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A ROOT Tool for 3D Event Visualization in ATLAS Calorimeters

Luciano Andrade

José de Seixas

Federal University of Rio de Janeiro/COPPE

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Outline

The LHC and ATLAS detector. ATLAS calorimeter system. Trigger system and Level 2 Trigger RoI. Commissioning phase with cosmics. The visualization tool. Some problems found by this tool. Conclusion and To-Do list.

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Inner Detector

Muon Chambers

Eletromagnetic Calorimeter

Hadronic Calorimeter

The LHC and ATLAS Detector LHC - it is being finished at CERN. ATLAS - high granularity, TBytes/sec of data. Trigger system – to save only relevant events.

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ATLAS Calorimeter SystemInner detector

Electromagnetic Calorimeter

Hadronic Calorimeter

Electromagnetic - LArg Liquid argon as detection medium. Charged particles generate eletromagnetic showers. Electric field captures free electrons → signal pulse.

Hadronic - TileCal Scintillating tiles. Iron to absorv the energy. Energetic hadrons interact with the tiles → light generation. Photomultipliers transform the light in a electrical signal.

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Calorimeter Segmentation

100,000 readout channels. Four layers.

ElectromagneticHadronic

64 Modules in φ coordinate. Two readout channels by cell. 10,000 readout channels. Three layers.

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Trigger System

Level 1 Trigger

Level 2 Trigger

Event Filter

1 GHz

100 kHz

1 kHz

100 Hz

Region of Interest (RoI)(Region with signal information)

RoI algorithm was checked with this visualization tool (simulated data)

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Commissioning with cosmic muons

1 2

3 4

dicriminator logic OR

dicriminator logic OR

LogicAND

coincidence board

Use of a standalone coincidence board. Bypass the Trigger System. Back-to-back coincidence – projective events. Use TileCal Trigger Towers. Commissioning of the calorimeters with real data.

trigger

Trigger tower

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The Visualization Tool - Motivation

Three-dimensional event visualization of the Calorimeter cells.

Tool used in the commissioning phase. Simple and intuitive way to look for potential problems. Easy connection with reconstructed data (ROOT). Two versions:

– Hadron Calorimeter specific.– Combined Eletromagnetic/Hadron Calorimeters.

Analysis examples:– Track visualization for cosmics – real data.– Level 2 Trigger RoI debug - simulated data.

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TileCal Specific Tool - Overview

• ROOT macro (TileCosmicView.C).• Input → standard TileCal reconstruction nTuple.

Standard Root GL Viewer Graphic User Interface (GUI)

TileCal

some activated cells

cosmic track

To open the nTuple

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Features

Fast response.

Color palette adjustment.

Threshold by cell energy.

Show individual PMTs.

Cell selection with mouse.

Projective views.

Show ADC counts.

Rotate and zoom.

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Combined Calorimeter Tool - Overview

• ROOT macro (CaloGeoView.C).• Input → standard Athena reconstruction nTuple.

Standard Root GL Viewer Graphic User Interface (GUI)

Example of a Level 2 Trigger RoI visualization

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Features

green palette - Eletromagnetic hot palette - Hadronic

log scale

Example of cosmic event reconstruction (real data)

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Detecting Problems – Cell ImbalanceTileCal cells have two readout channels

Cell

PMT rightPMT left

cell with asymmetric energy

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Detecting Problems – noisy modules

TileCal module LBA45 with high pedestals in most of the cells

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Threshold by Cell Energy

Level 2 Trigger RoI seen from inside of the detector

Low threshold in the Eletromagnetic Calorimeter (all cells are showed)

buttom to force same threshold

activated cells

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Threshold by Cell Energy

Level 2 Trigger RoI seen from inside of the detector

Threshold at 50 MeV (LArg detector)

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Threshold by Cell Energy

Level 2 Trigger RoI seen from inside of the detector

Threshold at 2 GeV (only activated cells are showed)

energy of some activated cells

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Identifying Problems – Level 2 RoI

wrong cell information

before fix the problemafter fix the problem

last cells (high eta) with wrong values

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Conclusion & To do list

Easy way to go through the events and check for problems.

Needs only Root (v5.14.00). Easy to run and to modify. No need to recompile. It has helped commissioning phase with cosmic. Some bugs in the L2 Trigger algorithms has been

found with this tool. Next steps: Include LArg EndCap and Inner Detector.