failure when generating VBF+gamma at NLO

Asked by Peyton Rose

Dear experts,

We are trying to generate events for VBF Higgs production in association with a photon. We've run into two (possibly related) problems.
First, during the process generation stage, we input:
***
> generate p p > h a j j [QCD]
***

During this stage, we get the following warning:
"WARNING: Some loop diagrams contributing to this process are discarded because they are not pure (QCD)-perturbation.
Make sure you did not want to include them."

Despite this error, we tried to proceed with event generation. However, we get the following error:
"aMCatNLOError: Poles do not cancel, run cannot continue"
, and the event generation exits.

Do you have suggestions for how we might solve one or both of these problems? I am using version 2.2.2, with default settings for the run/param cards.

Many thanks for your help,
Peyton

ps. I found a similar thread for p p > w- a j j here: https://answers.launchpad.net/mg5amcnlo/+question/238819 . I tried the steps followed by Marco, but still ran into the warning during process generation.

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
marco zaro Edit question
Solved by:
marco zaro
Solved:
Last query:
Last reply:
Revision history for this message
marco zaro (marco-zaro) said :
#1

Hi,
this is a problem which is common to VBF-like processes.
Loops with vector bosons (pentagons in VBF) are not computed. Most of the times they vanish for color conservation, in some cases (when you have both Z and W fusion for example) they give a totally negligible contribution and can be discarded.
However, their contribution hampers the cancelation of the poles. So the warning at the 'generate' step can be ignored.

The thread you were pointing to is related to quite an old brach.
In the current branch you can tell the code to ignore the poles check by editing the
Cards/FKS_params.dat file and set
#IRPoleCheckThreshold

and

#PrecisionVirtualAtRunTime

both to -1d0

This should normally make al the poles check pass.

Note, however, that h+photon in VBF is a fairly complicated process... therefore please let us know if it works well, or if you encounter further problems at runtime.

Many thanks,

Cheers,

Marco

Revision history for this message
Peyton Rose (pwrose21) said :
#2

Hi Marco,

I've run into problems at run time. The ME test failed for P0_ddx_haccx. I've copied below what was printed to the screen. Following the suggestion at the bottom, I set the width of the Higgs to 0 and retried, but still got the same result.

Regards,
Peyton

********
INFO: P0_ddx_hauux
INFO: Result for test_ME:
INFO: Passed.
INFO: Result for test_MC:
INFO: Passed.
INFO: Result for check_poles:
INFO: Poles successfully cancel for 20 points over 20 (tolerance=-1.0e+00)
INFO: P0_ddx_haccx
INFO: Result for test_ME:
INFO: Output of the failing test:
 Enter xi_i, y_ij to be used in coll/soft tests
  Enter -2 to generate them randomly
 Enter number of tests for soft and collinear limits
 Sum over helicity (0), or random helicity (1)
 A PDF is used, so alpha_s(MZ) is going to be modified
 Old value of alpha_s from param_card: 0.11799999999999999
  ****************************************
       NNPDFDriver version 1.0.3
   Grid: NNPDF23nlo_as_0119_qed_mem0.grid
  ****************************************
 New value of alpha_s from PDF nn23nlo: 0.11899999999999999
 Give FKS configuration number ("0" loops over all)

 =================================================

 NEW FKS CONFIGURATION:
 FKS configuration number is 1
 FKS partons are: i= 7 j= 1
 with PDGs: i= 21 j= 1

