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Observation of the top quark

Description: The D{O} collaboration reports on a search for the Standard Model top quark in p{bar p} collisions at {radical}s = 1.8 TeV at the Fermilab Tevatron, with an integrated luminosity of approximately 50 pb{sup -1}. We have searched for t{bar t} production in the dilepton and single-lepton decay channels, with and without tagging of b quark jets. We observe 17 events with an expected background of 3.8 {+-} 0.6 events. The probability for an upward fluctuation of the background to produce the observed signal is 2 x 10{sup -6} (equivalent to 4.6 standard deviations). The kinematic properties of the excess events are consistent with top quark decay. We conclude that we have observed the top quark and measure its mass to be 199{sub -21}{sup +19} (stat.) {+-}22 (syst.) GeV/c{sup 2}1 and its production cross section to be 6.4 {+-} 2.2 pb. Other decay channels are under study such as the t{bar t} to all-jets channel which might yield additional information about the top quark.
Date: October 1, 1995
Creator: Bantly, J.
Partner: UNT Libraries Government Documents Department

Transverse energy distributions within jets in p{anti p} collisions at {radical}s = 1.8 TeV

Description: The distribution of the transverse energy in jets has been measured in p{anti p} collisions at {radical}s = 1.8 TeV using the D0 detector at Fermilab. This measurement of the jet shape is made as a function of jet transverse energy in both the central and forward rapidity regions. Jets are observed to narrow both with increasing transverse energy and with increasing rapidity. Next-to-leading order partonic QCD calculations are compared to the data. Although the calculations qualitatively describe the data, they are shown to be very dependent on renormalization scale, parton clustering algorithm and jet direction definition and fail to consistently describe the data in all regions.
Date: July 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Measurement of the {gamma} cross section at D0 using dimuons

Description: The D0 experiment has measured the {gamma} differential cross section in p{bar p} collisions at {radical}s = 1.8 TeV for {vert_bar}y{sup {gamma}}{vert_bar} < 0.7. We find the measured cross section to be a factor of five larger than the O({alpha}{sub s}{sup 3}) QCD prediction for p{sub T}{sup {gamma}} > 5 GeV/c.
Date: July 1995
Creator: Abachi, S.; Abbott, B. & Abolins, M.
Partner: UNT Libraries Government Documents Department

Searches for supersymmetry and Higgs particles with D-Zero

Description: We report on searches for the Supersymmetric and the neutral scalar particles with the D{null} detector at {radical}{ital s} = 1.8 TeV. The three searches that we report here are: (1) SUGRA motivated SUSY search, (2) search for Charginos and neutralinos, and (3) search for heavy neutral scalar particle produced in association with W bosons.
Date: November 1, 1996
Creator: Mondai, N.K.
Partner: UNT Libraries Government Documents Department

Search for squarks and gluinos in p{bar p} collisions at the D0 detector with the jets and missing energy signature

Description: A search for squarks and gluinos has been performed using the D{null} detector at {radical}s = 1.8 TeV Tevatron {ital p{anti p}} collider. Data from the 1992-1993 collider run corresponding to an integrated luminosity of 13.5 pb{sup -1} were examined via the missing {ital E{sub T}} plus jets signature with two separate analyses. No events above the Standard Model backgrounds were observed.
Date: September 1, 1996
Creator: The DO Collaboration
Partner: UNT Libraries Government Documents Department

SUGRA-GUT motivated SUSY search in the dielectron channel at D0

Description: In this paper we present a search for events consistent with the production and decay of supersymmetric particles in the Supergravity- GUT framework in the D{null} detector at Fermilab. We examine the 1994-95 Run 1B data for events containing two or more electrons, two or more jets, and a substantial missing transverse energy. This is complementary to the search in the canonical jets and missing transverse energy channel. We observe 2 events in 92.9 pb{sup -1} or the Run 1B data consistent with the estimated total background contribution of 3.0 {+-} 1.3 events from the Standard Model. The non- observation of excess events has been interpreted as an excluded region on the two-dimensional {ital m}{sub 0} - {ital m}{sub 1/2} plane.
Date: September 1, 1996
Creator: Collaboration, The D0
Partner: UNT Libraries Government Documents Department

Jet azimuthal decorrelation studies with the D-zero detector

Description: Experimental results on the measurement of the azimuthal decorrelation between jets with pseudorapidity separation up to five units are presented. The data were taken at the Fermi National Accelerator Laboratory during the 1992-1993 collider run with the D{null} detector using {ital p{anti p}} collisions at center-of-mass energy {radical}{ital s} = 1.8 TeV. These results are compared to next-to-leading order (NLO) QCD predictions and to two leading-log approximations (LLA) where the leading terms are resummed to all orders in {alpha}{sub s}. The final state jets as predicted by NLO QCD show less azimuthal decorrelation than the data. The parton showering LLA Monte Carlo HERWIG describes the data well; an analytical LLA calculation based on Balitsky-Faclin-Kuraev-Lipatov resummation predicts more decorrelation than is present in the data.
Date: October 1, 1996
Creator: Feher, S.
Partner: UNT Libraries Government Documents Department

