Triggering on green frogs

You think physicists like to talk with formulas and complicated lingo ? Think better. You should have followed today’s meeting on high-level triggers for CMS, at the underground conference room of building 40.

The speaker was discussing triggering strategies for collecting multijet events. Basically that has to do with the thing we call the “Trigger” (ok, yes, some lingo here): a complicated set of filters that select the 100 or so proton-proton collisions worthy of being recorded to tape among the 40 millions happening in the core of the detector every second. The decision is based on the characteristics of the event as they can be inferred through a extremely fast reconstruction. Our data acquisition system cannot record more than about 100 events per second, and sadly, the rest has to go.

Because of its potential of throwing away whole categories of interesting events for the benefit of others, the trigger is a very sensitive issue, determining what physics one will be able to do and what will not be done because of the lack of a specific filter selecting the relevant data. In 15 years of particle physics, I have never seen people fighting, calling each other names, discussing philosophy, or just acting funny as in trigger meetings. An example ? Melissa Franklin’s famous “F*** everybody” wish before walking out the door, at a CDF meeting in 1992 when her favorite dataset was being penalized by raised calorimeter thresholds.

Ok, back to CERN. During today’s talk, a question from the audience sparked a lively discussion on the design details of the triggers collecting jet events. You would think you stand no chance of following the discussion, right ? Well, you could have, since at one point people stopped using technical language and started talking funny. Here is a rough account of the discussion:

“… So, to make it clear: if you filter the event at level 1 because you see two jets and a green frog, you better be sure that at level two you require the presence of the same green frog, at the very least.”

“Yes, but I am still free to require two green frogs at level two, can’t I ?”

“Sure, two green frogs are fine. But beware, at level two you will not be allowed to require two yellow frogs.”

“Ok, but what about more than two jets and a yellow frog then?…”

The discussion went on for quite a while until people from the audience (including yours truly) started suggesting scenarios with lizards and other creatures. These kinds of exchanges are not uncommon during the long meetings of the “Physics Days” of CMS… I should come here more often!