39 research outputs found
Counting and computing regions of -decomposition: algebro-geometric approach
New methods for -decomposition analysis are presented. They are based on
topology of real algebraic varieties and computational real algebraic geometry.
The estimate of number of root invariant regions for polynomial parametric
families of polynomial and matrices is given. For the case of two parametric
family more sharp estimate is proven. Theoretic results are supported by
various numerical simulations that show higher precision of presented methods
with respect to traditional ones. The presented methods are inherently global
and could be applied for studying -decomposition for the space of parameters
as a whole instead of some prescribed regions. For symbolic computations the
Maple v.14 software and its package RegularChains are used.Comment: 16 pages, 8 figure
Evidence of Color Coherence Effects in W+jets Events from ppbar Collisions at sqrt(s) = 1.8 TeV
We report the results of a study of color coherence effects in ppbar
collisions based on data collected by the D0 detector during the 1994-1995 run
of the Fermilab Tevatron Collider, at a center of mass energy sqrt(s) = 1.8
TeV. Initial-to-final state color interference effects are studied by examining
particle distribution patterns in events with a W boson and at least one jet.
The data are compared to Monte Carlo simulations with different color coherence
implementations and to an analytic modified-leading-logarithm perturbative
calculation based on the local parton-hadron duality hypothesis.Comment: 13 pages, 6 figures. Submitted to Physics Letters
Search for electroweak production of single top quarks in collisions.
We present a search for electroweak production of single top quarks in the electron+jets and muon+jets decay channels. The measurements use ~90 pb^-1 of data from Run 1 of the Fermilab Tevatron collider, collected at 1.8 TeV with the DZero detector between 1992 and 1995. We use events that include a tagging muon, implying the presence of a b jet, to set an upper limit at the 95% confidence level on the cross section for the s-channel process ppbar->tb+X of 39 pb. The upper limit for the t-channel process ppbar->tqb+X is 58 pb. (arXiv
Helicity of the W Boson in Lepton+Jets ttbar Events
We examine properties of ttbar candidates events in lepton+jets final states
to establish the helicities of the W bosons in t->W+b decays. Our analysis is
based on a direct calculation of a probability that each event corresponds to a
ttbar final state, as a function of the helicity of the W boson. We use the 125
events/pb sample of data collected by the DO experiment during Run I of the
Fermilab Tevatron collider at sqrt{s}=1.8 TeV, and obtain a longitudinal
helicity fraction of F_0=0.56+/-0.31, which is consistent with the prediction
of F_0=0.70 from the standard model
Hard Single Diffraction in pbarp Collisions at root-s = 630 and 1800 GeV
Using the D0 detector, we have studied 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 of root-s = 630 and 1800 Gev. The fractions of forward and central jet
events associated with such rapidity gaps are measured and compared to
predictions from Monte Carlo models. For hard diffractive candidate events, we
use the calorimeter to extract the fractional momentum loss of the scattered
protons.Comment: 11 pages 4 figures. submitted to PR