Good blog post to put some color on the differences between BPM and CEP (seems obvious, but the post makes it clear that it isn't always so):
CEP, on the other hand, gives an ability for an organization to aggregate nearly any event and to create automated processes from those events, not the other way around. Rules aren?t used to determine workflows, but instead are a way to classify (and reclassify) what is being discovered through an event or series of events. CEP is more situational and less coupled to an order of activities. CEP is used to react more quickly to threats and opportunities and is more flexible than BPM for this purpose.