Meaning of Scale of an events/process in MonteCarlo

[Alkass]

Meaning of "Scale" of an events/process in MonteCarlo

Hi there

I do have this question - I often hear that "this depends on the scale of the process" for example when it comes to match the matrix-elements with a parton-shower program (I am new to MonteCarlo world)

so, what does "scale" means ? Is just the Q that is carried out by the produced particle or is what we could define as factorization scale ie Q^2 = m^2(W) + Sum{JetPT(i)}

thanks

 

[RGevo]

Hello,

There are I guess 3 types of scale present normally.

The first is the momentum exchange of the process, Q^2. Which is determined by the incoming colliding particles or by a previous branching if you are talking about Parton showering.

Then there are two un physical scales. Renormalization and factorisation

This first if these is essentially a momentum cut off for loop integrals.

The second has to do with factoring some particle splittings into say a proton, as oppose to including it in a matrix element.

These last two scales are a remnant if the fact we are doing perturbation only to some order. I.e. because we are ignorant to higher orders we haven't calculated.

Hope this helps