A set of parameters with which the string fragmentation can be modified.

String_Tension (double, optional, default = 1.0 GeV/fm)
String tension \(\kappa\) connecting massless quarks in Hamiltonian:

\[H=|p_1|+|p_2|+\kappa |x_1-x_2|\]

This parameter is only used to determine particles' formation times according to the yo-yo formalism (in the soft string routine for now).

Gluon_Beta (double, optional, default = 0.5)
Parameter \(\beta\) in parton distribution function for gluons:

\[\mathrm{PDF}_g(x) \propto \frac{1}{x}(1-x)^{\beta+1}\]

Gluon_Pmin (double, optional, default = 0.001 GeV)
Smallest possible scale for gluon lightcone momentum. This is divided by sqrts to get the minimum fraction to be sampled from PDF shown above.

Quark_Alpha (double, optional, default = 2.0)
Parameter \(\alpha\) in parton distribution function for quarks:

\[\mathrm{PDF}_q\propto x^{\alpha-1}(1-x)^{\beta-1}\]

Quark_Beta (double, optional, default = 5.0)
Parameter \(\beta\) in PDF for quarks shown above.

Strange_Supp (double, optional, default = 0.12)
Strangeness suppression factor \(\lambda\):

\[\lambda=\frac{P(s\bar{s})}{P(u\bar{u})}=\frac{P(s\bar{s})}{P(d\bar{d})}\]

Defines the probability to produce a \(s\bar{s}\) pair relative to produce a light \(q\bar{q}\) pair

Diquark_Supp (double, optional, default = 0.03)
Diquark suppression factor. Defines the probability to produce a diquark antidiquark pair relative to producing a qurk antiquark pair.

Sigma_Perp (double, optional, default = 0.42)
Parameter \(\sigma_\perp\) in distribution for transverse momentum transfer between colliding hadrons \(p_\perp\) and string mass \(M_X\):

\[\frac{d^3N}{dM^2_Xd^2\mathbf{p_\perp}}\propto \frac{1}{M_X^2} \exp\left(-\frac{p_\perp^2}{\sigma_\perp^2}\right)\]

StringZ_A (double, optional, default = 0.68 as in Pythia)
Parameter a in pythia fragmentation function \(f(z)\):

\[f(z) = \frac{1}{z} (1-z)^a \exp\left(-b\frac{m_T^2}{z}\right)\]

StringZ_B (double, optional, default = 0.5)
Parameter \(b\) in pythia fragmentation function shown above.

Leading_Frag_Mean (double, optional, default = 1.0)
Mean of Gaussian used as fragmentation function for leading hadrons.

Leading_Frag_Width (double, optional, default = 0.6)
Width of Gaussian used as fragmentation function for leading hadrons.

String_Sigma_T (double, optional, default = 0.5) Standard deviation in Gaussian for transverse momentum distributed to string fragments during fragmentation.

Form_Time_Factor (double, optional, default = 1.0)
Factor to be multiplied with the formation time of string fragments from the soft string routine. Power_Particle_Formation (double, optional, default = -1.0)
If positive, the power with which the cross section scaling factor of string fragments grows in time until it reaches 1. If negative, the scaling factor will be constant and jump to 1 once the particle forms.

Use_Yoyo_Model (bool, optional, default = true) Calculate the string fragments' formation times from the yoyo-model if enabled. Else constant proper time defined by Formation_Time is used.

Prob_proton_to_d_uu (double, optional, default = 1/3) Probability of splitting an (anti)nucleon into the quark it has only once and the diquark it contains twice in terms of flavour in the soft string routine.