Figure 2

Identification of $\pi^{+/-}$ from the TPC d$E$/d$x$. The $x$- and $y$-axes show thedeviation of the measured energy loss from the Bethe-Bloch (BB) expectations for positive andnegative tracks, respectively. The scale is such that one unit corresponds to one standard deviation The circle, corresponding to $4 \sigma$, shows the selection used. The entries in the upperright corner are from $e^+e^-$ pairs produced in two-photon interactions. The plot is for eventssatisfying the requirements (i)-(iii) and (v)-(vi) described in the text