105 research outputs found
Expansion around half-integer values, binomial sums and inverse binomial sums
I consider the expansion of transcendental functions in a small parameter
around rational numbers. This includes in particular the expansion around
half-integer values. I present algorithms which are suitable for an
implementation within a symbolic computer algebra system. The method is an
extension of the technique of nested sums. The algorithms allow in addition the
evaluation of binomial sums, inverse binomial sums and generalizations thereof.Comment: 21 page
Antenna subtraction with massive fermions at NNLO: Double real initial-final configurations
We derive the integrated forms of specific initial-final tree-level
four-parton antenna functions involving a massless initial-state parton and a
massive final-state fermion as hard radiators. These antennae are needed in the
subtraction terms required to evaluate the double real corrections to
hadronic production at the NNLO level stemming from the partonic
processes and .Comment: 24 pages, 1 figure, 1 Mathematica file attache
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
Study of events and limits on anomalous and couplings in ppbar collisions at TeV
We present a measurement of the Z\gamma production cross section and limits
on anomalous ZZ\gamma and Z\gamma\gamma couplings for form-factor scales of
Lambda = 750 and 1000 GeV. The measurement is based on 138 (152) candidate
events in the ee\gamma (\mu\mu\gamma) final state using 320 (290) pb^{-1} of
ppbar collisions at \sqrt{s} = 1.96 TeV. The 95% C.L. limits on real and
imaginary parts of individual anomalous couplings are |h_{10,30}^{Z}|<0.23,
|h_{20,40}^{Z}|<0.020, |h_{10,30}^{\gamma}|<0.23, and
|h_{20,40}^{\gamma}|<0.019 for Lambda = 1000 GeV.Comment: submitted to Phys. Rev. Letter
A search for W bb and W Higgs production in ppbar collisions at sqrt(s)=1.96 TeV
We present a search for W b \bar{b} production in p \bar{p} collisions at
sqrt{s}=1.96 TeV in events containing one electron, an imbalance in transverse
momentum, and two b-tagged jets. Using 174 pb-1 of integrated luminosity
accumulated by the D0 experiment at the Fermilab Tevatron collider, and the
standard-model description of such events, we set a 95% C.L. upper limit on W b
\bar{b}WH--$135
GeV.Comment: 7 pages, 4 figures, 1 table, submitted to Physical Review Letter
Measurement of the Ratio of B+ and B0 Meson Lifetimes
The ratio of B+ and B0 meson lifetimes was measured using data collected in
2002-2004 by the D0 experiment in Run II of the Fermilab Tevatron Collider.
These mesons were reconstructed in B -> mu+ nu D*- X decays, which are
dominated by B0, and B ->mu+ nu D0bar X decays, which are dominated by B+. The
ratio of lifetimes is measured to be t+/t0 = 1.080 +- 0.016(stat) +-
0.014(syst).Comment: 7 pages, 2 figures, LaTeX, to be submitted to Physical Review Letter
A Search for the Flavor-Changing Neutral Current Decay B0_s -> mu^+mu^- in pp(bar) Collisions at \sqrt{s} = 1.96 TeV with the D0 Detector
We present the results of a search for the flavor-changing neutral current
decay B0_s -> mu+ mu- using a data set with integrated luminosity of 240
pb^{-1} of pp(bar) collisions at sqrt{s}=1.96 TeV collected with the D0
detector in Run II of the Fermilab Tevatron collider. We find the upper limit
on the branching fraction to be Br(B0_s -> mu+ mu-) \leq 5.0 x 10^{-7} at the
95% C.L. assuming no contributions from the decay B0_d -> mu+ mu- in the signal
region. This limit is the most stringent upper bound on the branching fraction
B0_s -> mu+ mu- to date.Comment: 7 pages, 3 figures, LaTeX, to be submitted to Physical Review
Letters, minor changes to text, reference adde
Double real radiation corrections to production at the LHC: the all-fermion processes
We present the double real radiation corrections to the hadronic
production stemming from partonic processes with fermions only. For this
purpose, we extend the NNLO antenna subtraction formalism developed originally
for the computation of jet observables in annihilation to include the
evaluation of hadronic observables involving a massive pair of particles. In
all partonic processes, we checked the validity of our subtraction terms given
for leading and subleading colour contributions numerically by showing that the
ratio between real radiation matrix elements and subtraction terms approaches
unity in all single and double unresolved configurations.Comment: 68 pages, 9 figure
Data assimilation in a system with two scales-combining two initialization techniques
11 pages, 11 figures, 1 tableFull-text version available Open Access at: http://clivar.iim.csic.es/?q=es/node/319An ensemble Kalman filter (EnKF) is used to assimilate data onto a non-linear chaotic model, coupling two kinds of variables. The first kind of variables of the system is characterized as large amplitude, slow, large scale, distributed in eight equally spaced locations around a circle. The second kind of variables are small amplitude, fast, and short scale, distributed in 256 equally spaced locations. Synthetic observations are obtained from the model and the observational error is proportional to their respective amplitudes. The performance of the EnKF is affected by differences in the spatial correlation scales of the variables being assimilated. This method allows the simultaneous assimilation of all the variables. The ensemble filter also allows assimilating only the large-scale variables, letting the small-scale variables to freely evolve. Assimilation of the large-scale variables together with a few small-scale variables significantly degrades the filter. These results are explained by the spurious correlations that arise from the sampled ensemble covariances. An alternative approach is to combine two different initialization techniques for the slow and fast variables. Here, the fast variables are initialized by restraining the evolution of the ensemble members, using a Newtonian relaxation toward the observed fast variables. Then, the usual ensemble analysis is used to assimilate the large-scale observationsThis study is supported by the Spanish National Science Program under contracts ESP2005–06823-C05 and ESP2007–65667-C04Peer reviewe
Quantum Darwinism
Quantum Darwinism describes the proliferation, in the environment, of
multiple records of selected states of a quantum system. It explains how the
fragility of a state of a single quantum system can lead to the classical
robustness of states of their correlated multitude; shows how effective
`wave-packet collapse' arises as a result of proliferation throughout the
environment of imprints of the states of quantum system; and provides a
framework for the derivation of Born's rule, which relates probability of
detecting states to their amplitude. Taken together, these three advances mark
considerable progress towards settling the quantum measurement problem
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