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The problems you are having are directly related to the way the generator fills the HepEvt common block. The parent/daughter relationships returned by the JAS classes for StdHep events directly reflect the info returned by the generator. I have dumped the parent/daughter structure from a typical tt bar event below. Some observations: 1) The initial state e+e- are listed as having no daughters and no parents 2) The parent-daughter relationship is non-intuitive, just becase B is A's daughter doesnt imply that A is B's parent (according to the generator). 3) Some particles (e.g the type 92 "string") have multiple parents. The only subtlety the JAS introduces in to the process is that there is both a getParent() and getParents() method in the Particle class. The getParent method works only in the case that the particle has a single parent (currently it returns null if there is either 0 parents, or >1 parent, in future it will throw an exception if there is >1 parent). getParents works in all cases, although its a little harder to use since it returns an enumeration which you have to loop over. In conclusion I think you can probably solve both the "work up" and "work down" cases by: 1) For work down, loop over the particles until you find the first non-electron and start from there. 2) For work up, use getParents rather than getParent I havent actually tested either of these but I think they should work. Tony Event 0 id=11 parents=0-0 daughters=0-0 id=-11 parents=0-0 daughters=0-0 id=11 parents=1-0 daughters=0-0 id=-11 parents=2-0 daughters=0-0 id=11 parents=3-0 daughters=0-0 id=-11 parents=4-0 daughters=0-0 id=23 parents=5-6 daughters=0-0 id=6 parents=7-0 daughters=0-0 id=-6 parents=7-0 daughters=0-0 id=24 parents=8-0 daughters=0-0 id=5 parents=8-0 daughters=0-0 id=-24 parents=9-0 daughters=0-0 id=-5 parents=9-0 daughters=0-0 id=-11 parents=10-0 daughters=0-0 id=12 parents=10-0 daughters=0-0 id=3 parents=12-0 daughters=0-0 id=-4 parents=12-0 daughters=0-0 id=23 parents=7-0 daughters=0-0 id=24 parents=10-0 daughters=21-22 id=-24 parents=12-0 daughters=29-40 id=-11 parents=14-0 daughters=0-0 id=12 parents=15-0 daughters=0-0 id=5 parents=11-0 daughters=41-41 id=21 parents=11-0 daughters=41-41 id=21 parents=11-0 daughters=41-41 id=21 parents=13-0 daughters=41-41 id=21 parents=13-0 daughters=41-41 id=-5 parents=13-0 daughters=41-41 id=-4 parents=17-0 daughters=55-55 id=21 parents=17-0 daughters=55-55 id=21 parents=17-0 daughters=55-55 id=21 parents=16-0 daughters=55-55 id=21 parents=16-0 daughters=55-55 id=21 parents=16-0 daughters=55-55 id=21 parents=16-0 daughters=55-55 id=21 parents=16-0 daughters=55-55 id=21 parents=16-0 daughters=55-55 id=21 parents=16-0 daughters=55-55 id=21 parents=16-0 daughters=55-55 id=3 parents=16-0 daughters=55-55 id=92 parents=23-28 daughters=42-54 id=-523 parents=41-0 daughters=74-75 id=211 parents=41-0 daughters=0-0 id=313 parents=41-0 daughters=76-77 id=-321 parents=41-0 daughters=0-0 id=213 parents=41-0 daughters=78-79 id=-213 parents=41-0 daughters=80-81 id=2112 parents=41-0 daughters=0-0 id=-2114 parents=41-0 daughters=82-83 id=321 parents=41-0 daughters=0-0 id=-323 parents=41-0 daughters=84-85 id=213 parents=41-0 daughters=86-87 id=-213 parents=41-0 daughters=88-89 id=523 parents=41-0 daughters=90-91 id=92 parents=29-40 daughters=56-73 id=-413 parents=55-0 daughters=92-93 id=111 parents=55-0 daughters=94-95 id=211 parents=55-0 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id=211 parents=71-0 daughters=0-0 id=111 parents=71-0 daughters=148-149 id=-211 parents=72-0 daughters=0-0 id=111 parents=72-0 daughters=150-151 id=310 parents=73-0 daughters=152-153 id=423 parents=74-0 daughters=154-155 id=-211 parents=74-0 daughters=0-0 id=221 parents=74-0 daughters=156-158 id=310 parents=76-0 daughters=159-160 id=22 parents=77-0 daughters=0-0 id=22 parents=77-0 daughters=0-0 id=22 