Template Overlap Method for Massive Jets

TL;DR

The paper introduces template overlaps, an infrared-safe framework to compare the energy flow inside jets with predefined boosted-decay templates, enabling discrimination of highly boosted top and Higgs decays from QCD backgrounds. It formalizes Ov(j,f) as the maximum overlap with LO three-body (top) or two-body (Higgs) templates and augments discrimination with jet-shape observables like planar flow and angularities. Across multiple event generators, LO templates provide substantial background rejection when combined with jet-mass cuts, with Higgs and top signals achieving order-of-magnitude suppression relative to backgrounds. The approach is modular and systematically improvable by including higher-order emissions in the templates and refining the overlap functional, offering a robust, infrared-safe tool for tagging boosted hadronic decays in LHC data.

Abstract

We introduce a new class of infrared safe jet observables, which we refer to as template overlaps, designed to filter targeted highly boosted particle decays from QCD jets and other background. Template overlaps are functional measures that quantify how well the energy flow of a physical jet matches the flow of a boosted partonic decay. Any region of the partonic phase space for the boosted decays defines a template. We will refer to the maximum functional overlap found this way as the template overlap. To illustrate the method, we test lowest-order templates designed to distinguish highly-boosted top and Higgs decays from backgrounds produced by event generators. For the functional overlap, we find good results with a simple construction based on a Gaussian in energy differences within angular regions surrounding the template partons. Although different event generators give different averages for our template overlaps, we find in each case excellent rejection power, especially when combined with cuts based on jet shapes. The template overlaps are capable of systematic improvement by including higher order corrections in the template phase space.

Figures (10)

• Figure 1: Comparison of histograms of template overlap $Ov$, Eq. (\ref{['3particletemplate']}), with top jets and QCD jets from different MCs [upper left (right) Pythia (MG/ME) and Sherpa on the bottom], for $R=0.5$, 950 GeV$\le P_{0} \le$1050 GeV, 160 GeV$\le m_J \le$190 GeV and $m_{top}=174$ GeV.
• Figure 2: A scatter plot of template overlap, Eq. (\ref{['3particletemplate']}) and $Pf$ for LO parton-level MC output for top quark decay, with $P_{0}=1$ TeV, $m_{top}=174$ GeV.
• Figure 3: Comparison of scatter plots of planar flow $Pf$vs. template overlap $Ov$ for top jets (right) and QCD jets (left) from different MC (from top to bottom: Pythia, MG/ME, Sherpa), for $R=0.5$, 950 GeV$\le P_{0} \le$1050 GeV, 160 GeV$\le m_J \le$190 GeV and $m_{top}=174$ GeV.
• Figure 4: Comparison of fake rate vs. efficiency with various cuts on template overlap $Ov$ and $Pf$ with top jets and QCD jets from different MC [upper left (right) Pythia (MG/ME) and Sherpa on the bottom], for $R=0.5$, 950 GeV$\le P_{0} \le$1050 GeV, 160 GeV$\le m_J \le$190 GeV and $m_{top}=174$ GeV. The lines show the effect of cuts in planar flow ($Pf$) for fixed overlap ($Ov$), with the lowest (most inclusive) $Pf$ cuts to the right. The green dot is for $Pf>0.6$ and $Ov>0.4$.
• Figure 5: A scatter plot of template overlap, Eq. (\ref{['2particletemplate']}) and the angular distance $\Delta R$ between the two partons coming from the Higgs decay, with $P_{0}=1$ TeV, $m_H=120\rm \,GeV$.