First, the conclusions: the M shape is the same across different charges and is the same in the eta and phi planes.  And while part of it is an SMD effect, probably having to do with the SMD being deeper into the BEMC at higher eta, a large part of it is not.

Figure 1: L to R, total # of tracks vs. BSMDE eta, # of + tracks vs BSMDE eta, # of - tracks vs BSMDE eta (all cuts)

Figure 2: L to R, total # of tracks vs. BSMDP eta, # of + tracks vs BSMDP eta, # of - tracks vs BSMDP eta (all cuts)

Figure 3: L, total # of tracks vs. BSMDE eta; R, total # of tracks vs. BSMDP eta (all cuts).

Figure 4: track momentum vs BSMDE eta, all cuts

Figure 5: L, total # of tracks vs. BSMDE eta, all cuts; R, total # of tracks vs. BSMDE eta, no SMD cuts

Figure 6: average BSMDE cluster ADC vs. eta in p and ADC bins