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 $t \to bW^+$ 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 $t \bar{t}$, an estimate follows for $P(m_t|rate)$, the probability distribution for $m_t$. The one reported configuration allows an independent estimate for $P(m_t|\mu^\pm e^\mp \,2jets)$. 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 ``$\mu^\pm e^\mp \,2jets$'' events and can be analysed to give estimates for $P(m_t|l\, 4jets)$. 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 $(b \bar{b})$ 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.