[en] We have carried out a direct search in bulk matter for free fractional electric charge elementary particles using the largest mass single sample ever studied--about 17.4 mg of silicone oil. The search used an improved and highly automated Millikan oil drop technique. No evidence for fractional charge particles was found. The concentration of particles with fractional charge more than 0.16e (e being the magnitude of the electron charge) from the nearest integer charge is less than 4.71x10^-22 particles per nucleon with 95% confidence. (c) 2000 The American Physical Society

[en] A new analysis of the hadronic peak cross section at LEP 1 implies a small amount of missing invisible width in Z decays, while the effective weak charge in atomic parity violation has been determined recently to 0.6% accuracy, indicating a significantly negative S parameter. As a consequence, the data are described well if the presence of an extra Z^' boson, such as predicted in grand unified theories, is assumed. Moreover, the data are now rich enough to study an arbitrary extra Z^' boson and to determine its couplings in a model independent way. An excellent fit to the data is obtained in this case, suggestive of a family nonuniversal Z^' similar to those predicted in a class of superstring theories. (c) 2000 The American Physical Society

[en] The E815 (NuTeV) neutrino experiment has performed a search for a 33.9 MeV/c² weakly interacting neutral particle produced in pion decay. Such a particle may be responsible for an anomaly in the timing distribution of neutrino interactions in the KARMEN experiment. E815 has searched for this particle's decays in an instrumented decay region; no evidence for this particle was found. The search is sensitive to pion branching ratios as low as 10^-13 . (c) 2000 The American Physical Society

[en] We have searched for second-generation leptoquark (LQ) pairs in the μμ+jets channel using 94±5 pb^-1 of pp collider data collected by the D0 experiment at the Fermilab Tevatron during 1993-1996. No evidence for a signal is observed. These results are combined with those from the μν+jets and νν+jets channels to obtain 95% confidence level (C.L.) upper limits on the LQ pair production cross section as a function of mass and β , the branching fraction of a LQ decay into a charged lepton and a quark. Lower limits of 200(180) GeV/c² for β=1((1/2)) are set at the 95% C.L. on the mass of scalar LQ. Mass limits are also set on vector leptoquarks as a function of β . (c) 2000 The American Physical Society

[en] We use 106 pb^-1 of data collected with the Collider Detector at Fermilab to search for narrow-width, vector particles decaying to a top and an antitop quark. Model independent upper limits on the cross section for narrow, vector resonances decaying to tt are presented. At the 95% confidence level, we exclude the existence of a leptophobic Z^' boson in a model of top-color-assisted technicolor with mass M_Z^'<480 GeV/c² for natural width Γ=0.012M_Z^' , and M_Z^'<780 GeV/c² for Γ=0.04M_Z^' . (c) 2000 The American Physical Society

[en] We present results of a search for a new form of hadronic matter, a six-quark, dibaryon state called the H⁰ , a state predicted to exist in several theoretical models. Analyzing data collected by experiment E799-II at Fermilab, we searched for the decay H⁰→Λpπ^- and found no candidate events. We place an upper limit on [B(H⁰→Λpπ^- )dσ_H/dΩ]/( dσ_Ξ/dΩ) and, in the context of published models, exclude the region of lightly bound mass states just below the ΛΛ mass threshold, 2.194< M_H<2.231 GeV /c² , with lifetimes from ∼5x10^-10 sec to ∼1x10^-3 sec . (c) 2000 The American Physical Society

[en] The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data, accounting for the neutron background, give limits on the spin-independent WIMP-nucleon elastic-scattering cross section that exclude unexplored parameter space above 10 GeV/c² WIMP mass and, at >75% C.L., the entire 3σ allowed region for the WIMP signal reported by the DAMA experiment. (c) 2000 The American Physical Society

[en] We report the results of a search for second and third generation leptoquarks using 88 pb^-1 of data recorded by the Collider Detector at Fermilab. Color triplet technipions, which play the role of scalar leptoquarks, are investigated due to their potential production in decays of strongly coupled color octet technirhos. Events with a signature of two heavy flavor jets and missing energy may indicate the decay of a second (third) generation leptoquark to a charm (bottom) quark and a neutrino. As the data are found to be consistent with standard model expectations, mass limits are determined. (c) 2000 The American Physical Society

[en] Decays of superheavy relic particles may produce extremely energetic neutrinos. Their annihilations on the relic neutrinos can be the origin of the cosmic rays with energies beyond the Greisen-Zatsepin-Kuzmin cutoff. The redshift acts as a cosmological filter selecting the sources at some particular value z_e±δz , for which the present neutrino energy is close to the Z pole of the annihilation cross section. We predict no directional correlation of the ultrahigh-energy cosmic rays with the galactic halo. At the same time, there can be some directional correlations in the data, reflecting the distribution of matter at redshift z=z_e±δz . Both of these features are manifest in the existing data. Our scenario is consistent with the neutrino mass reported by super-Kamiokande and requires no lepton asymmetry or clustering of the background neutrinos. (c) 2000 The American Physical Society

[en] Using data corresponding to an integrated luminosity of 79 pb^-1 , D0 has searched for events containing multiple jets and large missing transverse energy in pp collisions at √(s)=1.8 TeV at the Fermilab Tevatron collider. Observing no significant excess beyond what is expected from the standard model, we set limits on the masses of squarks and gluinos and on the model parameters m₀ and m_1/2 , in the framework of the minimal low-energy supergravity models of supersymmetry. For tan β=2 and A₀=0 , with μ<0 , we exclude all models with m_q(tildesign)<250 GeV/c² . For models with equal squark and gluino masses, we exclude m<260 GeV/c² . (c) 1999 The American Physical Society