Asked by Alessandro Davoli on 2018-02-07

Hi,

I'm using MadWidth to study the branching ratio of a model I wrote.

The model is SM + a Z' boson and two fermions, x1 and x2.
Z' is coupled to quarks, x2 and x1, so that the production channel for x2 and x1 is something like p p > zp > x1~ x2.
x1 and x2 are also directly coupled to SM quarks through an effective, D=6, operator.

When I execute "compute_widths x2", only the channel x2 > zp x1, (zp > q~ q) seems to be taken into account (the only displayed diagram for x2 decay in the temp file contains the exchange of Z').

- is it possible to exclude some decay channels from MadWidth? (I'd like to exclude Z' in the decay)
- can MadWith deal with effective operators for decay?

Thanks!
Alessandro

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Olivier Mattelaer
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2018-02-07
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2018-02-07
 Olivier Mattelaer (olivier-mattelaer) said on 2018-02-07: #1

Hi,

- is it possible to exclude some decay channels from MadWidth? (I'd like to exclude Z' in the decay)

MadWidth does not allow you to play with the decay channel.
Now you can typically define yourself the decay channel in madgraph and directly go to the phase-space integration.

So you can do something like
define pos_decay = all / x2
generate x2 > all all all / z'
output
launch

If you want to be a bit closer of what madwidth is doing you can do

define pos_decay = all / x2
generate x2 > all all all / z'
output
launch -i
calculate_decay_widths

The difference between the two is that the first targets precision on the total width, while the second
targets precision on each channel independently.
Also the first mode focus on generating N events, while the second care does not care about the number of events generated.
The second mode will also write a new param_card including BR information (like MadWidth).

- can MadWith deal with effective operators for decay?

If this is a pure python UFO model then yes this is supported. Please read the MadWidth manual since the definition of coupling_order
is quite critical to have it work in some complex case (mainly for cases with effective operator with gluon and photon)

Cheers,

Olivier

On 7 Feb 2018, at 14:13, Alessandro Davoli <<email address hidden><mailto:<email address hidden>>> wrote:

Hi,

I'm using MadWidth to study the branching ratio of a model I wrote.

The model is SM + a Z' boson and two fermions, x1 and x2.
Z' is coupled to quarks, x2 and x1, so that the production channel for x2 and x1 is something like p p > zp > x1~ x2.
x1 and x2 are also directly coupled to SM quarks through an effective, D=6, operator.

When I execute "compute_widths x2", only the channel x2 > zp x1, (zp > q~ q) seems to be taken into account (the only displayed diagram for x2 decay in the temp file contains the exchange of Z').

- is it possible to exclude some decay channels from MadWidth? (I'd like to exclude Z' in the decay)
- can MadWith deal with effective operators for decay?

Thanks!
Alessandro

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