Session #2: Title: Hard Diffraction at DZero Abstract: Using the DZero detector, we study events produced in proton- antiproton collisions that contain large forward regions with very little energy deposition (`rapidity gaps') and concurrent jet production, at center-of-mass energies 630 and 1800 GeV. In addition, we measure properties for similar topologies, but with W or Z bosons produced instead of accompanying jets. The fractions of hard scattering events that have rapidity gaps are compared with predicitons from Monte Carlo models. The DZero calorimeter is also used to extract the fractional momentum loss of the scattered protons for hard-diffractive candidate events. Session #3: Title: Measurement of the Differential Production Cross Section of W Bosons as a function of Transverse Momentum at sqrt(s)= 1.8 TeV Abstract: We present a measurement of the transverse momentum distribution of W bosons produced in proton-antiproton collisions at sqrt(s)=1.8 TeV. The data were collected by the DZero experiment at the Fermilab Tevatron Collider during the 1994-1995 run, and correspond to 85.0 pb**-1. Based on a combined perturbative QCD and soft-gluon resummation calculation, we find good agreement between our results and theoretical predictions over the measured range of transverse momentum (0-200 GeV/c). Session #3: Title: Measurement of the Angular Distribution of Electrons from W to e nu Decays in pbar p Collisions at sqrt(s)= 1.8 TeV Abstract: We present a preliminary measurement of the alpha_2 parameter in W to e nu decays using data collected by the DZero detector during the 1994-1995 Tevatron run. We compare our results with next-to-leading order perturbative QCD, which predicts an angular distribution of (1 +/- alpha_1 cos theta*+ alpha_2 cos^2theta*), where theta* is the angle between the charged lepton and the antiproton in the Collins-Soper frame. In the presence of QCD corrections, the parameters alpha_1 and alpha_2 become functions of p_T(W), the transverse momentum of the W. We present the first measurement of alpha_2 as a function of p_T(W). This measurement provides a test of next-to-leading order QCD corrections, which have a non-negligible impact on the measurement of the W mass.
Session #3: Title: Inclusive Jet Cross Section using the kT Algorithm Abstract: DZero has previously measured the central inclusive jet cross section at sqrt(s)=1.8 TeV using the fixed-cone algorithm. The kT jet algorithm, based on a successive combination of jets, has recently been implemented at DZero. A preliminary measurement of the inclusive jet cross section at sqrt(s)=1.8 TeV using the kT algorithm, will be presented. Session #3: Title: Probing BFKL Dynamics in the Dijet Cross Section at Large Abstract: Rapidity Intervals in pbar p Collisions at sqrt(s)=1800 and 630 GeV Inclusive dijet production for large pseudorapidity intervals (delta_eta) between the two jets has been suggested as a regime for observing BFKL dynamics. We have measured the dijet cross section for large delta_eta in pbar p collisions at sqrt(s)=1800 and 630 GeV using the DZero detector. The partonic cross section increases strongly with the size of delta_eta. The observed growth is even stronger than expected on the basis of BFKL resummation in the leading logarithmic approximation. The growth of the partonic cross section can be accommodated with an effective BFKL intercept of alpha_BFKL(20 GeV)=1.65+/-0.07. Session #3: Title: Rapidity Dependence of Inclusive Jet Cross Section in pbar p Collisions at sqrt(s)=1.8 TeV Abstract: We report on a new measurement of the rapidity dependence of the inclusive jet production cross section in pbar p collisions at sqrt(s)=1.8 TeV using 92 pb**-1 of data collected by the DZero detector at the Fermilab Tevatron collider. The differential cross section d^2sigma/dEt deta, is presented as a function of jet transverse energy (ET) in five pseudorapidity (eta) intervals, up to |eta|=3, thereby significantly extending previous CDF and DZero measurements beyond |eta|=0.7. The results are compared to next-to-leading order QCD predictions. The extended range of the measurement promises to provide greater discrimination among different parton distribution functions. Session #3: Title: The Ratio of Dimensionless Jet Cross Sections at sqrt(s)=630 GeV and 1800 GeV Abstract: The DZero collaboration has measured the inclusive jet cross section in pbar p collisions at sqrt(s)=630 GeV. The data for pseudorapidities less than 0.5 are combined with data previously collected at sqrt(s)=1800 GeV to form a dimensionless ratio with smaller uncertainties. Although next-to-leading order predictions exhibit only modest agreement with the 630 GeV cross section, agreement is more satisfactory with the ratio. In particular, for most parton distribution functions, the dependence on transverse momentum is acceptable, but the absolute value disagrees with data by 10 to 15%. Session #3: Title: Ratios of Multijet Cross Sections in pbar p Collisions at sqrt(s)=1.8 TeV Abstract: We report a study of the ratio of inclusive three-jet to two-jet production cross sections as a function of total transverse energy, in pbar p collisions at sqrt(s)=1.8 TeV, for data collected with the DZero detector during the 1992-1993 run of the Fermilab Tevatron Collider. The measurements are well described by next-to-leading order QCD calculations, and can be used to gauge the sensitivity of the calculation to renormalization scales used in modeling soft-jet emission. Session #3: Title: Subjet Multiplicities Based on a kT Jet Algorithm Abstract: Using the DZero detector, we measure the subjet multiplicity M in jets reconstructed with a successive-combination type of jet algorithm (kT). We select jets with 55/=1.91. Session #7: Title: Search for Single Top Quark Production at DZero Abstract: We present a