1,347 research outputs found
Photon pair production at flavour factories with per mille accuracy
We present a high-precision QED calculation, with 0.1% theoretical accuracy,
of two photon production in annihilation, as required by more and
more accurate luminosity monitoring at flavour factories. The accuracy of the
approach, which is based on the matching of exact next-to-leading order
corrections with a QED Parton Shower algorithm, is demonstrated through a
detailed analysis of the impact of the various sources of radiative corrections
to the experimentally relevant observables. The calculation is implemented in
the latest version of the event generator BabaYaga, available for precision
simulations of photon pair production at colliders of moderately high
energies.Comment: 11 pages, 5 figures, 1 tabl
Impact of QED corrections to Higgs decay into four leptons at the LHC
At the LHC a precise measurement of the Higgs boson mass (if discovered), at
the level of 0.1-1%, will be possible through the channel g g --> H --> 4l for
a wide range of Higgs mass values. To match such an accuracy, the systematic
effects induced by QED corrections need to be investigated. In the present
study the calculation of O(alpha) and higher order QED corrections is
illustrated as well as their impact on the Higgs mass determination, once
realistic event selection criteria for charged leptons and photons are
considered.Comment: 5 pages, 5 figures, 1 table. Presented at HEP2005 July 21st-27th,
2005, Lisboa, Portugal and at RADCOR 2005, Shonan Village, October 2nd-7th,
2005, Japa
Global gravitational instability of FLRW backgrounds - interpreting the dark sectors
The standard model of cosmology is based on homogeneous-isotropic solutions
of Einstein's equations. These solutions are known to be gravitationally
unstable to local inhomogeneous perturbations, commonly described as evolving
on a background given by the same solutions. In this picture, the FLRW
backgrounds are taken to describe the average over inhomogeneous perturbations
for all times. We study in the present article the (in)stability of FLRW dust
backgrounds within a class of averaged inhomogeneous cosmologies. We examine
the phase portraits of the latter, discuss their fixed points and orbital
structure and provide detailed illustrations. We show that FLRW cosmologies are
unstable in some relevant cases: averaged models are driven away from them
through structure formation and accelerated expansion. We find support for the
proposal that the dark components of the FLRW framework may be associated to
these instability sectors. Our conclusion is that FLRW cosmologies have to be
considered critically as for their role to serve as reliable models for the
physical background.Comment: 15 pages, 13 figures, 1 table. Matches published version in CQ
Matrix elements and Parton Shower in the event generator BABAYAGA
A new version of the event generator BABAYAGA is presented, which is based on
an original matching of the Parton Shower approach with the complete exact
O(alpha) matrix element for the inclusion of the QED radiative corrections to
the Bhabha process at flavour factories. The theoretical accuracy of the
improved generator is conservatively estimated to be 0.2%, by comparison with
independent calculations. The generator is a useful tool for precise luminosity
determination at flavour factories, for center of mass energies below 10 GeV.Comment: 4 pages, 2 figures. To appear in the proceedings of the International
Workshop e+ e- Collisions from phi to psi, Novosibirsk (Russia), 27 Feb - 2
Mar 200
Precision electroweak calculation of the production of a high transverse-momentum lepton pair at hadron colliders
We present a detailed study of the production of a high transverse-momentum
lepton pair at hadron colliders, which includes the exact O(alpha) electroweak
corrections properly matched with leading logarithmic effects due to multiple
photon emission, as required by the experiments at the Fermilab Tevatron and
the CERN LHC. Numerical results for the relevant observables of single Z-boson
production at hadron colliders are presented. The impact of the radiative
corrections is discussed in detail. The presence in the proton of a photon
density is considered and the effects of the photon-induced partonic
subprocesses are analyzed. The calculation has been implemented in the new
version of the event generator HORACE, which is available for precision
simulations of the neutral and charged current Drell-Yan processes.Comment: October 2007, 22p
Multi-photon corrections to W boson mass determination at hadron colliders
The impact of higher-order final-state photonic corrections on the precise
determination of the W-boson mass at the Tevatron and LHC colliders is
evaluated. The W-mass shift from a fit to the transverse mass distribution is
found to be about 10 MeV in the W --> mu nu channel and a few MeV in the W -->
e nu channel. The calculation, which is implemented in the Monte Carlo event
generator HORACE for data analysis, can contribute to reduce the uncertainty
associated to the W mass measurement at present and future hadron collider
experiments.Comment: 3 pages, 2 figures, to appear in the proceedings of International
Europhysics Conference on High-Energy Physics (EPS 2003), Aachen, Germany,
17-23 Jul 200
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