440 research outputs found
Effect of ultrafiltration of bakers’ and brewers’ yeast extracts on their nitrogen content and turbidity
Five commercial yeast extracts (YE) were fractionated by ultrafiltration (UF) with 10 000, 3000 and 1000 Da molecular weight cutoff membranes in the aim of evaluating the effect of UF on the turbidity and total nitrogen content of YE. Membrane pore size had much more influence on UF permeation rates than the source of the YE. UF filtration rates were on the average 4 times lower when the YE were treated with the 3000 Da membrane as compared to the 10 000 Da filter, and the 1000 Da unit gave rates approximately 40% lower than those observed with the 3000 Da pore size membrane. Pre-filtration with a 8 ?m membrane reduced between 47 and 96% the original YE turbidities, while UF with a 1000 to10 000 Da membranes gave filtrates having between 80 and 99.9% less turbidity than the original YE. On the average, UF with the 10 000 Da unit removed 12% of total solids, while UF with 3000 and 1000 Da cutoff membranes generated the retention of 20 and 23% of solids, respectively. Brewers' YE had lower total nitrogen content than bakers' YE, and UF increased the total nitrogen content of the dried yeast extract filtrates (YEF) obtained. The powders obtained after freeze-drying of brewers' YEF tended to have higher moisture contents than bakers', and this was quite significant with the YEF powders obtained with the filtrates generated with the 1000 Da membrane
Search for Higgs bosons decaying to tautau pairs in ppbar collisions at sqrt(s) = 1.96 TeV
We present a search for the production of neutral Higgs bosons decaying into
tautau pairs in ppbar collisions at a center-of-mass energy of 1.96 TeV. The
data, corresponding to an integrated luminosity of 5.4 fb-1, were collected by
the D0 experiment at the Fermilab Tevatron Collider. We set upper limits at the
95% C.L. on the product of production cross section and branching ratio for a
scalar resonance decaying into tautau pairs, and we then interpret these limits
as limits on the production of Higgs bosons in the minimal supersymmetric
standard model (MSSM) and as constraints in the MSSM parameter space.Comment: 7 pages, 5 figures, submitted to PL
Measurement of three-jet differential cross sections d sigma-3jet / d M-3jet in p anti-p collisions at sqrt(s)=1.96 TeV
We present the first measurement of the inclusive three-jet differential
cross section as a function of the invariant mass of the three jets with the
largest transverse momenta in an event in p anti-p collisions at sqrt(s) = 1.96
TeV. The measurement is made in different rapidity regions and for different
jet transverse momentum requirements and is based on a data set corresponding
to an integrated luminosity of 0.7 fb^{-1} collected with the D0 detector at
the Fermilab Tevatron Collider. The results are used to test the three-jet
matrix elements in perturbative QCD calculations at next-to-leading order in
the strong coupling constant. The data allow discrimination between
parametrizations of the parton distribution functions of the proton.Comment: 10 pages, 4 figures, 2 tables, submitted to Phys. Lett. B, corrected
chi2 values for NNPD
Search for pair production of the scalar top quark in muon+tau final states
We present a search for the pair production of scalar top quarks
(), the lightest supersymmetric partners of the top quarks, in
collisions at a center-of-mass energy of 1.96 TeV, using data
corresponding to an integrated luminosity of {7.3 } collected with the
\dzero experiment at the Fermilab Tevatron Collider. Each scalar top quark is
assumed to decay into a quark, a charged lepton, and a scalar neutrino
(). We investigate final states arising from and
. With no significant excess of events observed above the
background expected from the standard model, we set exclusion limits on this
production process in the (,) plane.Comment: Submitted to Phys. Lett.
