PYTHIA 6.4 Physics and Manual

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8.6.3 Left–Right Symmetry and Doubly Charged Higgs Bosons . . . . . . 1558.6.4 Leptoquarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1568.6.5 Compositeness and anomalous couplings . . . . . . . . . . . . . . . 1578.6.6 Excited fermions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1588.6.7 Technicolor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1598.6.8 Extra Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1648.7 Supersymmetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1658.7.1 General Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 1658.7.2 Extended Higgs Sector . . . . . . . . . . . . . . . . . . . . . . . . . 1668.7.3 Superpartners of Gauge and Higgs Bosons . . . . . . . . . . . . . . 1688.7.4 Superpartners of Standard Model Fermions . . . . . . . . . . . . . . 1698.7.5 Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1718.7.6 SUSY examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1748.7.7 R-Parity Violation . . . . . . . . . . . . . . . . . . . . . . . . . . . 1758.7.8 NMSSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1778.7.9 Long-lived coloured sparticles . . . . . . . . . . . . . . . . . . . . . 1778.8 Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1788.9 Main Processes by Machine . . . . . . . . . . . . . . . . . . . . . . . . . . 1788.9.1 e + e − collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1788.9.2 Lepton–hadron collisions . . . . . . . . . . . . . . . . . . . . . . . . 1798.9.3 Hadron–hadron collisions . . . . . . . . . . . . . . . . . . . . . . . . 1809 The Process Generation Program Elements 1819.1 The Main Subroutines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1819.2 Switches for Event Type and Kinematics Selection . . . . . . . . . . . . . . 1859.3 The General Switches and Parameters . . . . . . . . . . . . . . . . . . . . 1939.4 Further Couplings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2179.5 Supersymmetry Common-Blocks and Routines . . . . . . . . . . . . . . . . 2239.6 General Event Information . . . . . . . . . . . . . . . . . . . . . . . . . . . 2299.7 How to Generate Weighted Events . . . . . . . . . . . . . . . . . . . . . . 2349.8 How to Run with Varying Energies . . . . . . . . . . . . . . . . . . . . . . 2409.9 How to Include External Processes . . . . . . . . . . . . . . . . . . . . . . 2429.9.1 Run information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2449.9.2 Event information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2509.9.3 An example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2569.9.4 PYTHIA as a generator of external processes . . . . . . . . . . . . 2609.9.5 Further comments . . . . . . . . . . . . . . . . . . . . . . . . . . . 2609.10 Interfaces to Other Generators . . . . . . . . . . . . . . . . . . . . . . . . . 2649.11 Other Routines and Common Blocks . . . . . . . . . . . . . . . . . . . . . 26810 Initial- and Final-State Radiation 28610.1 Shower Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28610.1.1 The evolution equations . . . . . . . . . . . . . . . . . . . . . . . . 28710.1.2 The Sudakov form factor . . . . . . . . . . . . . . . . . . . . . . . . 28810.1.3 Matching to the hard scattering . . . . . . . . . . . . . . . . . . . . 28910.2 Final-State Showers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29010.2.1 The choice of evolution variable . . . . . . . . . . . . . . . . . . . . 29110.2.2 The choice of energy splitting variable . . . . . . . . . . . . . . . . 29110.2.3 First branchings and matrix-element matching . . . . . . . . . . . . 29210.2.4 Subsequent branches and angular ordering . . . . . . . . . . . . . . 29410.2.5 Other final-state shower aspects . . . . . . . . . . . . . . . . . . . . 29610.2.6 Merging with massive matrix elements . . . . . . . . . . . . . . . . 29710.2.7 Matching to four-parton events . . . . . . . . . . . . . . . . . . . . 299
10.2.8 A new p ⊥ -ordered final-state shower . . . . . . . . . . . . . . . . . . 30010.3 Initial-State Showers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30210.3.1 The shower structure . . . . . . . . . . . . . . . . . . . . . . . . . . 30210.3.2 Longitudinal evolution . . . . . . . . . . . . . . . . . . . . . . . . . 30410.3.3 Transverse evolution . . . . . . . . . . . . . . . . . . . . . . . . . . 30610.3.4 Other initial-state shower aspects . . . . . . . . . . . . . . . . . . . 30810.3.5 Matrix-element matching . . . . . . . . . . . . . . . . . . . . . . . . 31010.3.6 A new p ⊥ -ordered initial-state shower . . . . . . . . . . . . . . . . . 31110.4 Routines and Common-Block Variables . . . . . . . . . . . . . . . . . . . . 31311 Beam Remnants and Underlying Events 32511.1 Beam Remnants — Old Model . . . . . . . . . . . . . . . . . . . . . . . . . 32611.1.1 Hadron Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32611.1.2 Photon Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32711.1.3 Lepton Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32711.1.4 Primordial k ⊥ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32811.1.5 Remnant Kinematics . . . . . . . . . . . . . . . . . . . . . . . . . . 32811.2 Multiple Interactions — Old Model . . . . . . . . . . . . . . . . . . . . . . 32911.2.1 The basic cross sections . . . . . . . . . . . . . . . . . . . . . . . . 33011.2.2 The simple model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33211.2.3 A model with varying impact parameters . . . . . . . . . . . . . . . 33411.3 Beam Remnants (and Multiple Interactions) — Intermediate Model . . . . 33711.3.1 Flavour and x Correlations . . . . . . . . . . . . . . . . . . . . . . . 33811.3.2 Colour Topologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33911.3.3 Primordial k ⊥ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34111.3.4 Beam-Remnant Kinematics . . . . . . . . . . . . . . . . . . . . . . 34211.4 Multiple Interactions (and Beam Remnants) – New Model . . . . . . . . . 34211.4.1 Joined Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . 