Spin correlations in final-state parton showers and jet observables

Alexander Karlberg,Ludovic Scyboz,Gavin P Salam,Rob Verheyen

doi:10.1140/epjc/s10052-021-09378-0

Alexander Karlberg, Ludovic Scyboz + Show 2 more

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https://doi.org/10.1140/epjc/s10052-021-09378-0

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Abstract

As part of a programme to develop parton showers with controlled logarithmic accuracy, we consider the question of collinear spin correlations within the PanScales family of parton showers. We adapt the well-known Collins–Knowles spin-correlation algorithm to PanScales antenna and dipole showers, using an approach with similarities to that taken by Richardson and Webster. To study the impact of spin correlations, we develop Lund-declustering based observables that are sensitive to spin-correlation effects both within and between jets and extend the MicroJets collinear single-logarithmic resummation code to include spin correlations. Together with a 3-point energy correlation observable proposed recently by Chen, Moult and Zhu, this provides a powerful set of constraints for validating the logarithmic accuracy of our shower results. The new observables and their resummation further open the pathway to phenomenological studies of these important quantum mechanical effects.

Highlights

In this article we consider collinear spin correlations in the context of the PanScales programme [23,24,25] of QCD parton-shower development
The developments shown in this paper are among the last remaining aspects needed in order to claim complete next-to-leading logarithmic (NLL) accuracy in the sense of Ref. [24] for the PanScales family of parton showers
The approach we have taken is largely based on that proposed by Collins and Knowles, and in part on the extension to dipole showers proposed by Richardson and Webster

Summary

Introduction

In this article we consider collinear spin correlations in the context of the PanScales programme [23,24,25] of QCD parton-shower development. To claim NLL accuracy, we firstly require a shower to reproduce the correct matrix element for any configuration of emissions where all branchings are well separated from each other in the Lund diagram. One class of configuration that is not addressed by the Collins algorithm is that of two or more commensurateangle energy-ordered soft emissions followed by a collinear splitting of one or more of them These configurations should be addressed for NLL accuracy, we defer their study to future work. We introduce a new set of spin-correlation sensitive observables based on Lund declustering.

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