Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC
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Regular Article - Experimental Physics
Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC The ATLAS Collaboration CERN, 1211 Geneva 23, Switzerland
Received: 6 March 2012 / Revised: 19 April 2012 / Published online: 2 March 2013 © CERN for the benefit of the ATLAS collaboration 2013. This article is published with open access at Springerlink.com
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 √ s = 900 GeV and 7 TeV collected during 2009 and 2010. Then, using the decay of Ks and Λ 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.
1 Introduction Partons scattered in proton-proton interactions are measured with the ATLAS detector as collimated jets of hadrons. The uncertainty on the jet energy scale is the largest source of detector-related systematic uncertainty for many physics analyses carried out by the ATLAS Collaboration, from the di-jet cross-section and top mass measurements, to searches for new physics with jets in the final state. It is thus the subject of an extensive and detailed study [1]. The jet energy measured by the calorimeter is corrected for calorimeter non-compensation and energy loss in dead material. The corresponding jet energy scale correction factor is referred to as the JES. The JES is derived from Monte Carlo (MC) simulations by comparing the calorimeter en e-mail:
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ergy of an isolated reconstructed jet to that of the particle jet1 that points to it [1]. The uncertainty on the calorimeter energy response is a significant component of the total uncertainty on the JES. It is derived in this paper by convolving the measured uncertainty on the single charged hadron energy response and the estimated uncertainty on the neutral particle energy response with the expected particle spectrum within a jet. The calorimeter response to single isolated charged hadrons, and the accuracy of its Monte Carlo simulation description, can be evaluated from the ratio of the calorimeter energy E to the associated isolated track momentum p. The aim of the measurement is to estimate the systematic uncertainty on jet calorimeter response and therefore the focus is on data-to-MC comparison. The ratio E/p is measured using proton-proton collisions at centre-of-mass energies of √ s = 900 GeV and 7 TeV over a wide range of track momenta in the
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