34511.5 Pile-up Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34511.6 Common-Block Variables and Routines . . . . . . . . . . . . . . . . . . . . 34612 Fragmentation 35912.1 Flavour Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35912.1.1 Quark flavours and transverse momenta . . . . . . . . . . . . . . . 35912.1.2 Meson production . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36012.1.3 Baryon production . . . . . . . . . . . . . . . . . . . . . . . . . . . 36112.2 String Fragmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36512.2.1 Fragmentation functions . . . . . . . . . . . . . . . . . . . . . . . . 36512.2.2 Joining the jets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36712.2.3 String motion and infrared stability . . . . . . . . . . . . . . . . . . 36912.2.4 Fragmentation of multiparton systems . . . . . . . . . . . . . . . . 37012.2.5 Junction topologies . . . . . . . . . . . . . . . . . . . . . . . . . . . 37312.3 Independent Fragmentation . . . . . . . . . . . . . . . . . . . . . . . . . . 37412.3.1 Fragmentation of a single jet . . . . . . . . . . . . . . . . . . . . . . 37412.3.2 Fragmentation of a jet system . . . . . . . . . . . . . . . . . . . . . 37512.4 Other Fragmentation Aspects . . . . . . . . . . . . . . . . . . . . . . . . . 37612.4.1 Small-mass systems . . . . . . . . . . . . . . . . . . . . . . . . . . . 37612.4.2 Interconnection Effects . . . . . . . . . . . . . . . . . . . . . . . . . 37812.4.3 Bose–Einstein effects . . . . . . . . . . . . . . . . . . . . . . . . . . 380
Page 1 and 2: hep-ph/0603175LU TP 06-13FERMILAB-P
Page 4 and 5: Contents1 Introduction 11.1 The Com
Page 8 and 9: 13 Particles and Their Decays 38413
Page 10 and 11: another sense, the overall energy f
Page 13 and 14: p ⊥ -ordered parton showers and a
Page 15 and 16: you expect to happen if you do not
Page 17 and 18: The history of the Pythia program i
Page 19 and 20: andom, according to the relative co
Page 21 and 22: Of course, the above ‘resonance
Page 23 and 24: 2.2.1 Matrix elementsMatrix element
Page 25 and 26: analysis strongly suggests the scal
Page 27 and 28: y calling PYEVNW instead of PYEVNT,
Page 29 and 30: charge Casimir operators, N C /C F
Page 31 and 32: 3 Program OverviewThis section cont
Page 33 and 34: Table 2: The main versions of Pythi
Page 35 and 36: • A new master event-generation r
Page 37 and 38: A test program, PYTEST, is included
Page 39 and 40: argument is used with a value that
Page 41 and 42: &XMI(2,240),Q2MI(240),IMISEP(0:240)
Page 43 and 44: original u and u. The parentheses e
Page 45 and 46: C...End of particle and event loops
Page 47 and 48: PMAS(25,1)=300D0CKIN(1)=290D0CKIN(2
Page 49 and 50: third the particle-flavour code (wh
Page 51 and 52: 4 Monte Carlo TechniquesQuantum mec
Page 53 and 54: different g i ’s, it is possible
Page 55 and 56: The last equality is most easily se
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Purpose: to generate a (pseudo)rand
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5 The Event RecordThe event record
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Table 4: Gauge boson and other fund
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Table 7: Meson codes, part 1.KF Nam
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Table 10: QCD effective states.KF P
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is then required. Normally this mea
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quarks. Note that the positions nee
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original entries appear with pointe
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consistent summary, but then in div
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= 3 : a documentation line, defined
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6 The Old Electron-Positron Annihil
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6.1.2 First-order QCD matrix elemen
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6.1.4 Second-order three-jet matrix
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evaluated and compared with a param
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The angular orientation of a 3- or
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these offer unique possibilities to
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6.3.3 Common-block variablesThe sta
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3-jet cross section, so large that
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fraction of events containing a rad
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! PYSPHE to work on it (unusual)CAL
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Pdflib has been frozen in recent ye
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modelling of γp and γγ events, s
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One can obtain the positron distrib
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7.2 Kinematics and Cross Section fo
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7.3 Resonance ProductionThe simples
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y a factor 1/N C = 1/3. Secondly, t
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This choice certainly is not unique
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The phase-space points tested at in
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spin-1 resonance the expression is,
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probabilities.In some processes, su
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where decay channels are chosen acc
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and for a resonance-antiresonance p
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The Regge formulae above for single
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emnant, but this remnant has a larg
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called direct, our direct×VMD and
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are also covered in other places in
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Table 17: Subprocess codes, part 2.
