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Variables

In the data sets provided are many variables. Their meanings are described here.

Coordinate System

LHCb uses a right-handed coordinate system with the origin at the nominal interaction point. The 'z' axis is along the beam pipe, from the interaction point towards the muon stations. 'y' is vertically upwards and 'x' is towards the centre of the LHC.

Particles

  • The final state particles are labelled by K, Pi, mu_plus, mu_minus. The K and Pi combination is labelled by Kstar and the two muons are combined into J_psi. Finally the the B candidate is labelled by B0.

Variables

  • ProbNNx - the probability that a given track is positively identified as a given hypotheses. For example mu_plus_ProbNNmu is the probability that the mu_plus is a real muon, (1 - mu_plus_ProbNNpi) would be the probability that it is not a pion.
  • PV - primary vertex, the point of the proton-proton collision
  • ENDVERTEX - position of the reconstructed decay vertex of the particle
  • ENDVERTEX_CHI2 - of the vertex fit. Essentially how well do the tracks form a vertex
  • IPCHI2 - The IP . The IP is the impact parameter - the perpendicular distance between a trajectory and the PV. The uncertainty is a combination of the vertex and the uncertainty on the particle trajectory. The IPCHI2 is the square of the IP divided by the square of the uncertainty to from a type qauntity.
  • P - momentum of the particle in units of MeV
  • PT - momentum of the particle transverse to the beam line in units of MeV
  • PX, PY, PZ, PE - components of the 4-momentum.
  • M, 'mass' - the invariant mass of a particle. If the particle is composite the mass is the product of a fit of the kinematics of the decay products.
  • FD - distance between a particles end vertex and origin vertex in units of mm
  • FDCHI2 - FD , where the uncertainty is the combination of the of the two vertices
  • ETA - the pseudorapidity of the particle
  • DIRA - the cosine of the angle between the particle's flight vector and momentum vector
  • OWNPV - quantities labelled with OWNPV mean they are calculated with respect to that particle's assigned primary vertex.