Software

The HEP software consists of SDRAM (Simulation, Digitization, Reconstruction, Analysis) Chain and the DAQ software. Our Software Chain is mainly focus on the SDRAM.

The CEPC SCRAM consists of five pillars: the Generator, the Simulation, the Digitization, the Reconstruction and the Analysis, see Fig BBB. In addition, the CEPC uses Marlin and LCIO from ilcsoft, as the data management and data format.

The CEPC SCRAM uses Whizard as the generator tool. It generates the energy and momentum information for the final state particles for any given physics process at given center of mass energy. A more detailed description is given in XXX1.

For the simulation, we developed a Geant4 simulation package, MokkaPlus, from Mokka, the simulation software used for linear collider studies. It could construct the detector geometry using virtual geometry volumes and calculate the energy deposition information via Geant 4, and create simulated detector hits accordingly. More detailed description could be found in XXX2.

Proper description of the detector hardware response is vital for the detector simulation. The knowledge of detector response is summarized and integrated to the Software chain via digitization modules. The digitization modules read the simulated detector hits, convolute it with detector response (time, energy), and produce the digitized detector hits, which should mimics the real experimental detector hits at satisfactory level. In principle, one digitization framework is needed for each different sub-detector and its performances need to be validated at real experimental data. In addition, the parameterization of each digitization needs to be updated according to the in-situ data monitoring at the real experiments. Therefore, the development and validation of dedicated digitization modules – framework and parameterization is therefore a continuing effort during the HEP experiments. At the R&D stage, the digitization study mainly focus on the modeling of the leading effects at the detector response, and the clarification of the performance at technology level. Several digitization modules are developed, see XXX3.

The reconstruction is always the most difficult, the trickiest and the most interesting part. In short, the reconstruction takes in the detector hits – digitized hits from simulation or experimental hits from the data acquisition, and interpret them into the physics objects, with measured quantities such as particle type, energy, momentum, etc. A detailed description of the CEPC reconstruction and its characteristic performance is described in XXX4.

The analysis is the procedure that actually measures the interested physics quantities from the reconstructed physics objects. It consists of at least three steps: the construction of observables, the classification between signal and background, and the extraction of the value of the physically interested quantities. Several examples are given XXX5.

The CEPC reconstruction is developed following the Particle Flow principle. That’s to say, the reconstruction interprets all the detector hits into final state particles, each final state particle is then measured in the most precise sub-detector system. Explicitly, reconstruct the charged particle in the tracking system – whose momentum resolution is usually superior comparing to the energy resolution at calorimeter, reconstruct the photons at the ECAL, and reconstruct the neutral hadron particle at the calorimeter system. The PFA algorithm provides a global consistent description of the entire detector hits, a common basis for all the physics object reconstruction and therefore boost the corresponding efficiency and purity. In addition, it significantly improves the measurement accuracy for the composed physics objects as tau and jets – since most of their energy is carried by the charged particle that can be measured at a much better precision at the PFA.

The Particle Flow Principle also enables general fast simulation algorithms, that mimic the final state particle information directly from the MCParticle information at the generator level. Several fast simulation packages are developed accordingly, see XXX6.