1,863 research outputs found
The specificity of searches for , and coming from extra dimensions
We discuss the specificity of searches for hypothetical ,
and bosons at hadron colliders in single top
quark and production and Drell-Yan processes assuming these
particles to be the Kaluza-Klein excitations of the gauge bosons of the
Standard Model. In this case any process mediated by is also mediated by
the whole KK tower of its excitations, whereas to the processes mediated by
and there is not only a contribution from their KK towers, but also
from that of the graviton. The contributions of the towers above ,
and and above the first excitation of the
graviton are included with the help of effective four-fermion Lagrangians. We
compute the cross-sections of these processes taking into account the
contributions of the Standard Model gauge bosons, of their first KK modes and
of the corresponding KK towers and discuss the impact of the interference
between them. For pp-collisions at the LHC with the center of mass energy 14
TeV we found specific changes of the distribution tails due to the interference
effects. Such a modification of distribution tails is characteristic for the
processes mediated by particles coming from extra dimensions and should always
be taken into account when looking for them.Comment: 14 pages, 12 figures, LaTeX. References added, figures added, text
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Расчет гидродинамики потока в электроциклоне
To analyze the elektrocyclone flow hydrodynamic computer calculation using the finite element method (FEM) is applied. The geometry of the model corresponds to the laboratory elektrocyclone. k-ε-turbulence model is used for the computation. The system of equations is solved by SIMPLE algorithm. The calculation results give a pattern of the flow velocity distribution and flow lines in different sections. There is conclusion based on the results about elektrocyclone flow hydrodynamic.Для анализа гидродинамики потока в электроциклоне применен компьютерный расчет с использованием метода конечных элементов (МКЭ). Геометрия модели соответствует лабораторному электроциклону. Для расчетов использована k-ε-модель турбулентности. Система уравнений решается с помощью алгоритма SIMPLE. Результаты расчета дают картину распределения скоростей потока и линий тока в различных сечениях. На основании результатов делается вывод о гидродинамике электроциклона. Выявлен факт, что в бункере электроциклона отсутствует вихревое движение, также нет развитого течения в области стенок, а ниже выхлопного отверстия скорость потока близка к 0. Это благоприятно сказывается на эффективности очистки, т. к. выходящий чистый газ не увлекает с собой осевшие частицы. Выводы: 1) гидродинамика электроциклона может быть описана с помощью математической модели и рассчитана с помощью МКЭ; 2) поток в электроциклоне, как и ожидалось, имеет закрученную структуру, угол закрутки зависит от длины активной зоны; 3) конструкция бункера обеспечивает выход очищенного газа без вовлечения в него уловленных частиц
Journal Staff
We present the first measurements of the differential cross section d sigma/dp(T)(gamma) for the production of an isolated photon in association with at least two b-quark jets. The measurements consider photons with rapidities vertical bar y(gamma)vertical bar < 1.0 and transverse momenta 30 < p(T)(gamma) < 200 GeV. The b-quark jets are required to have p(T)(jet) > 15 GeVand vertical bar y(jet)vertical bar < 1.5. The ratio of differential production cross sections for gamma + 2 b-jets to gamma + b-jet as a function of p(T)(gamma) is also presented. The results are based on the proton-antiproton collision data at root s = 1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. The measured cross sections and their ratios are compared to the next- to- leading order perturbative QCD calculations as well as predictions based on the k(T)- factorization approach and those from the sherpa and pythia Monte Carlo event generators
Measurement of the semileptonic charge asymmetry in B0 meson mixing with the D0 detector
We present a measurement of the semileptonic mixing asymmetry for B0 mesons,
a^d_{sl}, using two independent decay channels: B0 -> mu+D-X, with D- ->
