MadGraph5_aMC@NLO

Pb with MadSpin and Anomalous top decay

Asked by Eric Conte

Dear MadGraph author,

I have a FeynRules model describing FCNC anomalous coupling of the top quarks at LO. I would like to a pair of top-quarks where one top is decaying anomalously into a Higgs and a quark. To sum up, I would to produce the following process:
p p > t t~, t > h u, (t~ > w- b~, w- > l- vl~)

First, I have no problems to do it within MadGraph.

BUT, as I would like to produce it with 0,1,2 extra-jets + MLM-merging technique, I thought that MadSpin could take care of the top decay (in order to save processing time).

First attempt:
---------------
at MG level:
generate u u~ > t t~,
at MadSpin level:
decay t~ > w- b~, w- > l- vl~
decay t > h u
The problem here is that MadSpin do not find the decay "t > h u". Only the "t > w b" decay is found.
See the log file: log.txt

In MadGraph, if I ask to compute all top decays:
generate t > all all
--> my anomalous decay is found (and its amplitude is not null).

BUT if I put the top decay width to "auto" in the parameter card,
MadGraph founds only "t > b w".

Second attempt:
-----------------------
I try to put in the parameter card the top partial width. But MadSpin crashes.

I use the MG5_aMC@NLO 2_3_3.
I will attach my UFO model, a simple proc_card and a madspin card.

Thanks in advance for your help,
Cheers,
Eric Conte

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Eric Conte (eric-conte) said : 		#1

Log file:

************************************************************
* *
* W E L C O M E to M A D S P I N *
* *
************************************************************
INFO: Extracting the banner ...
INFO: process: u u~ > t t~
INFO: options:
INFO: detected model: TopFCNC_UFO-epsilon_hut_ProdConventions. Loading...
set max_weight_ps_point 400 # number of PS to estimate the maximum for each event
decay t > h u
decay t~ > w- b~, w- > l- vl~
launch
INFO: Will use seed 438911617
INFO: generating Madspin matrix element
INFO: We need to recalculate the branching fractions for t~,w-,t
INFO: Using MadWidth (arXiv:1402.1178)
INFO:
INFO: decay channels for t~ : ( width = 1.4669 GeV )
INFO: BR d1 d2
INFO: 1.000000e+00 b~ w-
INFO:
INFO:
INFO: decay channels for w- : ( width = 2.002499 GeV )
INFO: BR d1 d2
INFO: 3.164147e-01 d u~
INFO: 3.162799e-01 s c~
INFO: 1.111361e-01 e- ve~
INFO: 1.111361e-01 mu- vm~
INFO: 1.110512e-01 ta- vt~
INFO: 1.699477e-02 s u~
INFO: 1.698727e-02 d c~
INFO:
INFO:
INFO: decay channels for w+ : ( width = 2.002499 GeV )
INFO: BR d1 d2
INFO: 3.164147e-01 d~ u
INFO: 3.162799e-01 s~ c
INFO: 1.111361e-01 e+ ve
INFO: 1.111361e-01 mu+ vm
INFO: 1.110512e-01 ta+ vt
INFO: 1.699477e-02 s~ u
INFO: 1.698727e-02 d~ c
INFO:
INFO:
INFO: decay channels for t : ( width = 1.4669 GeV )
INFO: BR d1 d2
INFO: 1.000000e+00 b w+
INFO:
INFO: generating the production square matrix element
INFO: generate u u~ > t t~ --no_warning=duplicate;
INFO: Done 5.749
INFO: generating the full square matrix element (with decay)
INFO: generate u u~ > t t~, (t~ > b~ w- , w- > l- vl~ QCD=99), t > h u QCD=99 --no_warning=duplicate;
Command "generate_events run_01" interrupted with error:
InvalidCmd : No matrix elements generated, check overall coupling orders
quit
INFO:

INFO:

Revision history for this message
Eric Conte (eric-conte) said : 		#2

proc_card:
import model TopFCNC_UFO-epsilon_hut_ProdConventions --modelname
generate u u~ > t t~ NP=1

madspin_card:
set max_weight_ps_point 400 # number of PS to estimate the maximum for each event
decay t > w+ b
decay t~ > h u~ NP=1
launch

Additional comment: I try with and without NP=1 flags

Revision history for this message
Eric Conte (eric-conte) said : 		#3

UFO model:
https://drive.google.com/file/d/0B8sLz-hbU9yiek82V1JNWk1SMlk/view?usp=sharing

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#4

Hi Eric,

This a QCD problem:

I have this warning when computing the width:
partial width of particle t lower than QCD scale:0.0019046009123. Set it to zero. ((2, 25))

Cheers,

Olivier

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