This manual describes the Pythia event generator, most recent version of an evolving physics tool used to answer fundamental questions in particle physics. The program is often generate high-energy-physics collision “events”, i.e. sets particles produced association with two incoming high-energy particles, but has several uses beyond that. guiding philosophy produce and re-produce properties experimentally obtained collisions as accurately possible. includes a wide ranges reactions within...

We outline a new technique for the fully-differential matching of final-state parton showers to NNLO calculations, focussing here on simplest case leptonic collisions with two jets. The strategy is facilitated by working in antenna formalism, making use subtraction fixed-order side and sector-antenna framework shower side. As long as combined real-virtual double-real corrections do not overcompensate real-emission term three-jet region, negative weights can be eliminated from scheme....

We discuss and illustrate the properties of several parton-shower algorithms available in Pythia Vincia, context Higgs production via vector boson fusion (VBF). In particular, distinctive colour topology VBF processes allows to define observables sensitive coherent radiation pattern additional jets. study a set such observables, using Vincia sector-antenna shower as our main reference, contrast it Pythia's transverse-momentum-ordered DGLAP well dipole-improved shower. then investigate...

A bstract We present next-to-leading order perturbative QCD predictions for four-jet-like event-shape observables in hadronic Higgs decays. To this end, we take into account two Higgs-decay categories: involving either the Yukawa-induced decay to a $${\text{b}}\overline{{\text{b}} }$$ pair or loop-induced gluons via an effective Higgs-gluon-gluon coupling. results distributions related variables thrust minor, light-hemisphere mass, narrow jet broadening, D -parameter, and Durham...

In conventional parton showers (including ones based on dipoles/antennae), a given $(\mathrm{Born}+m)$-parton configuration can typically be reached via ${\mathcal O}(m!)$ different "shower histories". the context of matrix-element-correction and merging procedures, accounting for these histories mandates fairly complex resource-intensive algorithms. A so far little-explored alternative in shower is to divide branching phase spaces into distinct "sectors", each which only receives...

This manual describes the PYTHIA 8.3 event generator, most recent version of an evolving physics tool used to answer fundamental questions in particle physics. The program is often generate high-energy-physics collision "events", i.e. sets particles produced association with two incoming high-energy particles, but has several uses beyond that. guiding philosophy produce and reproduce properties experimentally obtained collisions as accurately possible. includes a wide ranges reactions within...

A bstract The implementation of a new final-state parton-shower algorithm in the P ythia event generator is described. shower algorithm, dubbed pollo , combines central aspects V incia antenna with global transverse-recoil scheme laric framework order to achieve formal consistency next-to-leading logarithmic (NLL) resummation. constructed such way that it facilitates straightforward combination fixed-order calculations. As an explicit proof concept, general for matrix-element corrections...

A bstract We present resummed predictions at next-to-leading logarithmic accuracy matched to the exact order results for a set of classical event-shape observables in hadronic Higgs decays, i.e., channels H → gg and $$ b\overline{b} <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>b</mml:mi> <mml:mover> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> . furthermore consider soft-drop grooming final states derive corresponding NLO+NLL′ groomed thrust observable. Differences QCD...

We present for the first time resummed predictions at NLO + NLL′ accuracy Durham jet-resolution scales yn,n+1 in multijet production e+e− collisions. Results are obtained using an implementation of well known Caesar formalism within Sherpa framework. For 4-, 5- and 6-jet resolutions we discuss particular impact subleading colour contributions compare to matrix-element plus parton-shower from Vincia.

A bstract The antenna subtraction method has been successfully applied to a wide range of processes relevant for the Large Hadron Collider at next-to-next-to-leading order in α s (NNLO). We propose an algorithm building functions any number real emissions from identified pair hard radiator partons directly specified list unresolved limits. use explicitly build all single- and double-real QCD compare them previous functions, which were extracted matrix elements. improved should be more easily...

We present a major update of the publicly available EERAD3 package to calculate perturbative corrections in strong coupling hadronic Higgs and $Z$-boson decays. describe theoretical framework underlying numerical implementation provide guide usage program.

A bstract We introduce multi-jet merging for deep inelastic scattering in the V incia parton shower Monte Carlo event generator P ythia 8. Merging combines samples of different multiplicities with logarithmically enhanced parton-shower radiation. consider up to five outgoing partons using two algorithms. vary relevant scale choices and compare experimental data by H1 collaboration at HERA collider. Results show that improves description data, especially low virtuality events, jet...

