UL: V-tagging

[mcremone]

Similar to the top-tagging one, but this is more complicated. We need to:

1. Identify V-tagging working points. Typically the logic is to use a working point that gives at least 90% signal efficiency. Since we do not have mono-Z' signals yet, I would do this using a mono-V or a Higgs invisible signal sample. This would be the first step to do once the mono-Z' processor is ready.

2. Measure the scale factors. In this case we will not be measuring mis-tagging scale factors because those will be calibrated in-situ. But we do need to measure signal scale factors.

To do that, we should follow the standard procedure used in CMS for V-tagging. We need to find it digging into twikies. The group that typically measure these scale factors is JMAR. I suggest reaching out to the conveners in case the information is hard to find.

The we need to make a processor, that we will call vtagsf.py to perform such scale factor measurement, following the example of the one used for double-b tagging:

https://github.com/mcremone/decaf/blob/master/analysis/processors/doublebsf.py

3. As for top-tagging, a class in corrections.py must be implemented to apply the scale factors, as in here:

https://github.com/mcremone/decaf/blob/UL/analysis/utils/corrections.py#L521