Jet mass and substructure of inclusive jets in sqrt(s) = 7 TeV pp collisions with the ATLAS experiment

TL;DR

This study tests the reliability of jet substructure modeling in early LHC data by measuring jet mass and substructure observables for large-radius anti-$k_t$ and Cambridge–Aachen jets and comparing to LO parton-shower MC. It introduces and applies a splitting and filtering procedure, along with $k_T$ splitting scales and $N$-subjettiness, to characterize jet substructure and distinguish boosted decays from QCD jets. The results show broad agreement with MC in most variables, with mass spectra showing the largest discrepancies, while the filtering approach yields strong data–MC consistency and mitigates pile-up effects. Overall, the findings support using jet substructure techniques in boosted-object searches and provide quantified systematic controls for data unfolding and detector effects.

Abstract

Recent studies have highlighted the potential of jet substructure techniques to identify the hadronic decays of boosted heavy particles. These studies all rely upon the assumption that the internal substructure of jets generated by QCD radiation is well understood. In this article, this assumption is tested on an inclusive sample of jets recorded with the ATLAS detector in 2010, which corresponds to 35 pb^-1 of pp collisions delivered by the LHC at sqrt(s) = 7 TeV. In a subsample of events with single pp collisions, measurementes corrected for detector efficiency and resolution are presented with full systematic uncertainties. Jet invariant mass, kt splitting scales and n-subjettiness variables are presented for anti-kt R = 1.0 jets and Cambridge-Aachen R = 1.2 jets. Jet invariant-mass spectra for Cambridge-Aachen R = 1.2 jets after a splitting and filtering procedure are also presented. Leading-order parton-shower Monte Carlo predictions for these variables are found to be broadly in agreement with data. The dependence of mean jet mass on additional pp interactions is also explored.

Figures (17)

• Figure 1: $p_{\mathrm{T}}$ (left) and $\eta$ distribution (right) of Cambridge-Aachen $R=1.2$ jets with $p_{\mathrm{T}} > 200\mathrm{\ Ge V} \textrm{Ge V}$.
• Figure 2: $p_{\mathrm{T}}$ (left) and $\eta$ distribution (right) of anti-$k_{t}$$R=1.0$ jets with $p_{\mathrm{T}} > 200\mathrm{\ Ge V} \textrm{Ge V}$.
• Figure 3: $p_{\mathrm{T}}$ (left) and $\eta$ distribution (right) of Cambridge-Aachen $R=1.2$ jets after splitting and filtering with $p_{\mathrm{T}} > 200\mathrm{\ Ge V} \textrm{Ge V}$.
• Figure 4: Mass distributions for jets with $|y| < 2.0$ in the 300--400 Ge V$p_{\mathrm{T}}$ bin. Jets shown are Cambridge-Aachen (top left), Cambridge-Aachen after splitting and filtering (top right) and anti-$k_{t}$ (bottom).
• Figure 5: Distributions for $\sqrt{d_{12}}$ (left) and $\sqrt{d_{23}}$ (right) of anti-$k_{t}$$R=1.0$ jets with $|y| < 2.0$ in the 300--400 Ge V$p_{\mathrm{T}}$ bin.