Revisiting the Lund Fragmentation Model

We present a new method to implement the Lund Model fragmentation distributions for multi-gluon situations. The method of Sjoestrand, implemented in the well-known Monte Carlo simulation program JETSET, is robust and direct and according to his findings there are no observable differences between different ways to implement his scheme. His method can be described as a space-time method because the breakup proper time plays a major role. The method described in this paper is built on energy-momentum space methods. We make use of the χ-curve, which is defined directly from the energy momentum vectors of the partons. We have shown that the χ-curve describes the breakup properties and the final state energy momentum distributions in the mean. We present a method to find the variations around the χ-curve, which also implements the basic Lund Model fragmentation distributions (the area-law and the corresponding iterative cascade). We find differences when comparing the corresponding Monte Carlo implementation REVJET to the JETSET distributions inside the gluon jets. (au)