This plot marks several milestones.
First, it si the first new plot I've made in almost two months of any data at all. The last two months, when I've not been busy with the hiring, I've been busy trying to make "pretty" plots. This form of Yak Shaving means making the same plot over and over, adjusting a font size, or the position of some text.
Second, my former graduate student told me to make this plot (instead of the other way around). He was reviewing another analysis when he saw something odd in the way we were applying btagging (I'm co-leader of that group at DZERO), and brought it to my attention. What was really special about this was he gave a talk at the btagging meeting -- and used this plot in his talk. It used to be he would do all this great work, and then I'd use his plots to show how much I was doing to the rest of the world. Roll reversal! I suspect it won't be the last time.
Third, and not least, it presents a potential problem. The x axis is the Z coordinate a our proton-anti-proton collision (in centimeters). There are about 1000 of them in this plot. The large spread is expected: it is impressive that the accelerator division can make the the protons and anti-protons collide moving at almost the speed of light at all, let along in a +/- 30cm area. The solid line (we call it a "histogram") represents the number of "taggable jets" found as a function of Z. Loosely, a jet is a stream of particles that deposit energy in a calorimeter (which does just as you'd expect from a "calorie" point of view). A "taggable" jet means we found at least two low pT charged particles (like a pion) near the jet. The crosses represent a prediction using a technique called a Taggable Rate Function. You'll note that the prediction is low in the middle of the plot and high at the edges: in an ideal world they should be identical. Now that we know we have a problem, we have to figure out exactly how big it is? Does it effect anything? BTW, there is another potential problem this plot represents that I'm not discussing here. More on that later if it pans out. That is my goal for this Weds morning -- there is a physics analysis meeting then. And in the afternoon I dissapear off to San Franciso for some vacation (till Saturday, whoo-hoo!).
But instead of working on that right now, I need to finish off the grades for my class!