Automation of NLO QCD and EW corrections with Sherpa and Recola

Biedermann, Benedikt; Bräuer, S.; Denner, Ansgar; Pellen, Mathieu; Schumann, Steffen; Thompson, J.

doi:10.1140/epjc/s10052-017-5054-8

Cited by 63 publications

(64 citation statements)

References 95 publications

(203 reference statements)

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“…For the evaluation of virtual corrections at NLO accuracy SHERPA relies on interfaces to dedicated one-loop providers, e.g. BLACKHAT [13], OPENLOOPS [14] and RECOLA [15,16]. The default parton-showering algorithm of the SHERPA 2.2 series is the CSSHOWER [17], based on Catani-Seymour dipole factorisation [9,10,18].…”

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confidence: 99%

Event generation with Sherpa 2.2

et al. 2019

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SHERPA is a general-purpose Monte Carlo event generator for the simulation of particle collisions in high-energy collider experiments. We summarise essential features and improvements of the SHERPA 2.2 release series, which is heavily used for event generation in the analysis and interpretation of LHC Run 1 and Run 2 data. We highlight a decade of developments towards ever higher precision in the simulation of particle-collision events. Figure 1: Overview of the SHERPA 2.2 event generator framework. Interfaces/OutputsAMEGIC [6] and COMIX [7,8]. They are used for the simulation of parton-level events within the Standard Model and beyond, and for the decay of heavy resonances such as W , Z, or Higgs bosons or top quarks. Both include automated methods for efficient phase-space integration and algorithms for the subtraction of infrared divergences in calculations at next-to-leading order (NLO) in QCD [9, 10, 11] and the electroweak theory [12]. For the evaluation of virtual corrections at NLO accuracy SHERPA relies on interfaces to dedicated one-loop providers, e.g. BLACKHAT [13], OPENLOOPS [14] and RECOLA [15,16]. The default parton-showering algorithm of the SHERPA 2.2 series is the CSSHOWER [17], based on Catani-Seymour dipole factorisation [9,10,18]. As of version 2.2.0 SHERPA also features an independent second shower implementation, DIRE [19,20,21]. For the matching of NLO QCD matrix elements with parton showers SHERPA implements the MC@NLO method [22,23]. For NNLO QCD calculations the UN 2 LOPS method [24, 25] is used. The merging of multi-jet production processes at leading order [26,27,28] and next-to-leading order [29,30] is based on truncated parton showers. Multiple parton interactions are implemented via the Sjöstrand-van-Zijl model [31]. The hadronisation of partons into hadrons is modelled by a cluster fragmentation model [32]. Alternatively, in particular for uncertainty estimations, an interface to the Lund fragmentation model [33] of PYTHIA [34] is available. SHERPA provides a large library for the simulation of τ -lepton and hadron decays, including many form-factor models. Furthermore, a module for the simulation of QED final-state radiation in particle decays [35], which is accurate to first order in α for many channels is built-in. To account for spin correlations in production and subsequent decay processes the algorithm described in [36] is implemented. Events generated with SHERPA can be cast into various output formats for further processing, with the HEPMC [37] format being the most commonly used. In the specific case of parton-level events, at the leading and next-to-leading order in QCD, additional output formats are supported. They include Les Houches Event Files [38], NTUPLE files for NLO QCD events [39] and cross-section interpolation grids produced via MCGRID [40,41] in the APPLGRID [42] and FASTNLO [43,44] formats. To analyse events on-the-fly a runtime interface to the RIVET package [45] can be used conveniently.

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Event generation with Sherpa 2.2

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“…We use OpenLoops [44] for one-loop virtual corrections to 3-, 4-, and 5-parton matrix elements. Virtual corrections to 6-parton matrix elements are generated with Recola [45,46,47]. Note that σ (2) is not needed in our matching formulas, and hence there is no need to compute any purely virtual corrections of order α (n−2) s α 2 s , while still achieving NLO accuracy in the normalised differential distribution.…”

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confidence: 99%

Resummed predictions for jet-resolution scales in multijet production in e+e− annihilation

Baberuxki

Preuss

Reichelt

et al. 2020

J. High Energ. Phys.

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

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“…In this combination SHERPA provides the tree-level matrix elements, infrared subtraction, process management and phase-space integration of all contributions to all processes considered in this publication through its tree-level matrix element generator Amegic [14]. Its inbuilt infrared subtraction [15,16,17,18,19,20,21,22] is performed in the QED generalisation of the Catani-Seymour scheme [23,24,25,26] and includes the appropriate initial state mass factorisation counter terms. RECOLA, on the other hand, provides the virtual corrections to all processes, using the COLLIER library [27] for the evaluation of its scalar and tensor integrals.…”

Section: Calculational Setupmentioning

confidence: 99%

“…RECOLA, on the other hand, provides the virtual corrections to all processes, using the COLLIER library [27] for the evaluation of its scalar and tensor integrals. Both programs, SHERPA and RECOLA, are interfaced through the dedicated interface introduced in [19]. All processes in the present paper are calculated including all triple, double, single and non-resonant topologies, as well as all interferences between channels with different vector boson intermediate states (W, Z, γ) as the calculations presented here (in the limit of a massless τ ).…”

Section: Calculational Setupmentioning

confidence: 99%