Minimum bias

MSEL = 1, 2
ISUB =

91	elastic scattering
92	single diffraction ($AB \to XB$)
93	single diffraction ($AB \to AX$)
94	double diffraction
95	low-$p_{\perp}$ production

These processes are briefly discussed in section . They are mainly intended for interactions between hadrons, although one may also consider $\gamma\mathrm{p}$ and $\gamma\gamma$ interactions in the options where the incoming photon(s) is (are) assumed resolved.

Uncertainties come from a number of sources, e.g. from the parameterizations of the various cross sections and slope parameters.

In diffractive scattering, the structure of the selected hadronic system may be regulated with MSTP(101). No high-$p_{\perp}$ jet production in diffractive events is included so far; one would have to use add-on programs like POMPYT [Bru96] for that.

The subprocess 95, low-$p_{\perp}$ events, is somewhat unique in that no meaningful physical border-line to high-$p_{\perp}$ events can be defined. Even if the QCD $2 \to 2$ high-$p_{\perp}$ processes are formally switched off, some of the generated events will be classified as belonging to this group, with a $p_{\perp}$ spectrum of interactions to match the `minimum-bias' event sample. The generation of such jets is performed with the help of the auxiliary subprocess 96, see section . Only with the option MSTP(82) = 0 will subprocess 95 yield strictly low-$p_{\perp}$ events, events which will then probably not be compatible with any experimental data. A number of options exist for the detailed structure of low-$p_{\perp}$ events, see in particular MSTP(81) and MSTP(82). Further details on the model(s) for minimum-bias events are found in sections -.