GramsReadoutSim

GramsReadoutSim

Author: Satoshi Takashima

If you want a formatted (or easier-to-read) version of this file, scroll to the bottom of GramsSim/README.md for instructions. If you're reading this on github, then it's already formatted.

• GramsReadoutSim
  • grams::ReadoutMap
  • Design note

Table of contents generated with markdown-toc

The purpose of this program is to model the readout geometry of the GRAMS detector.

As of Nov-2022, it's anticipated that the readout of the GRAMS LArTPC will be a pixel detector. However, other LArTPC detectors have used wires, and in the future yet another charge readout technologies may be developed. Hence the readout system is modeled in a program of its own.

In GramsDetSim, the ionization left by charged-particle tracks was divided into electron clusters and drifted to the anode of the LArTPC. GramsReadoutSim assigns a pixel ID to each cluster, with the pixel ID defined as an integer pair in (x,y).

Sketch by Satoshi Takashima of the operation of GramsReadoutSim. Note that after he created this diagram, he choose a different scheme for assigning a pixel ID. The pixel ID is assigned as pair of integers (x,y) instead of an consecutive integer over a grid.

See GramsSim/util/README.md for a description of how to control the operation of gramsreadoutsim through the options.xml file and the command line.

Since the readout is presently modeled as a simple 2D grid in x and y, the GramsReadoutSim parameters are equally simple:

• gdml : The ROOT-compatible gdml file emitted by GramsG4

• anodeTileVolume: The volume in gdml file that corresponds to Anode Tile plane. You extract the dimensions of the pixel grid from this

• x_resolution and y_resolution: Number of pixels along the x/y direction(s)

• readout_centerx and readout_centery: The x- and y-offset of the center of the readout geometry from the (x=0,y=0) coordinate of the detector geometry.

grams::ReadoutMap

As you look through the description below, consult the GramsDataObj/include directory for the header files. These are the files that define the methods for accessing the values stored in this object. Documentation may be inaccurate; the code is actual definition. If it helps, a std::map is a container whose elements are stored in (key,value) pairs. If you're familiar with Python, they're similar to dicts.

Sketch of the grams::ReadoutMap data object.

The purpose of GramsReadoutSim is to assign the electron clusters derived in GramsDetSim to readout channels for an event; the data object grams::ReadoutMap contains the result. Each readout channel is assigned a grams::ReadoutID. The data object grams::ReadoutMap is a map of all the channels that have clusters. Each channel has a std::set (the equivalent of Python list) of electron clusters associated with that channel.

Rather than storing the complete grams::ElectronCluster for each cluster, only the key to the grams::ElectronClusters map is stored. Therefore, to see the information for the clusters for a given readout channel, you'll typically have to open both of the output files from GramsDetSim and GramsReadoutSim, and use the grams::ReadoutMap to look up the information within grams::ElectronClusters.

If this is confusing, see the code for GramsElecSim. Here's an excerpt from that program (without comments or error detection):

// Define the two input trees as friends.
auto input = TFile::Open("gramsreadoutsim.root");
auto tree = input->Get<TTree>("ReadoutMap");
tree->AddFriend("ElectronClusters","gramselecsim.root")
auto reader = new TTreeReader(tree);
// 
TTreeReaderValue<grams::ElectronClusters> clusters = {*reader, "ElectronClusters"};
TTreeReaderValue<grams::ReadoutMap> readoutMap     = {*reader, "ReadoutMap"};
// ...
    
// For each row in the input tree:
while ( (*reader).Next() ) {

    // For each readout cell that received any electron clusters:
    for ( const auto& [ readoutID, clusterKeys ] : (*readoutMap) ) {

      // for each electron cluster assigned to this readout cell:
      for ( const auto& clusterKey: clusterKeys ) {

        // Find the key for this cluster in our list of electron clusters. 
        const auto search = clusters->find( clusterKey );

        // We found the cluster's key in the list of electron
        // clusters. Fetch that cluster; remember that a map consists of
        // pairs (first,second).
        const auto& cluster = (*search).second;

        // 'cluster' is a grams::ElectronCluster assigned to this ReadoutID
        // Do whatever with 'cluster'...``
    }
}

Design note

It's reasonable to ask why the functions of GramsDetSim, GramsReadoutSim, and GramsElecSim are in three separate programs.

Functionally, each of these programs relates to a different aspect of an experiment's simulation:

• GramsDetSim relates to the physics of charge transport in the detector.

• GramsReadoutSim relates to the geometry of the readout anode.

• GramsElecSim relates to the design of the data-acquisition electronics.

Experience has taught us that for the purpose of planning, testing, studies, and maintenance, it's best to have these functions in separate programs, rather than one large program.