Parton shower Monte Carlos vs resummed calculations for interjet energy flow observables

TL;DR

This paper compares parton shower Monte Carlo simulations with analytical resummation calculations to evaluate their accuracy in predicting interjet energy flow observables in QCD, revealing the limitations of current shower models.

Contribution

It assesses the numerical differences between parton showers and resummed calculations for interjet energy flow, highlighting areas where parton showers may lack accuracy.

Findings

Parton showers show significant deviations from resummed calculations for interjet energy flow.

Analytical resummation provides more accurate predictions for certain observables.

The study identifies the limitations of angular ordering in parton shower algorithms.

Abstract

Parton showers in Monte Carlo event generators reflect to a certain accuracy our understanding of QCD radiation at all orders. For observables sensitive to interjet energy flow in well defined regions of phase space, it has been known for some time that relevant all-order dynamics is substantially more complicated than that encoded via angular ordering in parton shower algorithms, even to leading logarithmic accuracy. Here we investigate the extent of the numerical mismatch between leading logarithmic analytical estimates (resummation) and parton showers in an effort to better understand the accuracy of parton showers for such observables.