E-Lab Calibration Studies
From QNFellows
Calibration studies explore the "rediscovery" of known physical quantities to verify the proper operation of the CMS detector. This is the rough equivalent of verifying that a scale is working properly by weighing an object whose mass is independently well known. The rest masses of the Z boson (and other particles) is the well-known object in this CMS e-Lab calibration exercise. Its rest mass, approximately 91 GeV, is determined through measurement of the combined kinetic energies of the particles (a muon-antimuon pair) into which it decays.
Conservation of energy is the principle justifying this derivation of the mass of the parent (the Z boson) from the total energy of its dimuon offspring. Conservation of charge is verified by also exploring the possibility of like-signed children (mu+mu+, or mu-mu-); none of these are found in energy (referred to in this study, following the convention of particle physicists, as "mass") measurements of these like-charged combinations of leptons. In the advanced mode, conservation of lepton number can also be verified by looking at oppositely charged combinations of different leptons (e+mu-, for example).
As long as the e-Lab still uses simulated data, these studies require deliberate creation of file types with particles and any background simulated intentionally, one particle type at a time; the results are thus a bit messy. But the steps a student would take in the e-Lab are the same as they will be with run data and the conclusions they can reach are similar: that the (simulated) detector is functioning properly, since it verifies well-known physics results. Once run data is available in the e-Lab, the whole process will become cleaner: all particles and background will be delivered by nature, and the same data set will contain multiple points of verification. Events passing the dimuon filter, for example, will contain Upsilon, J-Psi, and Z signatures, as well as a range of background that passes the filter's requirements. That same data set can be used to see reflections of conservation of energy, charge, and lepton number, as well as energy-momentum rough equivalence (given the relatively small rest masses of muons, compared to the high energies involved in LHC collisions.) See the screen grab below, and interpret the "coming soon" as "when run data becomes available during academic year 2010-2011."
