14 research outputs found
Thread-Scalable Evaluation of Multi-Jet Observables
A leading-order, leading-color parton-level event generator is developed for
use on a multi-threaded GPU. Speed-up factors between 150 and 300 are obtained
compared to an unoptimized CPU-based implementation of the event generator. In
this first paper we study the feasibility of a GPU-based event generator with
an emphasis on the constraints imposed by the hardware. Some studies of Monte
Carlo convergence and accuracy are presented for PP -> 2,...,10 jet observables
using of the order of 1e11 events.Comment: 16 pages, 5 figures, 3 table
Kinematical Limits on Higgs Boson Production via Gluon Fusion in Association with Jets
In this paper, we analyze the high-energy limits for Higgs boson plus two jet
production. We consider two high-energy limits, corresponding to two different
kinematic regions: a) the Higgs boson is centrally located in rapidity between
the two jets, and very far from either jet; b) the Higgs boson is close to one
jet in rapidity, and both of these are very far from the other jet. In both
cases the amplitudes factorize into impact factors or coefficient functions
connected by gluons exchanged in the t channel. Accordingly, we compute the
coefficient function for the production of a Higgs boson from two off-shell
gluons, and the impact factors for the production of a Higgs boson in
association with a gluon or a quark jet. We include the full top quark mass
dependence and compare this with the result obtained in the large top-mass
limit.Comment: 35 pages, 6 figure
Scattering amplitudes with massive fermions using BCFW recursion
We study the QCD scattering amplitudes for \bar{q}q \to gg and \bar{q}q \to
ggg where q is a massive fermion. Using a particular choice of massive fermion
spinor we are able to derive very compact expressions for the partial spin
amplitudes for the 2 \to 2 process. We then investigate the corresponding 2 \to
3 amplitudes using the BCFW recursion technique. For the helicity conserving
partial amplitudes we again derive very compact expressions, but were unable to
treat the helicity-flip amplitudes recursively, except for the case where all
the gluon helicities are the same. We therefore evaluate the remaining partial
amplitudes using standard Feynman diagram techniques.Comment: 21 page
The fully differential single-top-quark cross section in next-to-leading order QCD
We present a new next-to-leading order calculation for fully differential
single-top-quark final states. The calculation is performed using phase space
slicing and dipole subtraction methods. The results of the methods are found to
be in agreement. The dipole subtraction method calculation retains the full
spin dependence of the final state particles. We show a few numerical results
to illustrate the utility and consistency of the resulting computer
implementations.Comment: 37 pages, latex, 2 ps figure
Gauge invariant sub-structures of tree-level double-emission exact QCD spin amplitudes
In this note we discuss possible separations of exact, massive, tree-level
spin amplitudes into gauge invariant parts. We concentrate our attention on
processes involving two quarks entering a color- neutral current and, thanks to
the QCD interactions, two extra external gluons. We will search for forms
compatible with parton shower languages, without applying approximations or
restrictions on phase space regions. Special emphasis will be put on the
isolation of parts necessary for the construction of evolution kernels for
individual splittings and to some degree for the running coupling constant as
well. Our aim is to better understand the environment necessary to optimally
match hard matrix elements with partons shower algorithms. To avoid
complications and ambiguities related to regularization schemes, we ignore, at
this point, virtual corrections. Our representation is quite universal: any
color-neutral current can be used, in particular our approach is not restricted
to vector currents only.Comment: 27 pages, formula in section 5 correcte
Production at the Fermilab Tevatron Collider: Gauge Invariance and Radiation Amplitude Zero
The electroweak process is calculated
at tree level, including finite W width effects. In order to obtain a gauge
invariant amplitude, the imaginary parts of triangle graphs and
box diagrams have to be included, in addition to resumming the
imaginary contributions to the W polarization. We demonstrate the existence of
a radiation amplitude zero in , and discuss how it may be observed in correlations of
the and lepton rapidities at the Fermilab Tevatron.Comment: 37 pages,12 figures, postscript file also available via anonymous ftp
at ftp://ucdhep.ucdavis.edu/han/vvv/Wgmgm.p