treatment of quarks from resonances decays (W,Z,t,susy) in the MEPS matching procedure ?

Hi Renaud,

You are looking in the wrong file.
The file hep2lhe doesn't have anything to do with the matching. This file is just a jet algorithm in order to be able to have a simple output file for simple study/plots.
I think that what your are looking for is around line 246 of the file
pythia-pgs/src/ME2pythia.f

Cheers,

Olivier

On May 14, 2013, at 5:46 AM, renaud <email address hidden> wrote:

> New question #228844 on MadGraph5:
> https://answers.launchpad.net/madgraph5/+question/228844
>
> Dear MadGraph gurus,
>
> I was trying to understand how light quarks (u,d,s,c,b?) from resonance decays (mainly W,Z) are treated by the MEPS matching procedure when the decay is done in MadGraph ?
> Let say that for example we generate a sample with charginos decaying to W + neutralinos. The mass difference between charginos and neutralinos is large leading to boosted W.
> generate p p > x1+ x1-, (x1+ > W+ n1, W+ > j j), (x1- > W- n1, W- > j j)
> add process p p > x1+ x1- j, (x1+ > W+ n1, W+ > j j), (x1- > W- n1, W- > j j)
> I was trying to browse the interface between MadEvent and Pythia6, but I have not seen in any place (like in hep2lhe.f) anything which prevents quarks from W decays to be included in the matching procedure.
> Therefore, if the two quarks from the W are reconstructed in a single jet (because of the boost), the event will be wrongly vetoed since there is no double counting happening (pythia parton shower does not radiate W bosons).
> Did I miss something ?
> If not, does it mean we should avoid to decay particles to quarks inside madgraph (and do it only in pythia) ?
>
> Cheers,
> Renaud
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Bonjour Olivier,

thanks a lot but looking at ME2pythia.f, line 246 I get:
      WRITE(STRFMT(3:5),'(I3)') MAXLEN

C...Loop until finds line beginning with "<event>" or "<event ".

the middle line is 246 => empty.
Could you just copy/paste the peace of code where it is done ?

Cheers,
Renaud

Sure,

Here it is (indeed I was wrong line, the correct one is 441)

      IF(ickkw.gt.0) THEN
c
c Sort particles so direct particles come first, decayed afterwards
c
         ndirect=2
         nfinal=0
         do i=3,NUP
            if(ISTUP(i).eq.1) nfinal=nfinal+1
            if(ISTUP(i).eq.1.and.MOTHUP(1,i).le.2)THEN
               ndirect=ndirect+1
               if (i.gt.ndirect) then
c This particle needs to be moved down to come before resonances
                  CALL SHIFTPART(i,ndirect,nfinal)
               endif
            endif
         enddo

c
c Set up number of jets
c
         NLJETS=0
         NPART=0
         do i=3,NUP
            if(ISTUP(i).ne.1) cycle
            NPART=NPART+1
c Remove non-partons and partons originating from t-channel singlets
            if(iabs(IDUP(i)).gt.nqmatch.and.IDUP(i).ne.21.or.
     $ ptclus(NPART).gt.(2-1d-3)*sqrt(ebmup(1)*ebmup(2))) cycle
            if(MOTHUP(1,i).gt.2) cycle
C Remove final-state partons that combine to color singlets
            IF((ABS(IDBMUP(1)).NE.11.OR.IDBMUP(1).NE.-IDBMUP(2)).AND.
     $ nosingrad) THEN
               DO II=3,NUP
                  IF(II.NE.i.AND.ISTUP(II).EQ.1)THEN
                     IF((IDUP(II).EQ.-IDUP(i).OR.
     $ IDUP(i).EQ.21.AND.IDUP(II).EQ.21).AND.
     $ ICOLUP(1,II).EQ.ICOLUP(2,i).AND.
     $ ICOLUP(2,II).EQ.ICOLUP(1,i))then
c print *,'Found color singlet'
                        CALL PYLIST(7)
                        GOTO 140
                     endif
                  ENDIF
               ENDDO
            ENDIF
            NLJETS=NLJETS+1
 140 continue

On May 14, 2013, at 11:01 AM, renaud <email address hidden> wrote:

> Question #228844 on MadGraph5 changed:
> https://answers.launchpad.net/madgraph5/+question/228844
>
> Status: Answered => Open
>
> renaud is still having a problem:
> Bonjour Olivier,
>
> thanks a lot but looking at ME2pythia.f, line 246 I get:
> WRITE(STRFMT(3:5),'(I3)') MAXLEN
>
> C...Loop until finds line beginning with "<event>" or "<event ".
>
> the middle line is 246 => empty.
> Could you just copy/paste the peace of code where it is done ?
>
> Cheers,
> Renaud
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Thanks a lot Olivier !

this is exactly the peace of code I was looking for :)
Now what is puzzling is that the version you are pointing is the one coming with:
pythia-pgs_V2.1.21.tar.gz
pythia-pgs/src/ME2pythia.f

Previously, I downloaded directly from your download page the following file:
interfaces2ME_V3.0.1.tar.gz
and there the ME2pythia.f does not contain the peace of code you are pointing in your latest mail.
See also the version there:
http://madgraph.phys.ucl.ac.be/Downloads/interfaces/ME2pythia.f

Maybe it is intended becaue they are different versions, but unfortunately, I looked to the wrong version of ME2pythia.f
Anyway, I'm glad to see you are treating properly those. Now I need to check whether we do it also correctly.

Cheers,
Renaud