PYTHIA 6.2 Tunes for Run II

PYTHIA 6.2 Tunes for Run II Outline of Talk Min-Bias Collisions! Min-Bias Generators Hadron Hadron! The in Hard Scattering Processes Proton Outgoing Parton PT(hard) Initial-State Radiation AntiProton Outgoing Parton Final-State Radiation Flavor Creation b-quark! Initial-State Radiation and b-bbar Correlations Proton AntiProton Initial-State Radiation b-quark Rick Field Page

Min-Bias &! What happens when a high energy proton and an antiproton collide? Proton AntiProton! Most of the time the proton and antiproton ooze through each other and fall apart (i.e. no hard scattering). The outgoing particles continue in roughly the same direction as initial proton and antiproton. A Min-Bias collision.! Occasionally there will be a hard parton-parton collision resulting in large transverse momentum outgoing partons. Also a Min-Bias collision.! The underlying event is everything except the two outgoing hard scattered jets. It is an unavoidable background to many collider observables. Proton Proton Soft Collision (no hard scattering) Hard Scattering Outgoing Parton Beam-Beam Remnants Final-State Radiation Outgoing Parton PT(hard) underlying event has initial-state radiation! Min-Bias AntiProton Initial-State Radiation AntiProton Beam-Beam Remnants Initial-State Radiation Rick Field Page 2

CDF Min-Bias Data Charged Particle Density Charged Particle Pseudo-Rapidity Distribution: dn/dη Charged Particle Density: dn/dηdφ 7 6 CDF Published.0 0.8 CDF Published dn/dη 5 4 3 2 CDF Min-Bias.8 TeV CDF Min-Bias 630 GeV all PT 0-4 -3-2 - 0 2 3 4 Pseudo-Rapidity η dn/dηdφ 0.6 0.4 0.2 CDF Min-Bias 630 GeV CDF Min-Bias.8 TeV all PT 0.0-4 -3-2 - 0 2 3 4 Pseudo-Rapidity η <dn chg /dη> = 4.2 <dn chg /dηdφ> = 0.67! Shows CDF Min-Bias data on the number of charged particles per unit pseudo-rapidity at 630 and,800 GeV. There are about 4.2 charged particles per unit η in Min-Bias collisions at.8 TeV ( η <, all P T ).! Convert to charged particle density, dn chg /dηdφ, by dividing by 2π. There are about 0.67 charged particles per unit η-φ in Min-Bias collisions at.8 TeV ( η <, all P T ). Rick Field Page 3

.4.2.0 CDF Min-Bias Data Charged Particle Density: dn/dηdφ Herwig "Soft" Min-Bias P T Dependence 4 TeV.0E+0.0E+00 Charged Particle Density CDF Preliminary Lots of hard scattering in Min-Bias! η < dn/dηdφ 0.8 0.6 0.4 0.2 0.0 630 GeV.8 TeV -6-4 -2 0 2 4 6 Pseudo-Rapidity η all PT! Shows the energy dependence of the charged particle density, dn chg /dηdφ, for Min-Bias collisions compared with HERWIG Soft Min-Bias. Charged Density dn/dηdφdpt (/GeV/c).0E-0.0E-02.0E-03.0E-04.0E-05.0E-06 CDF Min-Bias Data at.8 TeV HW "Soft" Min-Bias at 630 GeV,.8 TeV, and 4 TeV 0 2 4 6 8 0 2 4 PT (GeV/c)! Shows the P T dependence of the charged particle density, dn chg /dηdφdp T, for Min-Bias collisions at.8 TeV collisions compared with HERWIG Soft Min-Bias.! HERWIG Soft Min-Bias does not describe the Min-Bias data! The Min-Bias data contains a lot of hard parton-parton collisions which results in many more particles at large P T than are produces by any soft model. Rick Field Page 4

