It is time to come back to my work on calorimetry, following my previous post, before I get distracted again by other things. This time I’m blogging on the couch, not on a plane, though.
So, where did I leave off last time? One of the key goals for ILC calorimeters is to achieve unprecedented jet energy resolution. The calorimeters developed by the CALICE collaboration rely in Particle Flow Algorithms (PFA) to achieve this goal, as discussed in my last post. What is needed to make PFA work? First and foremost: Extremely granular detectors, with high 3D resolution to provide a detailed image of the particle showers.
This is needed to provide what is most important for PFA: The separation of individual particles in a shower. The PFA principle is simple: Measure each particle in the jet (actually, each particle in the event) as good as you can. This will then give you the best possible jet energy resolution. Depending on the particle type, this measurement comes from different detectors. Charged particles are best measured in the tracking detectors, photons (mostly from the decay of neutral pions) in the electromagnetic calorimeter, and neutral hadrons in the hadron calorimeter. Now, the problem is that charged hadrons also give a signal in the calorimeters, and to make PFA work, the deposits of each of these particles has to be separated. This is only possible with very granular detectors, as illustrated in the figure on the right.
That is why, in CALICE, we are studying the best technique to build highly granular calorimeters optimized for this new idea. I am currently focusing on an idea for the hadronic calorimeter, based on small scintillator cells read out with tiny, novel photo detectors.
But that again is the topic for another post. For now, I have to get ready for a workshop on pixel detectors, a completely different part of modern particle physics detectors.