SRC-CT ReactionFilter

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The ReactionFilter is a reconstruction plugin used by Hall D analyses to examine specified final states in a flexible manner that incorporates kinematic fitting of the given constraints. Using the ReactionFilter for nuclear-target experiments can require some care due because most reactions are non-exclusive; that is, some energy and momentum is often carried by one or more undetected particle.

Important Plugin Flags

Reaction1, Reaction2...

This flag allows the user to specify the reaction being fit by the reconstruction. An example of the format is

1_45__8_9_14_m13

The number before the double underscore specify the particles in the initial state, those being the beam photon and the target, in this case a deuteron. The numbers following the double underscore are the particles in the final state, here specified to be a π+, a π-, a proton, and a neutron. The 'm' before the 13 specifies that the neutron in the final state is undetected, but that its mass (the mass of the missing 4-momentum) may be used as an additional constraint in the kinematic fit.

Example Reactions:

1_45__9_14_14

This reaction consists of γ + d → π- + p + p, with all the particles in the final state being specified.

1_45__7_9_14_14

This reaction consists of γ + d → π0 + π- + p + p, with all the particles in the final state being specified. In this case the π0 decays and the decay products (usually γγ) are what are directly detected. The mass of the π0 provides an additional constrain in this case, and the decay products of the intermediate particle may be specified using another flag.

1_67__11_12_14_m0

This reaction consists of γ + 12C → K+ + K- + p + X. In this case only the protons and the kaons are detected, with the rest of the nuclear system being unmeasured; the 'm0' indicates that there is missing energy and momentum consisting of unknown particles.

Useful PID values:

The following PID numbers are particularly useful for ongoing analyses:

  • 0 - Unknown
  • 1 - Photon
  • 7 - Pi0
  • 8 - PiPlus
  • 9 - PiMinus
  • 11 - KPlus
  • 12 - KMinus
  • 13 - Neutron
  • 14 - Proton
  • 45 - Deuteron
  • 47 - Helium-4
  • 67 - Carbon-12

A full list of the PID numbers can be found here.