CDF Min-Bias Data P T Dependence.4.2 Charged Particle Density: dn/dηdφ Herwig "Soft" Min-Bias 4 TeV.0E+00 Charged Particle Density CDF Preliminary η < dn/dηdφ.0 0.8 0.6 0.4 0.2 0.0 630 GeV -6-4 -2 0 2 4 6.8 TeV Pseudo-Rapidity η all PT! Shows the energy dependence of the charged particle density, dn chg /dηdφ, for Min-Bias collisions compared with HERWIG Soft Min-Bias.! Shows the P T dependence of the charged particle density, dn chg /dηdφdp T, for Min-Bias collisions at.8 TeV collisions compared with HERWIG Soft Min-Bias and MBR.! Although MBR has a harder P T distribution it is a soft model and has no hard scattering. MBR does nt describe the correlation in the min-bias data (i.e. the data have jets ) and MBR does not. Charged Density dn/dηdφdpt (/GeV/c).0E-0.0E-02.0E-03.0E-04.0E-05.0E-06 CDF Min-Bias Data at.8 TeV 0 2 4 6 8 0 2 4 PT (GeV/c) MBR "Soft" Min-Bias at.8 TeV HW "Soft" Min-Bias at.8 TeV Rick Field Page 5

dn/dηdφ.6.4.2.0 0.8 0.6 0.4 0.2 0.0 HW "Soft" Min-Bias Min-Bias: Combining Hard and Soft Collisions Charged Particle Density: dn/dηdφ -4-3 -2-0 2 3 4 Pseudo-Rapidity η HW PT(hard) > 3 GeV/c.8 TeV all PT CDF Min-Bias Data Herwig Jet3 Herwig Min-Bias! HERWIG hard QCD with P T (hard) > 3 GeV/c describes well the high P T tail but produces too many charged particles overall. Not all of the Min-Bias collisions have a hard scattering with P T (hard) > 3 GeV/c! Charged Density dn/dηdφdpt (/GeV/c).0E+0.0E+00.0E-0.0E-02.0E-03.0E-04.0E-05.0E-06 Charged Particle Density CDF Preliminary 0 2 4 6 8 0 2 4 HERWIG soft Min-Bias does not fit the Min-Bias data! HW PT(hard) > 3 GeV/c PT (GeV/c) Herwig Jet3 Herwig Min-Bias CDF Min-Bias Data.8 TeV η < HW "Soft" Min-Bias! One cannot run the HERWIG hard QCD Monte-Carlo with P T (hard) < 3 GeV/c because the perturbative 2-to-2 cross-sections diverge like /P T (hard) 4? Rick Field Page 6

dn/dηdφ.6.4.2.0 0.8 0.6 0.4 0.2 0.0 HW "Soft" Min-Bias Min-Bias: Combining Hard and Soft Collisions Charged Particle Density: dn/dηdφ -4-3 -2-0 2 3 4 Pseudo-Rapidity η HW PT(hard) > 3 GeV/c.8 TeV all PT CDF Min-Bias Data Herwig Jet3 Herwig Min-Bias! HERWIG hard QCD with P T (hard) > 3 GeV/c describes well the high P T tail but produces too many charged particles overall. Not all of the Min-Bias collisions have a hard scattering with P T (hard) > 3 GeV/c! Charged Density dn/dηdφdpt (/GeV/c).0E+0.0E+00.0E-0.0E-02.0E-03.0E-04.0E-05.0E-06 Charged Particle Density CDF Preliminary 0.00 0 2 4 6 8 0 2 4 HERWIG soft Min-Bias does not fit the Min-Bias data! Hard-Scattering Cross-Section PT (GeV/c) CTEQ5L.8 TeV Herwig Jet3 Herwig Min-Bias CDF Min-Bias Data.8 TeV η < PYTHIA HERWIG 0.0 HW PT(hard) > 3 GeV/c 0 2 4 6 8 0 2 4 6 8 20 Hard-Scattering Cut-Off PTmin HW "Soft" Min-Bias! One cannot run the HERWIG hard QCD Monte-Carlo with P T (hard) < 3 GeV/c because the perturbative 2-to-2 cross-sections diverge like /P T (hard) 4? σ HC Cross-Section (millibarns) 00.00.00 0.0 HERWIG diverges! PYTHIA cuts off the divergence. Can run P T (hard)>0! Rick Field Page 7

