789 research outputs found
Multivariate Fitting and the Error Matrix in Global Analysis of Data
When a large body of data from diverse experiments is analyzed using a
theoretical model with many parameters, the standard error matrix method and
the general tools for evaluating errors may become inadequate. We present an
iterative method that significantly improves the reliability of the error
matrix calculation. To obtain even better estimates of the uncertainties on
predictions of physical observables, we also present a Lagrange multiplier
method that explores the entire parameter space and avoids the linear
approximations assumed in conventional error propagation calculations. These
methods are illustrated by an example from the global analysis of parton
distribution functions.Comment: 13 pages, 5 figures, Latex; minor clarifications, fortran program
made available; Normalization of Hessian matrix changed to HEP standar
Radiation Reaction fields for an accelerated dipole for scalar and electromagnetic radiation
The radiation reaction fields are calculated for an accelerated changing
dipole in scalar and electromagnetic radiation fields. The acceleration
reaction is shown to alter the damping of a time varying dipole in the EM case,
but not the scalar case. In the EM case, the dipole radiation reaction field
can exert a force on an accelerated monopole charge associated with the
accelerated dipole. The radiation reaction of an accelerated charge does not
exert a torque on an accelerated magnetic dipole, but an accelerated dipole
does exert a force on the charge. The technique used is that originally
developed by Penrose for non-singular fields and extended by the author for an
accelerated monopole charge.Comment: 11 page
A new numerical method for obtaining gluon distribution functions , from the proton structure function
An exact expression for the leading-order (LO) gluon distribution function
from the DGLAP evolution equation for the proton structure
function for deep inelastic scattering has
recently been obtained [M. M. Block, L. Durand and D. W. McKay, Phys. Rev.
D{\bf 79}, 014031, (2009)] for massless quarks, using Laplace transformation
techniques. Here, we develop a fast and accurate numerical inverse Laplace
transformation algorithm, required to invert the Laplace transforms needed to
evaluate , and compare it to the exact solution. We obtain accuracies
of less than 1 part in 1000 over the entire and spectrum. Since no
analytic Laplace inversion is possible for next-to-leading order (NLO) and
higher orders, this numerical algorithm will enable one to obtain accurate NLO
(and NNLO) gluon distributions, using only experimental measurements of
.Comment: 9 pages, 2 figure
Usable pasts forum: critically engaging food security
In this inaugural Usable Pasts Forum, we make the case that archaeology has a critical role to play in reframing approaches to food security in the African continent
Error Estimates on Parton Density Distributions
Error estimates on parton density distributions are presently based on the
traditional method of least squares minimisation and linear error propagation
in global QCD fits. We review the underlying assumptions and the various
mathematical representations of the method and address some technical issues
encountered in such a global analysis. Parton distribution sets which contain
error information are described.Comment: Latex, 12 pages, 5 figures. Needs iopart.cls and iopart12.clo.
Presented at New Trends in HERA Physics 2001, Ringberg Castle, Tegernsee,
Germany, June 17-22, 200
The t-tbar cross-section at 1.8 and 1.96 TeV: a study of the systematics due to parton densities and scale dependence
We update the theoretical predictions for the t-tbar production cross-section
at the Tevatron, taking into account the most recent determinations of
systematic uncertainties in the extraction of the proton parton densities.Comment: 12 pages, 1 figure, Late
Next-to-leading Log Resummation of Scalar and Pseudoscalar Higgs Boson Differential Cross-Sections at the LHC and Tevatron
The region of small transverse momentum in q qbar- and gg-initiated processes
must be studied in the framework of resummation to account for the large,
logarithmically-enhanced contributions to physical observables. In this paper,
we will calculate the fixed order next-to-leading order (NLO) perturbative
total and differential cross-sections for both a Standard Model (SM) scalar
Higgs boson and the Minimal Supersymmetric Standard Model's (MSSM) pseudoscalar
Higgs boson in the Heavy Quark Effective Theory (HQET) where the mass of the
top quark is taken to be infinite. Resummation coefficients B^2_g, C^2_gg for
the total cross-section resummation for the pseudoscalar case are given, as
well as C^1_gg for the differential cross-section.Comment: 18 pages, REVTeX4, 5 eps figures. v2: Typos corrected, references
added, a discussion of uncertainties was adde
The impact of new neutrino DIS and Drell-Yan data on large-x parton distributions
New data sets have recently become available for neutrino and antineutrino
deep inelastic scattering on nuclear targets and for inclusive dimuon
production in pp pd interactions. These data sets are sensitive to different
combinations of parton distribution functions in the large-x region and,
therefore, provide different constraints when incorporated into global parton
distribution function fits. We compare and contrast the effects of these new
data on parton distribution fits, with special emphasis on the effects at large
x. The effects of the use of nuclear targets in the neutrino and antineutrino
data sets are also investigated.Comment: 24 pages, 13 figure
Syntax as an exponent of morphological features
In this paper we investigate a selection of issues in the morphology-syntax interface. This has been the locus of intense research activity in recent years particularly within lexicalist theories of grammar such as Lexical Functional Grammar (LFG). A central question addressed in LFG is the way that across languages or within a single language a whole host of morphological, lexical and syntactic means can be deployed to express essentially the same set of meanings or functions. One very specific example of this is seen when very similar (or even identical) grammatical meanings/functions are sometimes expressed by inflected morphological word forms and sometimes by means of syntactic constructions, that is, when a single set of grammatical properties receives synthetic and analytic expression within the same language
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