erep-sim

A library to support simulating the energy response generated using edep-sim. While this is initially simulated the 3DST scintillator cube detector, it is using the same techiques (and almost the same class structure) as the T2K elecSim. It is well suited to simulated any detector (that is likely to be used) in the DUNE ND. The current simulation handles the 3DST, the SAND TPCs and the KLOE ECals. It can merge events to build full-spill simulations and provides several options to cherry pick events from multiple input files.

Requirements

This needs to find ROOT, edep-sim and their dependencies in the cmake search path.

Implementation Status

This is a growing simulation

• The 3DST and TPC response models (as of 1.2021)

  • The detector identifiers for TPC have been defined. The 3DST remains as detector type 13. The TPC now uses detector types 25 (downstream), 26 (top), and 27 (bottom).

  • A simple TPC response model will drift electrons to the micromegas. For efficiency, it samples the electrons to be drifted. It uses the simplified sensor models for each of the pads, and the simple multihit TDC/ADC DAQ simulation. The charge migration between the pads is handled a simple Gaussian spread, and the current simulation overestimates the hit resolution.

  • The response model for the 3DST is relatively complete. It includes the important effects like energy to photons, light crossing between cubes, photon arrival times, attenuation, and such.

  • The sensor model is idealized. It directly translates the input classes to the output classes. For the 3DST, this is "almost" sufficient since the photon detection efficiency can be approximated by the MeV to carrier normalization, but it doesn't include the sensor jitter (timing or charge), or non-linear effects.

  • The TDC/ADC DAQ simulation will return either the time of that the threshold is crossed, or the time of the average charge arrival. The first mode is appropriate for the 3DST, and the second is appropriate for the TPC. The integration window, and dead time can be independently configured.

• The ECal detector response model (as of 1.2021)

  • Look for the output of sand-stt and use the hits, if they are available.

  • The sand-stt implementation only works on single edep-sim events. Since a full spill is too complex for a single event, that means the deadtime model is not correct. This is fixed when the events are combined.

Design

The simulation is divided into three basic steps, and base classes are provided for each. The steps are the response, sensing, and DAQ processes. These steps are then combined using detector classes which handle each sub-detector being simulated.

Response Simulation

The first step simulates the detector response, which translates the energy deposition into a "Carrier". This class accepts a container of edep-sim hit segments and translates them into carriers. The carrier represents a photon, ionization electron (or cloud of electrons) that can be transported to the sensor. The response classes are responsible for simulating the effects of transporting the carrier to the sensor.

Sensor Simulation

The second step simulates the sensor. This simulates the effect of a photo-sensor, micromegas, or other sensor on the carriers produced by the detector response. The output of the sensor step is are impulses of current (or a vector of current vs time) that is sent to the DAQ step. The impulses are represented by the time, total charge, and time width of the current produced by the sensor.

Electronics, DAQ, and Calibration

The third step simulates the "DAQ" which handles the effects of digitization of the current coming from the sensors, and then "calibrates" the digitized values into hits.

Overall Detector Class

The detector class is called by the main loop and is responsible using the response, sensor and DAQ classes to simulate the response of a particular detector. It takes EDepSim hit segments and uses the other classes to build a "calibrated" hit that is saved in the output tree.

Output

The output of the simulation is a very simple tree that is suitable to be used as a "friend" of the edep-sim tree. All of the information is saved in vectors (of int or float). There is a second "Property" tree that is created with a map from strings to float and string values.

The trees can be easily managed by hand, but you can also copy the ERepSimInput.hxx include file into your own project. This has some skeleton code to attach to the tree and declare the branches.