215 research outputs found
Prosopis, Retama monosperma. Phragmites y Arundo donax en cosechas sucesivas a uno y dos años de crecimiento, para la elaboración de pasta celulósica y papel
Se evalúa la aptitud de ciertas especies regeneradoras de terrenos degradados: Prosopis (variedades: alba y juliflora),Retama monosperma, Phragmites y Arundo donax, para la fabricación de pastas celulósicas y hojas de papel, mediante un proceso de pasteo organosolv alcalino. Se caracterizan y comparan las materias primas, pastas celulósicas y hojas de papel, para cosechas de un año (más rebrotes de un año de edad, después de haberlas cortado al año) y dos años de crecimiento. Las especies Retama monosperma, Phragmites y Arundodonax muestran potencialidad para su aprovechamientoindustrial, en cosechas de corta rotación, para la obtenciónde pastas celulósicas y papel. Los números kappa de las pastas de 2º año están entre 10,3 y 12,6, con números de tracción entre 13,7 y 20,9 kNm·kg–1 en las pastas sin refinar. Sin embargo la explotación industrial de las dos variedades de Prosopis precisaría su adecuación a tiempos de explotación más largos, que los estudiados en este trabajo
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
Measurement of the dijet invariant mass cross section in proton anti-proton collisions at sqrt{s} = 1.96 TeV
The inclusive dijet production double differential cross section as a
function of the dijet invariant mass and of the largest absolute rapidity of
the two jets with the largest transverse momentum in an event is measured in
proton anti-proton collisions at sqrt{s} = 1.96 TeV using 0.7 fb^{-1}
integrated luminosity collected with the D0 detector at the Fermilab Tevatron
Collider. The measurement is performed in six rapidity regions up to a maximum
rapidity of 2.4. Next-to-leading order perturbative QCD predictions are found
to be in agreement with the data.Comment: Published in Phys. Lett. B, 693, (2010), 531-538, 8 pages, 2 figures,
6 table
Measurement of Z/gamma*+jet+X angular distributions in ppbar collisions at sqrt{s}=1.96 TeV
We present the first measurements at a hadron collider of differential cross
sections for Z+jet+X production in delta phi(Z, jet), |delta y(Z, jet)| and
|y_boost(Z, jet)|. Vector boson production in association with jets is an
excellent probe of QCD and constitutes the main background to many small cross
section processes, such as associated Higgs production. These measurements are
crucial tests of the predictions of perturbative QCD and current event
generators, which have varied success in describing the data. Using these
measurements as inputs in tuning event generators will increase the
experimental sensitivity to rare signals.Comment: Published in Physics Letters B 682 (2010), pp. 370-380. 15 pages, 6
figure
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt{s} = 1.96 TeV using Kinematic Characteristics of Lepton + Jets Events
We present a measurement of the top quark pair ttbar production cross section
in ppbar collisions at a center-of-mass energy of 1.96 TeV using 230 pb**{-1}
of data collected by the DO detector at the Fermilab Tevatron Collider. We
select events with one charged lepton (electron or muon), large missing
transverse energy, and at least four jets, and extract the ttbar content of the
sample based on the kinematic characteristics of the events. For a top quark
mass of 175 GeV, we measure sigma(ttbar) = 6.7 {+1.4-1.3} (stat) {+1.6- 1.1}
(syst) +/-0.4 (lumi) pb, in good agreement with the standard model prediction.Comment: submitted to Phys.Rev.Let
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s)=1.96 TeV using Lepton + Jets Events with Lifetime b-tagging
We present a measurement of the top quark pair () production cross
section () in collisions at TeV
using 230 pb of data collected by the D0 experiment at the Fermilab
Tevatron Collider. We select events with one charged lepton (electron or muon),
missing transverse energy, and jets in the final state. We employ
lifetime-based b-jet identification techniques to further enhance the
purity of the selected sample. For a top quark mass of 175 GeV, we
measure pb, in
agreement with the standard model expectation.Comment: 7 pages, 2 figures, 3 tables Submitted to Phys.Rev.Let
Evidence for a mixed mass composition at the `ankle' in the cosmic-ray spectrum
We report a first measurement for ultra-high energy cosmic rays of the
correlation between the depth of shower maximum and the signal in the water
Cherenkov stations of air-showers registered simultaneously by the fluorescence
and the surface detectors of the Pierre Auger Observatory. Such a correlation
measurement is a unique feature of a hybrid air-shower observatory with
sensitivity to both the electromagnetic and muonic components. It allows an
accurate determination of the spread of primary masses in the cosmic-ray flux.
Up till now, constraints on the spread of primary masses have been dominated by
systematic uncertainties. The present correlation measurement is not affected
by systematics in the measurement of the depth of shower maximum or the signal
in the water Cherenkov stations. The analysis relies on general characteristics
of air showers and is thus robust also with respect to uncertainties in
hadronic event generators. The observed correlation in the energy range around
the `ankle' at differs significantly from
expectations for pure primary cosmic-ray compositions. A light composition made
up of proton and helium only is equally inconsistent with observations. The
data are explained well by a mixed composition including nuclei with mass . Scenarios such as the proton dip model, with almost pure compositions, are
thus disfavoured as the sole explanation of the ultrahigh-energy cosmic-ray
flux at Earth.Comment: Published version. Added journal reference and DOI. Added Report
Numbe
Search for charged Higgs bosons in top quark decays
We present a search for charged Higgs bosons in top quark decays. We analyze
the \eplus, \muplus, , , , \etau and \mutau final states from
top quark pair production events, using data from about 1 of
integrated luminosity recorded by the \dzero experiment at the Fermilab
Tevatron Collider. We consider different scenarios of possible charged Higgs
boson decays, one where the charged Higgs boson decays purely hadronically into
a charm and a strange quark, another where it decays into a lepton and a
neutrino and a third one where both decays appear. We extract limits on
the branching ratio for all these models. We use two methods,
one where the production cross section is fixed, and one where the
cross section is fitted simultaneously with . Based on the
extracted limits, we exclude regions in the charged Higgs boson mass and parameter space for different scenarios of the minimal supersymmetric
standard model.Comment: 10 pages, 8 figures, submitted to PL
Transport coefficients and resonances for a meson gas in Chiral Perturbation Theory
We present recent results on a systematic method to calculate transport
coefficients for a meson gas (in particular, we analyze a pion gas) at low
temperatures in the context of Chiral Perturbation Theory (ChPT). Our method is
based on the study of Feynman diagrams taking into account collisions in the
plasma by means of the non-zero particle width. This implies a modification of
the standard ChPT power counting scheme. We discuss the importance of
unitarity, which allows for an accurate high energy description of scattering
amplitudes, generating dynamically the and mesons. Our
results are compatible with analyses of kinetic theory, both in the
non-relativistic very low- regime and near the transition. We show the
behavior with temperature of the electrical and thermal conductivities as well
as of the shear and bulk viscosities. We obtain that bulk viscosity is
negligible against shear viscosity, except near the chiral phase transition
where the conformal anomaly might induce larger bulk effects. Different
asymptotic limits for transport coefficients, large- scaling and some
applications to heavy-ion collisions are studied.Comment: Invited talk given at the international workshop Hot Quarks 2008,
Estes Park, Colorado, USA, August 18-23 2008. Accepted as a regular article
in Eur.Phys.J.C. 18 pages EPJC style, 23 figure
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