PYTHIA 6.4 Physics and Manual

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Dedicated tothe Memory ofBo Andersson1937 – 2002originator, inspirator
Page 1: hep-ph/0603175LU TP 06-13FERMILAB-P
Page 5 and 6: 6.1.9 Alternative matrix elements .
Page 7 and 8: 10.2.8 A new p ⊥ -ordered final-s
Page 9 and 10: 1 IntroductionMultiparticle product
Page 11: Monte Carlo world, the rôle of the
Page 14 and 15: there is every reason to cite them.
Page 16 and 17: plays an important rôle in many of
Page 18 and 19: 2 Physics OverviewIn this section w
Page 20 and 21: conservation, and even more so if o
Page 22 and 23: quark, lepton or neutrino. The whol
Page 24 and 25: ments, thus giving a decent descrip
Page 26 and 27: a colour triplet quark and a colour
Page 28 and 29: Let us now turn to the fragmentatio
Page 30 and 31: 2.4.2 DecaysA large fraction of the
Page 32 and 33: Table 1: The main versions of Jetse
Page 34 and 35: WDTPM, WDTEM, XLAM and IDLAM, have
Page 36 and 37: Unfortunately, experience with many
Page 38 and 39: as showers, fragmentation and decay
Page 40 and 41: Routines that are only used interna
Page 42 and 43: at 20 GeV energy. To do this, write
Page 44 and 45: V matrix contains decay vertices; t
Page 46 and 47: • Switching off of generator part
Page 48 and 49: events generated in the various all
Page 50 and 51: C...Loop over reading and setting p
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1. select an x with even probabilit
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With f(t) = c this is nothing but t
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in a subsequent run the random gene
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initialization of the random number
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Table 3: Quark and lepton codes.KF
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Table 6: Diquark codes. For brevity
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Table 9: Baryon codes. For brevity,
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Table 14: Exotic particle codes.KF
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matches the = 12 of ordinary parton
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5.3.1 A simple exampleThe first exa
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space-like, what is actually listed
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tation, etc., so the standard commo
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The conversion of momenta is trivia
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where 0 ≤ P ± T ≤ 1 and −1
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fixed at 0.01 also in those events.
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6.1.5 The matrix-element event gene
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where r ′ 1 = r 1 ,r 2 ′ 33 −
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e simply taken over for the case of
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Purpose: to generate a complete eve
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α em and Z 0 and quark masses (inc
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MSTJ(120) : (R) type of continuum e
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6.4 ExamplesAn ordinary e + e − a
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7 Process GenerationMuch can be sai
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In sets 1 the Q 0 scale is picked a
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A separate issue is that electron b
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where the k i are the incoming lept
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whereThen ˆt and û are modified t
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integral over the W ± Breit-Wigner
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nominal energy of the machine. Also
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which do not receive contributions
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these events assigned a lower, more
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For a resolved electron, the fe e p
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program does not contain W L or Z L
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the lightest resonances and moving
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and σ el = σ 2 tot/16πB el . The
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struck quark and the remnant diquar
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As an illustration of this scenario
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The region where k ⊥ is the small
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Table 16: Subprocess codes, part 1.
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Page 137 and 138:
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summarized in Appendix A. Only proc
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The difference between this express
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the naïve cross section is multipl
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(e.g. g → gg → cccc) turn out t
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and 8.4.1. These interactions may b
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cut-off procedures follows from the
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Processes 137-140, finally, are ext
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8.4.2 Single W/Z productionMSEL = 1
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8.4.3 W/Z pair productionMSEL = 15I
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process 121. Assuming no t parton d
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masses below 500 GeV.The decay prod
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8.5.4 Charged Higgs sectorMSEL = 23
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width that increases linearly with
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in KFDP(MDCY(42,2),2). The former m
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8.6.7 TechnicolorMSEL = 50, 51ISUB
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distributed according to phase spac
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In the original TCSM outlined above
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The further processes 393-395 are i
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agreement occurs for slightly diffe
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Note that for the R-parity-violatin
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the left-handed squark mass paramet
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REAL XISAIN,XSUGIN,XGMIN,XNRIN,XAMI
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This example shows you how to get a
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where m qi is the arithmetic mean o
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Process 141 contains a Z ′0 , inc
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9 The Process Generation Program El
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= ’pbar-’ : antiproton.= ’K+
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the rightmost column of the table,
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the hard-scattering subsystem, whil
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e switched on explicitly if needed.
