We consider QCD radiative corrections to $$ {W}^{+}{W}^{-}b\overline{b} $$ production with leptonic decays and massive bottom quarks at the LHC. We perform an exact next-to-leading order (NLO) calculation within the $\textit{q}$ -subtraction formalism and validate it against an independent computation in the dipole subtraction scheme. Non-resonant and off-shell effects related to the top quarks and the leptonic decays of the $\textit{W}$ bosons are consistently included. We also consider the approximation in which the real-emission contribution is computed exactly while the virtual is evaluated in the double-pole approximation (DPA), which formally requires the inclusion of both factorisable and non-factorisable corrections. We evaluate such contributions and show that the DPA performs remarkably well at both the inclusive and differential levels. We then extend our calculation to the next-to-next-to-leading order (NNLO). All tree-level and one-loop amplitudes are evaluated exactly, while the missing two-loop virtual contribution is estimated using the DPA. The factorisable two-loop corrections are explicitly computed by relying on available results for the polarised two-loop on-shell top-quark pair production amplitudes and the corresponding top-quark decays. The non-factorisable contributions are inferred by exploiting the cancellation of logarithmic singularities in the Γ → 0 limit through an on-shell matching procedure. The NNLO corrections for the inclusive cross section are found to increase the NLO prediction by approximately 11%, with a numerical uncertainty that is conservatively estimated to be below the 2% level — significantly smaller than the 5% residual perturbative uncertainties.

Switzerland

Luca Buonocore

Massimiliano Grazzini

Stefan Kallweit

United Kingdom

Jonas Lindert

Germany

Chiara Savoini

Towards NNLO QCD predictions for off-shell top-quark pair production and decays

We report on the complete computation of the mixed QCD-electroweak corrections to the neutral-current Drell-Yan process. Our calculation holds in the entire range of dilepton invariant masses. We present phenomenological results for several kinematical distributions in the case of bare muons both in the resonant region and for high invariant masses. We also consider the forward-backward asymmetry, which is a key observable to measure the weak mixing angle. We finally extend our calculation to dressed leptons and compare our results in the massless limit to those available in the literature.

Belgium

Italy

Tommaso Armadillo

Roberto Bonciani

Simone Devoto

India

Narayan Rana

Alessandro Vicini

Mixed QCD-EW corrections to the neutral-current Drell-Yan process

We present the first fully differential next-to-next-to-leading order (NNLO) QCD calculation for the production of a top-antitop quark pair in association with a Higgs boson $$ \left(t\overline{t}H\right) $$ at hadron colliders. The computation is exact, except for the finite part of the two-loop virtual contribution, which we estimate using two different methods that yield consistent results within their respective uncertainties. The first method relies on a soft-Higgs factorisation formula that we develop up to the three-loop order. The second is based on a high-energy expansion in the small top-mass limit. Combining the newly computed corrections with the complete set of next-to-leading order (NLO) QCD+EW results provides the most advanced perturbative prediction currently available at the LHC for both inclusive and differential $$ t\overline{t}H $$ cross sections. The uncertainties due to the missing exact two-loop contribution are conservatively estimated to be at the percent level, both for the total cross section and for most of the differential distributions, and therefore subleading compared to the residual perturbative uncertainties.

Javier Mazzitelli

Precise predictions for

The production of a top-antitop quark pair in association with a <math><mrow><mi>W</mi></mrow></math> boson (<math><mi>t</mi><mover><mi>t</mi><mo>¯</mo></mover><mi>W</mi></math>) is one of the heaviest signatures currently probed at the Large Hadron Collider. Since the first observation reported in 2015, the corresponding rates have been found to be consistently higher than the standard model predictions, which are based on next-to-leading order calculations in the QCD and electroweak interactions. We present the first next-to-next-to-leading order QCD computation of <math><mi>t</mi><mover><mi>t</mi><mo>¯</mo></mover><mi>W</mi></math> production at hadron colliders. The calculation is exact, except for the finite part of the two-loop virtual corrections, which is estimated using two different approaches that lead to consistent results within their uncertainties. We combine the newly computed next-to-next-to-leading order QCD corrections with the complete next-to-leading order QCD plus electroweak results, thus obtaining the most advanced perturbative prediction available to date for the <math><mi>t</mi><mover><mi>t</mi><mo>¯</mo></mover><mi>W</mi></math> inclusive cross section. The tension with the latest ATLAS and CMS results remains at the <math><mrow><mn>1</mn><mi>σ</mi><mtext>−</mtext><mn>2</mn><mi>σ</mi></mrow></math> level.

Luca Rottoli

Precise Predictions for the Associated Production of a <math><mi>W</mi></math> Boson with a Top-Antitop Quark Pair at the LHC

In this paper, the existence of a massive dark photon, associated with a new gauge group is considered. The dark photon can be kinetically mixed with the photon. To study some applications, the thermo field dynamics formalism is used. Exploring the topological structure of this approach, the influence of dark photons on the Stefan–Boltzmann law and the Casimir effect at zero and finite temperature is calculated.

