305 research outputs found
Factorisation and Subtraction beyond NLO
We provide a general method to construct local infrared subtraction
counterterms for unresolved radiative contributions to differential cross
sections, to any order in perturbation theory. We start from the factorised
structure of virtual corrections to scattering amplitudes, where soft and
collinear divergences are organised in gauge-invariant matrix elements of
fields and Wilson lines, and we define radiative eikonal form factors and jet
functions which are fully differential in the radiation phase space, and can be
shown to cancel virtual poles upon integration by using completeness relations
and general theorems on the cancellation of infrared singularities. Our method
reproduces known results at NLO and NNLO, and yields substantial
simplifications in the organisation of the subtraction procedure, which will
help in the construction of efficient subtraction algorithms at higher orders.Comment: 34 pages, 3 figure
NLO QCD corrections to polarised di-boson production in semi-leptonic final states
Understanding the polarisation structure and providing precise predictions
for multi-boson processes at the LHC is becoming urgent in the light of the
upcoming run-3 and high-luminosity data. The CMS and ATLAS collaborations have
already started using polarised predictions to perform template fits of the
data, getting access to the polarisation of W and Z bosons. So far, only
fully-leptonic decay channels have been considered in this perspective. The
natural step forward is the investigation of hadronic decays of electroweak
bosons. In this work, we compute NLO QCD corrections to the production and
decay of WZ pairs at the LHC in final states with two charged leptons and jets.
The calculation relies on the double-pole approximation and the separation of
polarised states at the level of Standard Model amplitudes. The presented
NLO-accurate results are necessary building blocks for a broad understanding
and precise modelling of polarised di-boson production in semi-leptonic decay
channels.Comment: 25 pages (one-column PRD layout), 12 figures, 3 tables. Refined
structure, added comments and numbers about DPA accuracy and irreducible
backgrounds, further minor corrections. Matches published version in PR
NLO QCD and EW corrections to off-shell production at the LHC
The production of a single top quark in association with a boson
( production) at the LHC is a relevant probe of
the electroweak sector of the Standard Model as well as a window to possible
new-physics effects. The growing experimental interest in performing
differential measurements for this process demands an improved theoretical
modelling in realistic fiducial regions. In this article we present an
NLO-accurate calculation that includes
complete off-shell effects and spin correlations, combining QCD and electroweak
radiative corrections to the LO signal. Integrated and differential
cross-sections are shown for a fiducial setup characterized by three charged
leptons, two jets, and missing energy.Comment: 24 pages, 10 figure
Polarized vector boson scattering in the fully leptonic WZ and ZZ channels at the LHC
Isolating the scattering of longitudinal weak bosons at the LHC is an
important tool to probe the ElectroWeak Symmetry Breaking mechanism. Separating
polarizations of and bosons is complicated, because of non resonant
contributions and interference effects. Additional care is necessary when
considering bosons, due to the mixing in the coupling to charged
leptons.
We propose a method to define polarized signals in and
scattering at the LHC, which relies on the separation of weak boson
polarizations at the amplitude level in Monte Carlo simulations.
After validation in the absence of lepton cuts, we investigate how polarized
distributions are affected by a realistic set of kinematic cuts (and neutrino
reconstruction, when needed). The total and differential polarized cross
sections computed at the amplitude level are well defined, and their sum
reproduces the full results, up to non negligible but computable interference
effects which should be included in experimental analyses. We show that
polarized cross sections computed using the reweighting method are inaccurate,
particularly at large energies. We also present two procedures which address
the model independent extraction of polarized components from LHC data, using
Standard Model angular distribution templates.Comment: version published in JHE
Complete NLO corrections to off-shell production at the LHC
Measuring precisely top-pair-associated processes at hadron colliders will
become possible with the upcoming LHC running stages. The increased data
statistics will especially enable differential measurements leading to an
improved characterisation of such processes. Aiming at a consistent data-theory
comparison, precise Standard-Model predictions are needed, including
higher-order corrections and full off-shell effects. In this work we present
NLO-accurate predictions for the production and decay of a top-antitop pair in
association with a Z boson at the LHC, in the multi-lepton decay channel. The
complete set of LO contributions and NLO corrections of EW and QCD origin is
included. The calculation is based on full matrix elements, computed with all
resonant and non-resonant contributions, complete spin correlations and
interference effects. Integrated and differential cross-sections are presented
for a realistic fiducial setup.Comment: 38 pages, 10 pdf figure files, 24 png figure file
Different polarization definitions in same-sign scattering at the LHC
We study the polarization of positively charged 's in the scattering of
massive electroweak bosons at hadron colliders. We rely on the separation of
weak boson polarizations in the gauge-invariant, doubly-resonant part of the
amplitude in Monte Carlo simulations. Polarizations depend on the reference
frame in which they are defined. We discuss the change in polarization
fractions and in kinematic distributions arising from defining polarization
vectors in two different reference frames which have been employed in recent
experimental analyses.Comment: added reference to CMS measurement, typos corrected, matches PLB
published versio
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