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Table 25: Subprocess codes, part 10
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8.2 QCD ProcessesObviously most pro
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1. if MSEL = 4 - 8 then the flavour
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into the cross section. However, cu
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Uncertainties come from a number of
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If you are only concerned with stan
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for MSTP(14) = 1 and the VMD part o
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vertex. MSTP(66) offer some alterna
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calculation is preferred. Some caut
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contains a full two-Higgs-multiplet
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8.5.2 Heavy Standard Model HiggsISU
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parton-distribution-function approa
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The advantage of the explicit pair
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handed neutrinos. The Higgs fields
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former and ŝ for the latter. To ma
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mode is therefore tt, if kinematica
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through a vector-dominance mechanis
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where α a = ga/4π.2The phenomenol
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has two scalar partners, one associ
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above. To obtain proper linking wit
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or (ii) the masses of the first- an
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mSUGRA model input parameters shoul
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stable. If this is not the case, MW
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is no a priori generic prediction f
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tools exist. Therefore the producti
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’gamma/lepton’ machinery. There
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numerical precision may suffer; if
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call, e.g. at the end of the run, o
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on so as to give the full (paramete
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MSEL = 10) (ISUB = 19, 20, 22, 23,
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CKIN(7), CKIN(8) : (D = −10., 10.
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For two resonances that are identic
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= 1 : you should set couplings for
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or GVMD; we will use both interchan
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MSTP(17) : (D = 4) possibility of a
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h 0 and H 0 . It is mainly intended
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correct only in the Standard Model
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for three technicolors, based on sc
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esponsibility on you.Note 2: when P
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= 1 : the recommended standard for
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where a reconnection is actually ma
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MSTP(145) : (D = 0) choice of polar
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PARP(32) : (D = 2.0) special K fact
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PARP(121) : (D = 1.) the maxima obt
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Q2 : the momentum transfer scale Q
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1-PARU(136) corresponding to the sa
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cot θ 3 .ITCM(5) : (D = 0) presenc
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are SUGRA, SSMSSM and VISAJE, locat
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IMSS(22) : (D = 0) Read-in of SLHA
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it is the constant of proportionali
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k = 1 : only possibility.ISUB = 13,
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number is obtained as a by-product
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vanishing if no splitting is needed
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CALL PYINIT(’CMS’,’p’,’pb
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C...Histograms.CALL PYBOOK(1,’dn_
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Of course, the separation of which
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does imply an infinite total cross
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Pythia. The solution adopted here
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est strategy would vary, depending
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tered during the course of the run,
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NPRUP entries of the XSECUP, XERRUP
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should be denoted by using the valu
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more information than is provided b
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9.9.3 An exampleTo exemplify the ab
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DOUBLE PRECISION EBMUP,XSECUP,XERRU
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momenta and masses can be reconstru
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quantity, the effect of such events
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9.10 Interfaces to Other Generators
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= 2 : assign the interference contr
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value before the routine is called.
