1,182 research outputs found
APFELgrid: A high performance tool for parton density determinations
We present a new software package designed to reduce the computational burden of hadron collider measurements in Parton Distribution Function (PDF) fits. The APFELgrid package converts interpolated weight tables provided by APPLgrid files into a more efficient format for PDF fitting by the combination with PDF and as evolution factors provided by APFEL. This combination significantly reduces the number of operations required to perform the calculation of hadronic observables in PDF fits and simplifies the structure of the calculation into a readily optimised scalar product. We demonstrate that our technique can lead to a substantial speed improvement when compared to existing methods without any reduction in numerical accuracy.
Program Summary
Program Title: APFELgrid
Program Files doi: http://dx.doi.org/10.17632/mhwjt5nsg7.1
Licensing provisions: MIT license
Programming language: C++
Nature of problem: Fast computation of hadronic observables under the variation of parton distribution functions.
Solution method: Combination of interpolated weight grids from APPLgrid files and evolution factors from APFEL into efficient FastKernel tables.
External routines/libraries: APPLgrid, APFE
Structure functions and perturbative hysteresis
We discuss hysteresis effects in the perturbative solution of
renormalization group equations for the strong coupling and parton
distribution functions, and study their impact on precision determinations of proton's deep-inelastic structure functions F2 and FL
Kaon oscillations in the Standard Model and Beyond using Nf=2 dynamical quarks
We compute non-perturbatively the B-parameters of the complete basis of
four-fermion operators needed to study the Kaon oscillations in the SM and in
its supersymmetric extension. We perform numerical simulations with two
dynamical maximally twisted sea quarks at three values of the lattice spacing
on configurations generated by the ETMC. Unwanted operator mixings and O(a)
discretization effects are removed by discretizing the valence quarks with a
suitable Osterwalder-Seiler variant of the Twisted Mass action. Operators are
renormalized non-perturbatively in the RI/MOM scheme. Our preliminary result
for BK(RGI) is 0.73(3)(3).Comment: 7 pages, 3 figures, 1 table, proceedings of the XXVII Int'l Symposyum
on Lattice Field Theory (LAT2009), July 26-31 2009, Peking University,
Beijing (China
PAMELA's cosmic positron from decaying LSP in SO(10) SUSY GUT
We propose two viable scenarios explaining the recent observations on cosmic
positron excess. In both scenarios, the present relic density in the Universe
is assumed to be still supported by thermally produced WIMP or LSP (\chi). One
of the scenarios is based on two dark matter (DM) components (\chi,X) scenario,
and the other is on SO(10) SUSY GUT. In the two DM components scenario,
extremely small amount of non-thermally produced meta-stable DM component
[O(10^{-10}) < n_X /n_\chi] explains the cosmic positron excess. In the SO(10)
model, extremely small R-parity violation for LSP decay to e^\pm is naturally
achieved with a non-zero VEV of the superpartner of one right-handed neutrino
(\tilde{\nu}^c) and a global symmetry.Comment: 6 pages, Talks presented in PASCOS, SUSY, and COSMO/CosPA in 201
The partonic structure of the electron at the next-to-leading logarithmic accuracy in QED
By working in QED, we obtain the electron, positron, and photon Parton
Distribution Functions (PDFs) of the unpolarised electron at the
next-to-leading logarithmic accuracy. The PDFs account for all of the universal
effects of initial-state collinear origin, and are key ingredients in the
calculations of cross sections in the so-called structure-function approach. We
present both numerical and analytical results, and show that they agree
extremely well with each other. The analytical predictions are defined by means
of an additive formula that matches a large- solution that includes all
orders in the QED coupling constant , with a small- and
intermediate- solution that includes terms up to .Comment: 60 pages, 25 figures; the overall normalisation of eq.(5.56) and
eq.(5.57), and a couple of grammatical mistakes, have been correcte
The impact of heavy quark mass effects in the NNPDF global analysis
We discuss the implementation of the FONLL general-mass scheme for heavy
quarks in deep-inelastic scattering in the FastKernel framework, used in the
NNPDF series of global PDF analysis. We present the general features of FONLL
and benchmark the accuracy of its implementation in FastKernel comparing with
the Les Houches heavy quark benchmark tables. We then show preliminary results
of the NNPDF2.1 analysis, in which heavy quark mass effects are included
following the FONLL-A GM scheme.Comment: 5 pages, 3 figures; to appear in the proceedings of DIS 2010, Firenz
Progress in the Neural Network Determination of Polarized Parton Distributions
We review recent progress towards a determination of a set of polarized
parton distributions from a global set of deep-inelastic scattering data based
on the NNPDF methodology, in analogy with the unpolarized case. This method is
designed to provide a faithful and statistically sound representation of parton
distributions and their uncertainties. We show how the FastKernel method
provides a fast and accurate method for solving the polarized DGLAP equations.
We discuss the polarized PDF parametrizations and the physical constraints
which can be imposed. Preliminary results suggest that the uncertainty on
polarized PDFs, most notably the gluon, has been underestimated in previous
studies.Comment: 5 pages, 2 figures; to appear in the proceedings of DIS 2010, Firenz
Improving methods and predictions at high-energy e+e− colliders within collinear factorisation
We illustrate how electron Parton Distribution Functions (PDFs) with next-to-leading collinear logarithmic accuracy must be employed in the context of perturbative predictions for high-energy e+e−-collision processes. In particular, we discuss how the renormalisation group equation evolution of such PDFs is affected by the presence of multiple fermion families and their respective mass thresholds, and by the dependences on the choices of the factorisation and renormalisation schemes. We study the impact of the uncertainties associated with the PDFs on physical cross sections, in order to arrive at realistic precision estimates for observables computed with collinear-factorisation formulae. We do so by presenting results for the production of a heavy neutral object as well as for tt¯ and W+W− pairs, including next-to-leading-order effects of electroweak origin
- …