Alignment and Residual Studies of the sPHENIX TPC

The Time Projection Chamber (TPC) is one of the main tracking detectors in the sPHENIX experiment at RHIC, providing precise measurements of charged particle tracks in heavy-ion collisions. The signals from the TPC are collected using 48 layers of zigzag-patterned readout pads, divided into 36 modules on each side of the detector. There are three modules radially in each of twelve azimuthal sectors, covering the full detector acceptance. Accurate track reconstruction in the TPC requires precise alignment of these readout modules and a detailed understanding of residual distributions, defined as the differences between measured hit positions and projected track positions. In data recorded in the absence of a magnetic field, residual patterns are used to extract alignment parameters. However, in the presence of the 1.4 T magnetic field in sPHENIX, the effective geometry of the detector can be slightly modified. Furthermore, under full field conditions, residuals become sensitive to module-edge, static, and time-varying distortions that impact reconstructed tracks. In this case, residuals serve as a powerful diagnostic tool for evaluating how well these effects are understood and corrected in the track reconstruction. We present a study of azimuthal residuals in data recorded with magnetic field on and off, along with the alignment procedure of the TPC modules. Residuals, calculated based on data, collected with the magnetic field turned on, are also analyzed to study effectiveness of various distortion correction strategies. These studies contribute to ongoing efforts to improve TPC tracking performance and enable high-precision physics measurements at sPHENIX.