PYTHIA Min-Bias Soft + Hard Tuned to fit the underlying event! dn/dηdφ.0 0.8 0.6 0.4 0.2 0.0 CDF Published Charged Particle Density: dn/dηdφ Pythia 6.206 Set A CDF Min-Bias.8 TeV -4-3 -2-0 2 3 4 Pseudo-Rapidity η.8 TeV all PT Charged Particle Density! PYTHIA regulates the perturbative 2-to-2.0E-05 parton-parton cross sections with cut-off CDF Preliminary parameters which allows one to run with.0e-06 Lots of hard scattering 0 2 4 6 8 0 2 4 P T (hard) in > Min-Bias! 0. One can simulate both hard PT(charged) (GeV/c) and soft collisions in one program.! The relative amount of hard versus soft depends on the cut-off and can be tuned.! This PYTHIA fit predicts that 2% of all Min-Bias events are a result of a hard 2-to-2 parton-parton scattering with P T (hard) > 5 GeV/c (% with P T (hard) > 0 GeV/c)! Charged Density dn/dηdφdpt (/GeV/c).0E+00.0E-0.0E-02.0E-03.0E-04 PT(hard) > 0 GeV/c Pythia 6.206 Set A CDF Min-Bias Data.8 TeV η < 2% of Min-Bias events have P T (hard) > 5 GeV/c! % of Min-Bias events have P T (hard) > 0 GeV/c! Rick Field Page 8

Transverse region is very sensitive to the underlying event! Charged Jet # Direction Evolution of Charged Jets Toward-Side Jet φ Charged Particle φ Correlations P T > 0.5 GeV/c η < Toward-side jet (always) Charged Jet # Direction φ Look at the charged particle density in the transverse region! 2π Away Region Transverse Region Toward Toward φ Leading Jet Transverse Away-side jet (sometimes) Away Transverse Away-Side Jet Transverse Away Transverse Perpendicular to the plane of the 2-to-2 hard scattering Toward Region Transverse Region Away Region 0 - η +! Look at charged particle correlations in the azimuthal angle φ relative to the leading charged particle jet.! Define φ φ < 60 o as Toward, 60 o < φ φ < 20 o as Transverse, and φ φ > 20 o as Away.! All three regions have the same size in η-φ space, ηx φ φ = 2x20 o = 4π/3. Rick Field Page 9

Charged Particle Density Transverse P T Distribution "Transverse" Charged Density.25.00 0.75 0.50 0.25 0.00 Min-Bias "Transverse" Charged Particle Density: dn/dηdφ CDF Preliminary data uncorrected 0 5 0 5 20 25 30 35 40 45 50 PT(charged jet#) (GeV/c) CDF Min-Bias data <dn chg /dηdφ> = 0.25 CDF Min-Bias CDF JET20 Factor of 2!.8 TeV η <.0 PT>0.5 GeV P T (charged jet#) > 30 GeV/c Transverse <dn chg /dηdφ> = 0.56 Charged Density dn/dηdφdpt (/GeV/c).0E+00.0E-0.0E-02.0E-03.0E-04.0E-05.0E-06 Min-Bias Charged Particle Density.8 TeV η < PT>0.5 GeV/c "Transverse" PT(chgjet#) > 5 GeV/c 0 2 4 6 8 0 2 4 PT(charged) (GeV/c) CDF Preliminary data uncorrected "Transverse" PT(chgjet#) > 30 GeV/c! Compares the average transverse charge particle density with the average Min-Bias charge particle density ( η <, P T >0.5 GeV). Shows how the transverse charge particle density and the Min-Bias charge particle density is distributed in P T. Rick Field Page 0

HERWIG 6.4 Transverse P T Distribution "Transverse" Charged Density.00 0.75 0.50 0.25 0.00 "Transverse" Charged Particle Density: dn/dηdφ CDF Data data uncorrected theory corrected Total "Remnants" "Hard" 0 5 0 5 20 25 30 35 40 45 50 PT(charged jet#) (GeV/c) Herwig 6.4 CTEQ5L PT(hard) > 3 GeV/c.8 TeV η <.0 PT>0.5 GeV Charged Density dn/dηdφdpt (/GeV/c).0E+00.0E-0.0E-02.0E-03.0E-04.0E-05 "Transverse" Charged Particle Density PT(chgjet#) > 5 GeV/c CDF Data data uncorrected theory corrected.8 TeV η < PT>0.5 GeV/c PT(chgjet#) > 30 GeV/c HERWIG has the too steep of a P T dependence of the beam-beam remnant component of the underlying event! Herwig 6.4 CTEQ5L.0E-06 0 2 4 6 8 0 2 4 PT(charged) (GeV/c)! Compares the average transverse charge particle density ( η <, P T >0.5 GeV) versus P T (charged jet#) and the P T distribution of the transverse density, dn chg /dηdφdp T with the QCD hard scattering predictions of HERWIG 6.4 (default parameters with P T (hard)>3 GeV/c. Shows how the transverse charge particle density is distributed in P T. Rick Field Page

