Search for new heavy quarks at the CERN proton-antiproton collider

Abstract

We report on a search for new heavy quarks using data collected by the UA1 experiment during 1983, 1984 and 1985 at the CERN proton-antiproton collider, corresponding to an integrated luminosity of approximately 700 nb⁻¹. Studying events with a muon or an isolated electron, accompanied by one or more jets, we find good agreement between our data and Monte Carlo predictions for the production of charm and beauty, without the need for a new quark. A top quark model, involving the decayW→t $\bar b$ and directt $\bar t$ production via the strong interaction, is used to determine our detection efficiency for top. This allows us to place an upper limit on the cross section for producing top quarks as a function of the top quark mass. Our analysis is not sensitive to theW→t $\bar b$ process alone. By comparing our limit with a calculation of thet $\bar t$ cross section, added to theW→t $\bar b$ cross section derived from our own measurements ofW →lv, we are able to place a lower limit on the mass of the top quark. From the lowest order (α ² _s ) calculation, using the choice of structure functions andQ ² scale that give the lowest cross section, we find:

$$m_{top} > 44GeV/c^2 \left( {95\% c.l.} \right).$$

Including an estimate of the next higher order (α ² _s ) and calculating the cross section with the EUROJET QCD Monte Carlo program using a less extreme choice for the structure functions andQ ² scale gives:

$$m_{top} > 56GeV/c^2 \left( {95\% c.l.} \right).$$

A search has also been made for a fourth generation, charge 1/3 quark (b'). Assuming that theb' mass is smaller than that of the top quark and that it can-not be produced inW decays, the mass limits, using the above procedures, are respectivelym _b' >32 GeV/c² andm _b' >44 GeV/c², both at 95% confidence level.