Changes between Version 63 and Version 64 of Reweight

Timestamp:

Aug 3, 2020, 10:09:09 PM (4 years ago)

Author:

Olivier Mattelaer

Comment:

--

Reweight

@@ -166 +166 @@
  for the LO and NLO cases respectively.
 
+ == Code limitation
+
+   1. The re-weighting assumes that the matrix-element is symmetric for identical particles. This is a limitation for process like
+      generate p p > Z j j, z > j j. In general such issues are automatically detected but in some particular case the re-weighting can fail to detect it and produce result which might be un-expected.
+   2. The ordering of the particles in the event file is not guaranteed and information about internal propagator not save to use. Consequently process like
+      "p p > e+ e- X, X > mu+ mu-" and "p p > mu+ mu- Y, Y > e+ e-" can not be distinguish. The re-weighting will systematically crash when this happens.
+
+   Work around for those limitations can be done by setting some special flag in the reweight_card and carefully generating the input event:
+   a. '''use_eventid True''': This allow to use the event id flag of the leshouche event file to distinguish different process. Within MG5aMC, you should use the "@" syntax in order to put such eventid in the leshouches file: for example "generate p p > e+ e- X, X > mu+ mu- @1; add process p p > mu+ mu- Y, Y > e+ e- @2" (new in 2.7.4)
+   b. '''change keep_ordering True''': This assumes that particle written in the leshouches file are in the exact same order as the one used by madgraph (looks at the Feynman diagram for the the ordering) --use with great care-- (new in 2.7.0)
+
+
  == Content of the reweight_card
  
@@ -182 +194 @@
    9. '''change virtual_path PATH''': Allow to use an external library of standalone matrix-element (see details [#Generateexternallibrary here]) for the new theory for the virtual contribution. '''new in 2.5.6'''
    10. '''change systematics OPTS''': '''only for ouptut mode '2.0' ''', allows to run the systematics computation on the new flight with options "OPTS". Note that this assume that the orignal and final theory have the SAME power of alpha_s at born level. '''new in 2.5.6'''
-
+   11. '''change use_eventid''': see above
+   12. '''change keep_ordering'': see above --dangerous flag-- 
 
  2. '''Benchmark definition''':[[BR]]