Is there a smearing effect in MG5?

Hi,

> 1. I find the result particle number is 80,000, in fact ,some other process may get a result with a number of particle contain units digit(even I just run 10000 times evens). Why? why there are extra particles? and why some particle number change?

Intermediate particles are only written if they are consider as “onshell” since in that case the shower has to handle that process in a different way.
Off-shell particles are not written and therefore the number of particles written in the lhe file can be random.

> 2. when I reconstruct the invariant mass of z by l+ l- , I find a width, about 10 GeV , near 91 GeV , since Z is the on-shell particle, why there is a width?

The definition of the above syntax contains particles up to X-times the width. the default is 15 but is part of the run_card and can therefore be changed to smaller/bigger value. (Not sure what will happen if you set that parameter to zero)

Cheers,

Olivier

> On Nov 29, 2015, at 17:02, Li <email address hidden> wrote:
>
> New question #275970 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/275970
>
> Hi,
> I run e+ e- > z h , z > l+ l - , h > b b~ for 10,000 events and 200+200 GeV
>
> 1. I find the result particle number is 80,000, in fact ,some other process may get a result with a number of particle contain units digit(even I just run 10000 times evens). Why? why there are extra particles? and why some particle number change?
>
> 2. when I reconstruct the invariant mass of z by l+ l- , I find a width, about 10 GeV , near 91 GeV , since Z is the on-shell particle, why there is a width?
>
> wish you can help me!
>
> Best,
> Li
>
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