ptj cut not affeting radiation jet at NLO

Hi,

When you do
> p p > e+ e- mu+ vm [QCD=all]
You do not have any jet at parton level.
So all your jet are coming from the Real contribution of the NLO contribution.
If you impose a cut on such jet, you will spoil the cancelation of the divergence between the real and the virtual computation (since your cut will remove the divergencies of the real but would kept the one of the virtual).

Saying it differently, such cut would spoil the NLO accuracy of your computation that you ask for.

Depending of what you try to do, you may want to live with this (quite good) efficiency.
Or to add a jet at born level:
> p p > e+ e- mu+ vm j [QCD=all]
(you can also decide to move to LO generation)

Cheers,

Olivier

> On 27 Feb 2019, at 18:32, RAFIQUL RAHAMAN <email address hidden> wrote:
>
> New question #678834 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/678834
>
> Dear Experts,
>
> I am generating process of p p > e+ e- mu+ vm [QCD=all], which gives a jet in the final state 44% time of the total events. I generated events with minimum ptj cut of 25/10/5 GeV in the generation level. When I work with the final state particle it seems that jet pt starts from zero, i.e., minimum pt jet cut has not affect the radiation jet. If I put a minimum pt cut on jets of 10 GeV in the analysis level, total number of events reduced to 95%. (number of jet events reduces by 2.5%). So my cross section becomes 95% of the cross section at generation level. I am not sure whether I am supposed to loose cross section if I put minimum pt cut on the radiation jet.
> Could you explain me why the ptj cut in the generation level is not affecting the radiation jet at all. I need this because I want use jet veto, i.e, I want keep ptjmax to 10 GeV. Please guide me How can I implement it.
> P.S. I have implemented the maximum Mll cut, the pt cut on the ll system in the cut.f file.
>
> Thanking you
> Rafiqul Rahaman
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Dear Olivier,

Thank you for such a quick reply. I have a similar question on the same process. I want to remove ptj>10 GeV in the analysis level.
By doing so I loose 42% events. So for pp->e+e-mu+vm the the sigma_NLO=42 fb where as sigma_LO=22 fb. If I consider the cross
section for remaining 58% events it is 24.36 almost equals to sigma_LO. Is it correct? Am I allowed to put max ptj cut on the radiation jet theoretically?

Regards,
Rafiqul Rahaman

Hi,

I would suggest to read this paper: arXiv:1110.4738<http://arXiv.org/abs/arXiv:1110.4738>
which is related to that process if I'm correct. This will allow you to double check your LO/NLO number.

 If I consider the cross
section for remaining 58% events it is 24.36 almost equals to sigma_LO. Is it correct?

This is pure coincidence. I would rather expect to have a cross-section close to
pp->e+e-mu+vm j
with the equivalent cut on the jet.

Cheers,

Olivier

On 28 Feb 2019, at 08:43, RAFIQUL RAHAMAN <<email address hidden><mailto:<email address hidden>>> wrote:

Question #678834 on MadGraph5_aMC@NLO changed:
https://answers.launchpad.net/mg5amcnlo/+question/678834

RAFIQUL RAHAMAN posted a new comment:
Dear Olivier,

Thank you for such a quick reply. I have a similar question on the same process. I want to remove ptj>10 GeV in the analysis level.
By doing so I loose 42% events. So for pp->e+e-mu+vm the the sigma_NLO=42 fb where as sigma_LO=22 fb. If I consider the cross
section for remaining 58% events it is 24.36 almost equals to sigma_LO. Is it correct? Am I allowed to put max ptj cut on the radiation jet theoretically?

Regards,
Rafiqul Rahaman

--
You received this question notification because you are an answer
contact for MadGraph5_aMC@NLO.

Dear Olivier,

Thanks for the reply. However it did not clarify my doubt. The reference is for 4l final state where as my process is trilepton with missing energy at NLO. The question was if I remove jets with PT larger than 10 GeV, will that be inconsistent with the virtual loop
contribution. Can I put PT cut in the analysis level on the radiation jets or I should consider the entire spectrum of the jets for NLO.

Thanking you
Rafiqul Rahaman

Hi,

> Thanks for the reply. However it did not clarify my doubt. The reference is for 4l final state where as my process is trilepton with missing energy at NLO.

Sorry my mistake.

> Can I put PT cut in the analysis level on the radiation jets or I should consider the entire spectrum of the jets for NLO.

You can put a cut at the analysis level (so after parton-shower) as long as such cut is infrared safe.
So you have to use a jet clustering algorithm which is IR safe ( the cone algorithm is not but kt and anti-kt are).

Cheers,

Olivier

> On 1 Mar 2019, at 08:47, RAFIQUL RAHAMAN <email address hidden> wrote:
>
> Question #678834 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/678834
>
> RAFIQUL RAHAMAN posted a new comment:
> Dear Olivier,
>
> Thanks for the reply. However it did not clarify my doubt. The reference is for 4l final state where as my process is trilepton with missing energy at NLO. The question was if I remove jets with PT larger than 10 GeV, will that be inconsistent with the virtual loop
> contribution. Can I put PT cut in the analysis level on the radiation jets or I should consider the entire spectrum of the jets for NLO.
>
> Thanking you
> Rafiqul Rahaman
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.