Where is Top?

Possibilities are discussed for determining the top quark mass $m_{t}$ from observations on the decay processes for top-antitop pairs produced in antiproton-proton collisions, assuming that the $t \to b W^{+}$ decay channel is dominant and much faster than hadronization. The final states $t \bar{t} \to \bar{b} b \mu^\pm e^\mp$ provide the most striking signal, with little background, but they are rare ( $\approx 2 / 81$ ). If all candidate events prove to be from $t \overset{ˉ}{t}$ , an estimate follows for $P (m_{t} ∣ r a t e)$ , the probability distribution for $m_{t}$ . The one reported configuration allows an independent estimate for $P (m_{t} ∣ μ^{\pm} e^{\mp} 2 j e t s)$ . These two distributions are compatible,yielding an estimate of about 122 GeV. Decay events 1 energetic lepton($l$) + 4jets'' should appear twelve times as often as $\mu^\pm e^\mp ,2jets $^{''} e v e n t s a n d c a n b e a n a l y s e d t o g i v e e s t i m a t e s f o r$ P(m_t|l, 4jets)$. There may be background from non-top 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 this factor 12. Identification of either or both of the $(b \overset{ˉ}{b})$ jets would be a great step forward. We advocate an energetic approach to the analysis of individual events on an event by event basis, with the hope of finding a subgroup of events with a common mass estimate.