In all the developments described in this paragraph and also of some in other paragraphs, J. Ranft always acted as the main mentor and source of theoretical and often practical support. Even when he did not contributed to the code directly, his ideas, help and suggestions were essential part of its development. The two models developed by the Leipzig group were initially improved by removing a number of known bugs and approximations (mainly, but not only, in the kinematics). In the years 1990-1991 all hyperons and anti-hyperons were added as possible projectiles, and most important, nuclear effects, previously restricted to Fermi momentum, were expanded and treated more accurately, with an explicit treatment of the nuclear well potential, the inclusion of detailed tables of nuclear masses to account for nuclear binding energy, a consistent exact determination of nuclear excitation energy and an overall "exact" conservation of energy and momentum on an event-by-event basis. These changes were the minimal modifications required for introducing a sensible evaporation module and related low energy particle production: they made up the first stage of upgrade of the intermediate and high energy event generator and were performed by Ferrari and Sala. In the following years, negative Binomial multiplicity distribution, correlations between primary interactions and cascade particles and better energy-angle distributions were implemented. Sea quark distributions were updated, new distributions were used for the number of primary collisions using an improved Glauber cascade approach, and Reggeon mediated interactions (single chains) were introduced at the lower energy end of the application range of the Dual Parton Model. An initial improvement of the diffraction treatment as well of the hadronisation algorithm were performed. These developments ended up in the 1993 version, which represented the second stage of the high energy generator development (and which was made available to GEANT3 users, see later). Several major changes were performed on both the intermediate and high energy hadron generator in the years 1994-1996 by Ferrari and Sala. The latter was extensively improved, bringing its results into much better agreement with available experimental data from as low as 4 GeV up to several hundreds of GeV. A fully new treatment of transverse momentum and of all DPM in general was developed, including a substantially improved version of the hadronisation code and a new driver model for managing two-chain events. The existing treatment of high-energy photonuclear reactions, previously already based on the VMD model [Bau78] but in an approximate way, was improved by implementing the contribution of all different vector mesons, as well as the quasielastic contribution. The simulation of diffractive events was completely reworked distinguishing between resonant, single-chain and two-chain events, and a smeared mass distributions for resonance was introduced. This version of the model was completed in 1996 and performed very well together with the new "sophisticated" PEANUT when applied to a variety of problems, ranging from radiation protection, to cosmic ray showers in the atmosphere and to the test beam of the ATLAS calorimeters. The latest round of improvements originated by the new interest of Ferrari and Sala for neutrino physics, triggered by their participation in the ICARUS experiment and resulted in several improvements in the high-energy interaction model. In 1998, a new chain fragmentation/hadronisation scheme was put to use, and a new diffraction model was worked out once more according to rigorous scaling, including low mass diffraction and antibaryon diffraction. In 1999, charm production was set up by Ranft and Ferrari (reasonable at least for integrated rates), and charmed particle transport and decay were introduced. The chain building algorithm was thoroughly revised to ensure a continuous transition to low energies, and a significant reworking was done on the chain hadronisation process, providing a smooth and physically sound passage to chains made up by only two particles, resulting in an overall better description of particles emitted in the fragmentation region. This model was thoroughly benchmarked against data taken at WANF by NOMAD and the particle production data measured by SPY. It constituted the basis for all calculations performed for CNGS, both in the early physics design stage and later in the optimisation and engineering studies.
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