# Independent simulation of EFT terms don't match the cross sections of full process

Dear authors,

I have generated same-sign WW process as following:

generate p p > l+ l+ vl vl j j QCD=0 SMHLOOP=0 @1

add process p p > l- l- vl~ vl~ j j QCD=0 SMHLOOP=0 @2

The model I used is:

SMEFTsim_

https:/

When I tested operators whose Wilson coefficients are cqq3, cqq31, cqq1, cqq11. Those operators are all four-quark operators.

I generated processes with only one of those coefficients are 1. I used following settings:

1. Independent simulation:

simulate interference terms and quadratic terms by adding "NP=1 NP^2==1", "NP=1 NP^2==2"seperately. Then the total cross sections are xs_sm+xs_

2. Full process:

Just set "NP=1", the cross sections are xs_full

Then I got the cross sections of all the processes:

a. For cqq3

xs_

xs_full: 0.1898 pb

b. For cqq31

xs_

xs_full: 0.2017 pb

c. For cqq1

xs_

xs_full: 0.08374 pb

d. For cqq11

xs_

xs_full: 0.08261 pb

So I found the total cross sections are all small than full processes, and those operators' quadratic term cross sections are large than SM cross sections.

Also the variables distributions are different. For example, for cqq3, you can find the mjj distributions here: http://

But except those four operators, other operators have good agreement.

Do you know why such four-quark operators are not consistent? And what kind of settings we should trust, independent simulation or full process.

Thanks,

Jie

## Question information

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- Answered

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- Last query:
- 2020-08-21

- Last reply:
- 2020-08-21

Hi,

The first point to check is that you are using the same run_card for each simulation.

Indeed the interference term in particular has a different default setting by default (in particular since the default dynamical scale choice is not relevant for that case). The agreement should be done within scale uncertainty (i.e. around 50% precision).

In the same spirit, if you set the dynamical_

Therefore my suggestion is to use dynamical_

Finally, note that MG5aMC does not have a dedicated phase-space integrator for interference ONLY. It is advise to either integrate that part together with a square matrix-element or to carefully check that the phase-space integration converges as expected. You can find in launchpad a huge list of case where the integration of interference alone does not converge correctly.

Cheers,

Olivier

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