search for electroweak production of single top quarks in the e+jets/mu and mu+jets/mu decay channels. The measurement uses ~90 pb**-1 of data from Run1 of the Fermilab Tevatron Collider collected with the DZero detector from 1992 to 1995. We set upper limits on cross sections for the s-channel process ppbar->tb+X and the t-channel process ppbar->tqb+X. Session #7: Title: A DZero Measurement of b Jet Production Abstract: Bottom quark production in hadronic collisions is studied with the DZero detector at the Fermilab Tevatron pbar p collider at sqrt(s)=1.8TeV. The production cross section for jets containing b-quarks (b-jets) is measured in the pseudo-rapidity region |eta|<1. The differential cross section as a function of jet transverse energy is obtained from a sample of muon-tagged jets. With focus on b-jets rather than open b-quarks, this new measurement affords less model dependence in comparing data with theory. Within experimental and theoretical uncertainties, the observed cross section is higher than, but compatible with, next-to-leading order QCD predictions. Session #7: Title: Spin Correlation in ttbar Production from ppbar Collisions at sqrt(s)=1.8 TeV Abstract: The DZero Collaboration has performed a study of spin correlation in ttbar production for the process ttbar->bW+ bbarW-, where the W bosons decay to enu or munu. A sample of six events was collected during an exposure of the DZero detector to an integrated luminosity of approximately 125 pb**-1 of sqrt(s)=1.8 TeV ppbar collisions. The standard model (SM) predicts that the short lifetime of the top quark ensures the transmission of any spin information at production to the ttbar decay products. The degree of spin correlation is characterized by a correlation coefficient K. We find that K>-0.25 at the 68% confidence level, in agreement with the SM prediction of K=0.88. Session #11: Title: Search for Large Extra Dimensions at DZero Abstract: We have searched for the effects of virtual Kaluza-Klein gravitons predicted in the Arkani-Hamed, Dimopulous, Dvali theory of large spatial extra dimensions. Analyzing angular and invariant mass distributions of photon and electron pairs in 127 pb**-1 of data, we found complete agreement with expectations from the Standard Model. There were no anomalous events with high mass and low scattering angle, characteristic of the virtual graviton exchange. We set lower limits on the compactification scale of large extra dimensions between 1.0 and 1.4 TeV for the number of extra dimensions between 2 and 7. These are the most restrictive limits to date on large extra dimensions. Session #11: Title: Search for R-parity Violation in Multilepton Final States in pbar p Collisions at sqrt(s)=1.8 TeV Abstract: The negative result of a search for associated gaugino pair production with a trilepton signature at DZero, is reinterpreted in the framework of minimal supergravity models with R-parity violation via leptonic Yukawa couplings. The search used 95 pb**-1 of integrated luminosity of pbar p collisions at sqrt(s)=1.8 TeV. Session #11 Title: Search for Charged Higgs Bosons in Decays of Pair-produced Top Quarks in DZero Abstract: We present a search for t->bH+ in ttbar candidate events at DZero based on two methods. The first seeks a decrease in expected signal, which would imply the presence of a non-SM decay of the top quark. This search involves the full data sample of ~110 pb**-1 of ppbar collisions at sqrt(s)=1.8 TeV, collected with the DZero detector between 1992 and 1995. The second method looks for charged Higgs decays to taus (and associated neutrinos), and is based on a 62 pb**-1 subset of the aformentioned data sample. Session #11 Title: Search for New Physics in emuX Data at the Tevatron using Sherlock: A Quasi-Model-Independent Search Strategy for New Physics Abstract: We present a quasi-model-independent search for the physics responsible for electroweak symmetry breaking. We define final states to be searched, and construct a rule that identifies a set of relevant variables for any particular final state. A new algorithm (`Sherlock') searches for regions of excess in those variables, and quantifies the significance of any excess found. After demonstrating the sensitivity of the method, we apply it to the semi-inclusive channel emuX collected in 108 pb**-1 of pbar p collisions at sqrt(s)=1.8 TeV at the DZero experiment during 1992-96 at the Fermilab Tevatron. Beyond ttbar and WW production, we find no evidence of new high p_T physics in this sample. Session #11 Title: A Search for Dilepton Signatures from Minimal Low-Energy Supergravity in ppbar Collisions at sqrt(s)=1.8 TeV Abstract: We report on a search for supersymmetry using the DZero detector. The 1994-1996 data sample of sqrt(s)=1.8 TeV ppbar collisions was analyzed for events containing two leptons (e or mu), two or more jets, and missing transverse energy. Assuming the minimal supergravity model, with A0=0 and mu<0, various thresholds were employed to optimize the search. No events were found beyond expectation from background. We set a lower limit at the 95% CL of 255 GeV for equal mass squarks and gluinos for tanbeta=2, and present exclusion contours in the (m0, m1/2) plane for tanbeta=2 and 6. Session #11 Title: Limits on Quark Compositeness from High Energy Jets in ppbar Collisions at 1.8 TeV Abstract: Events in ppbar collisions at sqrt(s)=1.8 TeV with total transverse energy exceeding 500 GeV are used to set limits on quark substructure. The data are consistent with next-to-leading order QCD calculations. We set a lower limit of 2.0 TeV at 95% confidence on the energy scale Lambda_LL for compositeness in quarks, assuming a model with a left-left isoscalar contact interaction term. The limits on Lambda_LL are found to be insensitive to the sign of the interferencce term in the Lagrangian.