Search for anomalous WW and WZ production at D0

Description: We present a preliminary result from a search for anomalous WW and WZ production in p{bar p} collisions at {radical}s = 1.8 TeV using p{bar p} {yields} e{nu}jj events observed during the 1992-1993 run of the Fermilab Tevatron collider. A fit to the p{sub T} spectrum of W(e{nu}) yields direct limits on the CP-conserving anomalous WW{gamma} and WWZ coupling parameters of -0.89 < {Delta}{kappa} < 1.07 ({lambda} = 0) and -0.66 < {lambda} < 0.67 ({Delta}{kappa} = 0) at the 95% confidence level, assuming that the WWZ coupling parameters are equal to the WW{gamma} coupling parameters, and a form factor scale {Lambda} = 1.5 TeV.
Date: July 1, 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

The inclusive jet cross section in {bar p}p collisions at {radical}s = 1.8 TeV

Description: We report on the preliminary measurement of the inclusive jet cross section for {vert_bar}{eta}{vert_bar} {le} 0.5 at {radical}s = 1.8 TeV. Two data sets with integrated luminosities of 91 pb{sup {minus}1} and 14 pb{sup {minus}1} were collected at the Fermilab Tevatron {ovr p}p Collider with the D0 detector. The inclusive jet cross sections are measured and reported as a function of transverse jet energy (35 GeV {le} E{sub T} {le} 470 GeV) are in excellent agreement with next-to-leading order QCD. 11 refs., 4 figs.
Date: July 1, 1996
Creator: Bertram, I.A.
Partner: UNT Libraries Government Documents Department

Tests of QCD in W and Z production at Tevatron

Description: We present measurements of the production cross sections times leptonic branching fractions and the transverse momentum distributions of W and Z bosons in p{bar p} collisions at {radical}s = 1.8 TeV using data collected with the DO detector at the Fermilab Tevatron p{bar p} collider. A preliminary measurement of the W charge asymmetry is also presented.
Date: August 1, 1995
Creator: Abachi, S. & Collaboration, The D0
Partner: UNT Libraries Government Documents Department

Rapidity gaps in jet events at D{O}

Description: Preliminary results from the D0 experiment on jet production with rapidity gaps in p{bar p} collisions are presented. A class of dijet events with a forward rapidity gap is observed at center-of-mass energies {radical}s = 1800 GeV and 630 GeV. The number of events with rapidity gaps at both center-of-mass energies is significantly greater than the expectation from multiplicity fluctuations and is consistent with a hard single diffractive process. A class of events with two forward gaps and central dijets is also observed at 1800 GeV. This topology is consistent with hard double pomeron exchange. We also present results on the observation of a class of events with low particle multiplicity between jets, attributable to the exchange of a strongly-interacting color-singlet.
Date: July 1, 1996
Creator: Brandt, A.G.
Partner: UNT Libraries Government Documents Department

Rapidity correlations between high p{sub T} intermediate vector bosons and jets in {bar p}p collisions at {radical}s = 1.8 TeV

Description: D{O} has used W {yields} e{nu} and Z {yields} e{sup +}e{sup -} events produced in association with a high p{sub T}, jet to examine the effects of strong radiative corrections. We have compared the primary jet pseudorapidity distribution, as a function of reconstructed W or Z boson rapidity to leading order (LO) and Next-to-Leading order (NLO) QCD Monte Carlo generators, as well as a model based on extended color dipoles. We find that the primary jet is more central than either LO or NLO expectations. None of the Monte Carlo programs does a good job of predicting the shape of the jet distributions as a function of intermediate vector bosons rapidity.
Date: July 1, 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

The dijet mass spectrum and angular distributions with the D0 detector

Description: We present preliminary results from an analysis of dijet data collected during the 1994-95 Tevatron Collider run with an integrated luminosity of 91 pb{sup -1}. Measurements of dijet mass spectra and dijet angular distributions in {anti p}p collisions at {radical}s- = 1.8 TeV are compared with next-to-leading order QCD theory.
Date: July 1, 1996
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