K+pi-pi-; and B0 -> mu+D*-X, with D*- -> antiD0 pi-, antiD0 -> K+pi- (and
charge conjugate processes). We use a data sample corresponding to 10.4 fb^{-1}
of ppbar collisions at sqrt(s) = 1.96 TeV, collected with the D0 experiment at
the Fermilab Tevatron collider. We extract the charge asymmetries in these two
channels as a function of the visible proper decay length (VPDL) of the B0
meson, correct for detector-related asymmetries using data-driven methods, and
account for dilution from charge-symmetric processes using Monte Carlo
simulation. The final measurement combines four signal VPDL regions for each
channel, yielding a^d_{sl} = [0.68 \pm 0.45 \text{(stat.)} \pm 0.14
\text{(syst.)}]%. This is the single most precise measurement of this
parameter, with uncertainties smaller than the current world average of B
factory measurements.Comment: Version includes minor textual changes following peer review by
journal, most notably the updating of Ref. [21] to reflect the most recent
publicatio
Search for Decay
We have searched for the charmless hadronic decay of B0 mesons into two
neutral pions. Using 9.13fb^-1 taken at the Upsilon(4S) with the CLEO detector,
we obtain an improved upper limit for the branching fraction BR(B0-->pi0pi0) <
5.7*10^-6 at the 90% confidence level.Comment: pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
Search for Zgamma events with large missing transverse energy in ppbar collisions at sqrt(s)=1.96 TeV
We present the first search for supersymmetry (SUSY) in Zgamma final states
with large missing transverse energy using data corresponding to an integrated
luminosity of 6.2 fb-1 collected with the D0 experiment in ppbar collisions at
sqrt(s)=1.96 TeV. This signature is predicted in gauge-mediated SUSY-breaking
models, where the lightest neutralino is the next-to-lightest supersymmetric
particle (NLSP) and is produced in pairs, possibly through decay from heavier
supersymmetric particles. The NLSP can decay either to a Z boson or a photon
and an associated gravitino that escapes detection. We exclude this model at
the 95% C.L. for SUSY breaking scales of Lambda < 87 TeV, corresponding to
neutralino masses of < 151 GeV.Comment: submitted to Phys. Rev. Let
Measurement of Leptonic Asymmetries and Top Quark Polarization in ttbar Production
We present measurements of lepton (l) angular distributions in ttbar -> W+ b
W- b -> l+ nu b l- nubar bbar decays produced in ppbar collisions at a
center-of-mass energy of sqrt(s)=1.96TeV, where l is an electron or muon. Using
data corresponding to an integrated luminosity of 5.4fb^-1, collected with the
D0 detector at the Fermilab Collider, we find that the angular distributions of
l- relative to anti-protons and l+ relative to protons are in agreement with
each other. Combining the two distributions and correcting for detector
acceptance we obtain the forward-backward asymmetry A^l_FB = (5.8 +- 5.1(stat)
+- 1.3(syst))%, compared to the standard model prediction of A^l_FB (predicted)
= (4.7 +- 0.1)%. This result is further combined with the measurement based on
the analysis of the l+jets final state to obtain A^l_FB = (11.8 +- 3.2)%.
Furthermore, we present a first study of the top-quark polarization.Comment: submitted versio
Search for W' boson production in the W'->tb decay channel
We present a search for the production of a new heavy gauge boson W' that
decays to a top quark and a bottom quark. We have analyzed 230 pb^{-1} of data
collected with the Dzero detector at the Fermilab Tevatron collider at a
center-of-mass energy of 1.96 TeV. No significant excess of events above the
standard model expectation is found in any region of the final state invariant
mass distribution. We set upper limits on the production cross section of W'
bosons times branching ratio to top quarks at the 95% confidence level for
several different W' boson masses. We exclude masses between 200 GeV and 610
GeV for a W' boson with standard-model-like couplings, between 200 GeV and 630
GeV for a W' boson with right-handed couplings that is allowed to decay to both
leptons and quarks, and between 200 GeV and 670 GeV for a W' boson with
right-handed couplings that is only allowed to decay to quarks.Comment: 9 pages, 6 figures, accepted by Phys. Lett.
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