114 research outputs found
NNLO massive corrections to Bhabha scattering and theoretical precision of BabaYaga@NLO
We provide an exact calculation of next-to-next-to-leading order (NNLO)
massive corrections to Bhabha scattering in QED, relevant for precision
luminosity monitoring at meson factories. Using realistic reference event
selections, exact numerical results for leptonic and hadronic corrections are
given and compared with the corresponding approximate predictions of the event
generator BabaYaga@NLO. It is shown that the NNLO massive corrections are
necessary for luminosity measurements with per mille precision. At the same
time they are found to be well accounted for in the generator at an accuracy
level below the one per mille. An update of the total theoretical precision of
BabaYaga@NLO is presented and possible directions for a further error reduction
are sketched.Comment: 5 pages, 3 tables, contrib. to proceedings of International Workshop
on e+e- collisions: from Phi to Psi, PHIPSI11, BINP, Novosibirsk, Russia,
September 19-22, 201
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
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
Status and accuracy of the Monte Carlo generators for luminosity measurements
The status and accuracy of the precision Monte Carlo generators used for
luminosity measurements at flavour factories is reviewed. It is shown that,
thanks to a considerable, long-term effort in tuned comparisons between the
predictions of independent programs, as well as in the validation of the
generators against the presently available calculations of the
next-to-next-to-leading order QED corrections to Bhabha scattering, the
theoretical accuracy reached by the most precise tools is of about one per
mille. This error estimate is valid for realistic experimental cuts, appears to
be quite robust and is already sufficient for very accurate luminosity
measurements. However, recent progress and possible advances to further improve
it are also discussed.Comment: 6 pages, 1 table. Proceedings of the PhiPsi09 workshop, Oct. 13-16,
2009, Beijing, Chin
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
Mini-review on Monte Carlo programs for Bhabha scattering
We review the status of Monte Carlo generators presently used for simulations
of the large-angle Bhabha process at electron-positron colliders of moderately
high energy (flavour factories), operating at centre-of-mass energies between
about 1 GeV and 10 GeV. It is shown how the theoretical accuracy reached by
present Bhabha programs for physics at flavour factories is at the level of
0.1% and, therefore, comparable with that reached about a decade ago for
luminosity monitoring through small-angle Bhabha scattering at LEP.Comment: Contribution to the Proceedings of the 9th DESY workshop on "Loops
and Legs in Quantum Field Theory", Sondershausen, April 200
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
The relevance of polarized bZ production at LHC
We consider the Z polarization asymmetry
A_Z=(sigma(Z_R)-sigma(Z_L))/(sigma(Z_R)+sigma(Z_L)) in the process of
associated bZ production at the LHC. We show that in the Standard Model (SM)
this quantity is essentially given by its Born approximation, remaining almost
unaffected by QCD scales and parton distribution functions variations as well
as by electroweak corrections. The theoretical quantity that appears in A_Z is
the same that provides the LEP1 Z -> b bbar forward-backward asymmetry, the
only measured observable still in some contradiction with the SM prediction. In
this sense, A_Z would provide the possibility of an independent verification of
the possible SM discrepancy, which could reach, if consistency with LEP1
measurements is imposed, values of the relative ten percent size.Comment: 10 pages, 5 eps figure
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