MadGraph5_aMC@NLO

Cuts in MadAnalysis

Asked by Nick

I have a question about the syntax for cuts in MadAnalysis.
My events are ordered by pt (the default).
I tried using the following cuts in ma_card.dat (with not other cuts present) on a set of pgs data and obtained different results:

Cut 1:
etamax 1 2 2d0

Cut 2:
etamax 1 2 2d0
etamax 1 1 2d0

By the explanation at the top of ma_card, it would seem that these two cuts should do the same thing, but Cut 2 had fewer passing events than Cut 1. I know that a max cut is ignored if a particle does not exist. Does this mean that the cut in Cut 1 is ignored if 1 particle exists from class 1 but not a second?

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MadGraph5_aMC@NLO Edit question
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Rikkert Frederix Edit question
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Nick
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John Doe (kwcpsn) said : 		#1

Hi Nick. A comment from another user, pending confirmation or correction by the experts.

Indeed, upper bounds (or "max" cuts) are ignored if one of the particles on which they are to be applied does not exist. So, for events with two or more class 1 particles, your "Cut 1" and "Cut 2" have the same effect. But for events with only one class 1 particle, "Cut 1" has no effect at all, whereas in "Cut 2" the first line is equally ineffectual, but the second line rejects events not passing that cut.

Notice that if instead of setting upper bounds on eta with "etamax" you were setting a lower bound with "etamin", the effect of "Cut 1" and "Cut 2" would be the same. That's because events with only one class 1 particle would be dropped in both cases.

Whereas the behavior of "max" and "min" cuts is different, you can switch them by setting lower (resp. upper) bounds on -eta instead of upper (resp. lower) bounds on eta, by using one of the user functions X1, X2, X3 defined in MadAnalysis/kin_func.f.
You can define X1 to be -eta, and then set up cuts on X1.

Cheers.

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Nick (nick2u84o) said : 		#2

Thanks!

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Rikkert Frederix (frederix) said : 		#3

Dear Nick, John,

Sorry for taking a bit of time to react.

Indeed, you found a bug in MadAnalysis and I've committed a fix for this (should be available soon). The max cuts should apply on all particles in the current class. This was not correctly taken into account for cuts that are dependent on only one particle (such as rapidity, or pT). It was already correctly taken into account for cuts on more than one particle (like an invariant mass cut).

Best,
Rikkert