wrong higgs mass distribution in heft model for gg>h>ww>enumunu process

Asked by Adam Kaluza on 2012-01-06

I created events for the process p p > h > w+ w- , w+ > e+ ve , w- > mu- vm~ in the HEFT model with the web interface and with the downloaded MadGraph5_v1_3_30 version and plottet the invariant mass of all endproducts.
What I expected was, that the distributions for both ways looks the same and that there is only one nice peak around the higgs mass (120 GeV).
But the distributions doesn't look the same even all the cards are the same for both ways and when you investigate the mass distribution further, you can see besides the peak a continuous mass distribution for higher masses, which looks a bit like a mass distribution for the process p p > w+ w- , w+ > e+ ve , w- > mu- vm~ without the higgs.
Do you have an idea where the problem could be? If you need more information please write me.

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Solved by:
Johan Alwall
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Best Johan Alwall (johan-alwall) said : #1

Hello Adam,

In fact, the process you want is:
p p > h, h > w+ w- > e+ ve mu- vm~ or
p p > h, h > e+ ve mu- vm~ / z
This means that the Higgs is required to be onshell, decaying through a pair of W bosons which can be either on- or offshell. The process you wrote,
p p > h > w+ w- , w+ > e+ ve , w- > mu- vm~
requires both the w bosons to be onshell (meaning, within bwcutoff widths from the pole mass). With sufficiently large bwcutoff, you will get a Higgs peak since the w can go far enough down to allow the Higgs to be onshell. However, you also get a (non-gauge-invariant) off-shell Higgs contribution with both w:s onshell.

In general, the "required s-channel" syntax ( a b > c > d e) should not be used, since the result in general is not gauge-invariant. I would recommend to use the decay chain syntax as much as possible, since this avoids (non-gauge-invariant) offshell contributions.

All the best,

Adam Kaluza (adamkalu) said : #2

Thank you very much!! This solved the Problem.

Best regards,

Adam Kaluza (adamkalu) said : #3

Thanks Johan Alwall, that solved my question.