D{O} top quark mass analysis

Description: Based on (44-48 pb{sup -1}) of lepton + jets data, we review D0`s initial analysis of the top quark mass. The result, M{sub top} = 199 {+-} 19/21 (stat.) {+-} 22 (syst.) GeV/c{sup 2}, is insensitive to background normalization. The errors are based on ISAJET top Monte Carlo, with its more severe gluon radiation, and allow for ISAJET/HERWIG differences. Good progress is being made in reducing the systematic error. We present a new study based on two-dimensional distributions of reconstructed top quark vs. dijet mass. With 98.7% confidence we observe a peak in the top mass - dijet mass plane. The peak and its projections are similar both in shape and magnitude to expectations based on the decay sequence 1 {yields} bW, W {yields} jj.
Date: July 1, 1995
Creator: Strovink, M.
Partner: UNT Libraries Government Documents Department

Search for a fourth generation charge {minus}1/3 quark via flavor changing neutral currents

Description: There is some likelihood that a light (< m{sub t}) fourth generation charge -1/3 quark (b{prime}) would decay predominantly via loop induced flavor changing neutral currents. The charged current decay of b{prime} to charm would be highly Cabibbo suppressed due to the fact that it changes the generation number by two. The D0 experiment has searched for b{prime} pair production where one or both b{prime} quarks decays via b{prime} {r_arrow} b+{gamma}, giving signatures photon + three jets and two photons + two jets. WE don not see a significant excess of such events over background. In both modes, we set an upper limit on the cross section times branching ratio that is sufficient to rule out a standard sequential b{prime} decaying predominantly via FCNC in the mass range m{sub Z}/2 < m{sub b{prime}} < m{sub Z} + m{sub b}. For b{prime} masses larger than this, the dominant FCNC decay mode is expected to be b{prime} {r_arrow} b + Z. 14 refs., 13 figs., 5 tabs.
Date: July 1, 1996
Creator: Collaboration, The D0
Partner: UNT Libraries Government Documents Department

Search for fourth generation neutral heavy leptons

Description: A search for fourth generation neutral heavy leptons ({nu}{sub 4}) in W decays was carried out the D0 detector at the Fermilab Tevatron at {radical}{bar s} = 1.8 TeV. The {nu}{sub 4} is assumed to be produced via mixing with the first generation neutrino only. We looked for a three electron final state event topology. The data used in this analysis represent 12.2 pb{sup {minus}1} taken during the 1992--1993 run. No candidates were found. We set a preliminary limit beyond the LEP limit for the considered mixing case on the {vert_bar}U{sub e4}{vert_bar}{sup 2} {minus} m{sub {nu}4} plane.
Date: July 1, 1995
Creator: Abachi, S.; Abbott, B.; Abolins, M. & Collaboration, D0
Partner: UNT Libraries Government Documents Department

Search for light top squarks with the D{O} detector

Description: We present preliminary results of a search for pair produced top squarks, the supersymmetric partners to the top quark, under the assumption that the two-body decay {bar t}{sub 1} {yields} b{bar W}{sub 1} and three-body decay {bar t}{sub 1} {yields} bW{bar Z}{sub 1} are kinematically forbidden. This scenario is realized if {bar t}{sub 1} is considerably lighter than all other squarks as well as {bar W}{sub 1}, all {bar v}s, and the top quark. Such light top squarks will dominantly decay via {bar t}{sub 1} {yields} c{bar Z}{sub 1} yielding a signal of two acollinear jets with (E){sub T}. The data reported here were taken during the 1992-1993 run of the D0 detector at the Fermilab Tevatron p{bar p} collider operating at {radical}s = 1.8 TeV.
Date: July 1, 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

The b{bar b} production cross section and correlations in p{bar p} collisions at {radical}s = 1.8 TeV

Description: The authors present measurements of the b{bar b} production cross section and angular correlations between the b and {bar b}-quarks in p{bar p} collisions using the D0 detector at the Fermilab Tevatron operating at {radical}s = 1.8 TeV. The b-quark production cross section for {vert_bar}y{sup b}{vert_bar} < 1.0 and {rho}{sub {tau}}{sup b} > 8 GeV/c is extracted and found to be consistent with next-to-leading order QCD predictions. In addition, the angular correlations between the b and {bar b}-quarks are found to agree in shape with next-to-leading order QCD predictions.
Date: August 1, 1996
Creator: Gomez, B.; Hoeneisen, B. & Negret, J.P.
Partner: UNT Libraries Government Documents Department

Diphoton production in p{bar p} collisions at {radical}s = 1.8 TeV

Description: We present measurements of the inclusive {gamma}{gamma} cross section (as a function of invariant mass and photon {epsilon}{sub {tau}}), in p{bar p} collisions at {radical}s = 1.8 TeV, made using the D0 detector at the Fermilab Tevatron collider. The next is leading order (NLO) QCD prediction is found to be in good agreement with the data. The effects of invariant mass and diphoton balance cuts, which test the next-to-leading order contributions to the cross section, are investigated. We also compare the distribution of {kappa}{sub {tau}} between samples of diphotons and highly electromagnetic jets, and find that the NLO QCD prediction models the shape of the {gamma}{gamma} {kappa}{sub {tau}} distribution quite well.
Date: July 1, 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Inclusive muon and b quark production cross sections in p{bar p} collisions at {radical}s = 1.8 TeV

