Is REPLACE still needed?

Hi Vitaliano,

> MG itself will avoid to calculate the same graph for each lepton type.

This is true IF each lepton have the SAME mass parameter in the model.
this is the case for
sm-no_tau_mass
sm-no_masses
But if you use one of the following model:
sm
sm-no_b_mass
sm-full
then the computation will be duplicated.

Then indeed the relevance of that script is strongly reduced.

Cheers,

Olivier

On Sep 12, 2013, at 1:11 PM, Vitaliano Ciulli <email address hidden> wrote:

> New question #235602 on MadGraph5:
> https://answers.launchpad.net/madgraph5/+question/235602
>
> In CMS we are having problems with the replace.py script in slc6.
> Is this script still useful in the MG5 versions >= 1.5.11 to reduce the gridpack generation time as explained in https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/GridDevelopment ?
> We have been told that its use is now obsolete as MG itself will avoid to calculate the same graph for each lepton type.
> Thanks
> Vitaliano
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Hi Olivier,

just to be sure: what is the consequence of running the model sm-no_masses and how does it compare to using REPLACE?
I guess with sm_no-masses all the leptons, that have null mass, will acquire their mass when the event is hadronizes with Pythia, resulting in a small violation of energy-momentum conservation.
When using the REPLACE script was the mass added?
Energy-momentum conservation was enforced (e.g. reducing longitudinal momentum)?

Thanks
Vitaliano

Hi Vitaliano,

> just to be sure: what is the consequence of running the model sm-no_masses

1) you set all quark (but the top) and lepton masses to zero.
2) You remove all the interaction between the higgs and those massless particles

> how does it compare to using REPLACE?

REPLACE didn't change the kinematics of the final state particles.
This code is just changing the pdg_code associated to some particles in the file.
So using REPLACE assumes as well that all leptons have the same mass.
Therefore using sm-no_masses or REPLACE is the same.

> I guess with sm_no-masses all the leptons, that have null mass, will acquire their mass when the event is hadronizes with Pythia, resulting in a small violation of energy-momentum conservation.

I think the mass will be added at the shower stage when the kinematics of the events is modified anyway to allow ISR and FSR.
This will not violate energy-momentum conservation but Pythia can sometimes fails to do it leading to loose some events.

> When using the REPLACE script was the mass added?

no

Cheers,

Olivier

On Sep 13, 2013, at 12:21 AM, Vitaliano Ciulli <email address hidden> wrote:

> Question #235602 on MadGraph5 changed:
> https://answers.launchpad.net/madgraph5/+question/235602
>
> Status: Answered => Open
>
> Vitaliano Ciulli is still having a problem:
> Hi Olivier,
>
> just to be sure: what is the consequence of running the model sm-no_masses and how does it compare to using REPLACE?
> I guess with sm_no-masses all the leptons, that have null mass, will acquire their mass when the event is hadronizes with Pythia, resulting in a small violation of energy-momentum conservation.
> When using the REPLACE script was the mass added?
> Energy-momentum conservation was enforced (e.g. reducing longitudinal momentum)?
>
> Thanks
> Vitaliano
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Thanks Olivier Mattelaer, that solved my question.

Sorry, I still have a doubt.
From which MG5 version sm-no_masses is equivalent to REPLACE?
Thanks

Thanks Olivier Mattelaer, that solved my question.