Add fastNLO importer

[cschwan]

Similar to issue #17.

[enocera]

@cschwan It would be nice if we could make the fastNLO importer also work with DIS grids. One specific example is DIS+jet(s). Apparently, the grids available from Ploughshare have been removed (for instance, they were available at https://ploughshare.web.cern.ch/ploughshare/record.php?group=applfast&dataset=applfast-h1-incjets-fnlo-arxiv-1406.4709, but are no longer there). I suspect that the reason is that a bug in NNLOjet was discovered. Anyways, for the sake of looking at the fastNLO converter, I think that we could use the grids that I've got from Daniel Britzger some time ago. I've (temporarily) put them at this link https://data.nnpdf.science/fnlo_tables.tgz

[enocera]

The link includes several experiments from H1 and ZEUS, if the importer works with one grid, it should with all of them.

[cschwan]

Great, thanks a lot. I'll have a look at it soon.

[cschwan]

I've started working on this, and commit ea81006 adds a program fnlo2pine that can already read fastNLOCoeffAddFix tables. The numbers are still wrong, but not too far off, so there should only be a few bugs left to find. I'm also confident that reading out fastNLOCoeffAddFlex-type table should work similarly - this is the format of the tables you've linked above.

[cschwan]

Starting with commit 6a0b4f5 we can now convert one-dimensional fastNLOCoeffAddFix-type tables, for example Mitov's ttbar tables - all of them are working.

[cschwan]

Commits 0e18c22 and 8a5c7b9 add support for symmetrised fastNLO tables, such as the 2D and 3D jet cross sections that we're using.

[cschwan]

What's left to do for this issue is to implement support for the flexible-scale grids (these: https://data.nnpdf.science/fnlo_tables.tgz), which support different values for the factorisation and renormalisation scales. If I recall it correctly the linked DIS grids set the factorisation scale to Q^2 and the renormalisation scale to sqrt(Q^2 + ptjet^2). At the moment this unfortunately isn't supported in PineAPPL (nor is it in APPLgrid).

[cschwan]

Preliminary support for flexible-scale grids (the flexibility to change the scale function isn't retained, but independent renormalization and factorization scale choices are supported) has been added in commit c71dd92. I tested the following sets of tables from ploughshare with fastNLO 2.5.0:

• https://ploughshare.web.cern.ch/ploughshare/db/applfast/applfast-h1-incjets-fnlo-arxiv-0706.3722/applfast-h1-incjets-fnlo-arxiv-0706.3722.tgz
• https://ploughshare.web.cern.ch/ploughshare/db/applfast/applfast-h1-incjets-fnlo-arxiv-1406.4709/applfast-h1-incjets-fnlo-arxiv-1406.4709.tgz
• https://ploughshare.web.cern.ch/ploughshare/db/applfast/applfast-h1-incjets-fnlo-arxiv-1611.03421/applfast-h1-incjets-fnlo-arxiv-1611.03421.tgz
• https://ploughshare.web.cern.ch/ploughshare/db/applfast/applfast-zeus-incjets-fnlo-arxiv-0208037/applfast-zeus-incjets-fnlo-arxiv-0208037.tgz
• https://ploughshare.web.cern.ch/ploughshare/db/applfast/applfast-zeus-incjets-fnlo-arxiv-0608048/applfast-zeus-incjets-fnlo-arxiv-0608048.tgz

All of the grids are successfully converted for the central scale choice, however, scale variations need a bit more work.

[cschwan]

Commit 5569124 introduced a regression, which causes the conversion of fastNLO tables for dijets a single-jet inclusive to fail (numbers do no longer agree).

[cschwan]

The previously mentioned problem is fixed in commit 628472a.

[cschwan]

The remaining development is be found in #120 and subsequent Issues/PRs.