Orders_tag_plot explanation in fixed order analysis

Asked by matteo maltoni

Dear MG5 experts,

I am trying to perform a fixed order analysis of a process (p p > w+ w- w+ [QCD]) in the SMEFT, by modifying one of the analysis_HwU fortran files. Still, I don't understand how to divide the different LO and NLO contributions through the orders_tag_plot, and I didn't find any documentation anywhere: can you please explain me how are the three digits, in the orders_tag_plot indices, related to the QCD, QED and NP values?

In particular, how should I divide the NP=0,2,4 contributions at both LO and NLO?



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Best marco zaro (marco-zaro) said :

Ciao Matteo,
thanks for your question.
Indeed, the orders_tag_plot have not been documented well.
Basically, they are an integer computed from the coupling powers of the various contributions to the cross section.
To understand their behaviour, open orders.inc inside any of the P0 folders.
What you need is the ordersname list. For example, I find
the orders tag integer is computed as
1 * power of QCD + 100 * power of QED
or, more in general,
sum 100^(i-1) * power of ORDERNAMES[i]
note that the power are always in terms of gstrong, (not alpha_S, alpha) and refer to the amplitude squared.
In the SM, p p > w+ w- w+ would hence have
orders_tag_plot = 600 at the LO
and orders_tag_plot = 602 at NLO QCD.

Note that if you are using the pre-released v3.0.4, inside the various logs you will have a printout of the various values of orders_tag_plot, e.g

INFO: orders_tag_plot is computed as: + QCD * 1 + QED * 100
 orders_tag_plot= 204 for QCD,QED, = 4 , 2 ,
 AMP_SPLIT: 1 correspond to S.O. 4 2
 orders_tag_plot= 402 for QCD,QED, = 2 , 4 ,
 AMP_SPLIT: 2 correspond to S.O. 2 4
 orders_tag_plot= 600 for QCD,QED, = 0 , 6 ,
 AMP_SPLIT: 3 correspond to S.O. 0 6
 orders_tag_plot= 206 for QCD,QED, = 6 , 2 ,
 AMP_SPLIT: 4 correspond to S.O. 6 2
 orders_tag_plot= 404 for QCD,QED, = 4 , 4 ,
 AMP_SPLIT: 5 correspond to S.O. 4 4
 orders_tag_plot= 602 for QCD,QED, = 2 , 6 ,
 AMP_SPLIT: 6 correspond to S.O. 2 6

Let me know if you need more help.



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matteo maltoni (matteo-maltoni) said :

Thanks marco zaro, that solved my question.