Precision studies of observables in p p rightarrow W rightarrow lnu _l and pp rightarrow gamma ,Z rightarrow l^+ l^- processes at the LHC

Simone Alioli ,S Dittmaier,G Montagna,A Vicini,A Huss,F Piccinini,D Wackeroth,S Jadach,W Płaczek,A B Arbuzov,L Barzè,O Nicrosini,L V Kalinovskaya,Giancarlo Ferrera ,D Y Bardin ,S Bondarenko ,Daniel De Florian ,Alexander Karlberg ,Marek Schoenherr ,Catherine Bernaciak ,Massimiliano Grazzini ,Christian Schwinn ,Emanuele Ré ,Stefan Hoeche ,Mauro Chiesa ,Frank Krauss ,Paolo Nason ,A Mueck ,Stefan Prestel ,Francis John Petriello ,Z Wa̧s ,A Sapronov ,Y Li,H Martinez,C M Carloni Calame,Giulia Zanderighi

doi:10.1140/epjc/s10052-017-4832-7

Abstract

This report was prepared in the context of the LPCC Electroweak Precision Measurements at the LHC WG (https://lpcc.web.cern.ch/lpcc/index.php?page=electroweak_wg) and summarizes the activity of a subgroup dedicated to the systematic comparison of public Monte Carlo codes, which describe the Drell–Yan processes at hadron colliders, in particular at the CERN Large Hadron Collider (LHC). This work represents an important step towards the definition of an accurate simulation framework necessary for very high-precision measurements of electroweak (EW) observables such as the W boson mass and the weak mixing angle. All the codes considered in this report share at least next-to-leading-order (NLO) accuracy in the prediction of the total cross sections in an expansion either in the strong or in the EW coupling constant. The NLO fixed-order predictions have been scrutinized at the technical level, using exactly the same inputs, setup and perturbative accuracy, in order to quantify the level of agreement of different implementations of the same calculation. A dedicated comparison, again at the technical level, of three codes that reach next-to-next-to-leading-order (NNLO) accuracy in quantum chromodynamics (QCD) for the total cross section has also been performed. These fixed-order results are a well-defined reference that allows a classification of the impact of higher-order sets of radiative corrections. Several examples of higher-order effects due to the strong or the EW interaction are discussed in this common framework. Also the combination of QCD and EW corrections is discussed, together with the ambiguities that affect the final result, due to the choice of a specific combination recipe. All the codes considered in this report have been run by the respective authors, and the results presented here constitute a benchmark that should be always checked/reproduced before any high-precision analysis is conducted based on these codes. In order to simplify these benchmarking procedures, the codes used in this report, together with the relevant input files and running instructions, can be found in a repository at https://twiki.cern.ch/twiki/bin/view/Main/DrellYanComparison.

Highlights

Precision electroweak (EW) measurements in Drell–Yanlike processes at the Fermilab Tevatron and CERN Large Hadron Collider (LHC), pp( p p) → W ± → l±νl and pp( p p) → γ, Z → l+l− (l = e, μ), require the development of sophisticated simulation tools that should include the best theoretical knowledge available
Applications of the pole approximation (PA) to Next-to-leading order (NLO) EW corrections [17,25,42,85] have been validated by a comparison to the complete EW NLO calculations and show excellent agreement at the order of some 0.1% in kinematic distributions dominated by the resonance region
– In a tuned comparison at NLO, where all the input parameters and the simulation setup are identical and the matrix elements have the same accuracy for all the codes, we observe that the total cross sections agree at the 0.03% level both in the NLO EW and in the NLO quantum chromodynamics (QCD) calculations; the differential distributions differ at most at the 0.5% level

Summary

Introduction

Precision electroweak (EW) measurements in Drell–Yanlike processes at the Fermilab Tevatron and CERN Large Hadron Collider (LHC), pp( p p) → W ± → l±νl and pp( p p) → γ , Z → l+l− (l = e, μ), require the development of sophisticated simulation tools that should include the best theoretical knowledge available (for recent reviews see, e.g., [1,2,3]). Different subsets of corrections became available separately in the past years in codes that simulate purely QCD or purely EW effects. The combination of QCD and EW corrections is an important step in the development of the MC programs that will be used in high-precision measurements and is one of the main topics of the present report

Objectives

Results

Conclusion