  A large-volume Time Projection Chamber (TPC) is the main tracking and
particle identification (PID) detector of the ALICE experiment at the CERN LHC.
PID in the TPC is performed via specific energy-loss measurements (dE/dx),
which are derived from the average pulse-height distribution of ionization
generated by charged-particle tracks traversing the TPC volume. During Runs 1
and 2, until 2018, the gas amplification stage was based on multiwire
proportional chambers (MWPC). Signals from the MWPC show characteristic long
negative tails after an initial positive peak due to the long ion drift times
in the MWPC amplification region. This so-called ion tail can lead to a
significant amplitude loss in subsequently measured signals, especially in the
high-multiplicity environment of high-energy Pb-Pb collisions, which results in
a degradation of the dE/dx resolution. A detailed study of the signal shapes
measured with the ALICE TPC with the Ne-CO2 (90-10) and Ar-CO2 (90-10) gas
mixtures is presented, and the results are compared with three-dimensional
Garfield simulations. The impact of the ion tail on the PID performance is
studied employing the ALICE simulation framework and the feasibility of an
offline correction procedure to account for the ion tail is demonstrated.
