1

Status of Shower Parameterisation code in Athena

Andrea Dell’Acqua CERN PH-SFT

<dellacqu@mail.cern.ch>

2

Who

Most of the implementation work (and interfacing to Athena) done by Anthony Waugh (Univ. of Sydney)

Still willing to spend a significant fraction of his time on this subject but shifting emphasis

State of the art presented by Anthony at the recent LAr week

Available at: http://indico.cern.ch/conferenceDisplay.py?confid=a062981

Most of the gibbering here by meApologies if I misrepresent anything/anybody

3

What

Use G4 parameterisation interface “as is”

Re-implement G4Flash-like shower parameterisation procedure and customize it to the case of ATLAS LAr calorimeters

Concentrate on the LAr calorimeters

There is no reason why Tilecal can not be included, it was just a (wo)manpower issue until now

Stick to EM physics yet

Is there a need of parameterising hadronic interactions? Is there a safe way of parameterising hadronic interactions in ATLAS?

4

How

Fast simulation scheme

Only electrons/positrons are parameterised. Photons are followed by full sim. up to the point they convert (only then parameterisation kicks in)

Particles must be within allowable energy range, if not use full simulation

Shower must be contained within the calorimeter, in Z(95%) and R(95%). If not return to full simulation. When a fully contained electron is produced, it is parameterised

Showers starting before the calorimeter are handled by full simulation. Each particle entering the calorimeter is then handled separately by parameterisation mechanism

5

How (2)

If all boundary conditions are satisfied

The track is killed

Fake steps (10m) are simulated along the initial electron trajectory. Energy deposited and nr. of spots per steps are calculated

Sampling fluctuations are calculated, according to calo resolution

Energy and position of each spot are calculated

Fake steps are filled up and given to (standard) sensitive detector classes to generate hits

Standard simulation chain utilized to process hits

Loop until the total shower energy is deposited

6

Full vs. Fast

Shower profiles for EM barrel (10GeV e-)

BLUE - Full sim. RED - fast sim.

7

Full vs. fast (2)

Shower profiles for EM endcap (10GeV e-)

BLUE - Full sim. RED - fast sim.

8

Full vs. fast (3)

Shower profiles for FCAL (10GeV e-)

BLUE - Full sim. RED - fast sim.

9

Simulation time

Shower simulation time (electrons) for full and fast simulation

10

What is available?

In release 12.0.1

All machinery in place and working

Add (to standard job options)SimFlags.CalibrationRun.set_Value('')

…

AtlasG4Eng.G4Eng.add_FastSimModel("LArG4FastSimulation","LArFastShower","LArMgr::LAr::EMB::STAC")

AtlasG4Eng.G4Eng.add_FastSimModel("LArG4FastSimulation","LArFastShower","LArMgr::LAr::EMEC::OuterWheel")

AtlasG4Eng.G4Eng.add_FastSimModel("LArG4FastSimulation","LArFastShower","LArMgr::LAr::EMEC::InnerWheel")

AtlasG4Eng.G4Eng.add_FastSimModel("LArG4FastSimulation","LArFastShower","LArMgr::LAr::FCAL::Module1::Absorber")

Parameterised models CAN NOT be used together with calibration hits (obvious) but they don’t seem to go together with dead material hits either! To be understood and fixed…

Currently limited to LAr calorimeters only

Event sample (single particles) to be added to the standard test production exercise

11

What remains to be done?

Extend shower parameterisation to Tile/HEC/HadFCAL

Repackage code (currently in

LArCalorimeter/LArG4/LArG4FastSimulation )

Make steering parameters accessible via python/JO

G4 8.x coming along, require interface change (backwards incompatible)

Test, validate, improve

Single particles, full events

EM component of hadronic showers

Different (coarser?) parameterisation models

Speed?

Understand physics requirements and figure out physics channel specific parameterisation strategies

Where can we gain? How much? Is it worth the hassle?