Add PDF_VARIATION_BEAMS and PDF_VARIATION_ALPHAS_BEAM settings
Description
Add PDF_VARIATION_BEAMS and PDF_VARIATION_ALPHAS_BEAM settings
PDF_VARIATION_BEAMS can be used to restrict for which beams
a PDF variation is applied. Its default is "[1, 2]", i.e. both beams
will undergo a given PDF variation. Use "1" or "2" to only apply it to a
single beam. This is a global setting for all PDF variations, i.e. it is
currently not possible to do this on the basis of a single PDF
variation.
Now that the above is added, there is an ambiguity which beams's PDF
should be used to evaluate AlphaS. For that, PDF_VARIATION_ALPHAS_BEAM
has been added. Its default is "0", which means that the first
available beam's PDF is used. Use "1" or "2" to select a specific beam's
PDF instead.
Having different PDFs for each beam will be reflected in the variation
name (in Sherpa's output or the HepMC weight name), like in the
following example:
"MUR=1__MUF=1__LHAPDF.BEAM1=93300__LHAPDF.BEAM2=93301".Test Plan
The new settings PDF_VARIATION_BEAMS PDF_VARIATION_ALPHAS_BEAM are e.g. used in the following runcard, where only the second beam's PDF is varied, and the nominal first beam's PDF is used to evaluate AlphaS:
EVENTS: 1k
BEAMS: 2212
BEAM_ENERGIES: 7000
EVENT_GENERATION_MODE: W
SHOWER_GENERATOR: None
FRAGMENTATION: None
MI_HANDLER: None
ME_QED: None
BEAM_REMNANTS: false
FINISH_OPTIMIZATION: 0
ERROR: 0.99
SCALES: VAR{sqr(91.1876)}
OUTPUT_ME_ONLY_VARIATIONS: false
PDF_VARIATION_BEAMS: 2
PDF_VARIATION_ALPHAS_BEAM: 1
PDF_VARIATIONS:
- PDF4LHC21_40_pdfas/0
- PDF4LHC21_40_pdfas/1
- PDF4LHC21_40_pdfas/2
- PDF4LHC21_40_pdfas/3
- PDF4LHC21_40_pdfas/4
PROCESSES:
- 93 93 -> 11 -11:
Order: {QCD: 0, EW: 2}
SELECTORS:
- [Mass, 11, -11, 66, 166]Example Result
The above run card, for 100 events, gives the following cross sections:
-----------------------------------------------------------------------------------------------------
Nominal or variation name XS [pb] RelDev AbsErr [pb] RelErr
-----------------------------------------------------------------------------------------------------
Nominal 1947.86 0 % 235.383 12.08 %
MUR=1__MUF=1__LHAPDF.BEAM1=93300__LHAPDF.BEAM2=93301 1951.19 0.17 % 235.261 12.05 %
MUR=1__MUF=1__LHAPDF.BEAM1=93300__LHAPDF.BEAM2=93302 1943.64 -0.21 % 234.184 12.04 %
MUR=1__MUF=1__LHAPDF.BEAM1=93300__LHAPDF.BEAM2=93303 1948.31 0.02 % 235.324 12.07 %
MUR=1__MUF=1__LHAPDF.BEAM1=93300__LHAPDF.BEAM2=93304 1944.5 -0.17 % 235.42 12.1 %
MUR=1__MUF=1__LHAPDF=93300 1947.86 0 % 235.383 12.08 %
-----------------------------------------------------------------------------------------------------Additional Checklist Items
-
I have updated documentation as needed -
I considered if this should be cherry-picked/ported somewhere else (rel-2-x or master): This is currently not planned, since the implementation in rel-2-x is quite different.
Edited by Enrico Bothmann