Physics variables cheat sheet

This is a cheat sheet of the most common variables that appear in the CMS datasets. It can be useful when you don’t remember what different variables mean or you don’t remember the abbreviation for a certain variable.

Note that when there are multiple particles in a dataset, the variable names often include a number that specifies the particle (e.g. eta1 and eta2).

Variable	Description
Run	The run number of the event.
Event	The event number. An event is a collision of particles occurring in the detector.
E	The total energy of the particle GeV).
px,py,pz	The components of the momentum of the particle (GeV).
pt	The transverse momentum of the particle (GeV).
eta	The pseudorapidity of the particle.
phi	The phi angle of the particle (rad).
Q	The charge of the particle.
M	The invariant mass of two particles (GeV).
Type	For a muon, either a T or G, where T stands for tracker muon and G stands for global muon.
Type	For an electron, either EB or EE: whether the electron is in the barrel or in the endcap.
dxy	The impact parameter in the transverse plane with respect to the vertex of the particle.
isoTrack	The isolation variable for the particle in the tracker.
isoEcal	The isolation variable for the particle in the ECAL.
isoHcal	The isolation variable for the particle in the HCAL.
iso	The combined isolation (isoTrack + isoEcal + isoHcal) of the particle.
chiSq	The chi-squared per degree-of-freedom of the particle.
MET	The missing transverse momentum of the event (GeV).
phiMET	The phi angle of the missing transverse momentum (rad).

Above is a picture that illustrates what ‘eta’ (η) and ‘phi’ (ɸ) mean.