Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC

TL;DR

This paper quantifies the calorimeter energy response uncertainty for ATLAS jets by measuring the single-hadron E/p response in 900 GeV and 7 TeV data and by studying identified hadron responses via K_S and Λ decays. The measured E/p results are propagated through the MC jet composition to evaluate the jet energy scale (JES) uncertainty, with detailed treatment of neutral-hadron and high-momentum calibrations, cross-checks with test-beam data, and correlations. The study finds a central JES uncertainty of about 1–3% for jets in |η|<0.8 and pT from 15 GeV to 2.5 TeV, with total shifts typically below 1%, and provides a comprehensive framework for assessing JES correlations across jet categories. Overall, the work improves the precision of jet measurements by tightly constraining calorimeter response uncertainties and offering validated methods for background subtraction and particle-specific calibrations.

Abstract

The uncertainty on the calorimeter energy response to jets of particles is derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the calorimeter response to single isolated charged hadrons is measured and compared to the Monte Carlo simulation using proton-proton collisions at centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009 and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter response to specific types of particles (positively and negatively charged pions, protons, and anti-protons) is measured and compared to the Monte Carlo predictions. Finally, the jet energy scale uncertainty is determined by propagating the response uncertainty for single charged and neutral particles to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3% for the final calorimeter jet energy scale.

Figures (23)

• Figure 1: \ref{['fig:EoverPcentral']}$E/p$ distribution for isolated tracks with an impact point in the region $|\eta| < 0.6$ and with a momentum in the range $1.2 \leq p < 1.8$ GeV. \ref{['fig:EoverPforward']}$E/p$ distribution for tracks with impact points in the region $1.9 \leq |\eta| < 2.3$ and with momenta in the range $2.8 \leq p < 3.6$ GeV.
• Figure 2: \ref{['fig:correlationPositive']} Probability to measure a calorimeter response consistent with zero $P(E=0)$ as a function of the amount of material in nuclear interaction lengths in front of active volume of the calorimeter for $|\eta| < 1.0$. \ref{['fig:zp_vs_momentum']}$P(E=0)$ as a function of track momentum for $|\eta|<0.6$.
• Figure 3: Sketch of the background subtraction method, selecting isolated charged hadrons (ICH) that pass the EM calorimeter as minimum ionising particles (MIP) and shower in the hadronic calorimeter.
• Figure 4: $\langle E/p \rangle_{\mathrm{BG}}$ as a function of the track momentum at $\sqrt{s} = 900$ GeV for \ref{['fig:eopBG900_etaBin7']}$|\eta| < 0.6$ and \ref{['fig:eopBG900_etaBin6']}$0.6 \leq |\eta| < 1.1$. The black markers represent the background estimated from collision data, while the green rectangles represent the MC prediction, with the vertical width showing its statistical uncertainty. The lower panes show the ratio of the MC prediction to collision data. The MC prediction of the background energy deposit is obtained using the same procedure as applied to the data.
• Figure 5: $\langle E/p \rangle_{\mathrm{BG}}$ as a function of the track momentum at $\sqrt{s} = 7$ TeV for \ref{['fig:eopBG_etaBin7']}$|\eta| < 0.6$ and \ref{['fig:eopBG_etaBin6']}$0.6 \leq |\eta| < 1.1$. The black markers represent the background estimated from collision data, while the green rectangles represent the MC prediction, with the vertical width showing its statistical uncertainty. The lower panes show the ratio of the MC prediction to collision data. The MC prediction of the background energy deposit is obtained using the same procedure as applied to the data.