PYTHIA 6.4 Physics and Manual

Table 1: The main versions of Jetset, with their date of appearance, published manuals,and main changes from previous versions.No. Date Publ. Main new or improved features1 Nov 78 [Sjö78] single-quark jets2 May 79 [Sjö79] heavy-flavour jets3.1 Aug 79 — 2-jets in e + e − , preliminary 3-jets3.2 Apr 80 [Sjö80] 3-jets in e + e − with full matrix elements,toponium → ggg decays3.3 Aug 80 — softer fragmentation spectrum4.1 Apr 81 — baryon production and diquark fragmentation,fourth-generation quarks, larger jet systems4.2 Nov 81 — low-p ⊥ physics4.3 Mar 82 [Sjö82] 4-jets and QFD structure in e + e − ,Jul 82 [Sjö83] event-analysis routines5.1 Apr 83 — improved string fragmentation scheme, symmetricfragmentation, full 2 nd order QCD for e + e −5.2 Nov 83 — momentum-conservation schemes for IF,initial-state photon radiation in e + e −5.3 May 84 — ‘popcorn’ model for baryon production6.1 Jan 85 — common blocks restructured, parton showers6.2 Oct 85 [Sjö86] error detection6.3 Oct 86 [Sjö87] new parton-shower scheme7.1 Feb 89 — new particle codes and common-block structure,more mesons, improved decays, vertex information,Abelian gluon model, Bose–Einstein effects7.2 Nov 89 — interface to new standard common block,photon emission in showers7.3 May 90 [Sjö92d] expanded support for non-standard particles7.4 Dec 93 [Sjö94] updated particle data and defaults• The internal mapping of particle codes has changed.• The supersymmetric process machinery of SPythia has been included and furtherimproved, with several new processes.• Many new processes of beyond-the-Standard-Model physics, in areas such as technicolorand doubly-charged Higgs bosons.• An expanded description of QCD processes in virtual-photon interactions, combinedwith a new machinery for the flux of virtual photons from leptons.• Initial-state parton showers are matched to the next-to-leading order matrix elementsfor gauge boson production.• Final-state parton showers are matched to a number of different first-order matrixelements for gluon emission, including full mass dependence.• The hadronization description of low-mass strings has been improved, with consequencesespecially for heavy-flavour production.• An alternative baryon production model has been introduced.• Colour rearrangement is included as a new option, and several alternative Bose-Einstein descriptions are added.24