Changes in version 6.2:

By comparison, the move from PYTHIA 6.1 to PYTHIA 6.2 was rather less dramatic. Again update notes tell the full story. Some of the main new features, present from the beginning or added later on, which may affect backwards compatibility, are:

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A new machinery to handle user-defined external processes, according to the Les Houches Accord standard in [Boo01]. The old machinery is no longer available. Some of the alternatives for the FRAME argument in the PYINIT call have also been renamed to make way for a new 'USER' option.

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The maximum size of the decay channel table has been increased from 4000 to 8000, affecting the MDME, BRAT and KFDP arrays in the PYDAT3 common block.

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A number of internally used and passed arrays, such as WDTP, WDTE, WDTPP, WDTEP, WDTPM, WDTEM, XLAM and IDLAM, have been expanded from dimension 300 to 400.

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Lepton- and baryon-number-violating decay channels have been included for supersymmetric particles [Ska01,Sjö03]. Thus the decay tables have grown considerably longer.

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The string hadronization scheme has been improved and expanded better to handle junction topologies, where three strings meet. This is relevant for baryon-number-violating processes, and also for the handling of baryon beam remnants. Thus new routines have been introduced, and also e.g. new K(I,1) status codes.

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A runtime interface to ISASUSY has been added, for determining the SUSY mass spectrum and mixing parameters more accurately than with the internal PYTHIA routines.

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The Technicolor scenario is updated and extended. A new common block, PYTCSM, is introduced for the parameters and switches in Technicolor and related scenarios, and variables are moved to it from a few other common blocks. New processes 381-388 are introduced for standard QCD $2 \to 2$ interactions with Technicolor (or other compositeness) extensions, while the processes 11, 12, 13, 28, 53, 68, 81 and 82 now revert back to being pure QCD.

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The PYSHOW time-like showering routine has been expanded to allow showering inside systems consisting of up to 80 particles, which can be made use of in some resonance decays and in user-defined processes.

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The PYSSPA space-like showering routine has been expanded with a $\mathrm{q}\to \mathrm{q}\gamma$ branching.

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The PYSIGH routine has been split into several, in order to make it more manageable. (It had increased to a size of over 7000 lines, which gave some compilers problems.) All the phase-space and parton-density generic weights remain, whereas the process-specific matrix elements have been grouped into new routines PYSGQC, PYSGHF, PYSGWZ, PYSGHG, PYSGSU, PYSGTC and PYSGEX.

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Some exotic particles and QCD effective states have been moved from temporary flavour codes to a PDG-consistent naming, and a few new codes have been introduced.

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The maximum number of documentation lines in the beginning of the event record has been expanded from 50 to 100.

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The default parton distribution set for the proton is now CTEQ 5L.

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The default Standard Model Higgs mass has been changed to 115 GeV.