Decay to off-shell W/Z boson

Asked by Peter Meiring on 2020-03-04

Dear Madgraph experts,

I would like to generate events with a pair of electroweakino's, both of which decay to a very off-shell W/Z-boson and a neutralino.

Please find the proccard that I used below. I set the bwcutoff to a very high value so as to allow very low W/Z masses be considered on-shell as well. I then set the masses of the three electroweakino's.

After generating events this way, I find the n1 indeed has the correct mass (in this case 97 GeV), but the W/Z are both (close to) their nominal mass and the chi1 and n2 have much higher mass than I request.

Please also find an example event (LHE) below. Could you please indicate what I should do differently to force the electroweakino masses and have a very off-shell W/Z? Also I would be interested in understanding how the masses can end up differently from what I set.

Looking forward to your response. Best,
Peter Meiring

PROCCARD:

#************************************************************
#* MadGraph5_aMC@NLO *
#* *
#* * * *
#* * * * * *
#* * * * * 5 * * * * *
#* * * * * *
#* * * *
#* *
#* *
#* VERSION 2.6.6 2018-06-28 *
#* *
#* The MadGraph5_aMC@NLO Development Team - Find us at *
#* https://server06.fynu.ucl.ac.be/projects/madgraph *
#* *
#************************************************************
#* *
#* Command File for MadGraph5_aMC@NLO *
#* *
#* run as ./bin/mg5_aMC filename *
#* *
#************************************************************
import model MSSM_SLHA2-full
define p = g u c d s u~ c~ d~ s~
define j = g u c d s u~ c~ d~ s~
define p = p b b~
define j = j b b~
define sq = go ul ul~ ur ur~ dl dl~ dr dr~ sl sl~ sr sr~ cl cl~ cr cr~ b1 b1~ b2 b2~ t1 t1~ t2 t2~
define slep = el+ er+ mul+ mur+ ta1+ ta2+ el- er- mul- mur- ta1- ta2- sve svm svt sve~ svm~ svt~
#define ino = n1 n2 n3 n4 x2+ x2- h1 h2 h3 h- h+
define chi1 = x1+ x1-
define w = w+ w-
generate p p > chi1 n2, chi1 > w n1, n2 > z n1
output SMS-C1N2_mChi-100_nopythia -nojpeg
launch
analysis = OFF
0
set nevents 100
set bwcutoff 100000
set mass 1000001 100000.0
set mass 1000002 100000.0
set mass 1000003 100000.0
set mass 1000004 100000.0
set mass 1000005 100000.0
set mass 1000006 100000.0
set mass 2000001 100000.0
set mass 2000002 100000.0
set mass 2000003 100000.0
set mass 2000004 100000.0
set mass 2000005 100000.0
set mass 2000006 100000.0
set mass 1000021 100000.0
set mass 1000022 scan:[97]
set mass 1000023 100
set mass 1000024 100
set mass 1000025 100000.0
set mass 1000035 100000.0
set mass 1000037 100000.0
set mass 1000039 100000.0
set mass 1000011 100000.0
set mass 1000012 100000.0
set mass 1000013 100000.0
set mass 1000014 100000.0
set mass 1000015 100000.0
set mass 1000016 100000.0
set mass 2000011 100000.0
set mass 2000013 100000.0
set mass 2000015 100000.0
set use_syst False
0

EXAMPLE LHE EVENT

<event>
 9 1 +7.7320003e-10 6.17342700e+02 7.81653100e-03 9.87006500e-02
       -1 -1 0 0 0 501 -0.0000000000e+00 +0.0000000000e+00 +2.1525549945e+02 2.1525549945e+02 0.0000000000e+00 0.0000e+00 1.0000e+00
        2 -1 0 0 501 0 +0.0000000000e+00 -0.0000000000e+00 -4.4262751927e+02 4.4262751927e+02 0.0000000000e+00 0.0000e+00 -1.0000e+00
       24 2 1 2 0 0 +0.0000000000e+00 -1.4210854715e-14 -2.2737201982e+02 6.5788301872e+02 6.1734271755e+02 0.0000e+00 0.0000e+00
  1000024 2 3 3 0 0 -1.8682039800e+02 -5.6563065815e+01 -4.9268394819e+01 3.3062417020e+02 2.6226651648e+02 0.0000e+00 0.0000e+00
  1000023 2 3 3 0 0 +1.8682039800e+02 +5.6563065815e+01 -1.7810362500e+02 3.2725884852e+02 1.9307048239e+02 0.0000e+00 0.0000e+00
       24 1 4 4 0 0 -1.1332978955e+02 +2.6540365984e+01 -1.0196763959e+02 1.7412094242e+02 7.9829010000e+01 0.0000e+00 1.0000e+00
  1000022 1 4 4 0 0 -7.3490608447e+01 -8.3103431799e+01 +5.2699244770e+01 1.5650322778e+02 9.7000000000e+01 0.0000e+00 1.0000e+00
       23 1 5 5 0 0 +1.0752484595e+02 +4.0192923215e+01 -7.8015223159e+01 1.6606810956e+02 9.1187600000e+01 0.0000e+00 -1.0000e+00
  1000022 1 5 5 0 0 +7.9295552051e+01 +1.6370142599e+01 -1.0008840184e+02 1.6119073896e+02 9.7000000000e+01 0.0000e+00 1.0000e+00
</event>

Question information

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MadGraph5_aMC@NLO Edit question
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Last query:
2020-03-04
Last reply:
2020-03-07

Hi,

Since you have those particles in the final states and that we are using the S-matrix formalism (which assumes that all initial state are in a assymptotic states) it is required that the final states particles are onshell.
If you do not want that, you need to decay such particles.
So you would need to ask for the following type of syntax:
generate p p > chi1 n2, chi1 > l vl~ n1, n2 > l+ l- n1

Additionally it is typically a bad idea to have bwcutoff larger than 20.
So please do not do it but if you know that you will have no issue with gauge invariance at such large mass and if you have a method to correctly handle the wrong prediction such far away of the resonances.

Cheers,

Olivier

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