  The PANDA collaboration intends to build a state-of-the-art detector to study
the physics of antiproton annihilation in the charm mass region at the future
FAIR facility at GSI, Darmstadt. One major part of the PANDA detector is the
straw tube tracker. It will consist of about 6000 individual straws grouped in
11 double layers and filled with an Ar+10%CO_2 gas mixture. The required radial
spatial resolution is about 150 micron. Two different methods are considered
for longitudinal coordinate measurements - skewed double layers and a novel
method based on the time-dependent charge asymmetry. The latter method is
presented in this article.
