Lund multiplicity in QCD jets

Abstract

We compute the average Lund multiplicity of high-energy QCD jets. This extends an earlier calculation, done for event-wide multiplicity in e+e− collisions [1], to the large energy range available at the LHC. Our calculation achieves next-to-next-to-double logarithmic (NNDL) accuracy. Our results are split into a universal collinear piece, common to the e+e− calculation, and a non-universal large-angle contribution. The latter amounts to 10–15% of the total multiplicity. We provide accurate LHC predictions by matching our resummed calculation to fixed-order NLO results and by incorporating non-perturbative corrections via Monte Carlo simulations. Including NNDL terms leads to a 50% reduction of the theoretical uncertainty, with non-perturbative corrections remaining below 5% down to transverse momentum scales of a few GeV. This proves the suitability of Lund multiplicities for robust theory-to-data comparisons at the LHC.

The Lund jet plane: a tool for precision and discovery at the LHC

“…≥ ,cut . The resummation of this observable is presented in [9], up to NNDL, with the relevant log equal to = ln( / ,cut ). The calculation exploits universal ingredients from the + − event-wide result, with the presence of jet radius impacting the large-angle components starting at NDL in a process-dependent way (e.g.…”

Introduction to the PanScales framework, version 0.1

“…This paper documents the first public release of a new parton showering code, PANSCALES, version 0.1. It has been developed as part of a series of articles [1][2][3][4][5][6][7][8][9] investigating how to design parton shower algorithms that provide controlled and verifiable logarithmic accuracy, together with parallel analytical work on approaches to resummation at higher logarithmic accuracy and their connection with parton showers [10][11][12][13][14][15][16][17]. Several other groups have also recently been working on the question of logarithmic accuracy in showers, see e.g.…”