hadronization. The final states [Formula: see text] provide the most striking signal, with little background, but they are rare (≈2/81). If all three candidate events prove to be from [Formula: see text], an estimate follows for P(mt| rate ), the probability distribution for mt. The one reported configuration allows an independent estimate for P (mt|μ± e∓ 2 jets ). These two distributions are compatible and can be combined to give an mt estimate of about 122 GeV. Decay events “1 energetic lepton(ℓ)+4 jets” should appear 12 times as often as “ μ± e∓ 2 jets ” events and can be analyzed to give estimates for P(mt|ℓ 4 jets ); this is illustrated for a fictitious event. There may be background from nontop events but suitable cuts on the data and our analysis procedure together reduce this to a low level. The rate observed for these events does not appear to be as large as the factor 12. Identification of either or both of the [Formula: see text] jets would be a great step forward, separating out the “[Formula: see text]” and “[Formula: see text]” events of importance with little background. We advocate an energetic approach to the analysis of individual events [whether 2, 1 or no (b or [Formula: see text]) jets identified] on an event-by-event basis, with the hope of finding a subgroup of events with a common mass estimate.