hello,
at the GENIE neutrino generator http://www.genie-mc.org/ we are using TGenPhaseSpace as part of a KNO-based hadronization model, eg see: http://hepunx.rl.ac.uk/~candreop/generators/GENIE/devel/src/Fragmentation/KNOHadronization.cxx
When I run the generator in a mode producing *unweighted* events
(after selecting multiplicity and final state particles)
I use the rejection method and based on the weight reported by each
TGenPhaseSpace::Generate() I try to select an 'unweighted decay'.
The problem is that for events with:
(invariant mass) - (sum of final state particle masses) = (small)
TGenPhaseSpace reports a *huge* maximum weight:
many orders of magnitude away from the maximum weight one would
*ever* get by running the TGenPhaseSpace::Generate().
This can be seen in
http://hepunx.rl.ac.uk/~candreop/outbox/phaseSpace.gif
The red line corresponds to the max weight as reported by TGenPhaseSpace
*A macro to reproduce this plot is attached.*
For our generator this means that very few events (in the edges of our 'phase space' but still physical ones) take disproportionally long time to be generated - screwing the overall performance.
I can always search for the maximum weight myself, but I would like to understand better why this happens: Do I use TGenPhaseSpace incorrectly? a bug? a limitation?
cheers,
Costas
-- Dr. Constantinos Andreopoulos, CCLRC - Rutherford Lab. http://hepunx.rl.ac.uk/~candreop/Received on Wed May 10 2006 - 14:02:14 MEST
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