The It Plot

Every now and then a single plot takes over 90% of the general experimental talks. This plot will appear in all conference summary talks, in all seminars, and in all colloquium given by experimentalists. Generally, these plots are very high level and summarize person-decades of work. High level, by the way, means so abstract as to be useless in any truly scientific context.

A few years ago this was the Higgs Reach Plot at the Tevatron. This plot came out of the Higgs/SUSY working group, a more than one year long workshop. Brief aside: what is that plot???

The plot shows the (then) expected ability of the Tevatron to find the Higgs particle as a function of mass. The three different lines on the plot represent different outcomes. For example, the lowest line is the "95% confidence level limit". The way to read this is to pick a point on the line; the x-axis value represents a Higgs mass (in GeV/c^2) and the y-axis represents how much data we require (in inverse fempto-Barnes) in order to be able to achieve the limit. There are three lines. The lowest, the limit, describes the amount of data we would need in order to rule out the Higgs existence at that mass for that amount of data if it wasn't actually there. We'd be 95% confident that we'd not missed it. The next line is the 3-sigma discovery line. That is how much data you would need to declare there was "evidence" for the existence of the Higgs at that mass. The final line, the 5-sigma line, is the data required for a gold-plated discovery of the Higgs at that mass. We have to plot all those mass ranges because we have only a vague clue of what the Higgs mass is. One of the reasons this plot became the It plot is it almost directly translates into time and money; a perfect PR plot when talking to folks at science funding agencies. The vertical axis, data, directly translates into how long the Tevatron has to run. Check out this data-delivered-at-the-Tevatron plot. Note the axis for the small blue dots, on the right hand side of the plot, is in Pb-1 -- pico-Barnes. 1000 of those pico-Barnes is 1 fempto-barn. The x-axis is time! And, of course, money! ;-)

Now, back to the story. This workshop occur ed between Run I and Run II of the Tevatron and, as a result, there were a lot of people working on hardware and looking for physics to distract them. This workshop became it. We made a huge amount of progress on many topics. And this plot, which summarized about half the workshop, became the It plot. It remained the It plot for more than two years, the longest I'd ever seen an it plot remain around (in my short career). The plot was based on extrapolation, it had no real data behind it, and the plot was eventually discredited as real data started to accumulate at the Tevatron. Several optimistic assumptions had been made, a few techniques and search strategies were invented after the study, etc. I remember the first big talk I gave where I didn't use the plot -- I wrote at the end "First Talk Where I Didn't Show This Plot -->". ;-) BTW, no updated version really replaced that plot... the effort to redo the study from scratch was simply too great. Rather, it became obsolete and thus people stopped showing it.

So, what is the next It plot? There is one that I've seen around -- it is in most LHC plots. It is the same plot but for the LHC (the interpretation is slightly different, but the plot contains similar information). But I've not seen it shown nearly as much as the Tevatron version.

But I can't help but wonder if this is the next It plot here in the US. This is is another variant of the previous two plots. Again, along the x-axis is the mass of the Higgs particle, in the same units as before. The y-axis is cross section -- a guage of how often the Higgs will be created at the Tevatron per-unit-time (I'm being very loose with my definitions here). Now, the lower black lines are what we expect the Higgs to do. The upper colored lines are how sensitive we are -- another representation of the 95% limit I referred to above. As we collect more data the colored lines will slowly march down the plot until they meet the black lines. One hopes, at that point, you can declare discovery.

Though similar to the first two plots, it has some major differences which make it, I think, ideal to morph into the next It plot. First of all, it is based on real live data -- not speculation, as both the previous plots mentioned are. Second this plot will be updated continuously as a by-product of doing the analysis at the Tevatron. In short, this guy has legs! Third, this is a single-plot summary of the status of the race between the Tevatron and the future LHC. Discovery of the Higgs is going to be very difficult at the Tevatron -- there is a lot of space between the upper and lower sets of lines on that plot -- but if the Higgs has low enough mass it might just be in reach. And the goal is to find it before the LHC turns on.

What more could you want out of a summary plot? Competition, represents decades of work, reflects reality, and will be constantly updated for the next 4 years (for example).

Other candidates? ;-) The CMB is an obvious one, and I think it has ruled the roost for the past year or two...