MadGraph5_aMC@NLO

MG5 is not taking the branching ratios that are there in the param card.

Asked by Abhaya Kumar Swain

Hi,

I am trying to compute a process for a model written in Feynrules. I assume MG5 takes the branching ratios that are there in the param card with/without compute widths. But for some reason it is not doing that. Specifically, I am generating the process,

define ap = t t~ z h3 h2 h
P P > r, r > ap ap
 where r is pseudo-scalar with the following branching written in the param card after doing "compute_widths".

# PDG Width
DECAY 40 1.243398e+10
# BR NDA ID1 ID2 ...
   1.000000e+00 2 21 21 # 12433979929.1
   8.952411e-10 2 6 -6 # 11.1314101767
   1.748067e-12 2 5 -5 # 0.0217354265516

But when I am checking parton level events, all the events are decaying to top pair which I don't understand why.

<event>
 5 1 +1.5683000e-04 5.31377700e+02 7.81860800e-03 1.00589900e-01
       21 -1 0 0 503 502 +0.0000000000e+00 +0.0000000000e+00 +1.1969799891e+02 1.1969799891e+02 0.0000000000e+00 0.0000e+00 1.0000e+00
       21 -1 0 0 502 503 -0.0000000000e+00 -0.0000000000e+00 -5.8973885785e+02 5.8973885785e+02 0.0000000000e+00 0.0000e+00 1.0000e+00
       40 2 1 2 0 0 +0.0000000000e+00 +0.0000000000e+00 -4.7004085895e+02 7.0943685676e+02 5.3137768551e+02 0.0000e+00 0.0000e+00
        6 1 3 3 501 0 -4.3699897776e+01 -1.3384140848e+02 -4.0704756085e+01 2.2597362868e+02 1.7200000000e+02 0.0000e+00 1.0000e+00
       -6 1 3 3 0 501 +4.3699897776e+01 +1.3384140848e+02 -4.2933610286e+02 4.8346322808e+02 1.7200000000e+02 0.0000e+00 1.0000e+00
</event>
<event>
 5 1 +1.5683000e-04 1.08940900e+03 7.81860800e-03 9.21557600e-02
       21 -1 0 0 503 502 +0.0000000000e+00 +0.0000000000e+00 +1.2429505267e+03 1.2429505267e+03 0.0000000000e+00 0.0000e+00 1.0000e+00
       21 -1 0 0 502 503 -0.0000000000e+00 -0.0000000000e+00 -2.3870877135e+02 2.3870877135e+02 0.0000000000e+00 0.0000e+00 1.0000e+00
       40 2 1 2 0 0 +0.0000000000e+00 +0.0000000000e+00 +1.0042417553e+03 1.4816592980e+03 1.0894093686e+03 0.0000e+00 0.0000e+00
        6 1 3 3 501 0 -2.4319568638e+02 +8.3648087288e+01 +1.1118424455e+03 1.1540878510e+03 1.7200000000e+02 0.0000e+00 -1.0000e+00
       -6 1 3 3 0 501 +2.4319568638e+02 -8.3648087288e+01 -1.0760069012e+02 3.2757144701e+02 1.7200000000e+02 0.0000e+00 -1.0000e+00
</event>

Any suggestion to resolve this would be very helpful. At least I want know how to ask MG5 to take the branching ratios that are there in the param card.

Thanks in advance,
Abhaya

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

You do not allow decay to bottom, so for sure you will not have bottom in your final sample.
If you want to allow the decay to bottom, you need to add it in your definition of ap
i.e.
define ap = t t~b b~
P P > r, r > ap ap

This being said the "," syntax assumes narrow-width approximation which is clearly not your case (and the use of compute_widths also assumes narrow width approximation). So this is not clear to my why your syntax/computation makes sense.
In particular interference with the standard model can/might be large in part of the phase-space. So please check that point.

Cheers,

Olivier

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