The A2 active target time projection chamber

Abstract

The A2 Collaboration uses the Mainz Microtron to conduct measurements probing hadron structure. An upcoming experiment will study Compton scattering off 3He to obtain the polarizabilties of the neutron. To identify this reaction, the detection of the low-energetic recoil particles is necessary. This is not possible with the current equipment, and so an active target is required. A compact Time Projection Chamber (TPC) is being constructed for this purpose, to be used in combination with the existing photon calorimeters. The main goal of this work was to create a Geant4 simulation of the active target TPC. A signi cant limitation to the Geant4 software was discovered, but was overcome by the creation of a custom electron drift model. With the Geant4 simulation, it was possible to create an event reconstruction framework, and then study the functionality of the active target. The active target TPC is a new technological approach for A2, and so it is not without its challenges. This work revealed kinematic limitations to the proposed experiment. Various solutions are explored, providing essential input for the design of the active target TPC electronics and the Compton scattering on 3He experiment.