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Directed flow and particle production in Au+Au collisions from experiment E877 at the AGS

Description: In this article we summarize recent results on the study of Au+Au collisions at 10.8A GeV/c obtained at the AGS by the E877 Collaboration. New results on the directed sideward flow are presented. In particular, the dependence of proton and pion production on the direction of the reaction plane will be discussed. It is shown that the sideward flow is mainly due to nucleons and that pions show little flow effects. Two-pion correlation functions are studied to derive the density at freeze-out. Further, we inspect the correlations as a function of the pion direction relative to the reaction plane. A dependence of the deduced source sizes on the pair direction and momentum is observed. The measured source sizes are compared to results obtained in lighter systems. Measured m{sub t} spectra of pions and kaons are also presented. The pion spectra show an enhancement at low m{sub t} similar to that observed in Si+Pb and which was attributed to {triangle} resonance excitation. However, in contrast to Si+Pb now a clear difference between the {pi}{sup +} and {pi}{sup -} spectra is seen. The K{sup +} spectra, which showed a very steep component over a small p{sub t} range in the previously studied Si+Pb reaction exhibit for Au+Au an unexpected structure at very low p{sub t}.
Date: May 1, 1996
Creator: Barrette, J.
Partner: UNT Libraries Government Documents Department

A posteriori pointwise error estimates for the boundary element method

Description: This report presents a new approach for a posteriori pointwise error estimation in the boundary element method. The estimator relies upon the evaluation of hypersingular integral equations, and is therefore intrinsic to the boundary integral equation approach. This property allows some theoretical justification by mathematically correlating the exact and estimated errors. A methodology is developed for approximating the error on the boundary as well as in the interior of the domain. In the interior, error estimates for both the function and its derivatives (e.g. potential and interior gradients for potential problems, displacements and stresses for elasticity problems) are presented. Extensive computational experiments have been performed for the two dimensional Laplace equation on interior domains, employing Dirichlet and mixed boundary conditions. The results indicate that the error estimates successfully track the form of the exact error curve. Moreover, a reasonable estimate of the magnitude of the actual error is also obtained.
Date: January 1, 1995
Creator: Paulino, G.H.; Gray, L.J. & Zarikian, V.
Partner: UNT Libraries Government Documents Department

Gluon density in nuclei

Description: In this talk we present our detailed study (theory and numbers) on the shadowing corrections to the gluon structure functions for nuclei. Starting from rather controversial information on the nucleon structure function which is originated by the recent HERA data, we develop the Glauber approach for the gluon density in a nucleus based on Mueller formula and estimate the value of the shadowing corrections in this case. Then we calculate the first corrections to the Glauber approach and show that these corrections are big. Based on this practical observation we suggest the new evolution equation which takes into account the shadowing corrections and solve it. We hope to convince you that the new evolution equation gives a good theoretical tool to treat the shadowing corrections for the gluons density in a nucleus and, therefore, it is able to provide the theoretically reliable initial conditions for the time evolution of the nucleus-nucleus cascade. The initial conditions should be fixed both theoretically and phenomenologically before to attack such complicated problems as the mixture of hard and soft processes in nucleus-nucleus interactions at high energy or the theoretically reliable approach to hadron or/and parton cascades for high energy nucleus-nucleus interaction. 35 refs., 24 figs., 1 tab.
Date: October 1996
Creator: Ayala, A. L.; Ducati, M. B. G. & Levin, E. M.
Partner: UNT Libraries Government Documents Department

Jet Production at D0

Description: We report on preliminary measurements of the central ({vert_bar}{eta}{vert_bar}<0.5) inclusive jet cross section and the dijet angular distributions ({vert_bar}{eta}{vert_bar}<3) at {radical}s=1.8 TeV. The data were collected during the 1992-1993 and 1994-1995 runs at the Fermilab Tevatron p{anti p} Collider with the D0 detector. The measurements are in excellent agreement with next-to- leading order (NLO) QCD. Given the assumptions implicit in the theoretical models, we exclude quark compositeness to the 95% confidence level on a scale of {Lambda}{sub +}=2 TeV.
Date: August 1, 1997
Creator: Elvira, V. D.
Partner: UNT Libraries Government Documents Department

