MadGraph5_aMC@NLO

Cannot modify width of W boson

Asked by Zirui Wang

Dear experts,

When I use 2HDM model to generate tth3 events, I noticed that modifying width of top quark will give impact on the mass distribution. However, it won't show any change when I modify the W boson width.

My main syntax is :

import model 2HDM
generate g g > t t~ h3, (h3 > ta+ ta-),(t > W+ b),(t~ > W- b~)
set WW 15
set WT 15

When I extract the information from the output, the width of top quark obviously changed. But the W boson mass is still a narrow peak. I upload the mass distribution at https://drive.google.com/file/d/1BNXzMby7ZQCGKrhBCV_A7ipcRFpfZDMZ/view?usp=sharing

Actually, when under the default 2HDM parameter setting, say "WW=2.0028844418592" and "WT=1.5148707555575", the top mass distribution should be correct while the W peak is always just a narrow peak. You can find the plot at https://drive.google.com/file/d/11cVxlYHPeCdHAKZcmQVt2aSH5uyqQ5Be/view?usp=sharing

May I know the reason why setting W boson width doen't work? Or did I miss anything obviously? Thanks in advance.

Best,
Zirui

Question information

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Solved by:
Olivier Mattelaer
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Best Olivier Mattelaer (olivier-mattelaer) said : 		#1

your w are in the final state and therefore not decayed by madgraph they are then exactly on shell

Cheers

Olivier

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________________________________
From: <email address hidden> <email address hidden> on behalf of Zirui Wang <email address hidden>
Sent: Thursday, August 2, 2018 3:07:50 PM
To: Olivier Mattelaer
Subject: [Question #671309]: Cannot modify width of W boson

New question #671309 on MadGraph5_aMC@NLO:
https://answers.launchpad.net/mg5amcnlo/+question/671309

Dear experts,

When I use 2HDM model to generate tth3 events, I noticed that modifying width of top quark will give impact on the mass distribution. However, it won't show any change when I modify the W boson width.

My main syntax is :

import model 2HDM
generate g g > t t~ h3, (h3 > ta+ ta-),(t > W+ b),(t~ > W- b~)
set WW 15
set WT 15

When I extract the information from the output, the width of top quark obviously changed. But the W boson mass is still a narrow peak. I upload the mass distribution at https://drive.google.com/file/d/1BNXzMby7ZQCGKrhBCV_A7ipcRFpfZDMZ/view?usp=sharing

Actually, when under the default 2HDM parameter setting, say "WW=2.0028844418592" and "WT=1.5148707555575", the top mass distribution should be correct while the W peak is always just a narrow peak. You can find the plot at https://drive.google.com/file/d/11cVxlYHPeCdHAKZcmQVt2aSH5uyqQ5Be/view?usp=sharing

May I know the reason why setting W boson width doen't work? Or did I miss anything obviously? Thanks in advance.

Best,
Zirui

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Revision history for this message
Zirui Wang (ziruiality) said : 		#2

Thanks Olivier Mattelaer, that solved my question.