Syntax help for twh process

Asked by Shubhani Jain

Hi

I have been trying to generate bg>twh process using model 2HDMtII_NLO. I need some help with syntax formation, I want to decay the particles as follows:
syntax: b g > t w- h1
t > w+ b , w+ > l+ vl
w- > j j
h1 > z z where z decay leptonically

Ofcourse, we would want one of the z to be offshell. I have tried many version for h1 decay but all of them fails to reach the desired target of events. It is surprising because when I do this test for 100 events I am getting full statistics but for 10k events sometimes I get 30 events or 200 events depending upon the decay syntax for h1. I have tried

h1 > z z > l+ l- l+ l-
h1 > z > l+ l- l+ l-
h1 > z l+ l-, z > l+ l-
h1 > l+ l-l+ l-

Th full syntax I would like to generate is :
bs = b b~
generate bs g> t w- h1, ( t > w+ b , w+ > l+ vl ) , w- > j j , (h1 > zz with z > l+ l-)
add process bs g> t ~ w+ h1, ( t~ > w- b~ , w- > l- vl~ ) , w+> j j , (h1 > zz with z > l+ l-)

Any help would be much appreciated.

Thanks
Shubhani

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Shubhani Jain
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Olivier Mattelaer (olivier-mattelaer) said :
#1

Hi,

What is the mass for h1 (is that the Higgs=125GeV?)
and what is the width of that particle?
and what is the value of BWcut? (if you set it too large you will also allow the ZZ onshell but the phase-space integrator will not be ready for it due to your syntax that assumes h1 onshell-> few events generated)

If this is not a too large bwcut issue then my suggestion would be to generate the h1 onshell and decay h1 with madspin

bs = b b~
generate bs g> t w- h1, ( t > w+ b , w+ > l+ vl ) , w- > j j
add process bs g> t ~ w+ h1, ( t~ > w- b~ , w- > l- vl~ ) , w+> j j
output
launch
MadSpin=none #special mode of madspin
decay h1 > z > l+ l- l+ l-

Cheers,

Olivier

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Shubhani Jain (s2697661) said :
#2

Hi Olivier

The mass of h1 is 125 GeV. I am setting the decay width of h1 to Auto in param_card and using the default BWcut value.

I will these syntaxes a try. Thanks for the help.

Regards
Shubhani

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Olivier Mattelaer (olivier-mattelaer) said :
#3

For the Higgs, the width should not be set to auto since it miss the (important) contribution of the decay of the width via loop-induced process (h> g g and Higss to two photon).

the breit wigner cut is by default at 15 which is already quite large normally it should be fine for
h>ZZ but if you have BSM decay for any of those two particles, you might need to reduce that number.

Cheers,

Olivier

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Shubhani Jain (s2697661) said :
#4

Hi Olivier

Thanks for the reply.

I do have the decay width from 2HDMC run so will use that. I don't have any BSM decay for these two particles just Z decaying to twp leptons. I will have a look at BWcut.

Thanks
Shubhani

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Shubhani Jain (s2697661) said :
#5

Hi Olivier

I tried to reduce the BWcut value and set up a decay width of h, but the max no of events I get is 400. Is this normal for these types of processes or there should be something else I have to do?

Regards
Shubhani

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said :
#6

Well I do not know your model and I never study that production process (even in the standard model)
So I can not really comment here.

If you have issue with the number of events you can
- change sde_strategy to see if one value helps (possible value are 1 or 2)
- use the hard_survey option to force to increase all the maximum set in MG5aMC before giving up to reach requested number of events (the higher you set that parameter the slower the code will be)
- Drop the decay and see if the production matrix-element succeed/fails to generate events.
This can give you a hint of the issue (missing cut, failing of Narrow-width approximation,...) --if this is not a pure internal efficiency issue (in which case the two above fix will not help)

Cheers,

Olivier

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Shubhani Jain (s2697661) said :
#7

Hi Olivier

Thanks for replying.

I will try to follow these tests. I can also try to just use SM and see whether it is still giving me the same issue or not.

Regards
Shubhani

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Shubhani Jain (s2697661) said :
#8

Hi Olivier

Changing sde_strategy to 1 did the job.

I wanted to ask how to generate events when I have h1 > WW decay instead of h1 > zz , where h1 is the SM higgs.

Regards
Shubhani

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Olivier Mattelaer (olivier-mattelaer) said :
#9

I would use the same type of syntax:

decay h1 > w+ > l+ l- vl vl~

Cheers,

Olivier

Revision history for this message
Shubhani Jain (s2697661) said :
#10

Hi Olivier

Thanks for the reply, will implement this.

Regards
Shubhani