# Mathematical definition of xqcut

Asked by trenta coollime on 2020-02-12

Hello, experts.

I have been generating events with xqcut = 20 for p p > h > z zp, z> l+ l-, zp > b b~ and noticed some odd feature.

Even when I define xqcut = 20, which I believe to be equivalent to kT (pT) of jet, I see several events, which have jets with pT<20.

MG5 website says it's the minimal distance in the phase space allowed between extra partons.

What does that exactly mean? and is there a mathematical formula that defines the quantity precisely?

Thank you.

Best Regards.

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Olivier Mattelaer
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2020-02-12
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2020-02-12
 Olivier Mattelaer (olivier-mattelaer) said on 2020-02-12: #1

Hi,

xqcut is a (very) special cut use for MLM matching/merging.
It does not have any easy mathematical formula.
and the reference to the various paper pointed to that page.
Note that in the case of a single jet, this is equivalent to the pt of that particle.

In this specific case, matching/merging does not occur on particle coming from decay.
and therefore your b-quark are not cut by that cut. (in top of that that cut is applied in principle only on massless particles which also might explains why it does not appear here.

In version 2.7.0 of the code, you might not even have the xqcut in the run_card since we are now automatically hidding all cuts that does not have any impact for the process under consideration.

Cheers,

Olivier

> On 12 Feb 2020, at 16:28, trenta coollime <email address hidden> wrote:
>
> New question #688706 on MadGraph5_aMC@NLO:
>
> Hello, experts.
>
> I have been generating events with xqcut = 20 for p p > h > z zp, z> l+ l-, zp > b b~ and noticed some odd feature.
>
> Even when I define xqcut = 20, which I believe to be equivalent to kT (pT) of jet, I see several events, which have jets with pT<20.
>
> MG5 website says it's the minimal distance in the phase space allowed between extra partons.
>
> What does that exactly mean? and is there a mathematical formula that defines the quantity precisely?
>
> Thank you.
>
> Best Regards.
>
> --

 trenta coollime (trentacoollime) said on 2020-02-12: #2

One last question, when you say "Note that in the case of a single jet, this is equivalent to the pt of that particle."

does the "single jet" mean additional jet specified in "generate" level (ex) p p > t t~ j)? or any single jet?

 Olivier Mattelaer (olivier-mattelaer) said on 2020-02-12: #3

> does the "single jet" mean additional jet specified in "generate" level
> (ex) p p > t t~ j)? or any single jet?

when you have exactly one jet at parton level (what you call "generate" level)
so yes for
p p > t t~j or for p p > w+ w- j ,...

Cheers,

Olivier

> On 12 Feb 2020, at 19:57, trenta coollime <email address hidden> wrote:
>
> Question #688706 on MadGraph5_aMC@NLO changed:
>
> trenta coollime posted a new comment:
> Thank you for your response!
>
> One last question, when you say "Note that in the case of a single jet,
> this is equivalent to the pt of that particle."
>
> does the "single jet" mean additional jet specified in "generate" level
> (ex) p p > t t~ j)? or any single jet?
>
> --