String transition

Within Collision_Term section, the String_Transition section can be used to modify a series of parameters which interpolate linearly the cross section transition between resonances and strings. This also controls the shape of the total cross section around the intermediate energies. If this section is omitted, default values are used.

For example, this creates a relaxed transition starting immediately at the mass threshold:

Collision_Term:
    String_Transition:
        Sqrts_Range_NN: [1.9,4.5]
        Sqrts_Range_Npi: [1.1,2.5]
        Sqrts_Lower: 0
        Sqrts_Range_Width: 1.5

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KN_Offset — double, optional, default = 15.15 — Conditions on key value: None

Offset in GeV to turn on the strings for KN reactions.

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PiPi_Offset — double, optional, default = 1.12 — Conditions on key value: None

Offset in GeV to turn on the strings and elastic processes for \(\pi\pi\) reactions (this is an exception because the normal AQM behavior destroys the cross section at very low \(\sqrt{s}\) and around the \(f_2\) peak)

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Sqrts_Lower — double, optional, default = 0.9 — Conditions on key value: None

Lower end of transition region in GeV for the remaining interactions, in case of AQM this is added to the sum of masses.

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Sqrts_Range_NN — list of two doubles, optional, default = [3.5,4.5] — Conditions on key value:  \(x_1 \geq 1.876 \land x_1 < x_2\)

Transition range in NN collisions in GeV. The lowest value for the first parameter is the mass threshold 1.876. The default is tuned to reproduce experimental exclusive cross section data, and at the same time produce excitation functions that are as smooth as possible. The default of a 1 GeV range is preserved.

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Sqrts_Range_Npi — list of two doubles, optional, default = [1.9,2.2] — Conditions on key value:  \(x_1 \geq 1.076 \land x_1 < x_2\)

Transition region in N \(\pi\) scatterings in GeV. The lowest value for the first parameter is the mass threshold 1.076.

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Sqrts_Range_Width — double, optional, default = 1.0 — Conditions on key value: None

Width of the transition region in GeV for the remaining interactions, in case of AQM this is added to Sqrts_Lower.