Cross section 0.0 after matching for Powheg gridpack

[anirban1982]

Hello,

We have found an issue with GenXanalyser with Powheg gridpack, reported at:

https://hypernews.cern.ch/HyperNews/CMS/get/generators/3683.html

We get zero cross section after matching, however, we see events in LHE and in the root files after the hadronization step.

Can you please have a look into the issue?

Thanks, Anirban for Higgs MC contacts.

[efeyazgan]

@kdlong @qliphy

[ocharaf]

I have seen a very similar issue using the "calculateXSectionAndFilterEfficiency.sh" tool. You can see the thread at: https://hypernews.cern.ch/HyperNews/CMS/get/generators/3691.html. In my case, the final cross section after filter and matching is 0 and the one after matching is negative, giving a matching efficiency of -100%.

[perrozzi]

@anirban1982 I ran a few events and from the log log.log I see a few pythia warnings like:

 --------  PYTHIA Info Listing  ---------------------------------------- 

 Beam A: id =   2212, pz =  6.500e+03, e =  6.500e+03, m =  9.383e-01.
 Beam B: id =   2212, pz = -6.500e+03, e =  6.500e+03, m =  9.383e-01.

 In 1: id =   21, x =  6.495e-03, pdf =  1.149e+01 at Q2 =  2.025e+05.
 In 2: id =   21, x =  1.845e-01, pdf =  2.517e-01 at same Q2.
 Warning: above flavour/x info does not match incoming partons in event!

 Process Les Houches User Process(es) with code 9999 is 2 -> 2.
 Subprocess user process 9999 with code 9999 is 2 -> 2.
 It has sHat =  2.641e+05,    tHat = -7.132e+02,    uHat = -6.088e+04,
       pTHat =  1.282e+01,   m3Hat =  4.500e+02,   m4Hat =  3.815e-06,
    thetaHat =  2.156e-01,  phiHat =  2.490e-01.
     alphaEM =  7.647e-03,  alphaS =  1.841e-01    at Q2 =  1.644e+02.

 Impact parameter b =  9.761e-01 gives enhancement factor =  6.121e-01.
 Max pT scale for MPI =  1.300e+04, ISR =  1.300e+04, FSR =  1.300e+04.
 Number of MPI =     2, ISR =     6, FSRproc =    42, FSRreson =     1.

 --------  End PYTHIA Info Listing  ------------------------------------

which seems to indicate a color problem in POWHEG. However, the gridpack seems to be old ( Jul 20 2016) so I strongly suggest to produce it again, the problem should hae been fixed in the meanwhile

[anirban1982]

@perrozzi did the powheg version changed in CMSSW by this time, in between 20 July and now?

[perrozzi]

Jul 20 2016

[anirban1982]

aah, I see, I have informed the analyst to produce the new gridpack.