Question about interpreting PDG particle cross section data sets' metadata fields I have some question about interpreting PDG particle cross section data sets' metadata fields. The data sets I'm having questions for are http://pdg.lbl.gov/2011/hadronic-xsections/hadron.html
For example, the data set for p-bar p collision http://pdg.lbl.gov/2011/hadronic-xsections/pbarp_total.dat
The data set has meta data fields as shown at the top of the .dat file. I have questions about the following metadata fields. Apologies if the questions are silly.


*

*BEAM_MASS
Is this the energy of the beam particle w.r.t. lab coordinates?

*TARGET_MASS
Again, w.r.t. lab coordinates?

*THRESHOLD
Not exactly sure what this is, but most files has 0 for this value, what's it?

*FINAL_STATE_MULTIPLICITY
Is this multiplicity from phase space configuration? Could you given a reference or an example so I may check details of the derivation?

*PLAB(GEV/C)
Momentum of the beam particle w.r.t. lab reference coordinate?

*LAB_MIN, PLAB_MAX
Minimum and maximum of PLAB? So a data point in the plot will have an x coordinate with uncertainty? how should it be plotted then? It seems in the plot in the PDF the x-coordinate doesn't have "bars" but only the y-coordinate has it. How is the uncertainty of x taken into account?

*SY_ER+(PCT), SY_ER-(PCT):
What's this? is it visible in the plot at all?

*REFERENCE FLAG
For example, "ELIOFF 62        PR 128, 869", but what is the last number here? My guess is     .
 A: BEAM_MASS
mass of the beam particles in GeV
TARGET_MASS
mass of the target particles 
THRESHOLD
minimum energy for the reaction to occur
FINAL_STATE_MULTIPLICITY
number of particles in the final state
PLAB(GEV/C)
Momentum of the beam particle w.r.t. lab reference coordinate?
Yes
LAB_MIN, PLAB_MAX
Minimum and maximum of PLAB.
It is a bit of a problem, as one should change the standard chi2 formula, which only takes care of y errors. Typically, the fits presented neglect this.
SY_ER+(PCT), SY_ER-(PCT):
positive and negative systematic errors in %
REFERENCE FLAG
"ELIOFF 62 PR 128, 869", Author, year, journal (PR=physical Review), volume, page number
A: You may find a detailed explanation in the full PDG.
The file format looks somewhat--but not exactly--like the Evaluated Nuclear Data Format.
Just looking at the files I guess
The masses are those of the beam and target particles. In the example you give both are protons, thus a mass of 938 MeV. Note that this suggests a asymmetric treatment. One particle is the beam (moving in the lab frame) and one is the target (at rest in the lab). The proton--neutron files lets you disambiguate the convention.
Threshold will be the minimum energy at which the reaction can proceed. In you example it is simple scattering so there is no threshold. It is not immediately clear if that is a lab-frame beam energy or a CoM energy.
Final state multiplicity would normally be the number of particles in the final state. The example you choose is an inclusive cross-section (unspecified products), so I suspect that the zero means "anything".
The lab momentum values are almost certainly the weighted average and limits for the bin.
It is not instantly clear to me what the remaining numeric fields are.
The reference is a publication citation. In the case you exhibit that is Physical Review. Also present are Zeitshrift Für Physik (sp?), Physics Letters, Physical Review Letters. I'm not parsing "NC" just now.
The FLAG field is opaque to me just now.