Proton Parameter MSTP(8) MSTP(82) Multiple Parton Interactions Same parameter that cuts-off the hard 2-to-2 parton cross sections! Value Outgoing Parton 0 3 4 PYTHIA: Multiple Parton Interaction Parameters Outgoing Parton PT(hard) AntiProton Description Multiple-Parton Scattering off Multiple-Parton Scattering on Multiple interactions assuming the same probability, with an abrupt cut-off P T min=parp(8) Multiple interactions assuming a varying impact parameter and a hadronic matter overlap consistent with a double Gaussian matter distribution (governed by PARP(83) and PARP(84)), with a smooth turn-off P T0 =PARP(82) Pythia uses multiple parton interactions to enhance the underlying event. Multiple interactions assuming a varying impact parameter and a hadronic matter overlap consistent with a single Gaussian matter distribution, with a smooth turnoff P T0 =PARP(82) Multiple parton interaction more likely in a hard (central) collision! Hard Core and now HERWIG! Jimmy: MPI J. M. Butterworth J. R. Forshaw M. H. Seymour Rick Field Page 2

Proton Parameter MSTP(8) MSTP(82) Multiple Parton Interactions Same parameter that cuts-off the hard 2-to-2 parton cross sections! Value Outgoing Parton 0 3 4 PYTHIA: Multiple Parton Interaction Parameters Outgoing Parton PT(hard) AntiProton Note that Description since the same cut-off parameters govern both the primary hard scattering and the secondary MPI interaction, changing the amount of MPI also changes the amount of hard primary Multiple-Parton Scattering off Multiple-Parton Scattering on Multiple interactions assuming a varying impact parameter and a hadronic matter overlap consistent with a double Gaussian matter distribution (governed by PARP(83) and PARP(84)), with a smooth turn-off P T0 =PARP(82) Pythia uses multiple parton interactions to enhance the underlying event. Multiple interactions assuming the same probability, with an abrupt scattering cut-off P T min=parp(8) in PYTHIA Min-Bias events! Multiple interactions assuming a varying impact parameter and a hadronic matter overlap consistent with a single Gaussian matter distribution, with a smooth turnoff P T0 =PARP(82) Multiple parton interaction more likely in a hard (central) collision! Hard Core and now HERWIG! Jimmy: MPI J. M. Butterworth J. R. Forshaw M. H. Seymour Rick Field Page 3

Parameter Default PYTHIA: Multiple Parton Interaction Parameters Description PARP(83) PARP(84) PARP(85) PARP(86) PARP(89) PARP(90) PARP(67) 0.5 0.2 0.33 0.66 TeV 0.6.0 Double-Gaussian: Fraction of total hadronic matter within PARP(84) Double-Gaussian: Fraction of the overall hadron radius containing the fraction PARP(83) of the total hadronic matter. Probability that the MPI produces two gluons with color connections to the nearest neighbors. Probability that the MPI produces two gluons either as described by PARP(85) or as a closed gluon loop. The remaining fraction consists of quark-antiquark pairs. Determines the reference energy E 0. Determines the energy dependence of the cut-off P T0 as follows P T0 (E cm ) = P T0 (E cm /E 0 ) ε with ε = PARP(90) A scale factor that determines the maximum parton virtuality for space-like showers. The larger the value of PARP(67) the more initialstate radiation. Hard Core PT0 (GeV/c) 5 4 3 2 Color String Multiple Parton Interaction PYTHIA 6.206 Multiple Parton Interaction Color String Hard-Scattering Cut-Off PT0 Take E 0 =.8 TeV ε = 0.25 (Set A)) ε = 0.6 (default) Color String 00,000 0,000 00,000 CM Energy W (GeV) Reference point Rick Field at.8 TeV Page 4

PYTHIA default parameters Parameter MSTP(8) MSTP(82) PARP(8) PARP(82) PARP(89) PARP(90) PARP(67) 6.5.4.55 4.0 PYTHIA 6.206 Defaults MPI constant 6.25.9 2.,000 0.6 4.0 6.58.9 2.,000 0.6.0 6.206.9.9,000 0.6.0 "Transverse" Charged Density probability scattering.00 0.75 0.50 0.25 0.00 "Transverse" Charged Particle Density: dn/dηdφ CDF Data data uncorrected theory corrected Pythia 6.206 (default) MSTP(82)= PARP(8) =.9 GeV/c 0 5 0 5 20 25 30 35 40 45 50 PT(charged jet#) (GeV/c).8 TeV η <.0 PT>0.5 GeV CTEQ3L CTEQ4L CTEQ5L CDF Min-Bias CDF JET20! Plot shows the Transverse charged particle density versus P T (chgjet#) compared to the QCD hard scattering predictions of PYTHIA 6.206 (P T (hard) > 0) using the default parameters for multiple parton interactions and CTEQ3L, CTEQ4L, and CTEQ5L. Note Change PARP(67) = 4.0 (< 6.38) PARP(67) =.0 (> 6.38) Default parameters give very poor description of the underlying event! Rick Field Page 5

