We present a new calculation of next-to-leading-order corrections of the strong and electroweak interactions to like-sign W-boson scattering at the Large Hadron Collider, implemented in the Monte Carlo integrator Bonsay. The calculation includes leptonic decays of the W bosons. It comprises the whole tower of next-to-leading-order contributions to the cross section, which scale like   <math> <msubsup> <mi>α</mi> <mi>s</mi> <mn>3</mn> </msubsup> </math>  $$ {\alpha}_{\textrm{s}}^3 $$  α 4,   <math> <msubsup> <mi>α</mi> <mi>s</mi> <mn>2</mn> </msubsup> </math>  $$ {\alpha}_{\textrm{s}}^2 $$  α 5, α s α 6, and α 7 in the strong and electroweak couplings α s and α. We present a detailed survey of numerical results confirming the occurrence of large pure electroweak corrections of the order of ~ −12% for integrated cross sections and even larger corrections in high-energy tails of distributions. The electroweak corrections account for the major part of the complete next-to-leading-order correction, which amounts to 15–20% in size, depending on the details of the event selection chosen for analysing vector-boson-scattering. Moreover, we compare the full next-to-leading-order corrections to approximate results based on the neglect of contributions that are not enhanced by the vector-boson scattering kinematics (VBS approximation) and on resonance expansions for the W-boson decays (double-pole approximation); the quality of this approximation is good within ≲ 1.5% for integrated cross sections and the dominating parts of the differential distributions. Finally, for the leading-order predictions, we construct different versions of effective vector-boson approximations, which are based on cross-section contributions that are enhanced by collinear emission of W bosons off the initial-state (anti)quarks; in line with previous findings in the literature, it turns out that the approximative quality is rather limited for applications at the LHC.

Germany

Stefan Dittmaier

Philipp Maierhöfer

Christopher Schwan

Belgium

Ramon Winterhalder

Like-sign W-boson scattering at the LHC — approximations and full next-to-leading-order predictions

A detailed study of Higgs interference effects at the one-loop level in the 1-Higgs-Singlet extension of the Standard Model (1HSM) is presented for the W + W − and   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> </math>  $$ t\overline{t} $$  decay modes with fully leptonic W W decay. We explore interference effects for benchmark points with a heavy Higgs mass that significantly exceeds 2m  t . In the W W channel, the Higgs signal and the interfering continuum background are loop induced. In the   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> </math>  $$ t\overline{t} $$  channel, which features a tree-level background, we also calculate the interference with the one-loop background, which, due to the appearance of the absorptive part, is found to dominate the normalisation and shape of differential Higgs cross section distributions and should therefore be considered in experimental analyses. The commonly used geometric average K-factor approximation K interference ≈ (K Higgs K background)1/2 is not appropriate. We calculate with massive top and bottom quarks. Our 1HSM and SM implementation in Sherpa+OpenLoops is publicly available and can be used as parton-level integrator or event generator.

United Kingdom

Nikolas Kauer

Alexander Lind

Weimin Song

Higgs interference effects at the one-loop level in the 1-Higgs-Singlet extension of the Standard Model

We present the new version of OpenLoops, an automated generator of tree and one-loop scattering amplitudes based on the open-loop recursion. One main novelty of OpenLoops 2 is the extension of the original algorithm from NLO QCD to the full Standard Model, including electroweak (EW) corrections from gauge, Higgs and Yukawa interactions. In this context, among several new features, we discuss the systematic bookkeeping of QCD–EW interferences, a flexible implementation of the complex-mass scheme for processes with on-shell and off-shell unstable particles, a special treatment of on-shell and off-shell external photons, and efficient scale variations. The other main novelty is the implementation of the recently proposed on-the-fly reduction algorithm, which supersedes the usage of external reduction libraries for the calculation of tree–loop interferences. This new algorithm is equipped with an automated system that avoids Gram-determinant instabilities through analytic methods in combination with a new hybrid-precision approach based on a highly targeted usage of quadruple precision with minimal CPU overhead. The resulting significant speed and stability improvements are especially relevant for challenging NLO multi-leg calculations and for NNLO applications.