Brazil

V. Prata

A. Santos

Canada

Faqir Khanna

Stefan–Boltzmann law and Casimir effect for dark photons

In this work, we study the production of Higgs boson pairs at next-to-next-to-leading order in QCD matched to parton showers, using the Geneva framework and working in the heavy-top-limit approximation. This includes the resummation of large logarithms of the zero-jettiness   <math> <mi>T</mi> </math>  $$ \mathcal{T} $$  0 up to the next-to-next-to-next-to-leading-log accuracy. This process features an extremely large momentum transfer, which makes its study particularly relevant for matching schemes such as that employed in Geneva, where the resummation of a variable different from that used in the ordering of the parton shower is used. To further study this effect, we extend the original shower interface designed for Pythia8 to include other parton showers, such as Dire and Sherpa.

Simone Alioli

Georgios Billis

Austria

Alessandro Broggio

Alessandro Gavardi

Matthew Lim

Giulia Marinelli

Riccardo Nagar

Davide Napoletano

Double Higgs production at NNLO interfaced to parton showers in GENEVA

Transverse-momentum cuts on undistinguished particles in two-body final states induce an enhanced sensitivity to low momentum scales. This undesirable feature, which ultimately leads to an instability of the fixed-order series, poses additional challenges to non-local subtraction schemes. In this letter, we address this issue for general colour-singlet processes within the <math><msub><mrow><mi>q</mi></mrow><mrow><mi>T</mi></mrow></msub></math>-subtraction formalism, focusing on neutral-current Drell–Yan production. We present a simple procedure to reduce the dependence on the slicing parameter from linear to quadratic, by accounting for the linear power corrections through an appropriate recoil prescription. We observe a dramatical improvement of the numerical convergence and a reduction of the systematic uncertainties. We also discuss how a linear dependence in <math><msub><mrow><mi>q</mi></mrow><mrow><mi>T</mi></mrow></msub></math> can be avoided for Drell–Yan production by using staggered cuts, which, to the best of our understanding, could be used in experimental analyses. We show that our approach can be successfully applied also to on-shell ZZ production. We finally study diphoton production and verify that our approach is insufficient to capture the linear power corrections introduced by the isolation procedure. The recoil prescription is available in version 2.1 of Matrix.

Marius Wiesemann

Linear power corrections for two-body kinematics in the Subtraction Formalism

We describe a number of improvements to the Geneva method for matching NNLO calculations to parton shower programs. In particular, we detail changes to the resummed calculation used in the matching procedure, including disentangling the cross section dependence on factorisation and beam scales, and an improved treatment of timelike logarithms. We also discuss modifications in the implementation of the splitting functions which serve to make the resummed calculation differential in the higher multiplicity phase space. These changes improve the stability of the numerical cancellation of the nonsingular term at small values of the resolution parameter. As a case study, we consider the gluon-initiated Higgs boson production process gg → H. We validate the NNLO accuracy of our predictions against independent calculations, and compare our showered and hadronised results with recent data taken at the ATLAS and CMS experiments in the diphoton decay channel, finding good agreement.

Refining the GENEVA method for Higgs boson production via gluon fusion

We present the first calculation for the hadroproduction of a <math><mi>W</mi></math> boson in association with a massive bottom (<math><mi>b</mi></math>) quark-antiquark pair at next-to-next-to-leading order (NNLO) in QCD perturbation theory. We exploit the hierarchy between the <math><mi>b</mi></math>-quark mass and the characteristic energy scale of the process to obtain a reliable analytic expression for the two-loop virtual amplitude with three massive legs, starting from the corresponding result available for massless <math><mi>b</mi></math> quarks. The use of massive <math><mi>b</mi></math> quarks avoids the ambiguities associated with the correct flavor assignment in massless calculations, paving the way to a more realistic comparison with experimental data. We present phenomenological results considering proton-proton collisions at center-of-mass energy <math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13.6</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> for inclusive <math><mi>W</mi><mi>b</mi><mover><mi>b</mi><mo>¯</mo></mover></math> production and within a fiducial region relevant for the associated production of a <math><mi>W</mi></math> boson and a Higgs boson decaying into a <math><mi>b</mi><mover><mi>b</mi><mo>¯</mo></mover></math> pair, for which <math><mi>W</mi><mi>b</mi><mover><mi>b</mi><mo>¯</mo></mover></math> production represents one of the most relevant backgrounds. We find that the NNLO corrections are substantial and that their inclusion is mandatory to obtain reliable predictions.

Associated production of a <math><mi>W</mi></math> boson and massive bottom quarks at next-to-next-to-leading order in QCD

The associated production of a Higgs boson with a top-antitop quark pair is a crucial process at the LHC since it allows for a direct measurement of the top-quark Yukawa coupling. We present the computation of the radiative corrections to this process at the next-to-next-to-leading order (NNLO) in QCD perturbation theory. This is the very first computation for a <math><mrow><mn>2</mn><mo>→</mo><mn>3</mn></mrow></math> process with massive colored particles at this perturbative order. We develop a soft Higgs boson approximation for loop amplitudes, which enables us to reliably quantify the impact of the yet unknown two-loop contribution. At the center-of-mass energy <math><mrow><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></mrow></math>, the NNLO corrections increase the next-to-leading order result for the total cross section by about 4% and lead to a significant reduction of perturbative uncertainties.

Stefano Catani

Higgs Boson Production in Association with a Top-Antitop Quark Pair in Next-to-Next-to-Leading Order QCD