parents=79-0 daughters=0-0 id=22 parents=79-0 daughters=0-0 id=22 parents=81-0 daughters=0-0 id=22 parents=81-0 daughters=0-0 id=22 parents=83-0 daughters=0-0 id=22 parents=83-0 daughters=0-0 id=310 parents=84-0 daughters=161-162 id=22 parents=87-0 daughters=0-0 id=22 parents=87-0 daughters=0-0 id=22 parents=89-0 daughters=0-0 id=22 parents=89-0 daughters=0-0 id=-423 parents=90-0 daughters=163-164 id=211 parents=90-0 daughters=0-0 id=111 parents=90-0 daughters=165-166 id=311 parents=92-0 daughters=167-167 id=-20213 parents=92-0 daughters=168-169 id=22 parents=93-0 daughters=0-0 id=22 parents=93-0 daughters=0-0 id=310 parents=96-0 daughters=170-171 id=22 parents=110-0 daughters=0-0 id=22 parents=110-0 daughters=0-0 id=22 parents=113-0 daughters=0-0 id=22 parents=113-0 daughters=0-0 id=22 parents=115-0 daughters=0-0 id=22 parents=115-0 daughters=0-0 id=22 parents=117-0 daughters=0-0 id=22 parents=117-0 daughters=0-0 id=-211 parents=118-0 daughters=0-0 id=211 parents=118-0 daughters=0-0 id=421 parents=119-0 daughters=172-173 id=22 parents=119-0 daughters=0-0 id=111 parents=121-0 daughters=174-176 id=111 parents=121-0 daughters=177-178 id=111 parents=121-0 daughters=179-180 id=211 parents=122-0 daughters=0-0 id=-211 parents=122-0 daughters=0-0 id=111 parents=131-0 daughters=181-182 id=111 parents=131-0 daughters=183-184 id=-421 parents=136-0 daughters=185-189 id=111 parents=136-0 daughters=190-191 id=22 parents=138-0 daughters=0-0 id=22 parents=138-0 daughters=0-0 id=310 parents=139-0 daughters=192-193 id=113 parents=140-0 daughters=194-195 id=-211 parents=140-0 daughters=0-0 id=-211 parents=143-0 daughters=0-0 id=211 parents=143-0 daughters=0-0 id=-323 parents=154-0 daughters=196-197 id=211 parents=154-0 daughters=0-0 id=22 parents=156-0 daughters=0-0 id=-11 parents=156-0 daughters=0-0 id=11 parents=156-0 daughters=0-0 id=22 parents=157-0 daughters=0-0 id=22 parents=157-0 daughters=0-0 id=22 parents=158-0 daughters=0-0 id=22 parents=158-0 daughters=0-0 id=22 parents=161-0 daughters=0-0 id=22 parents=161-0 daughters=0-0 id=22 parents=162-0 daughters=0-0 id=22 parents=162-0 daughters=0-0 id=321 parents=163-0 daughters=0-0 id=-211 parents=163-0 daughters=0-0 id=-211 parents=163-0 daughters=0-0 id=211 parents=163-0 daughters=0-0 id=111 parents=163-0 daughters=198-199 id=22 parents=164-0 daughters=0-0 id=22 parents=164-0 daughters=0-0 id=211 parents=167-0 daughters=0-0 id=-211 parents=167-0 daughters=0-0 id=-211 parents=168-0 daughters=0-0 id=211 parents=168-0 daughters=0-0 id=-321 parents=172-0 daughters=0-0 id=111 parents=172-0 daughters=200-201 id=22 parents=189-0 daughters=0-0 id=22 parents=189-0 daughters=0-0 id=22 parents=197-0 daughters=0-0 id=22 parents=197-0 daughters=0-0 id=22 parents=0-0 daughters=0-0 id=22 parents=0-0 daughters=0-0 > -----Original Message----- > From: Mahalaxmi Krishnamurthy [mailto:[log in to unmask]] > Sent: Thursday, April 22, 1999 11:47 AM > To: [log in to unmask] > Cc: Robert Wilson > Subject: Getting complete hierarchy > > > > HI , > > Our goal is to associate final state particles with > initial partons. To do > this with highest statistics we want to use StdHEP event > generator datasets > (generated by Gray at SLAC?). We are using JAS to read them. > > Problem: The Particle.getParent() chain going up > terminates at "unknown" ( > id=92, probably the fragmentation string?) . > Particle.getDaughters() on the > initial partons is empty, so one cannot go in the other direction. > > Oddly enough, in the lcd-sim files one can follow the > daughters chain down > through the "Idontknowino" e.g. t->Wb->, W->ud-> > Idontknowino->physical > particles; and the tbar down through to its own > Idontknowino. This allows us > to associate final state particles with initial partons. > > Does anyone know how to get the information we need > (i.e. the complete > production/decay hierarchy) from stdhep files using JAS. > > > > Maha, Bob. > > > >