18.16} Hadron event generators

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 The two Leipzig event generators developed in the 80's, one for intermediate
 energies and the other for high energies (> 5 GeV), were a remarkable
 achievement with great potentialities. In particular the high energy
 model was among the first developed in the world based on partonic
 ideas and quark degrees of freedom (specifically on the so called
 Dual Parton Model [Cap80,Cap80a]).

 The part of the code concerning hadron-nucleus primary interactions at
 energies above 4 GeV has been extensively extended and updated since
 1987 and is now virtually a new model, even though the physics
 foundations are still essentially the same. Several bugs and
 approximations have been removed too. The intermediate energy resonance
 model has also been deeply modified and its use is currently restricted
 to few particles over a restricted energy range. The newly developed
 pre-equilibrium-cascade model PEANUT has progressively replaced this model.

 The main lines of the work developed mostly in Milan by Ferrari and
 Sala starting from 1990 can be summarised as follow [Fer96b,Col00]:

 * Further develop and improve the high energy DPM based part of the models.
   These was performed in 4 main stages, which eventually led to an
   almost completely new code still based on the same physics foundations
   with some extensions

 * Introduce a self-consistent nuclear environment in both the medium and
   high energy models, allowing for a physically meaningful excitation
   energy and excited residual A and Z calculations

 * Develop a state-of-the-art evaporation/fission/break up/deexcitation
   stage to be used to describe the "slow" part of nuclear interactions.
   These actually took place in two major steps

 * Develop a completely new model (PEANUT) based on a novel approach for
   describing the low-to-intermediate (up to a few GeV) energy range, while
   progressively phasing out the improved version of the intermediate energy
   Leipzig code. This effort took also place in two main steps.

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