In this work we consider the production of a top-antitop pair at the LHC when the mass of the pair is relatively near to the nominal threshold, that is to say to twice the top pole mass. In this regime, enhanced perturbative corrections arise that can be computed to all orders in perturbation theory. We present three generators of the NLO+PS kind (Next-to-Leading-Order that can be interfaced to parton showers) that include these threshold enhanced effects. Using these generators we address the following questions: what is the size of enhanced non-relativistic effects that are not already present in the well known NLO and NNLO perturbative results; what is the size of the contribution from these effects that can be loosely attributed to toponium production; and to what extent the finite width of the top quark affects threshold enhanced corrections. Our generators are relevant for the recent observation of enhanced tt̅ production near threshold in the pseudoscalar channel by the ATLAS and CMS collaborations.

We perform for the first time a full study of spin correlations in inclusive production of WZ boson pairs at the LHC with leptonic decays in the presence of next-to-leading-order QCD corrections and of effects from a dimension-six operator in the Standard-Model effective field theory (SMEFT) modifying the electroweak triple-gauge coupling. We carry out the complete quantum-state tomography of the diboson system and relate its results to common purity and spin-entanglement markers, highlighting the sizeable impact of both QCD corrections and SMEFT insertions. Additionally, we show how a na & iuml;ve truncation at dimension six in the SMEFT expansion of the spin-density matrix can lead to a cumbersome spin interpretation of the quantum-tomography results.

The production of a boosted Higgs boson in association with a charged weak (W) boson is a key process to scrutinize the electroweak symmetry breaking mechanism at hadron colliders. This reaction constitutes the dominant Higgs production channel at large transverse momentum, providing unique sensitivity to Higgs-boson interactions with other Standard Model particles as well as to physics beyond the Standard Model. In this Letter, we present the first fully differential calculation of this important scattering process at next-to-next-to-next-to-leading order (N^3LO) in perturbative Quantum Chromodynamics (QCD). We find that the N^3LO corrections, amounting to approximately +2% in the boosted regime, generally lie at the edge of or outside the standard scale variation band of the previous perturbative order. The residual dependence of the N^3LO prediction on perturbative scales is reduced to below the percent level, marking a milestone for the Higgs precision program.

Abstract In this paper we present the first application of the MiNLO method to the calculation of QED NLO corrections to the production of a neutral vector boson in Drell–Yan processes. We consider only the case of initial-state radiation, when the Z boson decays into neutrinos. We illustrate the abelianization procedure of the MiNLO formulae and discuss the impact that it has on the differential cross section. We then propose a variant of the MiNLO formulae in order to circumvent some of the problems that arise when dealing with QED emissions. Since this is a case study, we use ad-hoc parton distribution functions and a larger value of the electromagnetic coupling constant, in order to emphasize potential discrepancies with respect to the expected behavior of the MiNLO formulae. We quantify the uncertainties connected with the proposed method, also for a physical value of the electromagnetic coupling. The study presented here is a necessary first step towards incorporating full electroweak effects into the $$\text {MiNNLO}_{\text {PS}}$$ MiNNLO PS framework.

Abstract In this work we consider the QCD predictions for spin correlations in t t ¯ $$ t\overline{t} $$ production in hadronic collisions. In view of recent tensions between experimental data and theoretical calculations, it has been argued that one should include in the predictions also the effects of the production of the η t , i.e. the pseudoscalar t t ¯ $$ t\overline{t} $$ bound state, or alternatively the full effects of the non-relativistic dynamics of the t t ¯ $$ t\overline{t} $$ pair near threshold. This implies the resummation of all corrections that scale like powers of α s /v (where v is the velocity of the top quark in the t t ¯ $$ t\overline{t} $$ rest frame) which are dominated by values of v of order α s . In this work, we show that, since the observables that are usually considered for these studies are integrated cross sections up to a t t ¯ $$ t\overline{t} $$ mass cut that is not small, it is possible to perform the calculation using perturbation theory, considering only the contributions that scale as the first few powers of α s /v. We examine the implications of our approach by computing corrections to nominal Monte Carlo results for correlation-sensitive observables, and compare them with available data, showing that the tension with data is no longer present.