b-quark Production at the Tevatron Flavor Creation b-quark Flavor Excitation b-quark Parton Shower/Fragmentation Proton AntiProton Proton AntiProton Proton AntiProton b-quark Initial-State Radiation Initial-State Radiation gluon, quark, or antiquark b-quark Initial-State Radiation b-quark b-quark All three sources are important at the Tevatron!! The QCD leading-log Monte-Carlo models do a fairly good job in describing b-quark data at the Tevatron. The QCD Monte-Carlo models do a much better job fitting the b data than most people realize!! Clearly all three sources are important at the Tevatron.! Nothing is goofy (Rick Field, CDF B Group Talk, March 9, 200).! Next step is to study in detail b-bbar correlations and the compare the predictions of HERWIG, ISAJET, and PYTHIA in order to understand how reliable the estimates are.! Want to know what the leading-log QCD Monte-Carlo Models predict, how stable the estimates are, and how they compare with data. Also, if it is possible we would like to tune the Monte-Carlo models to fit the data. Rick Field Page 6

Inclusive b-quark b Cross Section.0E+02 Integrated b-quark Cross Section for PT > PTmin.0E+02 Integrated b-quark Cross Section for PT > PTmin.0E+0 PYTHIA 6.206 CTEQ5L PARP(67)= PY 6.206 (67=) Total Flavor Creation Flavor Excitation Shower/Fragmentation D0 Data CDF Data.0E+0 PYTHIA 6.206 CTEQ5L PARP(67)=4 PY 6.206 (67=4) Total Flavor Creation Flavor Excitation Shower/Fragmentation D0 Data CDF Data Cross Section (µb).0e+00.0e-0 Cross Section (µb).0e+00.0e-0.0e-02.8 TeV y <.0E-02.8 TeV y < Changed at version 6.38!.0E-03 0 5 0 5 20 25 30 35 40 PTmin (GeV/c).0E-03 0 5 0 5 20 25 30 35 40 PTmin (GeV/c)! Data on the integrated b-quark total cross section (P T > PTmin, y < ) for proton-antiproton collisions at.8 TeV compared with the QCD Monte-Carlo model predictions of PYTHIA 6.206 (CTEQ5L) with PARP(67)= (new default) and PARP(67)=4 (old default). The four curves correspond to the contribution from flavor creation, flavor excitation, shower/fragmentation, and the resulting total. PARP(67) is a scale factor that governs the amount of large angle initial-state radiation. Larger values of PARP(67) results in more large angle initial-state radiation! Rick Field Page 7

dσ/dφ (µb/deg) 0.0000 0.0000 0.0000 Azimuthal Correlations b-quark Correlations: Azimuthal φ Distribution.8 TeV PT > 5 GeV/c PT2 > 0 GeV/c y < y2 < PYTHIA 6.206 CTEQ5L PARP(67)= New PYTHIA default (less initial-state radiation) dσ/dφ (µb/deg) 0.0000 0.0000 0.0000 Old PYTHIA default (more initial-state radiation) b-quark Correlations: Azimuthal φ Distribution.8 TeV PT > 5 GeV/c PT2 > 0 GeV/c y < y2 < PYTHIA 6.206 CTEQ5L PARP(67)=4 "Toward" "Away" 0.0000 0 30 60 90 20 50 80 φ (degrees) PY62 (67=) Total Flavor Creation Flavor Excitation Shower/Fragmentation "Toward" "Away" 0.0000 0 30 60 90 20 50 80 φ (degrees) PY62 (67=4) Total Flavor Creation Flavor Excitation Shower/Fragmentation! Predictions of PYTHIA 6.206 (CTEQ5L) with PARP(67)= (new default) and PARP(67)=4 (old default) for the azimuthal angle, φ, between a b-quark with PT > 5 GeV/c, y < and bbar-quark with PT 2 > 0 GeV/c, y 2 < in proton-antiproton collisions at.8 TeV. The curves correspond to dσ/d φ (µb/ o ) for flavor creation, flavor excitation, shower/fragmentation, and the resulting total. b-quark direction Toward Away φ bbar-quark Rick Field Page 8

