PYTHIA 8 Physics and Technical Aspects P . Z. Skands (CERN-TH) LHCb Simulations Workshop, CERN, Jun 2 2010 1 Wednesday, June 2, 2010
PYTHIA 8 Ambition Current Status Cleaner code Ready and tuned for Min-Bias (+ diffraction More user-friendly improved over Pythia 6) Easy interfacing Improved shower model, but bug/problem Physics Improvements with underlying event? Team Members Contributors Marc Montull Stefan Ask Bertrand Bellenot Sparsh Navin Richard Corke Lisa Carloni MSTW , CTEQ, H1: PDFs Stephen Mrenna Tomas Kasemets DELPHI, LHCb: D/B BRs Torbjorn Sjostrand Mikhail Kirsanov + several bug reports & fixes Peter Skands Ben Lloyd 2 Wednesday, June 2, 2010
Physics (1/3) Perturbative Resonance Decays Angular correlations often included (on a process-by-process basis - no generic formalism) User implementations (semi-internal resonance) 3 Wednesday, June 2, 2010
Physics (1/3) Hard Physics SM almost all 2 → 1 almost all 2 → 2 A few 2 → 3 BSM: a bit of everything (see documentation) Perturbative Resonance Decays Angular correlations often included (on a process-by-process basis - no generic formalism) User implementations (semi-internal resonance) 3 Wednesday, June 2, 2010
Physics (1/3) Hard Physics External Input SM Les Houches Accord and LHEF (e.g., from MadGraph, almost all 2 → 1 CompHEP, AlpGen,…) almost all 2 → 2 User implementations (semi- A few 2 → 3 internal process) BSM: a bit of everything (see Inheriting from PYTHIA’s documentation) 2 → 2 base class, then modify to suit you Perturbative Resonance Decays Angular correlations often included (on a process-by-process basis - no generic formalism) User implementations (semi-internal resonance) 3 Wednesday, June 2, 2010
Physics (2/3) [T. Kasemets, arXiv:1002.4376] 4 Wednesday, June 2, 2010
Physics (2/3) Parton Distributions Internal (faster than LHAPDF) The standard CTEQ and MSTW LO sets, plus a few NLO ones New generation: MSTW LO*, LO**, CTEQ CT09MC [T. Kasemets, arXiv:1002.4376] Interface to LHAPDF Can use separate PDFs for hard scattering and UE (to ‘stay tuned’) 4 Wednesday, June 2, 2010
Physics (2/3) Parton Distributions Internal (faster than LHAPDF) The standard CTEQ and MSTW LO sets, plus a few NLO ones New generation: MSTW LO*, LO**, CTEQ CT09MC [T. Kasemets, arXiv:1002.4376] Interface to LHAPDF Can use separate PDFs for hard scattering and UE (to ‘stay tuned’) Showers Transverse-momentum ordered ISR & FSR (new: fully interleaved) Includes QCD and QED Dipole-style recoils (partly new) Improved high-p ⊥ behavior [R. Corke] 4 Wednesday, June 2, 2010
Physics (2/3) Parton Distributions Matrix-Element Matching Internal (faster than LHAPDF) Automatic first-order matching for most gluon-emission processes in The standard CTEQ and MSTW resonance decays, e.g.,: LO sets, plus a few NLO ones Z → qq → qqg, New generation: MSTW LO*, LO**, CTEQ CT09MC [T. Kasemets, arXiv:1002.4376] t → bW → bWg, Interface to LHAPDF H → bb → bbg, … Can use separate PDFs for hard scattering and UE (to ‘stay tuned’) Automatic first-order matching for internal 2 → 1 color-singlet Showers processes, e.g.: Transverse-momentum ordered pp → Z/W/Z’/W’+jet ISR & FSR (new: fully interleaved) pp → H+jet Includes QCD and QED More to come … Dipole-style recoils (partly new) Interface to AlpGen, MadGraph, … via Les Houches Accords Improved high-p ⊥ behavior [R. Corke] 4 Wednesday, June 2, 2010
Physics (3/3) 5 Wednesday, June 2, 2010
Physics (3/3) Underlying-Event and Min-Bias Multiple parton–parton interactions Multi-parton PDFs constructed from (flavor and momentum) sum rules Combined (interleaved) evolution MI + ISR + FSR downwards in p ⊥ (partly new) Optional rescattering [R. Corke] Beam remnants colour-connected to interacting systems String junctions → variable amount of baryon transport Defaults tuned to Tevatron MB Improved model of diffraction Diffractive jet production [S. Navin] 5 Wednesday, June 2, 2010
Physics (3/3) Underlying-Event and Min-Bias Hadronization Multiple parton–parton String fragmentation interactions Lund symmetric fragmentation function for (u,d,s) + Bowler Multi-parton PDFs constructed modification for heavy quarks (c,b) from (flavor and momentum) sum rules Combined (interleaved) evolution Hadron and Particle decays MI + ISR + FSR downwards in p ⊥ Usually isotropic, or: (partly new) User decays (DecayHandler) Optional rescattering [R. Corke] Link to external packages Beam remnants colour-connected EVTGEN for B decays to interacting systems TAUOLA for τ decays String junctions → variable Bose-Einstein effects amount of baryon transport Two-particle model (off by default) Defaults tuned to Tevatron MB Improved model of diffraction Diffractive jet production [S. Navin] 5 Wednesday, June 2, 2010
