a Search for Third Generation Leptoquarks in Proton - Collisions at 1.8 Tev.

This thesis presents the results of a search third generation leptoquarks in 72 pb^{-1 } of pp collisions at sqrt{s } = 1.8 TeV. The data were collected at the Collider Detector at Fermilab (CDF) during the 1992-1995 Collider runs. Leptoquarks (scLQ) are spin-0 or spin-1 particles which couple both to a quark and a lepton. Third generation leptoquarks are assumed to be produced in pairs and each to decay to a tau lepton + b quark with a branching ratio beta. The signature for leptoquarks investigated here is two taus plus two jets. Events with tau pairs are identified by the presence of a collimated high momentum jet, a high momentum electron or muon, and missing energy close to the lepton and transverse to the beam. At least two jets are required to reduce the background from QCD production of Z^circ bosons with associated jets and Z^circ to tau^+tau^-. No evidence for a leptoquark signal is observed. Upper limits on sigma(p| p to scLQLQ) times beta^2 are obtained as a function of M_{LQ } for scalar and vector lepto-quarks. Using theoretical predictions for leptoquark pair production cross sections, scalar leptoquarks are excluded for M _{LQ} < 94 GeV/c^2, non-gauge vector leptoquarks are excluded for M_{LQ} < 165 GeV/c ^2, and gauge vector leptoquarks are excluded for M_{LQ} < 220 GeV/ c^2 for beta = 100 % at the 95% C.L. Non-gauge vector leptoquarks are excluded for M_{LQ} < 120 GeV/c^2, and gauge vector leptoquarks are excluded for M_{LQ } < 178 GeV/c^2 for beta = 50% at the 95% C.L. The data do not constrain scalar leptoquarks for beta = 50% at the 95% C.L.