dσ/dφ (µb/deg) 0.0000 0.0000 0.0000 0.0000 Azimuthal Correlations b-quark Correlations: Azimuthal φ Distribution.8 TeV PT > 5 GeV/c PT2 > 0 GeV/c y < y2 < "Toward" HERWIG 6.4 CTEQ5L 0 30 60 90 20 50 80 φ (degrees) "Away" HW64 Total Flavor Creation Flavor Excitation Shower/Fragmentation Old PYTHIA default (more initial-state radiation) dσ/dφ (µb/deg) 0.00000 0.00000 0.00000 0.00000 0.00000 b-quark Correlations: Azimuthal φ Distribution.8 TeV PT > 5 GeV/c PT2 > 0 GeV/c y < y2 < PYTHIA 6.206 PARP(67)=4 "Toward" HERWIG 6.4 "Flavor Creation" CTEQ5L 0 30 60 90 20 50 80 φ (degrees) "Away" PYTHIA 6.206 PARP(67)=! Predictions of HERWIG 6.4 (CTEQ5L) for the azimuthal angle, φ, between a b-quark with PT > 5 GeV/c, y < and bbar-quark with PT 2 > 0 GeV/c, y 2 < in proton-antiproton collisions at.8 TeV. The curves correspond to dσ/d φ (µb/ o ) for flavor creation, flavor excitation, shower/fragmentation, and the resulting total. b-quark direction Toward Away φ bbar-quark New PYTHIA default (less initial-state radiation) Flavor Creation Rick Field Page 9

b-quark direction φ CDF Run I Analysis Azimuthal Correlations PARP(67) = maybe too narrow? Toward Away bbar-quark PARP(67) = 4 maybe too broad?! Kevin Lannon preliminary unblessed CDF Run I analysis of the azimuthal angle, φ, between a b-quark y < and bbar-quark y 2 < in protonantiproton collisions at.8 TeV. Rick Field Page 20

DiPhoton Correlations /σ dσ/dpt (/GeV/c) 0.25 0.20 0.5 0.0 0.05 Diphoton System Transverse Momentum PYC5 DiPhoton PARP(67)= PYC5 DiPhoton PARP(67)=4 CDF DiPhoton Data New Pythia.8 TeV PT > 2 GeV η < 0.9 Old Pythia /σ dσ/dφ (/deg) 0.4 0.2 0.0 0.08 0.06 0.04 0.02 DiPhoton Correlations: Azimuthal φ Distribution PYC5 DiPhoton PARP(67)=4 PYC5 DiPhoton PARP(67)= CDF DiPhoton Data New Pythia.8 TeV PT > 2 GeV η < 0.9 Old Pythia 0.00 0 2 4 6 8 0 2 4 6 8 Diphoton System PT (GeV/c) 0.00 90 05 20 35 50 65 80 φ (degrees)! Predictions of PYTHIA 6.58 (CTEQ5L) with PARP(67)= (new default) and PARP(67)=4 (old default) for diphoton system PT and the azimuthal angle, φ, between a photon with PT > 2 GeV/c, y < 0.9 and photon with PT 2 > 2 GeV/c, y 2 < 0.9 in protonantiproton collisions at.8 TeV compared with CDF data. Photon direction Toward Away φ Photon Rick Field Page 2

PYTHIA 6.206 CTEQ5L Parameter MSTP(8) MSTP(82) PARP(82) PARP(85) PARP(86) PARP(89) PARP(90) PARP(67) Tune D 3.6 GeV.0.0.8 TeV 0.25.0 Tuned PYTHIA 6.206 Tune C 3.7 GeV.0.0.8 TeV 0.25 4.0 Single Gaussian "Transverse" Charged Density.00 0.75 0.50 0.25 0.00 "Transverse" Charged Particle Density: dn/dηdφ CDF Preliminary data uncorrected theory corrected CTEQ5L PYTHIA 6.206 (Set D) PARP(67)= PYTHIA 6.206 (Set C) PARP(67)=4 0 5 0 5 20 25 30 35 40 45 50 PT(charged jet#) (GeV/c).8 TeV η <.0 PT>0.5 GeV! Plot shows the Transverse charged particle density versus P T (chgjet#) compared to the QCD hard scattering predictions of two tuned versions of PYTHIA 6.206 (CTEQ5L, Set D (PARP(67)=) and Set C (PARP(67)=4)). New PYTHIA default (less initial-state radiation) Old PYTHIA default (more initial-state radiation) Rick Field Page 22

