2,284 research outputs found
One-loop corrections to five-parton amplitudes with external photons
Recently the calculations of all five-parton one-loop QCD amplitudes have
been completed. In this letter we describe how to get the corresponding
amplitudes with one gluon replaced by a photon and we give the explicit results
for the process 0 \to 2q 2Q 1\y.Comment: 7 pages, late
in FDH
We investigate the regularization-scheme dependent treatment of
in the framework of dimensional regularization, mainly focusing on the
four-dimensional helicity scheme (FDH). Evaluating distinctive examples, we
find that for one-loop calculations, the recently proposed four-dimensional
formulation (FDF) of the FDH scheme constitutes a viable and efficient
alternative compared to more traditional approaches. In addition, we extend the
considerations to the two-loop level and compute the pseudo-scalar form factors
of quarks and gluons in FDH. We provide the necessary operator renormalization
and discuss at a practical level how the complexity of intermediate
calculational steps can be reduced in an efficient way.Comment: 28 pages, 7 figure
Lepton-flavour violating decays in theories with dimension 6 operators
Despite a large experimental effort, so far no evidence for flavour-violating
decays of charged leptons such as and
has been found. The absence of a signal puts very severe constraints on many
extensions of the Standard Model. Here we apply a model independent approach by
studying such decays in the Standard Model effective field theory. Going beyond
leading order in the Standard Model couplings and considering all dimension 6
operators that might lead to lepton-flavour violation, we are able to extract
limits on a large number of Wilson coefficients of such operators. We are also
able to compare the impact of particular searches and find, for example, that
flavour-violating decays of the -boson are much more
constrained from low-energy experiments than from the limits
of current and future direct searches at high energy.Comment: 7 pages, 5 Tables; to appear in the Proceedings of the FCCP2015
Worksho
Resonant particle production at hadron colliders
We present a method to compute off-shell effects for processes involving
resonant particles at hadron colliders with the possibility to include
realistic cuts on the decay products. The method is based on an effective
theory approach to unstable particle production and, as an example, is applied
to t-channel single top production at the LHC.Comment: 6 pages, to appear in the proceedings of the 9th International
Symposium on Radiative Corrections (RADCOR 2009), October 25-30 2009, Ascona,
Switzerlan
Two-loop Correction to the Leptonic Decay of Quarkonium
Applying asymptotic expansions at threshold, we compute the two-loop QCD
correction to the short-distance coefficient that governs the leptonic decay
of a S-wave quarkonium state and discuss its impact on the
relation between the quarkonium non-relativistic wave function at the origin
and the quarkonium decay constant in full QCD.Comment: 7 pages, LaTeX, 1 figure included via epsf.st
Fully differential NLO predictions for the radiative decay of muons and taus
We present a general purpose Monte Carlo program for the calculation of the
radiative muon decay and the radiative decays
and at
next-to-leading order in the Fermi theory. The full dependence on the lepton
masses and polarization of the initial-sate lepton are kept. We study the
branching ratios for these processes and show that fully-differential
next-to-leading order corrections are important for addressing a tension
between BaBar's recent measurement of the branching ratio and the Standard Model prediction. In addition, we
study various distributions of the process and
obtain precise predictions for the irreducible background to
searches, tailored to the geometry of the MEG detector.Comment: 14 pages, 5 figures, published versio
Renormalization-group improved fully differential cross sections for top pair production
We extend approximate next-to-next-to-leading order results for top-pair
production to include the semi-leptonic decays of top quarks in the
narrow-width approximation. The new hard-scattering kernels are implemented in
a fully differential parton-level Monte Carlo that allows for the study of any
IR-safe observable constructed from the momenta of the decay products of the
top. Our best predictions are given by approximate NNLO corrections in the
production matched to a fixed order calculation with NLO corrections in both
the production and decay subprocesses. Being fully differential enables us to
make comparisons between approximate results derived via different (PIM and
1PI) kinematics for arbitrary distributions. These comparisons reveal that the
renormalization-group framework, from which the approximate results are
derived, is rather robust in the sense that applying a realistic error estimate
allows us to obtain a reliable prediction with a reduced theoretical error for
generic observables and analysis cuts
Performance tests with a 4.75 inch bore tapered-roller bearings at high speeds
The tapered-roller bearings were tested at speeds to 15,000 rpm which results in a cone-rib tangential velocity of 130 m/sec. (25,500 ft/min). Lubrication was applied either by jets or directly to the cone-rib, augmented with jets. Additional test parameters included thrust loads to 53,400 N (12,000 lbs), radial loads to 26,700 N (6,000 lbs), lubricant flow rates from 1.9 x 0.000 to 15.1 x 0.001 cubic meter/min. (0.5 to 4.0 gpm), and lubricant inlet temperatures of 350 K and 364 K (170 F and 195 F). Temperature distribution, separator speed, and drive-motor power demand were determined as functions of these test parameters
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