Measurements of inclusive W+jets production rates as a function of jet transverse momentum in ppbar collisions at sqrt{s}=1.96 TeV
This Letter describes measurements of inclusive W (--> e nu) + n jet cross
sections (n = 1-4), presented as total inclusive cross sections and
differentially in the nth jet transverse momentum. The measurements are made
using data corresponding to an integrated luminosity of 4.2 fb-1 collected by
the D0 detector at the Fermilab Tevatron Collider, and achieve considerably
smaller uncertainties on W +jets production cross sections than previous
measurements. The measurements are compared to next-to-leading order
perturbative QCD (pQCD) calculations in the n =1-3 jet multiplicity bins and to
leading order pQCD calculations in the 4-jet bin. The measurements are
generally in agreement with pQCD predictions, although certain regions of phase
space are identified where the calculations could be improved
Measurement of spin correlation in ttbar production using dilepton final states
We measure the correlation between the spin of the top quark and the spin of
the anti-top quark in (ttbar -> W+ W- b bbar -> l+ nu b l- nubar bbar) final
states produced in ppbar collisions at a center of mass energy sqrt(s)=1.96
TeV, where l is an electron or muon. The data correspond to an integrated
luminosity of 5.4 fb-1 and were collected with the D0 detector at the Fermilab
Tevatron collider. The correlation is extracted from the angles of the two
leptons in the t and tbar rest frames, yielding a correlation strength C=
0.10^{+0.45}_{-0.45}, in agreement with the NLO QCD prediction within two
standard deviations, but also in agreement with the no correlation hypothesis.Comment: 10 pages, 3 figures, submitted to PL
Measurement of the ttbar production cross section using dilepton events in ppbar collisions
We present a measurement of the ttbar production cross section sigma(ttbar)
in ppbar collisions at sqrt{s} = 1.96 TeV using 5.4 fb-1 of integrated
luminosity collected with the D0 detector. We consider final states with at
least two jets and two leptons (ee, emu, mumu), and events with one jet for the
the emu final state as well. The measured cross section is sigma(ttbar)= 7.36
+0.90-0.79 (stat + syst) pb. This result combined with the cross section
measurement in the lepton + jets final state yields sigma(ttbar)=7.56
+0.63-0.56 (stat + syst) pb, which agrees with the standard model expectation.
The relative precision of 8% of this measurement is comparable to the latest
theoretical calculations.Comment: 9 pages, published in Phys. Lett.
Search for single top quarks in the tau+jets channel using 4.8 fb of collision data
We present the first direct search for single top quark production using tau
leptons. The search is based on 4.8 fb of integrated luminosity
collected in collisions at =1.96 TeV with the D0 detector
at the Fermilab Tevatron Collider. We select events with a final state
including an isolated tau lepton, missing transverse energy, two or three jets,
one or two of them tagged. We use a multivariate technique to discriminate
signal from background. The number of events observed in data in this final
state is consistent with the signal plus background expectation. We set in the
tau+jets channel an upper limit on the single top quark cross section of
\TauLimObs pb at the 95% C.L. This measurement allows a gain of 4% in expected
sensitivity for the observation of single top production when combining it with
electron+jets and muon+jets channels already published by the D0 collaboration
with 2.3 fb of data. We measure a combined cross section of
\SuperCombineXSall pb, which is the most precise measurement to date.Comment: 12 pages, 5 figure
b-Jet Identification in the D0 Experiment
Algorithms distinguishing jets originating from b quarks from other jet
flavors are important tools in the physics program of the D0 experiment at the
Fermilab Tevatron p-pbar collider. This article describes the methods that have
been used to identify b-quark jets, exploiting in particular the long lifetimes
of b-flavored hadrons, and the calibration of the performance of these
algorithms based on collider data.Comment: submitted to Nuclear Instruments and Methods in Physics Research
Search for pair production of the scalar top quark in the electron-muon final state
We report the result of a search for the pair production of the lightest
supersymmetric partner of the top quark () in
collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron
collider corresponding to an integrated luminosity of 5.4 fb. The scalar
top quarks are assumed to decay into a quark, a charged lepton, and a
scalar neutrino (), and the search is performed in the electron
plus muon final state. No significant excess of events above the standard model
prediction is detected, and improved exclusion limits at the 95% C.L. are set
in the the (,) mass plane
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