Perspectives for the migration of the LHCb geometry to the DD4hep toolkit

The LHCb experiment uses a custom made C++ detector and geometry description toolkit, integrated with the Gaudi framework, designed when the LHCb software was first implemented. With the LHCb upgrade scheduled for 2021, it is necessary for the experiment to review this choice and adapt to the evolution of software and computing (in terms of e.g multi-threading support or vectorization) The Detector Description Toolkit for High Energy Physics (DD4hep) is a good candidate for the replacement for LHCb’s geometry description framework: it is possible to integrate it with the LHCb core software framework and its features theoretically match the requirements: in terms of geometry and detector description but also concerning the possibility to add detector alignment parameters and the integration with simulation tools. In this paper we report on detailed studies undertaken to compare the feature set proposed by the DD4hep toolkit, to what is needed by LHCb. We show not only how the main description could be migrated, but also how to integrate the LHCb real-time alignment tools in this toolkit, in order to identify the main obstacles to the migration of the experiment to DD4hep.