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Asked by SUBHASISH BEHERA on 2021-05-07

Dear Olivier,

Just wanted to ask about the MG5 v1_5_15 and MG5 v2_5_1.
I was trying to reproduce CS for some processes with proton-electron collision now with MG5_v2_6_7. But earlier results are available with v1_5_15 and v_2_5_1, which are completely differ by around >30% of the latest results.

And also I am not able to find the older version from the launchpad.
Are these older versions redundant to be used?

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Olivier Mattelaer (olivier-mattelaer) said :


> And also I am not able to find the older version from the launchpad.
only the last "bug fix" version (last digit) for any given "feature" version (second digit) are available for download on launchpad (on that download page).
ALL other version are available either via bazaar or via launchpad if you go to the page of the associate revision.

Now even 2.6.7 is consider as a very old version and you should either use 2.9.x which is a long stable release or use 3.1.0



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SUBHASISH BEHERA (subhparasara) said :

Many thanks for super quick reply.
So, the difference in CS is usual (around 30% or even much much different in a few cases)?
In particular, for the case of "proton-electron" collision.

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Olivier Mattelaer (olivier-mattelaer) said :

My bet is that this is linked to scale uncertainty. Since we change at some point the scale for such type of collision.
Now 2.6.7 is so old, that I do not know if this was before/after that version that we did it.

So I would test with a more recent version and set all scale to fix to see if this provide consistent result.
Then double check that the param_card and the run_card are the same between the various version and so on.
(any change in cut/scale/benchmark can easily do a 30% difference)



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