Development and deployment of a fully parameterized fast Monte Carlo simulation in LHCb

Abstract

Faster alternatives to a full, GEANT4-based simulation are being pursued within LHCb experiment. In this context the integration of the Delphes toolkit in the LHCb simulation framework is intended to provide a fully parameterized option. Delphes is a modular software designed to perform fast simulations by propagating stable particles using a parametric approach and providing reconstructed physical objects as output. It includes propagation inside a magnetic field and parameterized response for tracking and muon systems as well as calorimetric response. Particle energies are computed by smearing the initial visible particles momenta according to detector resolution in a highly-customizable way. Delphes was initially designed for general-purpose experiments such as ATLAS and CMS where is already used. The present contribution illustrates the different aspect of the integration of the Delphes toolkit in Gauss, the LHCb simulation framework. Technically the particle transport performed by GEANT4 and subsequent mimicking of detector response and reconstruction has been replaced with a parametric response of the various detector elements. The implementation required extension to Delphes itself to constrain the particle transport inside the spectrometer acceptance, in order to match the LHCb dipole magnetic field. The configuration of various parameterizations of resolution and efficiency (charged particle tracking, mis-identification rate of particle identification algorithms, calorimeter, trigger response) is also a major aspect of the work to provide a fully functional simulation system. The output of the resulting fast simulation is formatted in such a way that can be used in the LHCb physics analysis framework. The status of the integration of Delphes is given.