Description: We report on the measurement of inclusive muon and b quark production by the D0 collaboration in p{bar p} collisions at {radical}s = 1.8 TeV at the Fermilab Tevatron Collider. The results represent a refined analysis of the previously published 1992--93 data. We measure the muon cross section due to b quark decays over the kinematic range 4 < p{sub T}{sup {mu}} < 30 GeV/c and {vert_bar}y{sup {mu}}{vert_bar} < 0.8. The extracted b quark production cross section is consistent with next to leading order QCD predictions within theoretical and experimental errors. The improved inclusive b quark production cross section is 6.9 {plus_minus}0.1(stat) {plus_minus} 2.2(syst) {mu}b for p{sub T}{sup {mu}} > 6 GeV/c and {vert_bar}y{sup b}{vert_bar} < 1.0.
Date: July 1, 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Studies of topological distributions of the three- and four-jet events in {bar p}p collisions at {radical}s = 1800 GeV with the D0 detector

Description: The global topologies of three- and four-jet events produced in {bar p}p interactions are described. the three- and four-jet events are selected from data recorded by the D0 detector at the Tevatron Collider operating at a center-of-mass energy of {radical}s = 1800 GeV. the measured normalized distributions of various topological variables are compared with parton-level predictions of the tree- level QCD calculations. The parton-level QCD calculations are found to be in good agreement with the data. The studies also show that the topological distributions of the different subprocesses involving different numbers of quarks are very similar and reproduce the measured distributions well.
Date: July 1, 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Top physics at D0

Description: The D0 collaboration reports on the observation of the Standard Model top quark in p{anti p} collisions at {radical}s = 1.8 TeV at the Fermilab Tevatron. The authors have searched for t{anti t} production with an integrated luminosity of approximately 50 pb{sup {minus}1} in the dilepton and single-lepton decay channels, with and without tagging of b quark jets. They observe 17 events with an expected background of 3.8 {+-} 0.6 events. The probability for an upward fluctuation of the background to produce the observed signal is 2 {times} 10{sup {minus}6} (equivalent to 4.6 standard deviations). The kinematic properties of the excess events are consistent with top quark decay. They measure the top quark mass to be 199{sub {minus}21}{sup +19} (stat.) {sub {minus}21}{sup +14} (syst.) GeV/c{sup 2} and its production cross section to be 6.4 {+-} 2.2 pb. D0 also sees a hadronic W mass peak (W {yields} jj) in the t{bar t} data events. Preliminary results from multivariate analyses and from the t{bar t} data events. Preliminary results from multivariate analyses and from the t{bar t} {yields} all-jets channel are discussed. Preliminary determination of the top quark mass using dilepton events yields 145 {+-} 25 (stat.) {+-}20 (syst.) GeV/C{sup 2}.
Date: September 1, 1995
Creator: Klima, B.
Partner: UNT Libraries Government Documents Department

New technologies in the D0 central tracker upgrade

Description: The D0 collaboration has undertaken an aggressive upgrade of its central tracking system. The existing tracker will be completely removed and replaced by a two Tesla superconducting solenoidal magnet, an 837 000 channel silicon vertex system, and 80 000 channel scintillating fiber tracker, followed by a 7 680 channel central preshower detector and a 16 000 channel forward preshower detector. In this paper the author discusses all of the subsystems of the D0 central tracker upgrade, but will emphasize those aspects which involve new technology: radiation hard scintillating fiber, VLPC`s and extruded scintillating strips.
Date: June 1, 1996
Creator: Lincoln, D.
Partner: UNT Libraries Government Documents Department

Hard single diffractive jet production at D0

Description: Preliminary results from the D{null} experiment on jet production with forward rapidity gaps in {ital p{anti p}} collisions are presented. A class of dijet events with a forward rapidity gap is observed at center-of-mass energies {radical}s = 1800 GeV and 630 GeV. The number of events with rapidity gaps at both center-of-mass energies is significantly greater than the expectation from multiplicity fluctuations and is consistent with a hard single diffractive process. A small class of events with two forward gaps and central dijets is also observed at 1800 GeV. This topology is consistent with hard double pomeron exchange.
Date: August 1, 1996
Creator: Abachi, S.; Abbott, B.; Abolins, M. & Collaboration, D0
Partner: UNT Libraries Government Documents Department