arXiv subjects

Lois Flower

Publications and source records attributed to Lois Flower.

6 recordsLinked to original sources

arXiv2026

A resonance-aware MC@NLO QCD+EW-matched calculation of lepton-pair production

As we approach HL-LHC, there is a growing need for increased precision in theoretical predictions so that meaningful comparisons with experimental data can be made. It is no longer sufficient to include only QCD higher-order corrections, with EW effects becoming increasingly important. Even at hadron colliders, QED radiation provides large corrections to some observables. In this paper, we present the first automated matching of NLO QCD+EW to an interleaved QCD+QED parton shower using the MC@NLO matching method in the Catani-Seymour dipole formalism. When considering such a matched parton shower, the presence of resonances can lead to spurious higher order terms, originating in the recoil assignment, within the standard dipole construction. We therefore develop a resonance-aware modification to the MC@NLO algorithm that can be applied to QCD- and QED-singlet resonances. We validate our interleaved matching and its resonance-aware modification against fixed-order NLO QCD+EW and pure MC@NLO QCD combined with YFS resummation. Finally, we present resonance-aware MC@NLO QCD+EW predictions for Drell-Yan lepton pair production, a vital precision process at hadron colliders.

hep-ph↗

arXiv2026

$e^+e^- \to ZH$ at NLO EW matched to a QED parton shower

To prepare for the next generation particle collider, likely to be a high-energy precision-frontier electron-positron machine, theoretical predictions must improve in tandem. One aspect in which it is necessary to build on the progress made at LEP and at low-energy $e^+e^-$ colliders is in the modelling of initial-state QED radiation from leptons. In this paper we combine the MC@NLO parton shower matching method with QED resummation methods such as the electron structure function to obtain an automated, process-independent NLO-matched QED parton shower. The case of an electron-positron collider provides a particular challenge to the method due to the integrable singularity present in the lepton structure function, at variance with QCD PDFs. We develop new methods to allow a standard dipole parton shower to operate in the presence of this singularity. We validate the method by examining its dependence on infrared parameters and by verifying both the NLO-correctness, and the resummation properties, of the MC@NLO prediction. Finally, we present results for the case of Higgs production in association with an on-shell $Z$ boson at two proposed FCC-ee energies, the first such predictions at EW NLO+PS accuracy.

hep-ph↗

arXiv2024

Radiative corrections and Monte Carlo tools for low-energy hadronic cross sections in $e^+ e^-$ collisions

We present the results of Phase I of an ongoing review of Monte Carlo tools relevant for low-energy hadronic cross sections. This includes a detailed comparison of Monte Carlo codes for electron-positron scattering into a muon pair, pion pair, and electron pair, for scan and radiative-return experiments. After discussing the various approaches that are used and effects that are included, we show differential cross sections obtained with AfkQed, BabaYaga@NLO, KKMC, MCGPJ, McMule, Phokhara, and Sherpa, for scenarios that are inspired by experiments providing input for the dispersive evaluation of the hadronic vacuum polarisation.

hep-ph↗

arXiv2024

Event generation with Sherpa 3

Sherpa is a general-purpose Monte Carlo event generator for the simulation of particle collisions in high-energy collider experiments. We summarise new developments, essential features, and ongoing improvements within the Sherpa 3 release series. Physics improvements include higher-order electroweak corrections, simulations of photoproduction and hard diffraction at NLO QCD, heavy-flavour matching in NLO multijet merging, spin-polarised cross section calculations, and a new model of colour reconnections. In addition, the modelling of hadronisation, the underlying event and QED effects in both production and decay has been improved, and the overall event generation efficiency has been enhanced.

hep-ph↗

arXiv2024

Automated inclusion of QED corrections in Monte Carlo event generators

In this thesis, we present automated, process-independent methods for the calculation of QED real radiative corrections. We review the construction of a parton shower based on Catani-Seymour dipole subtraction, and thus detail the implementation of a QED parton shower. We validate the predictions made by the shower against the YFS soft-photon resummation, and discuss the algorithmic choices made. We then present results for the production of a Higgs boson at the LHC and its decay to leptons, showing that the interleaved QCD+QED parton shower predicts distributions in excellent agreement with the YFS approach. We then study the MC@NLO method for matching a next-to-leading order calculation with a parton shower. Showing that the method preserves its accuracy for the case of QED corrections and of mixed QCD and QED corrections, we present the QCD+QED MC@NLO method. Validating the method against both the YFS resummation and the QED parton shower, we find very good agreement. Finally, we present an extension to the YFS soft-photon resummation, in which we use a one-step parton shower to resum the logarithms associated with charged particle pair production. Throughout this thesis we also discuss the impact of dressed lepton definitions on observables. The methods presented in this thesis are made available in a public Monte Carlo event generator and analysis framework.

hep-ph↗

arXiv2023

Photon splitting corrections to soft-photon resummation

In this paper we present an algorithm to add photon-splitting corrections to the Yennie-Frautschi-Suura-style soft-photon resummation available in the Sherpa Monte-Carlo event generator. Photon-splitting corrections enter at NNLO in QED and, as these effects are not incorporated in the standard QED FSR resummations, their size is larger than the pure hard photon-emission corrections at the same order. We introduce different lepton dressing strategies which incorporate further leptons and hadrons in addition to the customary photons, and discuss their sensitivity to dressing parameters such as the cone size. Finally, we quantify the effects of photon splittings into charged fermions and scalars under different such dressing strategies on $Z\to e^+e^-$ decays and find effects of up to 1% for suitably inclusive dressing strategies independent of the dressing cone size, and up to 9% if only photons are used in the dressing procedure with large dressing cones.

hep-ph↗