62 research outputs found
Universality in W+Multijet Production
We study -boson production accompanied by multiple jets at 7 TeV at the
LHC. We study the jet-production ratio, of total cross sections for +- to
+()-jet production, and the ratio of distributions in the total
transverse hadronic jet energy . We use the ratios to
extrapolate the total cross section, and the differential distribution in
, to +6-jet production. We use the BlackHat software
library in conjunction with SHERPA to perform the computations.Comment: Merge of Moriond 2014 and Loops & Legs 2014 proceedings, 6 pages, 2
figure
High multiplicity W+jets predictions at NLO
In these proceedings we present results from a recent calculation for the
production of a W boson in conjunction with five jets at next-to-leading order
in perturbative QCD. We also use results at lower multiplicities to extrapolate
the cross section to the same process with six jets.Comment: 5 pages, Proceedings for the DIS2013 conferenc
The BlackHat Library for One-Loop Amplitudes
We present recent next-to-leading order (NLO) results in perturbative QCD
obtained using the BlackHat software library. We discuss the use of n-tuples to
separate the lengthy matrix-element computations from the analysis process. The
use of n-tuples allows many analyses to be carried out on the same phase-space
samples, and also allows experimenters to conduct their own analyses using the
original NLO computation.Comment: Talk given at ACAT 2013, Beijing, China, May 16--21, 2013; 6 pages, 2
figures; added reference
NLO vector boson production with light jets
In this contribution we present recent progress in the computation of
next-to-leading order (NLO) QCD corrections for the production of an
electroweak vector boson in association with jets at hadron colliders. We focus
on results obtained using the virtual matrix element library BLACKHAT in
conjunction with SHERPA, focusing on results relevant to understanding the
background to top production.Comment: 4+2 epsilon pages, Submitted for the proceedings of TOP2011 - 4th
International Workshop on Top Quark Physics, 25-30th September 2011, Sant
Feliu de Guixols, Spai
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
From Yang-Mills Lagrangian to MHV Diagrams
We prove the equivalence of a recently suggested MHV-formalism to the
standard Yang-Mills theory. This is achieved by a formally non-local change of
variables. In this note we present the explicit formulas while the detailed
proofs are postponed to a future publication.Comment: Latex,11 pages, minor changes, reference added, version to appear in
JHE
Left-Handed W Bosons at the LHC
The production of W bosons in association with jets is an important
background to new physics at the LHC. Events in which the W carries large
transverse momentum and decays leptonically lead to large missing energy and
are of particular importance. We show that the left-handed nature of the W
coupling, combined with valence quark domination at a pp machine, leads to a
large left-handed polarization for both W^+ and W^- bosons at large transverse
momenta. The polarization fractions are very stable with respect to QCD
corrections. The leptonic decay of the W bosons translates the common
left-handed polarization into a strong asymmetry in transverse momentum
distributions between positrons and electrons, and between neutrinos and
anti-neutrinos (missing transverse energy). Such asymmetries may provide an
effective experimental handle on separating W + jets from top quark production,
which exhibits very little asymmetry due to C invariance, and from various
types of new physics.Comment: 32 pages, revtex, 17 figures, 3 tables, v2 minor corrections to ME+PS
results, no changes to conclusions, added reference
Color-dressed recursive relations for multi-parton amplitudes
Remarkable progress inspired by twistors has lead to very simple analytic
expressions and to new recursive relations for multi-parton color-ordered
amplitudes. We show how such relations can be extended to include color and
present the corresponding color-dressed formulation for the Berends-Giele, BCF
and a new kind of CSW recursive relations. A detailed comparison of the
numerical efficiency of the different approaches to the calculation of
multi-parton cross sections is performed.Comment: 31 pages, 4 figures, 6 table
On-shell recursion relations for all Born QCD amplitudes
We consider on-shell recursion relations for all Born QCD amplitudes. This
includes amplitudes with several pairs of quarks and massive quarks. We give a
detailed description on how to shift the external particles in spinor space and
clarify the allowed helicities of the shifted legs. We proof that the
corresponding meromorphic functions vanish at z --> infinity. As an application
we obtain compact expressions for helicity amplitudes including a pair of
massive quarks, one negative helicity gluon and an arbitrary number of positive
helicity gluons.Comment: 30 pages, minor change
MHV Techniques for QED Processes
Significant progress has been made in the past year in developing new `MHV'
techniques for calculating multiparticle scattering amplitudes in Yang-Mills
gauge theories. Most of the work so far has focussed on applications to Quantum
Chromodynamics, both at tree and one-loop level. We show how such techniques
can also be applied to abelian theories such as QED, by studying the simplest
tree-level multiparticle process, e^+e^- to n \gamma. We compare explicit
results for up to n=5 photons using both the Cachazo, Svrcek and Witten `MHV
rules' and the related Britto-Cachazo-Feng `recursion relation' approaches with
those using traditional spinor techniques.Comment: 19 pages, 10 figures. References adde
- âŠ