Phase diagram of the random-field Ising system Fe{sub 0.60}Zn{sub 0.40}F{sub 2} at intense fields

Description: The critical and irreversibility phase boundaries of the d = 3 diluted uniaxial antiferromagnet Fe{sub 0.60}Zn{sub 0.40}F{sub 2} have been determined under strong external magnetic fields by means of magnetization measurements. The data reveal that the random-field-induced glassy phase, previously observed in the upper part of the (H,T) phase diagram for highly diluted samples (x {approx_equal} 0.3), is extended to higher values of x.
Date: October 1, 1997
Creator: Montenegro, F.C.; Lima, K.A.; Torikachvili, M.S. & Lacerda, A.H.
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

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

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

Rapidity gaps between jets at D{O}

Description: We present studies of jet production via color-singlet events with low particle multiplicity between the jets. A preliminary study of the multiplicity in other regions of the color singlet events and the dependence of color-singlet exchange on jet transverse energy is also presented.
Date: July 1, 1996
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

The inclusive jet cross section at {radical}s = 630 GeV at D0

Description: The authors present a preliminary measurement of the cross section for central inclusive jet production at {radical}s = 630 GeV using {approximately} 400 nb{sup {minus}1} of data collected during the December 1995 Fermilab collider run at D0. These results are compared to NLO QCD predictions.
Date: September 1, 1996
Creator: Krane, J.
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: D0 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: D0 Collaboration
Partner: UNT Libraries Government Documents Department

The dijet mass spectrum with the D0 detector

Description: The authors present preliminary results from an analysis of dijet data collected during the 1994--1995 Tevatron Collider run with an integrated luminosity of 91 pb{sup {minus}1}. Measurements of dijet mass spectrum distributions in {anti p}p collisions at {radical}s = 1.8 TeV are compared with next-to-leading order QCD theory.
Date: September 1, 1996
Creator: Choi, S.
Partner: UNT Libraries Government Documents Department

Rapidity gaps in jet events at DØ

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

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

A study of multi-jet production ratios in p{anti p} collisions at D0

Description: The authors study inclusive jet multiplicity ratios in multi-jet events from p{anti p} collisions at {radical}s = 1.8 TeV recorded using the D0 detector at the Fermilab Tevatron collider. Preliminary average multi-jet production ratios are presented as a function of the scalar jet transverse energy and compared to NLO calculations.
Date: September 1, 1996
Creator: Gallas, E.
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

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

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

Inclusive jet cross section in p{bar p} collisions with the D0 detector

Description: The authors report on two preliminary measurements of the central inclusive jet cross section at {radical}s = 1.8 TeV. The two data sets with integrated luminosities of 91 pb{sup {minus}1} and 14 pb{sup {minus}1} were collected at the Fermilab Tevatron p{bar p} Collider with the D0 detector. The cross section, reported as a function of transverse jet energy 35 GeV {le} E{sub {tau}} {le} 470 GeV and in the pseudorapidity interval {vert_bar}{eta}{vert_bar} {le} 0.5, is in excellent agreement with next-to-leading order QCD.
Date: July 1, 1996
Creator: Gomez, B.; Hoeneisen, B. & Negret, J.P.
Partner: UNT Libraries Government Documents Department

WW and WZ production at the tevatron

Description: Direct limits are set on WWZ and WW{gamma} three-boson couplings in a search for WW and WZ production in p{bar p} collisions at {radical}s = 1.8 TeV using the D(0) and CDF detectors at the Fermilab Tevatron.
Date: April 1, 1995
Creator: Fuess, T.A.
Partner: UNT Libraries Government Documents Department

Multijet production at D{O}

Description: We describe studies of jet production in {bar p}p collisions at {radical}s = 1.8 TeV. We have investigated topological distributions in inclusive three and four-jet events and find them to be well- described by tree-level QCD matrix elements and also by the HERWIG Monte Carlo. We have measured the ratio of inclusive three-jet to two- jet cross sections as a function of summed jet transverse energy. This is found to be in good qualitative agreement with QCD; the data show some preference for a softer renormalization scale for emission of the third jet.
Date: July 1, 1996
Creator: Womersley, J.
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