  A theoretical study of $\bar{p}p \to \bar{p}n \pi^+ $ reaction for
anti-proton beam energy from 1 to 4 GeV is made by including contributions from
various known $N^*$ and $\Delta^*$ resonances. It is found that for the beam
energy around 1.5 GeV, the contribution of the Roper resonance $N^*_{(1440)}$
produced by the t-channel $\sigma$ exchange dominates over all other
contributions. Since such reaction can be studied in the forthcoming
$\bar{P}$ANDA experiment at Facility of Antiproton and Ion Research (FAIR), the
reaction will be realistically the cleanest place for studying the properties
of the Roper resonance and the best place for looking for other "missing" $N^*$
resonances with large coupling to $N\sigma$.
