I think you have to options.
- Get all the processes and filter it by your side.
- Query jbpm audit tables. You can check this class which does it:
https://github.com/droolsjbpm/jbpm/blob/5.4.x/jbpm-bam/src/main/java/org/jbpm/process/audit/JPAProcessInstanceDbLog.java
HTH,
Demian