README.md

DDDigi: The digitization tools of DD4hep

DDDigi is supposed to interprete the results of the detector simulation phase e.g. using the simulation toolket DDG4 with its command line interface ddsim. This is the final phase of data processing to obtain data from the simulation branch which are as close as possible to the response of the front-end electronics of a real experimental setup.

The simulation phase ejects for all subdetectors and the individual sensitive elements contained the energy deposits created by particles from a primary interaction passing the sensitive volume. These data have to processed for taking into accound imperfections of the apparatus such as

• uncertainties in cable lengths resulting in shifts of time of signal arriving.
• uncertainties in the position of sensitive volumes.
• dead or hot readout channels.
• conversion of the final signal data into the equivalent of ADC counts.
• ...

In addition these effects should be computed in the presence of

• multiple interactions in the same beam-crossing
• spillover signal from previous or following interactions due to the relaxation time of the apparatus.

DDDigi addresses these issues in a very modular way and implements a multi-threaded approach to perform such data processing. To support multi-threading and to avoid any complication for users due to data races the following basic assumptions were made:

• The signals from disjunct subdetectors are generally independent This means the detector response of any tracking subdetector is uncorrelated with the detector response of e.g. a calorimeter.
• Within a subdetector the response of disjunct units are uncorrelated. This means that e.g. hits on one layer of a layered tracking device are uncorrelated with the hits produced in another layer.
• Within one such a layered device the response of individual sensors is tyically uncorrelated.

These assumptions however are not strict, but rather require input from the designer of such a digitization application for a given appratus. These basic assumption only show the maximal level of parallelization possible when processing data signals. The parallelization can be configured for each subdetector at each level according to boundary conditions e.g. given by cross-talk or the data volume arising from the energy deposits of the simulation.

DDDigi Components

• DigiDDG4ROOT

  Reader for ROOT files produced with DDG4.
  Properties:
  

  Property	Data type	Description
  .input	vector	List of input files to be processed
  .tree	string	Name of the main data tree. default: EVENT
  .containers	vector	List of containers to be loaded to DDDigi.
  		If empty => all.
  .segment	string	Name of the input segment. default: "inputs"
  .mask	integer	Mask of this input source in the store. default: NO_MASK (0x0)
  .rescan	boolean	Rescan input sources for continuous execution. default: true
  .keep_raw	boolean	Keep raw input as opaque objects in the DDDigi store.

  Functionality: self explaining

• DigiAttenuator

  Deposit attenuator for energy deposits according to decay time constant.
  Properties:
  

  Property	Data type	Description
  .input	vector	List of input files to be processed
  .processor_type	string	Processor type used for single container attenuation.
  		default: DigiAttenuator
  .containers	vector	List of containers to be attenuated.
  .signal_decay	string	Decay function. default: exponential
  .t0	double	Time constant for exponential signal decay.