Evidence of anomalous WW and WZ production was sought in pbar{p} collisions at a center-of-mass energy of sqrt(s) = 1.8 TeV. The final states $WW (WZ) to mu-nu-jet-jet + X, WZ to mu-nu-e-e + X and WZ to e-nu-e-e + X were studied using a data sample corresponding to an integrated luminosity of approximately 90 pb-1. No evidence of anomalous diboson production was found. Limits were set on anomalous WWgamma and WWZ couplings and were combined with our previous results. The combined 95% confidence level anomalous coupling limits for Lambda=2 TeV are -0.25 LE Delta-kappa LE 0.39 (lambda=0) and -0.18 LE lambda LE 0.19 (Delta \kappa = 0), assuming the WWgamma couplings are equal to the WWZ couplings.

We have searched for second generation leptoquark (LQ) pairs in the \mu\mu+jets channel using 94+-5 pb^{-1} of pbar-p 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 \mu\nu+jets and \nu\nu+jets channels to obtain 95% confidence level (C.L.) upper limits on the LQ pair production cross section as a function of mass and $beta, the branching fraction of a LQ decay into a charged lepton and a quark. Lower limits of 200(180) GeV/c^2 for \beta=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 \beta.

Bottom quark production in pbar-p collisions at sqrt(s)=1.8 TeV is studied with 5 inverse picobarns of data collected in 1995 by the DO detector at the Fermilab Tevatron Collider. The differential production cross section for b jets in the central rapidity region (|y(b)| < 1) as a function of jet transverse energy is extracted from a muon-tagged jet sample. Within experimental and theoretical uncertainties, DO results are found to be higher than, but compatible with, next-to-leading-order QCD predictions.

We describe a search for the pair production of first-generation scalar and vector leptoquarks in the eejj and enujj channels by the D0 Collaboration. The data are from the 1992--1996 ppbar run at sqrt{s} = 1.8 TeV at the Fermilab Tevatron collider. We find no evidence for leptoquark production; in addition, no kinematically interesting events are observed using relaxed selection criteria. The results from the eejj and enujj channels are combined with those from a previous D0 analysis of the nunujj channel to obtain 95% confidence level (C.L.) upper limits on the leptoquark pair-production cross section as a function of mass and of beta, the branching fraction to a charged lepton. These limits are compared to next-to-leading-order theory to set 95% C.L. lower limits on the mass of a first-generation scalar leptoquark of 225, 204, and 79 GeV/c^2 for beta=1, 1/2, and 0, respectively. For vector leptoquarks with gauge (Yang-Mills) couplings, 95% C.L. lower limits of 345, 337, and 206 GeV/c^2 are set on the mass for beta=1, 1/2, and 0, respectively. Mass limits for vector leptoquarks are also set for anomalous vector couplings.

Results are presented on the exclusive production of four-prong final states in photon-photon collisions from the TPC/Two-Gamma detector at the SLAC e+e− storage ring PEP. Measurement of dE/dx and momentum in the time-projection chamber (TPC) provides identification of the final states 2π+2π−, K+K−π+π−, and 2K+2K−. For two quasireal incident photons, both the 2π+2π− and K+K−π+π− cross sections show a steep rise from threshold to a peak value, followed by a decrease at higher mass. Cross sections for the production of the final states ρ0ρ0, ρ0π+π−, and φπ+π− are presented, together with upper limits for φρ0, φφ, and K*0K¯ *0. The ρ0ρ0 contribution dominates the four-pion cross section at low masses, but falls to nearly zero above 2 GeV. Such behavior is inconsistent with expectations from vector dominance but can be accommodated by four-quark resonance models or by t-channel factorization. Angular distributions for the part of the data dominated by ρ0ρ0 final states are consistent with the production of JP=2+ or 0+ resonances but also with isotropic (nonresonant) production. When one of the virtual photons has mass (mγ2=-Q2≠0), the four-pion cross section is still dominated by ρ0ρ0 at low final-state masses Wγγ and by 2π+2π− at higher mass. Further, the dependence of the cross section on Q2 becomes increasingly flat as Wγγ increases.

We report a measurement of the reaction γγ→K+K−π+π− in both tagged and untagged events at PEP. The cross section rises with invariant γγ mass to about 15 nb at 2 GeV and falls slowly at higher masses. We find clear evidence for the processes γγ→φπ+π− and γγ→K*0(892)Kπ. Upper limits (95% C.L.) of 1.5 and 5.7 nb in the mass range from 1.7 to 3.7 GeV are obtained for φρ0 and K*0K¯*0 production, respectively.

We report cross sections for the process γγ→pp¯ at center-of-mass energies W from 2.0 to 2.8 GeV. These results have been extracted from measurements of e+e−→e+e−pp¯ at an overall center-of-mass energy of 29 GeV, using the TPC/Two-Gamma facility at the SLAC storage ring PEP. Cross sections for the untagged mode [both photons nearly real] are shown to lie well above QCD predictions. Results are also presented for the single-tagged mode [one photon in the range 0.16<Q2<1.6 (GeV/c)2].

We present a measurement of the total cross section for γγ→hadrons, with one photon quasireal and the other a spacelike photon of mass squared −Q2. Results are presented as a function of Q2 and the γγ center-of-mass energy W, with the Q2 range extending from 0.2 to 60 GeV2, and W in the range from 2 to 10 GeV. The data were taken with the TPC/Two-Gamma facility at the SLAC e+e− storage ring PEP, which was operated at a beam energy of 14.5 GeV. The cross section exhibits a gentle falloff with increasing W. Its Q2 dependence is shown to be well described by an incoherent sum of vector-meson and pointlike scattering over most of the observed W range. Agreement at high Q2 is improved if a minimum-pT cutoff (motivated by QCD) is imposed on the pointlike contribution.

We report measurements of the two-photon processes e+e−→e+e−π+π− and e+e−→e+e−K+K−, at an e+e− center-of-mass energy of 29 GeV. In the π+π− data a high-statistics analysis of the f(1270) results in a γγ width Γ(γγ→f)=3.2±0.4 keV. The π+π− continuum below the f mass is well described by a QED Born approximation, whereas above the f mass it is consistent with a QCD-model calculation if a large contribution from the f is assumed. For the K+K− data we find agreement of the high-mass continuum with the QCD prediction; limits on f′(1520) and θ(1720) formation are presented.

This paper presents the first measurement of the inclusive J/Psi production cross section in the forward pseudorapidity region 2.5<|eta|<3.7 in ppbar collisions at sqrt(s)=1.8TeV. The results are based on 9.8 pb-1 of data collected using the D0 detector at the Fermilab Tevatron Collider. The inclusive J/Psi cross section for transverse momenta between 1 and 16 GeV/c is compared with theoretical models of charmonium production.