Hi Norman, I'm looking back through an old e-mail and trying to implement something in hps-java. I need the GBL re-fit momentum xyz components for each particle which you described the method to obtain them here: package org.hps.analysis.examples; import java.util.List; import java.util.Map; import org.lcsim.event.EventHeader; import org.lcsim.event.Vertex; import org.lcsim.util.Driver; /** * * @author Norman A. Graf */ public class VertexAnalysis extends Driver { String vertexCollectionName = "TargetConstrainedV0Vertices"; protected void process(EventHeader event) { List<Vertex> vertices = event.get(Vertex.class, vertexCollectionName); for (Vertex v : vertices) { Map<String, Double> vals = v.getParameters(); System.out.println(vals); } } } My questions is how do I know which (e- or e+) corresponds to particle 1 and particle 2 of the vertexed pair? Is there a pointer or do I need to write some software to make a sophisticated guess? -Holly ######################################################################## Use REPLY-ALL to reply to list To unsubscribe from the HPS-SOFTWARE list, click the following link: https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=HPS-SOFTWARE&A=1