Matrix element squared value Madgraph vs Analytical result

Asked by Jacky on 2020-01-23

Dear Madgraph team,

I implemented a simple model containing a charged Higgs in Feynrules and then generating the UFO, I want to compare the numerical value of the Matrix element squared from Madgraph with my own analytical result. I found a huge discrepancy between the two.

For example, for the process u-bar d > h- > u-bar d, using my result

|M|^2 = (p1.p2) * (k1.k2) / ((p1+p2)**2-mH**2)**2

 (Note all NP couplings are set to 1), for one phase-space(below) point, the ME squared value is:

|M|^2=0.25000000042876996, while the Madgraph gives:

 External Params
  ---------------------------------

 mdl_r1 = 1.0000000000000000
 aEWM1 = 127.90000000000001
 mdl_Gf = 1.1663700000000000E-005
 aS = 0.11839999999999999
 mdl_ymb = 4.7000000000000002
 mdl_ymt = 172.00000000000000
 mdl_ymtau = 1.7769999999999999
 mdl_MZ = 91.187600000000003
 mdl_MTA = 1.7769999999999999
 mdl_MT = 172.00000000000000
 mdl_MB = 4.7000000000000002
 mdl_MH = 125.00000000000000
 mdl_MHch = 1000.0000000000000
 mdl_WZ = 2.4952000000000001
 mdl_WW = 2.0850000000000000
 mdl_WT = 1.5083359999999999
 mdl_WH = 4.0699999999999998E-003
 mdl_WHch = 1.0000000000000000E-004
  Internal Params
  ---------------------------------

 mdl_MZ__exp__2 = 8315.1783937600012
 mdl_MZ__exp__4 = 69142191.720053151
 mdl_sqrt__2 = 1.4142135623730951
 mdl_MH__exp__2 = 15625.000000000000
 mdl_complexi = (0.0000000000000000,1.0000000000000000)
 mdl_aEW = 7.8186082877247844E-003
 mdl_MW = 79.824359746197842
 mdl_sqrt__aEW = 8.8422894590285753E-002
 mdl_ee = 0.31345100004952897
 mdl_MW__exp__2 = 6371.9284088904105
 mdl_sw2 = 0.23369913342182447
 mdl_cw = 0.87538612427783857
 mdl_sqrt__sw2 = 0.48342438232036300
 mdl_sw = 0.48342438232036300
 mdl_g1 = 0.35807170271074895
 mdl_gw = 0.64839716719502682
 mdl_vev = 246.22056907348590
 mdl_vev__exp__2 = 60624.568634871241
 mdl_lam = 0.12886689630821144
 mdl_yb = 2.6995322804122722E-002
 mdl_yt = 0.98791394091683138
 mdl_ytau = 1.0206529494239589E-002
 mdl_muH = 88.388347648318444
 mdl_ee__exp__2 = 9.8251529432049817E-002
 mdl_sw__exp__2 = 0.23369913342182450
 mdl_cw__exp__2 = 0.76630086657817542
  Internal Params evaluated point by point
  ----------------------------------------

 mdl_sqrt__aS = 0.34409301068170506
 mdl_G__exp__2 = 1.4878582807401259
  Couplings of 0nunu_new
  ---------------------------------

        GC_16 = 0.00000E+00 0.10000E+01
   1000.0000000000000 500.00000000000000

  Phase space point:

 -----------------------------------------------------------------------------
 n E px py pz m
 1 0.5000000E+03 0.0000000E+00 0.0000000E+00 0.5000000E+03 0.0000000E+00
 2 0.5000000E+03 0.0000000E+00 0.0000000E+00 -0.5000000E+03 0.0000000E+00
 3 0.5000000E+03 0.1109243E+03 0.4448308E+03 -0.1995529E+03 0.9725608E-05
 4 0.5000000E+03 -0.1109243E+03 -0.4448308E+03 0.1995529E+03 0.1009274E-04
 -----------------------------------------------------------------------------
 Matrix element = 24999999999999.996 GeV^ 0
 -----------------------------------------------------------------------------

I am not able to figure out the problem, so it would be great if you can help to sort this out.

Best regards,

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
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Last query:
2020-01-23
Last reply:
2020-01-24

Well with that information, not sure what I can do to help you.
Did you run the "check process" command of MG5aMC?

It will check various method for MG5aMC to computte the same amplitude (we have at least two for this particular case) and this will allow to spot issue in our code.

