# Proton Proton Collisions Cross Section Plot by Stirling

I am struggling to understand some details of the cross section plot by Stirling that is very often shown when talking about LHC physics. See e.g. here: http://www.hep.ph.ic.ac.uk/~wstirlin/plots/crosssections2012_v5.pdf

I understand very well the discontinuity when switching from $p\bar{p}$ to pp collisions, however, what I don't get is what is meant with $\sigma_{b}$ and $\sigma_{t}$. Is this only referring to pair production, like $gg \rightarrow g \rightarrow b\bar{b}$ ? Or are processes that are experimenatally often called single-top production, like $qq' \rightarrow W \rightarrow tb$ included as well?

Moreover, what I completely miss is the meaning of the two lines splitting for the $\sigma_{b}$ cross section. Is this due to uncertainties as pdfs or different calculation schemes?

I would appreciate any help or kick into the right direction.

• all figures have a paragraph describing what is displayed. you have not linked that – anna v Nov 14 '17 at 17:36
• Apparently not. I took it from hep.ph.ic.ac.uk/~wstirlin/plots/plots.html and there is no detailed explanation what is shown. I searched as well for a publication where this appears but it does not seem to be the case especially since the author wants that one uses "private communication" for referencing his work. – Brian Nov 14 '17 at 18:34
• physics is about accuracy, not about guessing what the variables shown display. I can guess that it is about inclusive crossections , thats all. If you go to the link you supplied, there is an archive reference link where the paper with the words exists. arxiv.org/abs/0901.0002 It turns out it is a theoretical/phenomenological paper with fits before even the LHC started. If the author says private communication maybe you should send an email and ask for explanation of symbols. My guess is that σ_b and σ_t are the inclusive crossections for the bottom and top. – anna v Nov 15 '17 at 5:09
• I guess that the split in the b crossection must be related to CP violation by neutral bottom quark decays – anna v Nov 15 '17 at 5:28
• I know that physics is about accuracy and to be 100% sure one has to ask the author of the plot. I just thought maybe someone in this community came across the problem already earlier and knows. The paper you referenced does not even show the plot. It is from 2009 and describes how they created their PDF set one often usess. The plot I referenced is from 2012 (the Higgs boson has already been found at that time). I agree with you that the sigmas are the pair production cross section (whatever they defined to go in there). – Brian Nov 15 '17 at 7:51