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• PYSGQC : normal QCD processes,
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afterwards.)MINT(17), MINT(18) : fl
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= 0 : normal initialization.= 1 : i
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agrees with the Bjorken definition,
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action; used to find what is left f
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VINT(319) : photon flux factor in P
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COMMON/PYINT4/MWID(500),WIDS(500,5)
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Purpose: to store information on to
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10 Initial- and Final-State Radiati
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for the original parton a. On the o
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180 ◦ and therefore the emission
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anching activity of the gluon. (Wit
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anching of both the q and the q, in
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10.2.5 Other final-state shower asp
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wide selection of generic colour an
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e a function of the transverse mome
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That way we hope to achieve the mos
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step by step one moves ‘backwards
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in hadronic interactions, with the
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happens it is almost always for one
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need be.The scheme presented above
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with the new PYPTIS one. The advant
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of the system.)CALL PYPTFS(NPART,IP
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Note:a few non-standard options hav
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g → gg and reduced angle for g
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(MSTP(42) = 2) and MSTJ(46) = 3).PA
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= 3 : the k ⊥ of the anomalous/GV
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to the cut implied by PARP(65).PARP
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outlines where the intermediate and
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11.1.4 Primordial k ⊥It is custom
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mended first to read this section,
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In general, there is quite a strong
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• Scatterings of the gg → gg ty
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where the denominator comes from th
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hard processes in pp or pp collisio
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proton net flavour content, and ene
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can be used here, from sharing the
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There is also the matter of a lower
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The program needs to know the assum
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Λ FSR scale: PARJ(81) = 0.14D0;Bea
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‘correct’ total cross section.M
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generated with the new model (in PY
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e attached to the remnant, PARP(80)
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Determine physical PT2MAX and PT2MI
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COMMON/PYCTAG/NCT, MCT(4000,2)Purpo
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string is assumed to have no transv
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Only two baryon multiplets are incl
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Additional parameters include the r
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or the q one, ‘left-right symmetr
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are changed, some retuning should b
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end in the initial stages of the st
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The fact that the hadron should be
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(including the one between the two
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the ratio of rescaled jet momentum
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duly randomized, but properly it wo
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Other models include a simplified i
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The negative sign is exactly what w
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13 Particles and Their DecaysPartic
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multiplet m 0 kpseudoscalars and ve
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toIn Dalitz decays, π 0 or η →
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fragmentation description. This doe
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14 The Fragmentation and Decay Prog
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Initially the partons must be given
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SUBROUTINE PYZDIS(KFL1,KFL3,PR,Z) :
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MSTU(4) : (D = 4000) number of line
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full. Is reset at each PYEXEC call.
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= 4 : transverse momenta are compen
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included in the event. If the showe
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allowed to shower, is 0 if no pair
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an independent gluon jet generated
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• Increase PARJ(1) by about a fac
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With five possible flavours for q 1
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LFN :is intended for the program au
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where both KTAB1 and KTAB3 are know
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a fourth generation is small.Remark
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code it is possible to define chann
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to be borne out by comparisons with
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CALL PYEXEC! particles decay, excep
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15 Event Study and Analysis Routine
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it can be further specified to +z a
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= 8 : KF code (K(I,2)) for a remain
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15.2 Event ShapesIn this section we
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To find the thrust value and axis t
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Hence rapidity, azimuthal angle and
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as a starting point for the iterati
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may be performed in E rather than i
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Here n = ∑ j n j is the total mul
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MSTU(63) and PARU(61) - PARU(63). I
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H40 : H 4 /H 0 .Remark: the number
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V(I,2) - V(I,5) = statistical error
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PYTHRU, PYCLUS and PYCELL.= 1 : sto
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MSTU(53)).PARU(57) : (D = 3.2) maxi
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Purpose: to dump the contents of ex
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References[Abb87]A. Abbasabadi and
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[Bai83] R. Baier and R. Rückl, Z.
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[Bra64] S. Brandt, Ch. Peyrou, R. S
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[Djo97] A. Djouadi, J. Kalinowski a
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[Gie04]S. Gieseke, A. Ribon, M.H. S
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[Ing80] G. Ingelman and T. Sjöstra
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[Lan00] K. Lane, T. Rador and E. Ei
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[OPA91] OPAL Collaboration, M.Z. Ak
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[Sjö92][Sjö92a][Sjö92b]T. Sjöst
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Appendix A: Subprocess Summary Tabl
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No. Subprocess No. SubprocessNo. Su
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Appendix B: Index of Subprograms an
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PYK function 429PYKCUT subroutine 1
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