Operating the GridPix detector with helium-isobutane gas mixtures for a high-precision, low-mass Time Projection Chamber

High precision experiments with muons and pions often require tracking charged particles with 𝑂(100 μm) single-hit resolution, possibly with particle identification capabilities, down to very low momenta (𝑝 ≲ 100MeV/𝑐). In such conditions, the particle trajectories are strongly affected by the interaction with the detector material, and the reconstruction of the kinematic observables consequently deteriorates. A good compromise between resolution and material budget can be obtained with a Time Projection Chamber (TPC), if very light gases and a high-granularity readout are used. In this paper, we present a characterization of the GridPix detector in helium-isobutane gas mixtures, within a TPC with 9 cm maximum drift. Measurements of the main electron drift properties for these gas mixtures are also presented.