 Enter graph number (iconfig), '0' loops over all graphs
Using random seed offsets: 0 , 25 , 0
  with seed 32
 Ranmar initialization seeds 10729 9431
nFKSprocess: 1. Absolute lower bound for tau at the Born is 0.92456E-04 0.12500E+03 0.13000E+05
nFKSprocess: 1. Lower bound for tau is 0.14216E-03 0.15500E+03 0.13000E+05
nFKSprocess: 1. Lower bound for tau is (taking resonances into account) 0.27655E-03 0.21619E+03 0.13000E+05
nFKSprocess: 2. Absolute lower bound for tau at the Born is 0.92456E-04 0.12500E+03 0.13000E+05
nFKSprocess: 2. Lower bound for tau is 0.14216E-03 0.15500E+03 0.13000E+05
nFKSprocess: 2. Lower bound for tau is (taking resonances into account) 0.27655E-03 0.21619E+03 0.13000E+05
nFKSprocess: 3. Absolute lower bound for tau at the Born is 0.14216E-03 0.15500E+03 0.13000E+05
nFKSprocess: 3. Lower bound for tau is (taking resonances into account) 0.27655E-03 0.21619E+03 0.13000E+05
nFKSprocess: 4. Absolute lower bound for tau at the Born is 0.14216E-03 0.15500E+03 0.13000E+05
nFKSprocess: 4. Lower bound for tau is (taking resonances into account) 0.27655E-03 0.21619E+03 0.13000E+05
nFKSprocess: 5. Absolute lower bound for tau at the Born is 0.92456E-04 0.12500E+03 0.13000E+05
nFKSprocess: 5. Lower bound for tau is 0.14216E-03 0.15500E+03 0.13000E+05
nFKSprocess: 5. Lower bound for tau is (taking resonances into account) 0.27655E-03 0.21619E+03 0.13000E+05
nFKSprocess: 6. Absolute lower bound for tau at the Born is 0.92456E-04 0.12500E+03 0.13000E+05
nFKSprocess: 6. Lower bound for tau is 0.14216E-03 0.15500E+03 0.13000E+05
nFKSprocess: 6. Lower bound for tau is (taking resonances into account) 0.27655E-03 0.21619E+03 0.13000E+05

 Soft tests done for (Born) config 1
 Failures: 32
     Soft test 1 FAILED. Fraction of failures: 0.32

 Collinear tests done for (Born) config 1
 Failures: 0
Collinear test 1 PASSED. Fraction of failures: 0.00

 =================================================
 NEW FKS CONFIGURATION:
 FKS configuration number is 2
 FKS partons are: i= 7 j= 2
 with PDGs: i= 21 j= -1

 Enter graph number (iconfig), '0' loops over all graphs

 Soft tests done for (Born) config 1
 Failures: 15
     Soft test 2 PASSED. Fraction of failures: 0.15

 Collinear tests done for (Born) config 1
 Failures: 0
Collinear test 2 PASSED. Fraction of failures: 0.00

 =================================================

 NEW FKS CONFIGURATION:
 FKS configuration number is 3
 FKS partons are: i= 7 j= 5
 with PDGs: i= 21 j= 4

 Enter graph number (iconfig), '0' loops over all graphs

 Soft tests done for (Born) config 1
 Failures: 0
     Soft test 3 PASSED. Fraction of failures: 0.00
 Collinear tests done for (Born) config 1
 Failures: 3
Collinear test 3 PASSED. Fraction of failures: 0.03

 =================================================

 NEW FKS CONFIGURATION:
 FKS configuration number is 4
 FKS partons are: i= 7 j= 6
 with PDGs: i= 21 j= -4

 Enter graph number (iconfig), '0' loops over all graphs
 Soft tests done for (Born) config 1
 Failures: 0
     Soft test 4 PASSED. Fraction of failures: 0.00

 Collinear tests done for (Born) config 1
 Failures: 16
Collinear test 4 PASSED. Fraction of failures: 0.16

 =================================================
 NEW FKS CONFIGURATION:
 FKS configuration number is 5
 FKS partons are: i= 7 j= 1
 with PDGs: i= -1 j= 21

 Enter graph number (iconfig), '0' loops over all graphs

 Soft tests done for (Born) config 1
 Failures: 0
     Soft test 5 PASSED. Fraction of failures: 0.00

 Collinear tests done for (Born) config 1
 Failures: 0
Collinear test 5 PASSED. Fraction of failures: 0.00

 =================================================
 NEW FKS CONFIGURATION:
 FKS configuration number is 6
 FKS partons are: i= 6 j= 2
 with PDGs: i= 1 j= 21

 Enter graph number (iconfig), '0' loops over all graphs

 Soft tests done for (Born) config 1
 Failures: 0
     Soft test 6 PASSED. Fraction of failures: 0.00
 Collinear tests done for (Born) config 1
 Failures: 1
Collinear test 6 PASSED. Fraction of failures: 0.01
Error detected in "launch "
write debug file /export/home/prose/aMCNLO/MG5_aMC_v2_2_2/ppTOhajj_10Feb/run_02_tag_1_debug.log
If you need help with this issue please contact us on https://answers.launchpad.net/madgraph5
aMCatNLOError : Some tests failed, run cannot continue.
        Please check that widths of final state particles (e.g. top) have been set to 0 in the param_card.dat.
quit
INFO:
********************

