Dear Collaborators, As many of heard last Friday, the are rumors that both Zeus and H1 see mass bumps which could be interpreted as a signal for a first generation leptoquark lead to a meeting of the CDF and D0 spokes, NP convenors and the lab management. There are further rumors that they may present their results on Tuesday, 21-Jan-97, i.e. now. Just in case that rumor is true, the lab directorate and public relations office have asked for a short summary of the searches for leptoquarks which have been performed at CDF and D0 to help them prepare for any possible questions from the press. The D0 and CDF exotic group convenors have prepared a draft summary which is attached below. Please read it and send your comments to us as soon as possible since they want to see it at 10AM today! Note that all the results listed have either been published or reported in conference proceedings. Also, note that while this summary is not intended as a press release, they will likely draw from it to prepare a plain-english version for release. We are keeping a Web page going with information and results. The URL is http://d0wop.fnal.gov/www_buffer/new_phenomena/lqhera/welcome.html This posting is also reachable from this page. - Sarah Eno(eno@umdhep.umd.edu) and John Hobbs(hobbs@fnal.gov) ============================ Leptoquarks are hypothetical particles which carry both lepton and color quantum numbers and which mediate transitions between leptons and quarks. Leptoquarks (LQ's) are not expected within the Standard Model of particle physics but appear in many theories for physics beyond the Standard Model which predict a fundamental symmetry between leptons and quarks. In these theories leptoquarks appear as either scalar or vector particles. Because of experimental bounds on rare processes, LQ's which could be produced at Fermilab must be associated with a given standard model "generation" -- a LQ can be electron type (LQ_e), muon type (LQ_mu), or tau type (LQ_tau), but not an admixture. This constrains the decay modes to be e.g., for electron type, LQ_e -> eq or LQ_e -> v_e q' in which q is a u or d quark. The fraction of LQ_e decays which occur via LQ->eq is an important parameter and is called beta. Using this definition, if all LQ_e decay via LQ_e->eq then beta=1.0, and if all LQ_e decay via LQ_e->nuq, then beta=0. A fifty-fifty mix of LQ_e->eq and LQ_e->nuq implies beta=0.5." The proton-antiproton collisions in Fermilab's Tevatron could produce leptoquarks pairs of any generation. The leptoquark production cross-section decreases with the leptoquark mass, limiting the sensitivity to high mass leptoquarks, as quantified by the results below. The CDF and D0 experiments at Fermilab have searched for each generation of leptoquark in their existing data but have found no evidence as yet. As a result, they have determined limits on the leptoquark production cross-section which can be converted to a limit on the leptoquark mass using theoretical calculations. Some uncertainty remains in these calculations which could affect the mass limits by roughly 10%. Also, these mass limits depend on the branching fraction beta which is defined above. The D0 experiment has published mass limits for electron and muon type scalar leptoquarks using the data collected between 1992 and 1993. They reported a lower limit of 133 GeV/c^2 for the electron-type LQ and 111 GeV/c^2 for the muon-type LQ if beta=1. The limits are reduced to 120 GeV/c^2 and 89 GeV/c^2 if beta=0.5. The D0 experiment also has a preliminary result including more recent data for the electron type. This extends the limit to 194 GeV/c^2 for beta=1 and 143 GeV/c^2 for beta=0.5. The CDF experiment has published mass limits for electron type scalar leptoquarks using data collected in 1988-1989. They report a lower limit of 113 GeV/c^2 for beta=1 and 80 GeV/c^2 for beta=0.5. For the muon-type scalar leptoquark, CDF has published limits based on their 1992-1993 data of 131 GeV/c^2 for beta=1 and 96 GeV/c^2 for beta=0.5. They also have a preliminary result including more recent data which extends that limit to 180 GeV/c^2 for beta=1 and 140 GeV/c^2 for beta=0.5. Very recently, the CDF experiment has submitted a publication of limits on the tau-type scalar leptoquark using their 1992-1995 data. They report a mass limit of 99 GeV/c^2 for beta=1. The mass limits above are for scalar leptoquarks. Recently, calculations for vector leptoquarks have become available, and the cross-section for vectors is about an order of magnitude higher than the cross-section for scalars. As a result, the cross-section limits from CDF and D0 can be translated into higher mass limits for the case of vector leptoquarks than for the scalars listed above. CDF and D0 are currently working to complete the analysis of their present data. They will continue their searches with the additional data expected in their next running period beginning in 1999. This will extend their sensitivity to even higher masses.