Improving the Prompt Electromagnetic Energy Component of Jet Energy Resolution with pi0 Fitting in High Granularity Electromagnetic Calorimeters

TL;DR

This paper demonstrates that mass-constrained pi0 fitting in high granularity electromagnetic calorimeters significantly improves jet energy resolution, reducing the pi0 energy resolution by nearly half in simulated multi-hadronic events.

Contribution

It introduces a novel application of pi0 mass-constrained fitting to enhance jet energy resolution in high granularity calorimeters, utilizing advanced pairing algorithms.

Findings

Pi0 fitting improves energy resolution from 18.0% to 13.9% for 91.2 GeV Z0 events.

Optimal pairing could further reduce resolution to 12.2%.

Method effectively handles complex photon pairing scenarios.

Abstract

We investigate improving the hadronic jet energy resolution using mass-constrained fits of pi0 decays using high granularity electromagnetic calorimeters. Single pi0 studies have indicated a large potential for improvement in the energy resolution of pi0's, typically reducing the average energy resolution by a factor of two for 4 GeV pi0's. We apply this method to fully simulated multi-hadronic events with multiple pi0's with widely varying energies using the ILD00 detector model. Several methods for identifying the correct pairings of photons with parent pi0's were explored. The combinatorics become challenging as the number of pi0's increases and we employ the Blossom V implementation of Edmonds' matching algorithm for handling this. For events where both photons of the pi0 are detected, the resulting solutions lead to an improvement in the pi0 component of the event energy resolution for 91.2 GeV Z0 events from 18.0%/sqrt(E) to 13.9%/sqrt(E) using the ILD00 detector and its reconstruction algorithms. This can be compared to a maximum potential improvement to 12.2%/sqrt(E) if all photon pairs are matched correctly using the current photon reconstruction.