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Setting the jet energy scale for the ZEUS calorimeter

M. Wing

TL;DR

This work presents a refined calibration of the ZEUS jet energy scale by employing two independent correction strategies to account for energy loss in inactive material. Method 1 integrates tracking with calorimeter information via energy-flow objects and calibrates CAL-energy using balance in neutral current deep inelastic scattering events. Method 2 relies on calorimeter-cell jets with MC-derived corrections, validated against tracking information around jets; both approaches achieve data–MC agreement at the ~1% level, enabling ~5% cross-section uncertainties. The dual-method approach substantially reduces systematics and improves the precision of jet-related measurements in DIS.

Abstract

A much improved determination of the transverse energy of jets has been carried out in ZEUS, using a correction procedure based on two independent methods. The first is based on a combination of tracking and calorimeter information which optimises the resolution of reconstructed kinematic variables. The conservation of energy and momentum in neutral current deep inelastic e^+p scattering events is exploited to determine the energy corrections by balancing the kinematic quantities of the scattered positron with those of the hadronic final state. The method has been independently applied to data and simulated events. The second method uses calorimeter cells as inputs to the jet algorithm. Simulated events are then used to provide a correction for the energy loss due to inactive material in front of the calorimeter. A detailed comparison of the jet transverse energy and the transverse energy of tracks in a cone around the jet provides the final correction. This procedure relies on an accurate simulation of charged tracks and so is less reliant on simulating the energy loss of neutral particles in inactive material. Final comparisons of the data and simulated events for both methods allow an uncertainty +/- 1% to be assigned to the jet energy scale.

Setting the jet energy scale for the ZEUS calorimeter

TL;DR

This work presents a refined calibration of the ZEUS jet energy scale by employing two independent correction strategies to account for energy loss in inactive material. Method 1 integrates tracking with calorimeter information via energy-flow objects and calibrates CAL-energy using balance in neutral current deep inelastic scattering events. Method 2 relies on calorimeter-cell jets with MC-derived corrections, validated against tracking information around jets; both approaches achieve data–MC agreement at the ~1% level, enabling ~5% cross-section uncertainties. The dual-method approach substantially reduces systematics and improves the precision of jet-related measurements in DIS.

Abstract

A much improved determination of the transverse energy of jets has been carried out in ZEUS, using a correction procedure based on two independent methods. The first is based on a combination of tracking and calorimeter information which optimises the resolution of reconstructed kinematic variables. The conservation of energy and momentum in neutral current deep inelastic e^+p scattering events is exploited to determine the energy corrections by balancing the kinematic quantities of the scattered positron with those of the hadronic final state. The method has been independently applied to data and simulated events. The second method uses calorimeter cells as inputs to the jet algorithm. Simulated events are then used to provide a correction for the energy loss due to inactive material in front of the calorimeter. A detailed comparison of the jet transverse energy and the transverse energy of tracks in a cone around the jet provides the final correction. This procedure relies on an accurate simulation of charged tracks and so is less reliant on simulating the energy loss of neutral particles in inactive material. Final comparisons of the data and simulated events for both methods allow an uncertainty +/- 1% to be assigned to the jet energy scale.

Paper Structure

This paper contains 7 sections, 5 figures.

Table of Contents

  1. Introduction
  2. Electromagnetic energy scale uncertainty
  3. Jet energy scale uncertainty
  4. Method 1
  5. Method 2
  6. Jet energy scale uncertainty
  7. Conclusions

Figures (5)

  • Figure 1: Difference between data and MC of the energy scale for scattered positrons as a function of the energy, $E_{\rm DA}$.
  • Figure 2: Energy corrections as a function of cluster energy in bins of $\theta$. The corrections are shown separately for data (solid line) and Herwig MC (dashed line) and Ariadne MC simulations (dotted line).
  • Figure 3: Fractional difference between hadron-level jet $E_T$ and that reconstructed with (a) corrected EFOs, (b) uncorrected EFOs and (c) calorimeter cells as a function of the transverse energy. The shaded band shows the width of the distribution.
  • Figure 4: Comparison of (a) $r_{\rm TRACKS}$ and (b) $r_{\rm DIJET}$ for data (points) and MC simulation (histogram) and (c) the difference between data and MC as a function of pseudorapidity.
  • Figure 5: Jet energy scale uncertainty as a function of (a) $\eta^{\rm jet}$ and (b) $E_T^{\rm jet}$.