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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 .

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2 Answers 2

up vote 1 down vote accepted

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

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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.

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Thanks for the answer. About PLAB and PLAB_MIN and PLAB_MAX, using http://pdg.lbl.gov/2011/hadronic-xsections/hadronicrpp_page12.pdf as example, do you think the x-coordinate is just PLAB and the other two values aren't used in the plot? I'm still trying to figure out how/where to use PLAB_MIN and PLAB_MAX. –  Computist Oct 5 '11 at 21:11
    
Notice that the data have horizontal error bars as well as vertical? That's because each line in the file represents a measurement over a range of incident momenta. The limits are the MAX and MIN values and the PLAB value is an appropriately weighted average. If you look closely you'll see repeated central values with different limits and some chains of bins from the same paper that were clearly meant to span some region on interest. This is an accumulation of historical data. –  dmckee Oct 6 '11 at 1:53
    
OK, some points are drawn like a little cross where the x have min and max indicated by the ends of horizontal line section. There are also lots of points are drawn like a box plot in statistics -- for example in http://pdg.lbl.gov/2011/hadronic-xsections/hadronicrpp_page12.pdf. Are those not using/having the uncertainties with x-coordinate? –  Computist Oct 7 '11 at 23:08
    
Also, I tried to find the definitions to SY_ER+(PCT) and SY_ER-(PCT) in the full RPP but couldn't find. –  Computist Oct 7 '11 at 23:09
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