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.