25 research outputs found
Hydraulic Actuation System with Active Control for the Lateral Suspensions of High Speed Trains
High speed trains normally use actively controlled pneumatic systems to recenter the carbody with respect to the bogie when the train negotiates a curve. Pneumatic systems are used because of their softness, which adds a little contribution to the elastic force generated by the mechanical springs of the lateral suspension system, thereby allowing the neccessary dynamic isolation between carbody and bogie. Howeve, pneumatic systems have the drawbacks of large dimensions and slow response, often accompanied by a few damped oscillations. An innovative solution was developed which makes use of hydraulic actuators providing them with artificial compliance generated by an appropriate control, hence making hydraulic actuators suitable for this application. A carbody centering system is thus obtained presenting fast response, small volume and a softness comparable to that of a pneumatic system. The optimal control law for this system was defined, the system dynamic characteristics were analyzed and a technological demonstrator was built to assess the system merits. The paper outlines the theoretical grounds for the system control, its performance and the most significant results obtained during a test campaign conducted on the technological demonstrator
NLO QED Corrections to Hard-Bremsstrahlung Emission in Bhabha Scattering
In this paper we present a numerical implementation of the one-loop QED
corrections to the hard-bremsstrahlung process e- e+ \to e- e+ gamma. These
corrections can be included in the Monte Carlo event generators employed for
simulating Bhabha scattering events at low-energy high-luminosity
electron-positron colliders. The calculation is performed by employing the
reduction method developed by Ossola, Papadopoulos and Pittau. Our results are
implemented in a modular code for the numerical evaluation of the scattering
amplitudes for any given phase-space point. In a similar way, we also evaluate
the one-loop QED corrections to e- e+ \to mu- mu+ gamma, which represents an
interesting application of the method in the presence of two different mass
scales in the loops.Comment: 8 pages, 5 figures, v2 minor changes: comments and references added,
matches PLB versio
Soft gluon resummation of Drell-Yan rapidity distributions: theory and phenomenology
We examine critically the theoretical underpinnings and phenomenological
implications of soft gluon (threshold) resummation of rapidity distributions at
a hadron collider, taking Drell-Yan production at the Tevatron and the LHC as a
reference test case. First, we show that in perturbative QCD soft gluon
resummation is necessary whenever the partonic (rather the hadronic)
center-of-mass energy is close enough to threshold, and we provide tools to
assess when resummation is relevant for a given process. Then, we compare
different prescriptions for handling the divergent nature of the series of
resummed perturbative corrections, specifically the minimal and Borel
prescriptions. We assess the intrinsic ambiguities of resummed results, both
due to the asymptotic nature of their perturbative expansion, and to the
treatment of subleading terms. Turning to phenomenology, we introduce a fast
and accurate method for the implementation of resummation with the minimal and
Borel prescriptions using an expansion on a basis of Chebyshev polynomials. We
then present results for W and Z production as well as both high- and low-mass
dilepton pairs at the LHC, and show that soft gluon resummation effects are
generally comparable in size to NNLO corrections, but sometimes affected by
substantial ambiguities.Comment: 75 pages, 34 figures, pdflate
Combination of electroweak and QCD corrections to single W production at the Fermilab Tevatron and the CERN LHC
Precision studies of the production of a high-transverse momentum lepton in
association with missing energy at hadron colliders require that electroweak
and QCD higher-order contributions are simultaneously taken into account in
theoretical predictions and data analysis. Here we present a detailed
phenomenological study of the impact of electroweak and strong contributions,
as well as of their combination, to all the observables relevant for the
various facets of the p\smartpap \to {\rm lepton} + X physics programme at
hadron colliders, including luminosity monitoring and Parton Distribution
Functions constraint, precision physics and search for new physics signals.
We provide a theoretical recipe to carefully combine electroweak and strong
corrections, that are mandatory in view of the challenging experimental
accuracy already reached at the Fermilab Tevatron and aimed at the CERN LHC,
and discuss the uncertainty inherent the combination. We conclude that the
theoretical accuracy of our calculation can be conservatively estimated to be
about 2% for standard event selections at the Tevatron and the LHC, and about
5% in the very high transverse mass/lepton transverse momentum tails. We
also provide arguments for a more aggressive error estimate (about 1% and 3%,
respectively) and conclude that in order to attain a one per cent accuracy: 1)
exact mixed corrections should be computed in
addition to the already available NNLO QCD contributions and two-loop
electroweak Sudakov logarithms; 2) QCD and electroweak corrections should be
coherently included into a single event generator.Comment: One reference added. Final version to appear in JHE
Matching perturbative and Parton Shower corrections to Bhabha process at flavour factories
We report on a high-precision calculation of the Bhabha process in Quantum
Electrodynamics, of interest for precise luminosity determination of
electron-positron colliders involved in R measurements in the region of
hadronic resonances. The calculation is based on the matching of exact
next-to-leading order corrections with a Parton Shower algorithm. The accuracy
of the approach is demonstrated in comparison with existing independent
calculations and through a detailed analysis of the main components of
theoretical uncertainty, including two-loop corrections, hadronic vacuum
polarization and light pair contributions. The calculation is implemented in an
improved version of the event generator BABAYAGA with a theoretical accuracy of
the order of 0.1%. The generator is now available for high-precision
simulations of the Bhabha process at flavour factories.Comment: 34 pages, 8 figures, uses elsart.cls. Version to appear on Nuclear
Physics
An Actively Controlled Carbody Centering System for the Lateral Suspension of High Speed Trains
High speed trains normally use pneumatic actuation systems to recenter the carbody with respect to the bogie when the train negotiates a curve. Pneumatic systems are used because of their compliance, necessary to ensure dynamic isolation between carbody and bogie, but have the drawbacks of large dimensions and slow response, often accompanied by a few damped oscillations. An innovative solution was developed using hydraulic actuators with an adaptive control law providing the actuators with artificial compliance, hence making them suitable for this application. A carbody centering system is thus obtained presenting fast response, small volume and the necessary compliance. The optimal control law for this system was defined, the system dynamic characteristics were analyzed and a technological demonstrator was built to assess the system merits. The paper presents the theoretical grounds for the system control, its implementation and performance, and the most significant test results obtained with the technological demonstrator