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October 16th 2017 - Drell-Yan xsection
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Second meeting with the Drell-Yan paper. Nikola chairs. 

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Topics: 
	- systematics
	- cut and count
	- WE went over the tables in detail- pole mass: centre of resonance, parameter of mass but can be dressed.
	- table 3 and 4 are useful not only to show the signal, but more importantly validate the background
	- mu: fit histogram, normalize by the theory cross-section.
	- frequentist vs. bayseian
	- p-values: how do we set a limit, H->ttbar actually looked for a deficit in the background!
	

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Details:
	- cut and count: if we want to find some process, we can simply count up the number of events we have. Cut and count is a number of signal, a number of background. In this analysis we counted everything that passed a specific .
	- if you’re doing a search, if you model your background well you know that you have a signal. But for a measurement the signal uncertainty might matter more.
	- The Drell-Yan PDF can come from other measurements, e.g. CT collaboration in the PDF. But what do CT do? Measure the structure functions from DIS. Look at the dependence on Bjorken X and Q2. ATLAS can do strange, charm, and DY too.
	- we sometimes will include an additional measurement for isolation, even if it makes the uncertainty worse, because it can reduce background
	- jets don’t always have tracks so that’s why you’d also want to include the track
	- this table shows the impact, you can also have tables that show the source. systematic uncertainty due to beam energy  basically affect the available cross-section
	- the muon Identification efficiency is NA which may mean that it’s not been cut on or that it’s negligible
	- We have a theory: B = hypothesis 1, S+B= hypothesis 2.
	- CI are not valid when momentum transfer is on the same scale as Capital lambda.


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Misc:
	- top quark: the thing we measure and the thing the theorists want to know (a term in the lagrangian) is very interesting: W or top mass could be a good paper.
	- DY is the largest background, top quarks do not have enough stats to observe