# Simulation of EFT samples with amplitude decomposition

Dear experts,

I'm running Madgraph with an EFT model and with the decomposition method of the different contribution for the different terms in the amplitude. The model I'm using is this one:

I'm mainly testing the same-charge WW leptonic final state (for this particular model). My process definitions look like these (examples):

SM case:

define l+ = e+ mu+ ta+

define vl = ve vm vt

define l- = e- mu- ta-

define vl~ = ve~ vm~ vt~

define p = g u c d s u~ c~ d~ s~ b b~

define j = g u c d s u~ c~ d~ s~ b b~

generate p p > l+ vl l+ vl j j QCD=0 S0=1 S1=1 S2=1 M0=1 M1=1 T0=1 T1=1 T2=1 @1

add process p p > l- vl~ l- vl~ j j QCD=0 S0=1 S1=1 S2=1 M0=1 M1=1 T0=1 T1=1 T2=1 @1

Interference between SM and BSM:

[same particles]

generate p p > l+ vl l+ vl j j QCD=0 T0^2==1 @1

add process p p > l- vl~ l- vl~ j j QCD=0 T0^2==1 @1

Quadratic BSM term:

[same particles]

generate p p > l+ vl l+ vl j j QCD=0 T0^2==2 @1

add process p p > l- vl~ l- vl~ j j QCD=0 T0^2==2 @1

The problem that I'm seeing is in the validation of the decomposition method where I compare the sum of the latter three samples with a fully generated BSM sample. I define it as such:

[same particles]

generate p p > l+ vl l+ vl j j QCD=0 T0=1 @1

add process p p > l- vl~ l- vl~ j j QCD=0 T0=1 @1

Looking into the total cross sections after event generation, the closure looks totally fine:

SM = 0.037113 pb

SM-BSM interference = -9.626e-05 pb

BSM quadratic = 1.898e-03

Sum of the above = 0.038915 pb

Full sample = 0.038669 pb

This makes a 0.64% difference between the sum and the full sample which looks very good. The closure in the total cross section looks very good for all tested points (The ssWW process in sensitive to 8 of the 29 parameters of this model.) Now if I look further into differential distributions (after showering with Pythia8.240) many of the parameter points look very good. However, some of the parameters show discrepancies in the tails of some observables. I have put some plots for the invariant di-boson mass at ME level (mWW), the invariant di-lepton mass here:

https:/

I'm using MG version 5.2.6.5 for GP generation and 5.2.6.2 for event generation.

We have also seen similar issues with the WZjj fully leptonic final state in this model:

https:/

I also contacted Oscar Eboli who provided the model. He could not say where this was coming from, which is why I now write to the Madgraph support.

Thanks a lot for your reply.

Best regards,

Stefanie

## Question information

- Language:
- English Edit question

- Status:
- Solved

- Assignee:
- No assignee Edit question

- Solved by:
- Olivier Mattelaer

- Solved:

- Last query:

- Last reply: