Short description

A simulation of the HARPO detector is implemented. It is not yet a full description of the detector, and contains the following elements:

event generator

This generates ``events'' that are simply a list of high energy charge particles, with their nature and 4-momentum.

ionisation

This describes the ionisation of the gas in the TPC by the charge particle. It can be done with Geant4, which includes the PhotoAbsorption Ionisation model, and multiple scattering in the gas. A simple model is also implemented, describing straight (high momentum tracks) with a poissonian path and a simple ionisation model (power law). This produces a list of ionisation points along the track, with the number of electrons produced.

electron drift

Each ionisation electron is treted individually. The electron drift is described simply with a fixed drift velocity, a Gaussian diffusion proportional to the square root of the drift distance, and an exponential law for electron capture.

amplification and readout

The signal from each electron is first amplified with gain fluctuations following an appropriate model (for now, only an exponential law is implemented). The signal is then distributed on the readout strips using a spatial distribution function (Gaussian). Finally, the time response of the electronics is describe with a function ( ).