Revision history for this message
Best marco zaro (marco-zaro) said :
#3

Hi Peyton,
ok, i see, there is a test with 32% of failures…
these tests check the correct behaviour of the real matrix-element to match the local counterterms in the singular limit.
the threshold of failures above which a test is considered to fail is 30%. However, for complicated processes (like vbf+extra jet/photons) you may have some numerical instabilities for which you find a larger fraction of failure.
Note that in the case something is really wrong, the fraction of failures is typically of order 90%
Note also that these tests really push the real emission very close to the singular limit, which is unlikely to occur in the integration, as close to the limit real emission+ local counterterms = 0

So the solution in these cases is to allow for more (35-40%) failures.
You need to open the SubProcesses/symmetry_fks_test_ME.f file and edit the max_fail parameter
c define here the maximum fraction of failures to consider the test
c passed
      double precision max_fail, fail_frac
      parameter (max_fail=0.3d0)

setting it to 0.4d0

Let me know if the problem is still there.

Cheers,

Marco

On 11 Feb 2015, at 13:41, Peyton Rose <email address hidden> wrote:

> Question #261881 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/261881
>
> Peyton Rose posted a new comment:
> Hi Marco,
>
> I've run into problems at run time. The ME test failed for
> P0_ddx_haccx. I've copied below what was printed to the screen.
> Following the suggestion at the bottom, I set the width of the Higgs to
> 0 and retried, but still got the same result.
>
> Regards,
> Peyton
>
> ********
> INFO: P0_ddx_hauux
> INFO: Result for test_ME:
> INFO: Passed.
> INFO: Result for test_MC:
> INFO: Passed.
> INFO: Result for check_poles:
> INFO: Poles successfully cancel for 20 points over 20 (tolerance=-1.0e+00)
> INFO: P0_ddx_haccx
> INFO: Result for test_ME:
> INFO: Output of the failing test:
> Enter xi_i, y_ij to be used in coll/soft tests
> Enter -2 to generate them randomly
> Enter number of tests for soft and collinear limits
> Sum over helicity (0), or random helicity (1)
> A PDF is used, so alpha_s(MZ) is going to be modified
> Old value of alpha_s from param_card: 0.11799999999999999
> ****************************************
> NNPDFDriver version 1.0.3
> Grid: NNPDF23nlo_as_0119_qed_mem0.grid
> ****************************************
> New value of alpha_s from PDF nn23nlo: 0.11899999999999999
> Give FKS configuration number ("0" loops over all)
>
> =================================================
>
> NEW FKS CONFIGURATION:
> FKS configuration number is 1
> FKS partons are: i= 7 j= 1
> with PDGs: i= 21 j= 1
>
> Enter graph number (iconfig), '0' loops over all graphs
> Using random seed offsets: 0 , 25 , 0
> with seed 32
> Ranmar initialization seeds 10729 9431
> nFKSprocess: 1. Absolute lower bound for tau at the Born is 0.92456E-04 0.12500E+03 0.13000E+05
> nFKSprocess: 1. Lower bound for tau is 0.14216E-03 0.15500E+03 0.13000E+05
> nFKSprocess: 1. Lower bound for tau is (taking resonances into account) 0.27655E-03 0.21619E+03 0.13000E+05
> nFKSprocess: 2. Absolute lower bound for tau at the Born is 0.92456E-04 0.12500E+03 0.13000E+05
> nFKSprocess: 2. Lower bound for tau is 0.14216E-03 0.15500E+03 0.13000E+05
> nFKSprocess: 2. Lower bound for tau is (taking resonances into account) 0.27655E-03 0.21619E+03 0.13000E+05
> nFKSprocess: 3. Absolute lower bound for tau at the Born is 0.14216E-03 0.15500E+03 0.13000E+05
> nFKSprocess: 3. Lower bound for tau is (taking resonances into account) 0.27655E-03 0.21619E+03 0.13000E+05
> nFKSprocess: 4. Absolute lower bound for tau at the Born is 0.14216E-03 0.15500E+03 0.13000E+05
> nFKSprocess: 4. Lower bound for tau is (taking resonances into account) 0.27655E-03 0.21619E+03 0.13000E+05
