suggestion on systematics variation on MG matched sample

Hi,

> - varying the Q2 to 0.5 and 2 for both renormalization and fact scale (correlated or not)

This is indeed a common way to estimate this systematics.

> - concerning the matching, I see sentences like: "matching threshold shifted up or down by a factor of two relative to its default value". At the moment for my tt+np0/1/2/3 sample I use qtcut=20 GeV (in MG) and QCUT=30 GeV (in the pythia shower).
> If I change qtcut as a systematic uncertainty, hsould I also change QCUT accordingly (like respecting the condition qtcut<QCUT)?

yes you should.

Cheers,

Olivier

On Sep 12, 2013, at 11:01 AM, Valerio Dao <email address hidden> wrote:

> New question #235595 on MadGraph5:
> https://answers.launchpad.net/madgraph5/+question/235595
>
> Hello,
>
> I would like to ask some suggestion on estimating the systematics when producing a matched samples.
>
> Reading few notes on the topic I see that the 2 main approaches are:
> - varying the Q2 to 0.5 and 2 for both renormalization and fact scale (correlated or not)
>
> - concerning the matching, I see sentences like: "matching threshold shifted up or down by a factor of two relative to its default value". At the moment for my tt+np0/1/2/3 sample I use qtcut=20 GeV (in MG) and QCUT=30 GeV (in the pythia shower).
> If I change qtcut as a systematic uncertainty, hsould I also change QCUT accordingly (like respecting the condition qtcut<QCUT)?
>
> thanks a lot in advance,
>
> Valerio
>
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