Physics (3/3) Underlying-Event and Min-Bias Hadronization Multiple parton–parton String fragmentation interactions Lund symmetric fragmentation function for (u,d,s) + Bowler Multi-parton PDFs constructed modification for heavy quarks (c,b) from (flavor and momentum) sum rules Combined (interleaved) evolution Hadron and Particle decays MI + ISR + FSR downwards in p ⊥ Usually isotropic, or: (partly new) User decays (DecayHandler) Optional rescattering [R. Corke] Link to external packages Beam remnants colour-connected EVTGEN for B decays to interacting systems TAUOLA for τ decays String junctions → variable Bose-Einstein effects amount of baryon transport Two-particle model (off by default) Defaults tuned to Tevatron MB Output Improved model of diffraction Interface to HEPMC included Diffractive jet production [S. Navin] 5 Wednesday, June 2, 2010
Key differences between PYTHIA 8 and PYTHIA 6 6 Wednesday, June 2, 2010
Key differences between PYTHIA 8 and PYTHIA 6 New features, not found in 6.4 Up-to-date decay data and PDFs Underlying Event Interleaved MI + ISR + FSR Richer mix of underlying-event processes ( γ , J/ ψ , DY , . . . ) Possibility for two selected hard interactions in same event Alow parton rescattering Possibility to use one PDF set for hard process and another for rest Hard scattering in diffractive systems New SM and BSM processes 6 Wednesday, June 2, 2010
Key differences between PYTHIA 8 and PYTHIA 6 New features, not found in 6.4 Up-to-date decay data and PDFs Underlying Event Interleaved MI + ISR + FSR Richer mix of underlying-event processes ( γ , J/ ψ , DY , . . . ) Possibility for two selected hard interactions in same event Alow parton rescattering Possibility to use one PDF set for hard process and another for rest Hard scattering in diffractive systems SUSY with NMFV and/or CPV (not fully validated) New SM and BSM processes Large Extra Dimensions, Unparticles Hidden Valley scenario with hidden radiation 6 Wednesday, June 2, 2010
Key differences between PYTHIA 8 and PYTHIA 6 New features, not found in 6.4 Old features definitely removed Up-to-date decay data and PDFs Independent fragmentation Underlying Event Mass-ordered showers Interleaved MI + ISR + FSR Richer mix of underlying-event processes ( γ , J/ ψ , DY , . . . ) Possibility for two selected hard interactions in same event Alow parton rescattering Possibility to use one PDF set for hard process and another for rest Hard scattering in diffractive systems SUSY with NMFV and/or CPV (not fully validated) New SM and BSM processes Large Extra Dimensions, Unparticles Hidden Valley scenario with hidden radiation 6 Wednesday, June 2, 2010
Key differences between PYTHIA 8 and PYTHIA 6 New features, not found in 6.4 Old features definitely removed Up-to-date decay data and PDFs Independent fragmentation Underlying Event Mass-ordered showers Interleaved MI + ISR + FSR Richer mix of underlying-event processes ( γ , J/ ψ , DY , . . . ) Features omitted so far Possibility for two selected hard ep, γ p and γγ beams interactions in same event Alow parton rescattering Some matrix elements, in particular Technicolor, partly Possibility to use one PDF set for SUSY hard process and another for rest Hard scattering in diffractive systems SUSY with NMFV and/or CPV (not fully validated) New SM and BSM processes Large Extra Dimensions, Unparticles Hidden Valley scenario with hidden radiation 6 Wednesday, June 2, 2010
Key differences between PYTHIA 8 and PYTHIA 6 New features, not found in 6.4 Old features definitely removed Up-to-date decay data and PDFs Independent fragmentation Underlying Event Mass-ordered showers Interleaved MI + ISR + FSR Richer mix of underlying-event processes ( γ , J/ ψ , DY , . . . ) Features omitted so far Possibility for two selected hard ep, γ p and γγ beams interactions in same event Alow parton rescattering Some matrix elements, in particular Technicolor, partly Possibility to use one PDF set for SUSY hard process and another for rest Hard scattering in diffractive systems SUSY with NMFV and/or CPV (not fully validated) New SM and BSM processes Large Extra Dimensions, Unparticles Hidden Valley scenario with hidden radiation 6 Wednesday, June 2, 2010
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