Switzerland

Federico Buccioni

Jean-Nicolas Lang

Jonas Lindert

Stefano Pozzorini

Hantian Zhang

Max Zoller

OpenLoops 2

We present the first computation of the full next-to-leading-order QCD and electroweak corrections to the WZ scattering process at the LHC. All off-shell, gauge-boson-decay, and interference effects are taken into account for the process pp → μ + μ −e+ ν ej j + X at the orders   <math> <mi>O</mi> </math>  $$ \mathcal{O} $$ (α s α 6) and   <math> <mi>O</mi> </math>  $$ \mathcal{O} $$ (α 7). The electroweak corrections feature the typical Sudakov behaviour towards high energy and amount to −16% relative to the electroweak contribution to the integrated cross section. Moreover, the corrections induce significant shape distortions in differential distributions. The next-to-leading-order analysis of the quark- and gluon-induced channels is supplemented by a leading-order study of all possible contributions to the full 4ℓ + 2jets production cross section in a realistic fiducial phase-space volume.

Ansgar Denner

Mathieu Pellen

Italy

QCD and electroweak corrections to WZ scattering at the LHC

We report on the first fully differential calculation for double Higgs boson production through gluon fusion in hadron collisions up to next-to-next-to-leading order (NNLO) in QCD perturbation theory. The calculation is performed in the heavy-top limit of the Standard Model, and in the phenomenological results we focus on pp collisions at s = 14 $$ \sqrt{s}=14 $$ TeV. We present differential distributions through NNLO for various observables including the transverse-momentum and rapidity distributions of the two Higgs bosons. NNLO corrections are at the level of 10%-25% with respect to the next-to-leading order (NLO) prediction with a residual scale uncertainty of 5%-15% and an overall mild phase-space dependence. Only at NNLO the perturbative expansion starts to converge yielding overlapping scale uncertainty bands between NNLO and NLO in most of the phase-space. The calculation includes NLO predictions for pp → HH + jet + X . Corrections to the corresponding distributions exceed 50% with a residual scale dependence of 20%-30%.

Argentina

Daniel Florian

Massimiliano Grazzini

Catalin Hanga

Stefan Kallweit

Javier Mazzitelli

Dirk Rathlev

Differential Higgs boson pair production at next-to-next-to-leading order in QCD

We present differential cross sections for the production of top-quark pairs in conjunction with up to two jets, computed at next-to-leading order in perturbative QCD and consistently merged with a parton shower in the S herpa +O pen L oops framework. Top quark decays including spin correlation effects are taken into account at leading order accuracy. The calculation yields a unified description of top-pair plus multi-jet production, and detailed results are presented for various key observables at the Large Hadron Collider. A large improvement with respect to the multi-jet merging approach at leading order is found for the total transverse energy spectrum, which plays a prominent role in searches for physics beyond the Standard Model.

United States

Stefan Höche

Frank Krauss

Marek Schönherr

Frank Siegert

Next-to-leading order QCD predictions for top-quark pair production with up to two jets merged with a parton shower

We present the computation of the double real and real-virtual contributions to top-antitop pair production in the quark-antiquark channel at leading colour. The q q ¯ $$ q\overline{q} $$ → t t ¯ g $$ t\overline{t} g $$ amplitudes contributing to the real-virtual part are computed with O pen L oops , and their numerical stability in the soft and collinear regions is found to be sufficiently high to perform a realistic NNLO calculation in double precision. The subtraction terms required at real-real and real-virtual levels are constructed within the antenna subtraction formalism extended to deal with the presence of coloured massive final state particles. We show that those subtraction terms approximate the real-real and real-virtual matrix elements in all their singular limits.

Gabriel Abelof

Aude Gehrmann-De Ridder

NNLO QCD subtraction for top-antitop production in the q q ¯ $$ q\overline{q} $$ channel

We develop a Monte Carlo event generator for Higgs Boson pair production merged to exact one-jet matrix elements. The matrix elements are generated with OpenLoops and event generation is performed with the HERWIG++ general-purpose event generator. This allows us to simulate fully-exclusive hadronic final states with accurate description of the kinematics of the leading jet in conjunction with a parton shower. We use the implementation to examine in detail the systematic uncertainties which result from the merging procedure. We assess the magnitude of the impact of the merging on experimental searches of Standard Model di-Higgs production that aim to constrain the Higgs boson self-coupling. We find that the use of a merged sample can reduce theoretical systematic uncertainties in the efficiencies of cuts on certain observables. This constitutes the most accurate simulation of the process available to date. The Monte Carlo event generator developed for this project is available as an add-on to the HERWIG++ event generator at http://www.physik.uzh.ch/data/openloops/download/projects/hhmerge/ .

Andreas Papaefstathiou

Higgs boson pair production merged to one jet