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CKIN(41) - CKIN(44) : (D = 12., −
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light-cone is defined by the four-m
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effects of initial-state bremsstrah
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Note 1: the MSTP(14) options apply
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σ. This is formally required, but
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interactions (i.e. for incoming qua
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= 2 : on or off depending on their
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mass tail, where the parton distrib
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doing, it is recommended that you l
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main application is rather to gener
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are included.MSTP(127) : (D = 0) po
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ternally for the γ-hadron or γγ
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exceptions, notably γ ∗ /Z 0 and
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couplings of leptons to H ++ , assu
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PARU(108) : (I) the α em value obt
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PARU(177) : H 0 coupling to A 0 A 0
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RTCM(32) : (D = 0 Radians) phase fo
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= 1 : yes, calculate from given inp
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sign of µ is used.RMSS(5) : (D = 2
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SUBROUTINE PYPOLE : computes the Hi
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= 6 : VMD×anomalous.= 7 : anomalou
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PARI(35) : Feynman-x, x F = x 1 −
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tives correspond to stepwise or smo
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WTXS:wishes to enhance the producti
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RETURNENDNote that, in PYEVWT one c
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4. if event is rejected, then retur
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At times, simple solutions may be f
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equired.MAXPUP : the maximum number
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Internal processes are switched on
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the case that all events are stored
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INTEGER MAXNUPPARAMETER (MAXNUP=500
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according to the relative weight of
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ever, remember that the two incomin
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ENDThere PYINIT is called with ’U
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STOPENDHere unformatted read/write
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and error conditions.In several IDW
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tion on the hard scattering is avai
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the operation and can be put anywhe
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and the rest. For a normal three-bo
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Jacobian factors, for each of the s
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FUNCTION PYGAMM(X) : to give the va
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tion types.= 1 : no parton distribu
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MINT(122) : event class used in cur
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dependent p ⊥min derived from PAR
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VINT(213) : ɛ = ±1; choice betwee
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J = 4 : τ selected according to Br
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is the relevant combination, else t
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PYGGAM call.Note 1: the Bethe-Heitl
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10.1.1 The evolution equationsIn th
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10.1.3 Matching to the hard scatter
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10.2.1 The choice of evolution vari
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1 is considered, it is assumed that
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partons at large angles. Theoretica
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Table 26: Processes for which match
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In general, however, the new descri
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that the branching process is assoc
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Eq. (187) is closely related to eq.
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1. If parton b partook in the hard
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with (p 1 + p 2 ) 2 = ŝ.If, say, Q
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For proton beams, say, any c or b q
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must be used for the hardest branch
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like a colour singlet object, then
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is not yet a matching to avoid doub
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MSTJ(41) : (D = 2) type of branchin
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MSTJ(47) : (D = 3) matrix-element-m
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elements [Ing80, Alt78].Note: in al
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= 2 : as = 0 for most processes, bu
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11 Beam Remnants and Underlying Eve
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larger than the x at the hard scatt
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value, vanishing for an electron or
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The hard-scattering cross section a
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The total probability to have a sca
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it is mathematically convenient to
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It is interesting to understand how
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P g→qs q c(z) = 1 (z 2 + (1 − z
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tum picture, specified after transv
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We now advocate that, by the same r
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11.4.1 Joined InteractionsWhen the
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is therefore via the variables in t
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extra care if a run contains a loop
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this remnant is split into two jets
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= 4 : low-p ⊥ + double diffractiv
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side hadron for MSTP(91) = 1, i.e.
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are only set once a valence quark i
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12 FragmentationThe main fragmentat
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ate of L = 1 production is observed
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in which case there is no net colou
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the popcorn parameters β u and ∆
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• Charm and bottom data clearly i
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Assume now that two final hadrons h
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The string piece between the quark
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12.2.5 Junction topologiesWhen seve
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is decreased, however, since the je
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1. Normal string fragmentation. In
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that a virtual parton (of mass m
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Two comments can be made. The Bose-
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and its nearest identical partner.
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affect the cross section of a proce
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13.2.3 LifetimesClearly the lifetim
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less in agreement with the philosop
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two quark momenta are distributed a
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CALL PY3ENT(IP,KF1,KF2,KF3,PECM,X1,
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except if the command is to set MST
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ITAU : line number in the event rec
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stored as q 1 q 2 Jq 3 . In the lis
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PARU(1) : (R) π ≈ 3.141592653589
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that, one single particle. Normally
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known.= 2 : always done.MSTJ(38) -
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spin s of the meson.PARJ(18) : (D =
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allowed to take place in the MSTJ(2
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δβ = β s − β u . Used to supp
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have its antiquark partner in a pop
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= 1 : a nonidentical antiparticle e
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pressed code KC rather than by the
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= 14 : as = 11, but at least four h
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translation of particle codes. In p
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The jets could of course also be de
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the decay of any given particle by
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which has been analysed with PYSPHE
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V(I,4)) and, for unstable particles
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= 12 : transverse mass m ⊥ .= 13
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sphericity S lin and linearized apl
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P 1 (x) = x ,P 2 (x) = 1 2 (3x2 −
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visually look like belonging to the
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fragmentation scenarios. Although i
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of dd/uu/ss/cc/bb in e + e − anni
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program is affected by MSTU(44), MS
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K(N+i,2) = 98;K(N+i,3) : i, the jet
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subdivided into primary and seconda
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Most high-energy events have multip
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of the jet, obtained as(p x , p y ,
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ID :F :histogram number.rescaling f
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16 Summary and OutlookA complete de
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[And80] B. Andersson, G. Gustafson
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[Ben87a]M. Bengtsson and T. Sjöstr
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[Chi90]P. Chiappetta and M. Perrott
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[Ell86] R.K. Ellis and J.C. Sexton,
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[Gus94] G. Gustafson and J. Häkkin
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[Kno96]I.G. Knowles et al., in ‘P
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[Miu99] G. Miu and T. Sjöstrand, P
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[Sch80] G. Schierholz and D.H. Schi
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[UA183] UA1 Collaboration, G. Arnis
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No. Subprocess No. Subprocess31 f i
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No.SubprocessSUSY:201 f i f i →
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PDFSUP in HEPRUP 245PMAS in PYDAT2
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PYXTEE subroutine 81PYXTOT subrouti
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