Abstract
A prototype under development for the BESIII inner drift chamber upgrade is based on MAPS detectors. The detector module is the basic building and functional block of the detector prototype. Its design must meet the requirements of low material budget and high stiffness. To verify the design and quantify the performance of the detector module, a detector prototype system including five layer modules was tested at the beam facility at DESY. In order to reconstruct the 2D material budget image of the detector module, a dedicated track fitting method is developed, and the impact of multiple scattering on the track fitting is taken into account to improve the accuracy of the track reconstruction. After getting the distribution of the multiple scattering angles on the module, the material budget of the module is obtained based on the Highland formula. The test result shows that the material budget of the detector module is about 0.35 ± 0.03 (sys.)% X0, which is consistent with the calculated value of 0.37% X0.