PYTHIA 6.206 CTEQ5L Parameter MSTP(8) MSTP(82) PARP(82) PARP(83) PARP(84) PARP(85) PARP(86) PARP(89) PARP(90) PARP(67) Tune B 0.5 0.4.0.0.8 TeV 0.25.0 New PYTHIA default (less initial-state radiation) 4.9 GeV Tuned PYTHIA 6.206 Tune A 4 2.0 GeV 0.5 0.4 0.9 0.95.8 TeV 0.25 4.0 Double Gaussian "Transverse" Charged Density.00 0.75 0.50 0.25 0.00! Plot shows the Transverse charged particle density versus P T (chgjet#) compared to the QCD hard scattering predictions of two tuned versions of PYTHIA 6.206 (CTEQ5L, Set B (PARP(67)=) and Set A (PARP(67)=4)). Old PYTHIA default (more initial-state radiation) "Transverse" Charged Particle Density: dn/dηdφ CDF Preliminary data uncorrected theory corrected CTEQ5L PYTHIA 6.206 (Set B) PARP(67)= PYTHIA 6.206 (Set A) PARP(67)=4 0 5 0 5 20 25 30 35 40 45 50 PT(charged jet#) (GeV/c).8 TeV η <.0 PT>0.5 GeV Rick Field Page 23

Tuned PYTHIA 6.206 vs HERWIG 6.4 Transverse Densities Charged Jet # Direction φ Transverse Toward Away Transverse Charged Particle Density Charged PT sum Density "Transverse" Charged Density.00 0.75 0.50 0.25 0.00 "Transverse" Charged Particle Density: dn/dηdφ CDF Preliminary data uncorrected theory corrected CTEQ5L PYTHIA 6.206 (Set B) PARP(67)= PYTHIA 6.206 (Set A) PARP(67)=4 0 5 0 5 20 25 30 35 40 45 50 PT(charged jet#) (GeV/c) HERWIG 6.4.8 TeV η <.0 PT>0.5 GeV! Plots shows CDF data on the charge particle density and the charged PT sum density in the transverse region.! The data are compared with the QCD Monte-Carlo predictions of HERWIG 6.4 (CTEQ5L, P T (hard) > 3 GeV/c) and two tuned versions of PYTHIA 6.206 (P T (hard) > 0). "Transverse" PTsum Density (GeV).00 0.75 0.50 0.25 0.00 "Transverse" Charged PTsum Density: dptsum/dηdφ CDF Preliminary data uncorrected theory corrected CTEQ5L PYTHIA 6.206 (Set A) PARP(67)=4 PYTHIA 6.206 (Set B) PARP(67)= 0 5 0 5 20 25 30 35 40 45 50 PT(charged jet#) (GeV/c) HERWIG 6.4.8 TeV η <.0 PT>0.5 GeV Rick Field Page 24

Tuned PYTHIA 6.206 Transverse P T Distribution "Transverse" Charged Density.00 0.75 0.50 0.25 0.00 "Transverse" Charged Particle Density: dn/dηdφ CDF Preliminary data uncorrected theory corrected CTEQ5L PYTHIA 6.206 (Set B) PARP(67)= PYTHIA 6.206 (Set A) PARP(67)=4 0 5 0 5 20 25 30 35 40 45 50 PT(charged jet#) (GeV/c).8 TeV η <.0 PT>0.5 GeV Charged Density dn/dηdφdpt (/GeV/c).0E+00.0E-0.0E-02.0E-03.0E-04.0E-05 "Transverse" Charged Particle Density PT(chgjet#) > 5 GeV/c PT(chgjet#) > 30 GeV/c CDF Data data uncorrected theory corrected PYTHIA 6.206 Set A PARP(67)=4 PYTHIA 6.206 Set B PARP(67)= PARP(67)=4.0 (old default) is favored over PARP(67)=.0 (new default)!.8 TeV η < PT>0.5 GeV/c.0E-06 0 2 4 6 8 0 2 4 PT(charged) (GeV/c)! Compares the average transverse charge particle density ( η <, P T >0.5 GeV) versus P T (charged jet#) and the P T distribution of the transverse density, dn chg /dηdφdp T with the QCD Monte-Carlo predictions of two tuned versions of PYTHIA 6.206 (P T (hard) > 0, CTEQ5L, Set B (PARP(67)=) and Set A (PARP(67)=4)). Rick Field Page 25

