Comment 8 for bug 1731086

Hi Emma,

I’m a bit confused about your last message.

> Standalone, for the process Zach described above, I'm now able to
> reproduce the cross-section we got in 2.3.3 using 2.6.0 with your patch
> (with the default run_card that has MLM on and use_syst=T).

Ok that’s a good news.

> I made some quick plots - you can see the difference in the jet multiplicity distributions here (both before and after applying your patch to MG 2.6.0):
> http://ekuwertz.web.cern.ch/ekuwertz/njets_beforepatch.eps
> http://ekuwertz.web.cern.ch/ekuwertz/njets_afterpatch.eps

So those plot are for the case with ickkw=1/MLM merging right?
Looking at Njet distribution is not the most sensitive observables to look at difference between MG version since that observables is dominated by shower effect.
Are you using the same setup for pythia8 in both case? Note that the difference between before and after patch is within theoretical uncertainty.
This shows that such uncertainty is not that small so I would not worry too much about the remaining difference.
Which choice did you take for the renormalization/refactorization scale? If you use the default of MG5, the associate algorithms have been improved from 2.3.3 to 2.6.0.
Making that using that scale choice not suitable for comparison between version.

> I also put process directories from the 2.3.3 and 2.6.0 jobs here in case you are able to identify anything strange in our setup:
> http://ekuwertz.web.cern.ch/ekuwertz/MG-2.6.0.tar.gz
> http://ekuwertz.web.cern.ch/ekuwertz/MG-2.3.3.tar.gz

Those samples are generated with ickkw=0, is this intended? Here I can see that you use the default dynamical_scale_choice meaning that some difference are expected due to that point only.
(within theoretical error obviously)

Actually one good plot to see the change in the scale, would be to plot that scale.

Cheers,

Olivier

> On Nov 23, 2017, at 00:09, Emma Kuwertz <email address hidden> wrote:
>
> Hi Oliver,
>
> Standalone, for the process Zach described above, I'm now able to
> reproduce the cross-section we got in 2.3.3 using 2.6.0 with your patch
> (with the default run_card that has MLM on and use_syst=T).
>
> Unfortunately we still get the same slightly weird results for the
> individual processes in another job (which has ickkw=0). The difference
> in p p > go go j cross-sections mentioned in Zach's first message on
> this thread appears to lead to a difference in kinematics in the final
> state and we want to be sure that 2.6.0 is doing the right thing.
>
> I made some quick plots - you can see the difference in the jet multiplicity distributions here (both before and after applying your patch to MG 2.6.0):
> http://ekuwertz.web.cern.ch/ekuwertz/njets_beforepatch.eps
> http://ekuwertz.web.cern.ch/ekuwertz/njets_afterpatch.eps
>
> As you can see, it looks as though the patch does improve the agreement
> in the tail of the distribution, but it still looks as though there is a
> systematic effect.
>
> I also put process directories from the 2.3.3 and 2.6.0 jobs here in case you are able to identify anything strange in our setup:
> http://ekuwertz.web.cern.ch/ekuwertz/MG-2.6.0.tar.gz
> http://ekuwertz.web.cern.ch/ekuwertz/MG-2.3.3.tar.gz
>
> Do you think you could take a look to see whether there is any smoking
> gun in our setup?
>
> Thanks,
> Emma
>
> --
> You received this bug notification because you are subscribed to
> MadGraph5_aMC@NLO.
> https://bugs.launchpad.net/bugs/1731086
>
> Title:
> Change in production xsecs in SUSY models in 2.6.0
>
> Status in MadGraph5_aMC@NLO:
> New
>
> Bug description:
> Hi there,
>
> I'm hoping that you can help us track this issue down, as it's holding
> up our validation of MadGraph 2.6.0. Emma Kuwertz and I found that
> between older and newer MadGraph releases, the cross section of p p >
> go go j processes changed by 50% or more. I set up and run out of the
> box:
>
> import model mssm
> generate p p > go go
> add process p p > go go j
> output -f
>
> in MadGraph 2.3.3 and 2.4.3. I run the same in MadGraph 2.6.0, but
> with `import model MSSM_SLHA2`. In both releases I then set the
> masses of all SUSY particles to be 10**9 GeV, except the gluino which
> is set to 1 TeV. All other parameters I leave as they are, out of the
> box, but a quick check suggests that there aren't wild new cuts that
> have appeared. With 2.3.3 the cross section I get is:
>
> Cross-section : 0.662 +- 0.00212 pb
>
> With 2.4.3 and 2.6.0, I get the same answer:
>
> Cross-section : 0.7888 +- 0.002181 pb
>
> There, the cross section files suggest that most of the difference is
> due to a large (>25%) change in g g > go go g. I don't see any
> difference in the PDFs that might cause such a change, though.
>
> In Emma's run inside the ATLAS framework, we were looking at more
> modest total cross section changes, but large changes to the go go j
> cross section (of order 50%) that led to significantly harder
> kinematics in one case than the other.
>
> Is there some known feature of the releases that would have caused
> these differences? I tried to look over the update notes, but I
> didn't find anything sinister.
>
>
> Thanks,
> Zach
>
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