In this work we consider the QCD predictions for spin correlations in tt production in hadronic collisions. In view of recent tensions between experimental data and theoretical calculations, it has been argued that one should include in the predictions also the effects of the production of the ηt, i.e. the pseudoscalar tt bound state, or alternatively the full effects of the non-relativistic dynamics of the tt pair near threshold. This implies the resummation of all corrections that scale like powers of αs/v (where v is the velocity of the top quark in the tt rest frame) which are dominated by values of v of order αs. In this work, we show that, since the observables that are usually considered for these studies are integrated cross sections up to a tt mass cut that is not small, it is possible to perform the calculation using perturbation theory, considering only the contributions that scale as the first few powers of αs/v. We examine the implications of our approach by computing corrections to nominal Monte Carlo results for correlation-sensitive observables, and compare them with available data, showing that the tension with data is no longer present.

We present a computation of diboson production in the W^± Z channel at the Large Hadron Collider (LHC), incorporating leptonic decays of the gauge bosons and considering intermediate gauge bosons with definite polarization states. The analysis includes contributions from the Standard Model effective field theory (SMEFT) and is carried out at next-to-leading order accuracy in QCD, matched to a parton-shower simulation. Our implementation allows for the selection of specific helicity configurations, both in the Standard Model and in the presence of dimension-six operators inducing anomalous triple-gauge-boson couplings. This work provides a key ingredient for both polarization-template and quantum-tomography analyses of diboson systems at the LHC within the SMEFT framework.

Inclusive Higgs boson production at large transverse momentum is induced by different production channels. We focus on the leading production through gluon fusion, and perform a consistent combination of the state of the art calculations obtained in the infinite-top-mass effective theory at next-to-next-to-leading order (NNLO) and in the full Standard Model (SM) at next-to-leading order (NLO). We thus present approximate QCD predictions for this process at NNLO, and a study of the corresponding perturbative uncertainties. This calculation is then compared with those obtained with commonly used event generators, and we observe that the description of the considered kinematic regime provided by these tools is in good agreement with state of the art calculations. Finally, we present accurate predictions for other production channels such as vector boson fusion, and associated production with a gauge boson, and with a $t\bar{t}$ pair. We find that, at large transverse momentum, the contribution of other production modes is substantial, and therefore must be included for a precise theory prediction of this observable.

We provide an overview of the status of Monte-Carlo event generators for high-energy particle physics. Guided by the experimental needs and requirements, we highlight areas of active development, and opportunities for future improvements. Particular emphasis is given to physics models and algorithms that are employed across a variety of experiments. These common themes in event generator development lead to a more comprehensive understanding of physics at the highest energies and intensities, and allow models to be tested against a wealth of data that have been accumulated over the past decades. A cohesive approach to event generator development will allow these models to be further improved and systematic uncertainties to be reduced, directly contributing to future experimental success. Event generators are part of a much larger ecosystem of computational tools. They typically involve a number of unknown model parameters that must be tuned to experimental data, while maintaining the integrity of the underlying physics models. Making both these data, and the analyses with which they have been obtained accessible to future users is an essential aspect of open science and data preservation. It ensures the consistency of physics models across a variety of experiments.

This report presents a short summary of the activities of the "Standard Model" working group for the "Physics at TeV Colliders" workshop (Les Houches, France, 12-30 June, 2023).

[This corrects the article DOI: 10.1007/JHEP05(2020)143.].

We summarize the current status and near future prospects for next-to-next-to-leading order calculations matched to parton shower based on the MiNNLO_ PS method. We give a theoretical overview, illustrate selected results for ZZ→ 4ℓ and top-pair production processes at the LHC, and provide an outlook of the future challenges.

We present a novel method to combine QCD calculations at next-to-next-to-leading order (NNLO) with parton shower (PS) simulations, that can be applied to the production of heavy systems in hadronic collisions, such as colour singlets or a $$ t\overline{t} $$ pair. The NNLO corrections are included by connecting the MiNLO′ method with transverse- momentum resummation, and they are calculated at generation time without any additional reweighting, making the algorithm considerably efficient. Moreover, the combination of different jet multiplicities does not require any unphysical merging scale, and the matching preserves the structure of the leading logarithmic corrections of the Monte Carlo simulation for parton showers ordered in transverse momentum. We present proof-of-concept applications to hadronic Higgs production and the Drell-Yan process at the LHC.

