CellMaker

Cells are Atlfast physics output entities which correspond to energy deposits in the Calorimeter

CellMaker Overview

The DefaultReconstructedParticleMaker is an Athena-Algorithm which is created at the start of a job and executed once per event.
The following three public methods are executed by Athena, and are needed to honour the IAlgorithm interface

• initialise() - create helper classes and declare any jobOptions properties
• execute() - perform the algorithm's function once per event
• finalise() - perform any end of job tasks

1. Retrieve the relevant Monte Carlo HepMC::Particles from the TES
2. If particle lies in Calorimeter acceptance, calculate which Cell is struck
3. Add energy to Cell and keep a reference to the particle
4. Store all Cells above pT threshold on the TES

• Calorimeter suite - consists of Calorimeter, CalSections and Cells which represent the spatial layout of the calorimeter
• PtCutter - removes low pT particles that spiral in the magnetic field without hitting the calorimeter
• MagField - calculates phi bending in the B field
• ICellSelector - select cells with pT above a threshold
• TesIO - used to perform input/output to the TES

User Requirements Satisfied

The design fulfills requirements 3.1.3 if the ARD.

CellMaker Detail

jobOptions Properties

jobOptions properties are steering parameters which can be set by the user in the jobOptions file.
They are declared in the constructor and initialised to Default Values
The options for this algorithm are

• InputLocation - location on the TES of input MC particles
• OutputLocation - location on the TES of output Cells
• EtaCoverage - eta coverage of the calorimeter
• MinETCell - Cell eT threshold level
• BarrelForwardEta - eta value of the barrel/forward region boundary
• GranBarrelEta - eta granularity of calorimeter in the barrel
• GranBarrelPhi - phi granularity of calorimeter in the barrel
• GranForwardEta - eta granularity of calorimeter in the forward region
• GranForwardPhi - phi granularity of calorimeter in the forward region
• BFieldON - magnetic field flag (on/off)
• MCSelectorInd - Flag to choose MCSelector

Initialisation

The initialise method is called once at the beginning of the job. It is here that the helper classes are instantiated.
The Calorimeter is instantiated with three calorimeter sections, the PtCutter cuts on particles of less then 0.5 GeV.
CellMaker initialisation sequence diagram

Execution

The execute sequence diagram shows the following activites which result when the execute method of CellMaker are called:

1. MC Particles are read in from the TES, these are
   • Final State
   • Not muon or invisible (user selectable; usually neutrinos, could have other eg SuperSymmetry particles added to the list)
   • Passing Magnetic field Cuts (0.5 Gev for charged particles)
   • Passing photon momentum cuts (0.0 GeV default)
2. The low momentum particles are removed by the PtCutter object
3. Delta Phi due to the magnetic field is calculated
4. A vector of STL pairs is passed to the Calorimeter. The pair contains the phi at the calorimeter, and the HepMC particle
5. The calorimeter removes invisibles and muons, and passes to the vector to CalSections (forward end-cap, barrel, backward end-cap)
6. If the particle lies within the acceptance of the calorimeter section, the cell struck by the particle is calculated
7. For this cell
   • The particle counter is incremented by one.
   • The sum of the Pt is incremented by the Pt of the particle.
   • The particle is stored.
8. After processing all the particles, CellMaker requests a list of all cells satisfying the ICellSelector requirement
9. The cells above a pT threshold are stored in the TES
10. All cells are then reset
CellMaker execution sequence diagram

Class Diagram

The various classes discussed above are shown in the class diagram. CellMaker class diagram