> nFKSprocess: 5. Absolute lower bound for tau at the Born is 0.92456E-04 0.12500E+03 0.13000E+05
> nFKSprocess: 5. Lower bound for tau is 0.14216E-03 0.15500E+03 0.13000E+05
> nFKSprocess: 5. Lower bound for tau is (taking resonances into account) 0.27655E-03 0.21619E+03 0.13000E+05
> nFKSprocess: 6. Absolute lower bound for tau at the Born is 0.92456E-04 0.12500E+03 0.13000E+05
> nFKSprocess: 6. Lower bound for tau is 0.14216E-03 0.15500E+03 0.13000E+05
> nFKSprocess: 6. Lower bound for tau is (taking resonances into account) 0.27655E-03 0.21619E+03 0.13000E+05
>
>
> Soft tests done for (Born) config 1
> Failures: 32
> Soft test 1 FAILED. Fraction of failures: 0.32
>
>
> Collinear tests done for (Born) config 1
> Failures: 0
> Collinear test 1 PASSED. Fraction of failures: 0.00
>
> =================================================
> NEW FKS CONFIGURATION:
> FKS configuration number is 2
> FKS partons are: i= 7 j= 2
> with PDGs: i= 21 j= -1
>
>
> Enter graph number (iconfig), '0' loops over all graphs
>
>
> Soft tests done for (Born) config 1
> Failures: 15
> Soft test 2 PASSED. Fraction of failures: 0.15
>
>
> Collinear tests done for (Born) config 1
> Failures: 0
> Collinear test 2 PASSED. Fraction of failures: 0.00
>
> =================================================
>
> NEW FKS CONFIGURATION:
> FKS configuration number is 3
> FKS partons are: i= 7 j= 5
> with PDGs: i= 21 j= 4
>
>
> Enter graph number (iconfig), '0' loops over all graphs
>
>
> Soft tests done for (Born) config 1
> Failures: 0
> Soft test 3 PASSED. Fraction of failures: 0.00
> Collinear tests done for (Born) config 1
> Failures: 3
> Collinear test 3 PASSED. Fraction of failures: 0.03
>
> =================================================
>
> NEW FKS CONFIGURATION:
> FKS configuration number is 4
> FKS partons are: i= 7 j= 6
> with PDGs: i= 21 j= -4
>
>
> Enter graph number (iconfig), '0' loops over all graphs
> Soft tests done for (Born) config 1
> Failures: 0
> Soft test 4 PASSED. Fraction of failures: 0.00
>
>
> Collinear tests done for (Born) config 1
> Failures: 16
> Collinear test 4 PASSED. Fraction of failures: 0.16
>
> =================================================
> NEW FKS CONFIGURATION:
> FKS configuration number is 5
> FKS partons are: i= 7 j= 1
> with PDGs: i= -1 j= 21
>
>
> Enter graph number (iconfig), '0' loops over all graphs
>
>
> Soft tests done for (Born) config 1
> Failures: 0
> Soft test 5 PASSED. Fraction of failures: 0.00
>
>
> Collinear tests done for (Born) config 1
> Failures: 0
> Collinear test 5 PASSED. Fraction of failures: 0.00
>
> =================================================
> NEW FKS CONFIGURATION:
> FKS configuration number is 6
> FKS partons are: i= 6 j= 2
> with PDGs: i= 1 j= 21
>
>
> Enter graph number (iconfig), '0' loops over all graphs
>
>
> Soft tests done for (Born) config 1
> Failures: 0
> Soft test 6 PASSED. Fraction of failures: 0.00
> Collinear tests done for (Born) config 1
> Failures: 1
> Collinear test 6 PASSED. Fraction of failures: 0.01
> Error detected in "launch "
> write debug file /export/home/prose/aMCNLO/MG5_aMC_v2_2_2/ppTOhajj_10Feb/run_02_tag_1_debug.log
> If you need help with this issue please contact us on https://answers.launchpad.net/madgraph5
> aMCatNLOError : Some tests failed, run cannot continue.
> Please check that widths of final state particles (e.g. top) have been set to 0 in the param_card.dat.
> quit
> INFO:
> ********************
>
> --
> You received this question notification because you are a direct
> subscriber of the question.

Revision history for this message
Peyton Rose (pwrose21) said :
#4

Hi Marco,

Thanks for your help! I was able to generate events, and I now have an LHE file that I can start to play with.

Cheers,
Peyton

Revision history for this message
Peyton Rose (pwrose21) said :
#5

Thanks marco zaro, that solved my question.