This week I am in Foz do Arelho, Portugal for the ATLAS Hadronic Calibration Workshop. As you can see, it is beautiful here, but the 100 or so of us that are here aren’t here for a nice vacation (We have meetings all day every day, so it is a bit unfortunate that we see the beach all day but we can’t go sit on it). We are here to work, and prepare for the data we hope to get in a few months.
This workshop is a chance to review where we stand, and then make plans for the early phase of data taking, the next 18 months or so. Specifically, we are talking mainly about “jets” and “missing energy”, two major topics of particle detection.
“Jets” are what we call the huge number of particles that we detect after a quark or gluon is created in a collision in the center of our detector. It flies away from the center and quickly decays into other particles which all crash into our detector and create many other particles in the collisions.
“Missing energy”, what I mainly work on, is a topic that relies on the conservation of energy in a particle collision. The idea is that the energy held by two particles before a collision is equal to the energy held by particles created in that collision, and to the hundreds of particles that result from the subsequent collisions that happen as those particles travel through our detector, hit it, and in turn decay into more and more particles. Since no energy is missing before the collision, no energy ought to be missing after. If we detect all the resultant particles in our detector, and add up all their energies, we should get zero. The one major exception is if particles called neutrinos are produced, which we are not capable of detecting, so they fly away and take their energy with them. Other than that case, checking whether we actually get zero when we add up the energies of all the particles we detect is a really useful check of the performance of our detector.
What unifies the topics of “jets” and “missing energy” is that both rely on the hadronic calibration of the ATLAS detector, which is the subject of this workshop.
Hadronic calibration is the process of turning many of the signals we measure with our detector into the final measurements of the particles we use for physics studies. This process has many steps and takes a huge amount of work by many people, which is why we are here all week.