"Transverse" Charged Density.00 0.75 0.50 0.25 0.00 Min-Bias "Transverse" Charged Particle Density: dn/dηdφ CDF Preliminary data uncorrected theory corrected CTEQ5L Tuned PYTHIA 6.206 Set A 0 5 0 5 20 25 30 35 40 45 50 Set A Min-Bias <dn chg /dηdφ> = 0.24 PYTHIA 6.206 Set A PT(charged jet#) (GeV/c).8 TeV η <.0 PT>0.5 GeV Describes the rise from Min-Bias to underlying event! Set A P T (charged jet#) > 30 GeV/c Transverse <dn chg /dηdφ> = 0.60 Charged Density dn/dηdφdpt (/GeV/c).0E+00.0E-0.0E-02.0E-03.0E-04.0E-05 CDF Min-Bias CTEQ5L Charged Particle Density PYTHIA 6.206 Set A.8 TeV η < PT>0.5 GeV/c "Transverse" PT(chgjet#) > 5 GeV/c 0 2 4 6 8 0 2 4 PT(charged) (GeV/c) CDF Preliminary data uncorrected theory corrected "Transverse" PT(chgjet#) > 30 GeV/c! Compares the average transverse charge particle density ( η <, P T >0.5 GeV) versus P T (charged jet#) and the P T distribution of the transverse and Min-Bias densities with the QCD Monte-Carlo predictions of a tuned version of PYTHIA 6.206 (P T (hard) > 0, CTEQ5L, Set A). Describes Min-Bias collisions! Describes the underlying event! Rick Field Page 26

Summary Outgoing Parton Proton PT(hard) Initial-State Radiation AntiProton Min-Bias and the Outgoing Parton Final-State Radiation! PYTHIA (tune A and B ) does a good job of describing both min-bias collisions and the underlying event in hard scattering processes in the Run I data.! PYTHIA (tune A or B ) is the only min-bias generator that includes both soft and hard scattering.! Both ISAJET and HERWIG have the too steep of a P T dependence of the beam-beam remnant component of the underlying event and hence do not have enough beambeam remnants with P T > 0.5 GeV/c.! PYTHIA tune A is slightly favored over tune B, but eventually the best fit may be somewhere in between. The initial-state radiation in tune A with PARP(67) = 4 (used in all Run I simulations) looks more like HERWIG s initial-state radiation. Rick Field Page 27

Recommendations! I suggest the tune set A be used as the default for PYTHIA for the first round of Run II simulations.! Although PYTHIA set A does a better job on the underlying event that HERWIG I suggest that you continue to run both HERWIG and PYTHIA. Run II Monte-Carlo Simulations The underlying-event is only part of the overall event. It is very important to compare at least two Monte-carlo estimates.. In Run I the systematic error due to initial-state radiation was overestimated.! PYTHIA set B can be compared with set A to determine how sensitive a given analysis is to the initial-state radiation.! In addition to MBR one should use PYTHIA (set A or B ) to generate min-bias collisions.! As we study the Run II data I will update and improve the PYTHIA tunes.! See my tunes WEBsite at http://www.phys.ufl.edu/~rfield/cdf/tunes/rdf_tunes.html Rick Field Page 28

I know what tune A is doing. PARP(67) = 4 was used in Run I. Recommendations! I suggest the tune set A be used as the default for PYTHIA for the first round of Run II simulations.! Although PYTHIA set A does a better job on the underlying event that HERWIG I suggest that you continue to run both HERWIG and PYTHIA. Warning! Some of the preliminary comparisons of PYTHIA (set A ) with Run II data indicate that there is not enough! PYTHIA set B can be compared sumet in with the underlying event. set A to determine how sensitive I do not a understand this! given analysis is to the initial-state radiation.! In addition to MBR one should use PYTHIA (set A or B ) to generate min-bias collisions. Run II Monte-Carlo Simulations The underlying-event is only part of the overall event. It is very important to compare at least two Monte-carlo estimates.. In Run I the systematic error due to initial-state radiation was overestimated.! As we study the Run II data I will update and improve the PYTHIA tunes.! See my tunes WEBsite at http://www.phys.ufl.edu/~rfield/cdf/tunes/rdf_tunes.html Rick Field Page 29