Qjets: A Non-Deterministic Approach to Tree-Based Jet Substructure

TL;DR

This paper introduces Qjets, a non-deterministic method that considers multiple clustering trees for jet substructure analysis, leading to more stable observables and improved signal-background discrimination in particle physics experiments.

Contribution

Qjets proposes a novel non-deterministic approach that uses multiple clustering trees to analyze jet substructure, enhancing statistical stability and discrimination power.

Findings

Reduces fluctuations in pruned mass distributions.

Improves signal significance by analyzing distribution width.

Cuts on width outperform standard mass cuts.

Abstract

Jet substructure is typically studied using clustering algorithms, such as kT, which arrange the jets' constituents into trees. Instead of considering a single tree per jet, we propose that multiple trees should be considered, weighted by an appropriate metric. Then each jet in each event produces a distribution for an observable, rather than a single value. Advantages of this approach include: 1) observables have significantly increased statistical stability; and, 2) new observables, such as the variance of the distribution, provide new handles for signal and background discrimination. For example, we find that employing a set of trees substantially reduces the observed fluctuations in the pruned mass distribution, enhancing the likelihood of new particle discovery for a given integrated luminosity. Furthermore, the resulting pruned mass distributions for (background) QCD jets are found to be substantially wider than that for (signal) jets with intrinsic mass scales, e.g. jets containing a W decay. A cut on this width yields a substantial enhancement in significance relative to a cut on the standard pruned jet mass alone. In particular the luminosity needed for a given significance requirement decreases by a factor of two relative to standard pruning.