Cheers,

Olivier

> On 24 Jan 2020, at 01:04, Jacky <email address hidden> wrote:
>
> New question #688214 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/688214
>
> Dear Madgraph team,
>
> I implemented a simple model containing a charged Higgs in Feynrules and then generating the UFO, I want to compare the numerical value of the Matrix element squared from Madgraph with my own analytical result. I found a huge discrepancy between the two.
>
> For example, for the process u-bar d > h- > u-bar d, using my result
>
> |M|^2 = (p1.p2) * (k1.k2) / ((p1+p2)**2-mH**2)**2
>
> (Note all NP couplings are set to 1), for one phase-space(below) point, the ME squared value is:
>
> |M|^2=0.25000000042876996, while the Madgraph gives:
>
> External Params
> ---------------------------------
>
> mdl_r1 = 1.0000000000000000
> aEWM1 = 127.90000000000001
> mdl_Gf = 1.1663700000000000E-005
> aS = 0.11839999999999999
> mdl_ymb = 4.7000000000000002
> mdl_ymt = 172.00000000000000
> mdl_ymtau = 1.7769999999999999
> mdl_MZ = 91.187600000000003
> mdl_MTA = 1.7769999999999999
> mdl_MT = 172.00000000000000
> mdl_MB = 4.7000000000000002
> mdl_MH = 125.00000000000000
> mdl_MHch = 1000.0000000000000
> mdl_WZ = 2.4952000000000001
> mdl_WW = 2.0850000000000000
> mdl_WT = 1.5083359999999999
> mdl_WH = 4.0699999999999998E-003
> mdl_WHch = 1.0000000000000000E-004
> Internal Params
> ---------------------------------
>
> mdl_MZ__exp__2 = 8315.1783937600012
> mdl_MZ__exp__4 = 69142191.720053151
> mdl_sqrt__2 = 1.4142135623730951
> mdl_MH__exp__2 = 15625.000000000000
> mdl_complexi = (0.0000000000000000,1.0000000000000000)
> mdl_aEW = 7.8186082877247844E-003
> mdl_MW = 79.824359746197842
> mdl_sqrt__aEW = 8.8422894590285753E-002
> mdl_ee = 0.31345100004952897
> mdl_MW__exp__2 = 6371.9284088904105
> mdl_sw2 = 0.23369913342182447
> mdl_cw = 0.87538612427783857
> mdl_sqrt__sw2 = 0.48342438232036300
> mdl_sw = 0.48342438232036300
> mdl_g1 = 0.35807170271074895
> mdl_gw = 0.64839716719502682
> mdl_vev = 246.22056907348590
> mdl_vev__exp__2 = 60624.568634871241
> mdl_lam = 0.12886689630821144
> mdl_yb = 2.6995322804122722E-002
> mdl_yt = 0.98791394091683138
> mdl_ytau = 1.0206529494239589E-002
> mdl_muH = 88.388347648318444
> mdl_ee__exp__2 = 9.8251529432049817E-002
> mdl_sw__exp__2 = 0.23369913342182450
> mdl_cw__exp__2 = 0.76630086657817542
> Internal Params evaluated point by point
> ----------------------------------------
>
> mdl_sqrt__aS = 0.34409301068170506
> mdl_G__exp__2 = 1.4878582807401259
> Couplings of 0nunu_new
> ---------------------------------
>
> GC_16 = 0.00000E+00 0.10000E+01
> 1000.0000000000000 500.00000000000000
>
> Phase space point:
>
> -----------------------------------------------------------------------------
> n E px py pz m
> 1 0.5000000E+03 0.0000000E+00 0.0000000E+00 0.5000000E+03 0.0000000E+00
> 2 0.5000000E+03 0.0000000E+00 0.0000000E+00 -0.5000000E+03 0.0000000E+00
> 3 0.5000000E+03 0.1109243E+03 0.4448308E+03 -0.1995529E+03 0.9725608E-05
> 4 0.5000000E+03 -0.1109243E+03 -0.4448308E+03 0.1995529E+03 0.1009274E-04
> -----------------------------------------------------------------------------
> Matrix element = 24999999999999.996 GeV^ 0
> -----------------------------------------------------------------------------
>
> I am not able to figure out the problem, so it would be great if you can help to sort this out.
>
> Best regards,
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Jacky (singlajacky) said : #2

Dear Olivier,

finally using the check process command that you mentioned above, I am able to figure out the problems in my model file. However, for other parts of the model, the check process still indicates a problem. I will write to you with more details about it.

Thanks a lot,
Jacky

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