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Changes in version 6.3:

The major changes in 6.3 was the introduction of a new underlying-event framework for hadron collisions, together with new transverse-momentum-ordered initial- and final-state parton showers. Other changes include an interface to SUSY spectrum and decay calculators conformant to the SUSY Les Houches Accord. Early releases of PYTHIA 6.3, up to 6.312, were still experimental, and did not include the new parton showers. Details on these versions can be found in the update notes available on the web. We here concentrate on the structure of the program after (and including) version 6.312.

Firstly, there are no incompatibilities between PYTHIA 6.2 and PYTHIA 6.3 at the level of commonblock sizes or subroutine arguments (except for the PYSUGI interface to ISAJET, see below). That is, any program that ran with PYTHIA 6.2 also ought to run with PYTHIA 6.3, without any change required. Note, however, the following news:

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The old (6.2) master event-generation routine PYEVNT is still available; it uses the old underlying-event machinery (PYMULT) and parton showers (PYSSPA and PYSHOW). A `Tune A'-like set of parameters [Fie02] has been adopted as default. It reproduces Tune A at the Tevatron, but implies a slower energy rescaling, to give a more conservative estimate of the underlying activity at the LHC.
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A new master event-generation routine PYEVNW has been introduced, in parallel with PYEVNT. By calling PYEVNW instead of PYEVNT a completely new scenario for multiple interactions [Sjö04] and parton showers [Sjö04a] is obtained. This framework has still only been fully developed for hadron-hadron collisions (where a resolved photon counts as a hadron). Note that many of the default parameters now in PYTHIA are directly related to the PYEVNT model. These defaults are not appropriate to use with the new framework, and so all parameters should be set explicitly whenever PYEVNW is used. See e.g. examples available on the web.
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The current PYSUGI run-time interface to the ISASUSY evolution package is based on ISAJET version 7.71 (from PYTHIA 6.319 onwards). The dimensions of the SSPAR, SUGMG, SUGPAS and SUGXIN common blocks found in the PYSUGI routine could have to be modified if another ISAJET version is linked.
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The new routine PYSLHA introduces a generic interface to SUSY spectrum and decay calculators in agreement with the SUSY Les Houches Accord [Ska03] (SLHA), and thus offers a long-term solution to the incompatibility problems noted above. Without SUSY switched on, PYSLHA can still be used stand-alone to read in SLHA decay tables for any particle, see section [*].
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From version 6.321 a run-time interface to FeynHiggs [Hei99] is available, to correct the Higgs sector of SUSY spectra obtained with either of the PYSUGI and PYSLHA interfaces.
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From version 6.321 a new set of toy models for investigating final state colour reconnection effects are available, see [San05].
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From version 6.322 an option exists to extend the particle content recognized by PYTHIA to that of the NMSSM, for use in the context of interfaces to other programs, see [Puk05].
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Some new processes added, notably $\mathrm{J}/\psi $ and $\Upsilon$ production in an NRQCD colour-octet-model framework.
The update notes tell exactly with what version a new feature or a bug fix is introduced.


next up previous contents
Next: Changes in version 6.4: Up: Update History Previous: Changes in version 6.2:   Contents
Stephen Mrenna 2007-10-30