Merge lp:~maddevelopers/mg5amcnlo/flip_particle_antiparticle into lp:~madteam/mg5amcnlo/trunk

[Olivier Mattelaer]

[Johan Alwall (johan-alwall)]

Hello Olivier,

Excellent. This is indeed a very nice solution. The only problem is of course if there are different orderings between different interactions, but let's take that if and when it happens.

Cheers,
Johan

review: Approve

[Olivier Mattelaer (olivier-mattelaer)]

Yes sure,

but at least the model will fail to be imported.
So this is not too bad.

=== modified file 'models/import_ufo.py'
--- models/import_ufo.py	2012-02-06 19:57:04 +0000
+++ models/import_ufo.py	2012-02-11 06:16:19 +0000
@@ -218,6 +218,9 @@
                    [p.antiname.lower() for p in self.ufomodel.all_particles])):
             self.use_lower_part_names = True
 
+        # check which of the fermion/anti-fermion should be set as incoming
+        self.detect_incoming_fermion()
+
         for particle_info in self.ufomodel.all_particles:            
             self.add_particle(particle_info)
 
@@ -268,9 +271,10 @@
         
         # MG5 have only one entry for particle and anti particles.
         #UFO has two. use the color to avoid duplictions
-        if particle_info.pdg_code < 0:
+        pdg = particle_info.pdg_code
+        if pdg in self.incoming or (pdg not in self.outcoming and pdg <0):
             return
-        
+                        
         # MG5 doesn't use ghost (use unitary gauges)
         if particle_info.spin < 0:
             return 
@@ -369,7 +373,24 @@
                 output[anticolor.pdg_code] = -3
         
         return output
-
+    
+    def detect_incoming_fermion(self):
+        """define which fermion should be incoming
+           for that we look at F F~ X interactions
+        """
+        self.incoming = [] 
+        self.outcoming = []       
+        for interaction_info in self.ufomodel.all_vertices:
+            # check if the interation meet requirements:
+            pdg = [p.pdg_code for p in interaction_info.particles if p.spin==2]
+            for i in range(0, len(pdg),2):
+                if pdg[i] == - pdg[i+1]:
+                    if pdg[i] in self.outcoming:
+                        raise UFOImportError, 'Input output not coherent'
+                    elif not pdg[i] in self.incoming:
+                        self.incoming.append(pdg[i])
+                        self.outcoming.append(pdg[i+1])
+                     
             
     def add_interaction(self, interaction_info, color_info):
         """add an interaction in the MG5 model. interaction_info is the