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Steven Green, Mark Thomson

Particle Flow Calorimetry

A typical event topology

A typical event topology. Note that photons, charged hadrons and netural hadrons are seperated by different colours.

Improvements from hardware fine granularity and software particles clustering

Shift from traditional calorimetry to particle flow calorimetry. In particle flow calorimetry, it is possible to reconstruct the particle track. Therefore, the energy resolution for charged hadrons could be greatly imporved.

Silicon dectector (SiD) and International Large Detector (ILD)

Silicon dectector (SiD) and International Large Detector (ILD)

In a typical jet:
• 60% of jet energy in charged hadrons
• 30% in photons (mainly from π0→γγ)
• 10% in neutral hadrons (mainly n and KL)

Tradtional Calorimetric Approach

• Measure all components of jet energy in ECAL/HCAL
• Approximately 70% of energy measured in HCAL: σE/E ≈ 60% /√E(GeV)

Particle Flow Calorimetry

In particle flow calorimetry we aim to reconstruct the individual particles after a collision. This means that we can measure the energy of charged particles in the tracker, which offers essentially perfect energy resolution in comparison to the calorimeters. This means a much smaller amount of energy is measured in the calorimeters and so the overall detector resolution is greatly improved.
• Charged particle momentum measured in tracker (essentially perfectly)
• Photon energies measured in ECAL: σE/E < 20% /√E(GeV)
• Only neutral hadron energies (10% of jet energy) measured in HCAL

To apply particle flow calorimetry signficant changes have to be made to the hardware in comparison to traditional calorimetric approaches.

The calorimeters need to be able to resolve energy deposits from different particles, which requires highly granular detectors (as studied by CALICE).

Software needs to be able to identify energy deposits from each individual particle, that requires sophisticated reconstruction software to deal with complex events, containing many hits.

Calorimeter Requirements

Fine granularity particle flow must be studied in context of whole detector. Need detailed GEANT4 simulations of potential detector designs, e.g. ILC detector concepts:

Silicon Detector design:
• tracker radius 1.2m
• B-field: 5T
• Tracker: Silicon (5 layers)
• Calorimetry : fine granularity particle flow
• ECAL + HCAL inside large solenoid

International Large Detector:
• tracker radius 1.8m
• B-field: 3.5 T
• Tracker: TPC (220 layers)
• Calorimetry: fine granularity particle flow
• ECAL + HCAL inside large solenoid

Such studies allow us to put requirements on ECAL and HCAL design.

ECAL requirements:
• Minimise transverse spread of EM showers: Small Molière radius & transverse segmentation
• Longitudinally separate EM/Hadronic showers: Large ratio λI/X0
• Identification of EM showers: Longitudinal segmentation.

HCAL requirements:
• Fully contain hadronic showers: Small λI for absorber material
• Resolve hadronic shower structure: Longitudinal and transverse segmentation
• HCAL will be rather large: Cost and structural properties important