Abstract The evaluation of one-loop matrix elements is one the main bottlenecks in precision calculations for high-luminosity phase Large Hadron Collider. To alleviate this problem, a new C++ interface to "Image missing"<!-- image only, no MathML or LaTex --> parton-level Monte Carlo introduced, giving access an extensive library analytic results amplitudes. Timing comparisons are presented large set Standard Model processes. These relevant high-statistics event simulation context...

This manual describes the Pythia event generator, most recent version of an evolving physics tool used to answer fundamental questions in particle physics. The program is often generate high-energy-physics collision “events”, i.e. sets particles produced association with two incoming high-energy particles, but has several uses beyond that. guiding philosophy produce and re-produce properties experimentally obtained collisions as accurately possible. includes a wide ranges reactions within...

A bstract The antenna-subtraction technique has demonstrated remarkable effectiveness in providing next-to-next-to-leading order α s (NNLO) predictions for a wide range of processes relevant the Large Hadron Collider. In previous paper [1], we how to build real-radiation antenna functions any number real emissions directly from specified list unresolved limits. Here, extend this procedure mixed case and virtual radiation, emissions. novel feature algorithm is requirement match constructed...

A bstract The production of lepton pairs (Drell-Yan process) at the LHC is being measured to high precision, enabling extraction distributions that are triply differential in di-lepton mass and rapidity as well scattering angle described by leptons. measurements performed for a fiducial phase space, defined cuts on individual momenta rapidities. Based ATLAS triple-differential Drell-Yan measurement 8 TeV, we perform detailed investigation phenomenology this process based state-of-the-art...

A bstract We study the six classical event-shape observables in hadronic Higgs decays at next-to-leading order QCD. To this end, we consider decay of on-shell bosons to three partons, taking into account both Yukawa-induced b-quark pairs and loop-induced two gluons via an effective Higgs-gluon coupling. The results are discussed with a particular focus on discriminative power event shapes regarding these classes processes.

Jet production from hadronic Higgs decays at future lepton colliders will have significantly different phenomenological implications than jet via off-shell photon and $Z$-boson decays, owing to the fact that bosons decay both pairs of quarks gluons. We compute observables involving flavoured jets in three partons Born level including next-to-leading order corrections QCD (i.e up $\mathcal{O}(\alpha_\mathrm{S}^2))$. The calculation is performed framework an effective theory which boson...

We present resummed predictions at next-to-leading logarithmic accuracy matched to the exact order results for a set of classical event-shape observables in hadronic Higgs decays, i.e., channels $H\to gg$ and b\bar{b}$. furthermore consider soft-drop grooming final states derive corresponding $\text{NLO}+\text{NLL}^\prime$ groomed thrust observable. Differences QCD radiation pattern gluon- quark-initiated are imprinted distributions, offering separation power two decay channels. In...

The implementation of a new final-state parton-shower algorithm in the Pythia event generator is described. shower algorithm, dubbed Apollo, combines central aspects Vincia antenna with global transverse-recoil scheme Alaric framework order to achieve formal consistency next-to-leading logarithmic (NLL) resummation. constructed such way that it facilitates straightforward combination fixed-order calculations. As an explicit proof concept, general for matrix-element corrections (MECs) and two...

Jet production from hadronic Higgs decays at future lepton colliders will have significantly different phenomenological implications than jet via off-shell photon and

We introduce multi-jet merging for deep inelastic scattering in the Vincia parton shower Monte Carlo event generator Pythia 8. Merging combines samples of different multiplicities with logarithmically enhanced parton-shower radiation. consider up to five outgoing partons using two algorithms. vary relevant scale choices and compare experimental data by H1 collaboration at HERA collider. Results show that improves description data, especially low virtuality events, jet cross-sections converge...

We consider leading-colour 2-, 3- and 4-jet rates in hadronic $Z$-boson decay to derive matching conditions at next-to-next-to-leading order the sectorised VINCIA parton shower. In particular, we present a full subtraction-based calculation of coefficient required obtain NLO 3-jet rate. This is achieved through judicious choice counter-terms, which optimises numerical evaluation subtracted double-real matrix element. additionally give consistent prescription for incorporating interference...