32,921 research outputs found
The BaBar Electromagnetic Calorimeter: Status and Performance Improvements
The electromagnetic calorimeter at the BaBar detector, part of the asymmetric
B Factory at SLAC, measures photons in the energy range from 20 MeV to 8 GeV
with high resolution. The current status of the calorimeter, now in its seventh
year of operation, is being presented, as well as details on improvements made
to the analysis code during the last years.Comment: 6 pages, 15 figures, presented at the 2005 IEEE Nuclear Science
Symposium and submitted to the Conference Proceedings of the 2005 IEEE
Nuclear Science Symposiu
Iterative structure of finite loop integrals
In this paper we develop further and refine the method of differential
equations for computing Feynman integrals. In particular, we show that an
additional iterative structure emerges for finite loop integrals. As a concrete
non-trivial example we study planar master integrals of light-by-light
scattering to three loops, and derive analytic results for all values of the
Mandelstam variables and and the mass . We start with a recent
proposal for defining a basis of loop integrals having uniform transcendental
weight properties and use this approach to compute all planar two-loop master
integrals in dimensional regularization. We then show how this approach can be
further simplified when computing finite loop integrals. This allows us to
discuss precisely the subset of integrals that are relevant to the problem. We
find that this leads to a block triangular structure of the differential
equations, where the blocks correspond to integrals of different weight. We
explain how this block triangular form is found in an algorithmic way. Another
advantage of working in four dimensions is that integrals of different loop
orders are interconnected and can be seamlessly discussed within the same
formalism. We use this method to compute all finite master integrals needed up
to three loops. Finally, we remark that all integrals have simple Mandelstam
representations.Comment: 26 pages plus appendices, 5 figure
Four-gluon scattering at three loops, infrared structure and Regge limit
We compute the three-loop four-gluon scattering amplitude in maximally
supersymmetric Yang-Mills theory, including its full color dependence. Our
result is the first complete computation of a non-planar four-particle
scattering amplitude to three loops in four-dimensional gauge theory and
consequently provides highly non-trivial data for the study of non-planar
scattering amplitudes. We present the amplitude as a Laurent expansion in the
dimensional regulator to finite order, with coefficients composed of harmonic
poly-logarithms of uniform transcendental weight, and simple rational
prefactors. Our computation provides an independent check of a recent result
for three-loop corrections to the soft anomalous dimension matrix that predicts
the general infrared singularity structure of massless gauge theory scattering
amplitudes. Taking the Regge limit of our result, we determine the three-loop
gluon Regge trajectory. We also find agreement with very recent predictions for
sub-leading logarithms
- …