The alignment of the BESIII drift chamber using cosmic-ray data

BESIII experiment adopts a drift chamber as the central tracking detector. Big distortion of the chamber due to mechanical imperfection causes bad momentum resolution. Software alignment is the only possible strategy to estimate the displacements of sub-endplates of the chamber. We have developed an alignment software in the framework of the BESIII Offine Software System. Cosmic-ray data are used in preliminary alignment. The alignment method is introduced in the paper. The results of the alignment are also presented.