PARSIFAL: A toolkit for triple-GEM parametrized simulation

PARSIFAL (PARametrized SImulation) is a fast and reliable software tool that reproduces the complete response of a triple-GEM detector to the passage of a charged particle, taking into account the main physical effects. Starting from the detector configuration and the particle information, PARSIFAL reproduces ionization, spatial and temporal diffusion, effect of magnetic field, if present, and GEM amplification to provide the dependable triple-GEM detector response. In the design and optimization stages of this kind of detectors, simulations play an important role. Accurate and robust software programs, such as GARFIELD++, can simulate the transport of electrons and ions in a gas medium and their interaction with the electric field, but they are CPU-time consuming. The necessity to reduce the processing time while maintaining the precision of a full simulation is the main driver of this work. For a given set of geometrical and electrical settings, GARFIELD++ is run once -and-for-all to provide the input parameters for PARSIFAL. Once PARSIFAL is initialized and run, it produces the detector output, including the signal induction and the output of the electronics. The results of the analysis of the simulated data obtained with PARSIFAL are compared with the results of the experimental data collected during a testbeam: some tuning factors are applied to the simulation to improve the agreement. This paper describes the structure of the code and the methodology used to match the output to the experimental data. Nature of problem: Monte Carlo (MC) simulations are widely used in design and development of detectors for high energy physics as well as during data taking to understand how the detector geometry, acceptance, efficiency affect the experimental observations and hence infer the systematic effects. For triple-GEM detectors (one of the most used Micro Pattern Gaseous Detectors), the simulation of their response to the passage of particles is usually performed with GARFIELD++ (CERN) which provides a microscopic description of the signal creation, from the interaction of the particle with the gas to the induction of the signal on the anode. This detailed simulation is heavy and CPU-time consuming, hence it requires long computing periods to gain high statistics. Solution method: PARSIFAL software provides the MC simulation of the response of a triple-GEM detector to the passage of a charged particle by splitting the simulation into four independent steps: ionization, electron drift in gas and magnetic field, avalanche formation in the multiplication stages, signal induction on the anode and response of the electronics (APV-25 chip). For each step, PARSIFAL samples the variables of interest from distributions, obtained by using a set of input parameters. These parameters are extracted from a simulation run only once with GARFIELD++. Since the sampling is much faster than a full GARFIELD++ simulation, this reduces the CPU-time to collect a sample with high statistics. The results extracted by the PARSIFAL simulation have been tuned with experimental data collected during a testbeam at CERN and show a satisfactory compatibility.