We present a NNLO QCD accurate event generator for direct photon pair production at hadron colliders, based on the MiNNLOPS formalism, within the POWHEG BOX RES framework. Despite the presence of the photons requires the use of isolation criteria, our generator is built such that no technical cuts are needed at any stage of the event generation. Therefore, our predictions can be used to simulate kinematic distributions with arbitrary fiducial cuts. Furthermore, we describe a few modifications of the MiNNLOPS formalism in order to allow for a setting of the renormalization and factorization scales more similar to that of a fixed-order computation, thus reducing the numerical impact of higher-order terms beyond the nominal accuracy. Finally, we show several phenomenological distributions of physical interest obtained by showering the generated events with Pythia8, and we compare them with the 13 TeV data from the ATLAS Collaboration.

The Drell-Yan process at hadron colliders is a fundamental benchmark for the study of strong interactions and the extraction of electro-weak parameters. The outstanding precision of the LHC demands very accurate theoretical predictions with a full account of fiducial experimental cuts. In this letter we present a state-of-the-art calculation of the fiducial cross section and of differential distributions for this process at third order in the strict fixed-order expansion in the strong coupling, as well as including the all-order resummation of logarithmic corrections. Together with these results, we present a detailed study of the subtraction technique used to carry out the calculation for different sets of experimental cuts, as well as of the sensitivity of the fiducial cross section to infrared physics. We find that residual theory uncertainties are reduced to the percent level and that the robustness of the predictions can be improved by a suitable adjustment of fiducial cuts.

In these proceedings we study various sources of theoretical uncertainty in the Drell-Yan p_T^ℓℓ spectrum focussing on the p_T^ℓℓ≲ 100 GeV region. We consider several perturbative aspects related to the choice of the scale setting adopted in resummed calculations, and we assess their impact on the theoretical prediction both for the differential p_T^ℓℓ spectrum and for the N^3LO fiducial cross section. For both quantities, we find the results obtained with the different setups to be compatible with each other within the quoted uncertainty, highlighting the robustness of the theoretical prediction. In all cases, the experimental LHC data for the p_T^ℓℓ spectrum is well described by our calculation.

Abstract We consider the Higgsstrahlung process in hadronic collisions and present the computation of next-to-next-to-leading order predictions matched to parton showers for both production and H → $$ b\overline{b} $$ b b ¯ decay employing the MiNNLOPS method. We present predictions for ZH and W±H production including spin correlations and off-shell effects by calculating the full processes pp → ℓ+ℓ−H → ℓ+ℓ−$$ b\overline{b} $$ b b ¯ , pp → $$ {\nu}_{\ell }{\overline{\nu}}_{\ell }H $$ ν ℓ ν ¯ ℓ H → $$ {\nu}_{\ell }{\overline{\nu}}_{\ell }b\overline{b} $$ ν ℓ ν ¯ ℓ b b ¯ and pp → ℓ±νℓH → $$ {\ell}^{\pm }{\overline{\nu}}_{\ell }b\overline{b} $$ ℓ ± ν ¯ ℓ b b ¯ in the narrow-width approximation for the Higgs boson. For the W±H process, NNLO+PS accuracy in production and decay is achieved for the first time. Our calculations are validated against earlier simulations in the NNLOPS approach that includes NNLO corrections via multi-differential reweighting. The new MiNNLOPS generators for these processes, which evaluate NNLO corrections on-the-fly in the event generation, will supersede those earlier calculations. Our predictions are in good agreement with recent measurements of the Higgsstrahlung cross sections.

We consider the production of a pair of heavy quarks and illustrate the derivation of the MiNNLOPS method to match next-to-next-to-leading order calculations with parton showers (NNLO+PS) for this class of processes. As a first application, we construct an event generator for the fully differential simulation of hadronic top-quark pair production at NNLO+PS and discuss all details of its implementation in a parton shower Monte Carlo framework. We present new phenomenological results for the Large Hadron Collider obtained by including the tree-level decays of the top quarks, while accounting for spin-correlation effects. A comprehensive comparison to LHC measurements shows an excellent description of experimental data across multiple hadronic and leptonic particle-level observables. The computer code is available for download within the Powheg-Box.

This paper has been prepared by the HEP Software Foundation (HSF) Physics Event Generator Working Group (WG), as an input to the second phase of the LHCC review of High-Luminosity LHC (HL-LHC) computing, which is due to take place in November 2021. It complements previous documents prepared by the WG in the context of the first phase of the LHCC review in 2020, including in particular the WG paper on the specific challenges in Monte Carlo event generator software for HL-LHC, which has since been updated and published, and which we are also submitting to the November 2021 review as an integral part of our contribution.

I give an overview of the recent progress on the matching of fixed-order calculations and parton showers. The focus is on the matching with NNLO QCD corrections as well as with NLO EW ones.