Minimum Bias at CDF and CMS

Minimum Bias at CDF and CMS Minumum Bias Collisions Proton AntiProton CDF Run 2 CMS Outline of Talk Review the CDF Run 2 minimum bias tune (i.e. PYTHIA Tune A). UE&MB@CMS Show the minimum bias predictions for PYTHIA Tune A, Tune DW, Tune DWT, and the ATLAS tune at the LHC. Proton High P T Jets Initial-State Radiation Outgoing Parton PT(hard) AntiProton These tunes are discussed in our CMS note on the underlying event. CMS NOTE-2006/067 Outgoing Parton Final-State Radiation Rick Field Florida/CDF/CMS Page

PYTHIA Tune A Min-Bias 0.8 CDF Published Charged Particle Density: dn/dηdφ E+00 E-0 Charged Particle Density Pythia 6.206 Set A CDF Min-Bias Data dn/dηdφ 0.6 0.0 Pythia 6.206 Set A CDF Min-Bias.8 TeV - -3-2 - 0 2 3 Pseudo-Rapidity η.8 TeV all PT PYTHIA regulates the perturbative 2-to-2 parton-parton cross sections with cut-off parameters which allows one to run with P T (hard) > 0. One can simulate both hard and soft collisions in one program. Charged Density dn/dηdφdpt (/GeV/c) E-02 E-03 E-0 E-05 E-06 CDF Preliminary PT(hard) > 0 GeV/c.8 TeV η < 0 2 6 8 0 2 PT(charged) (GeV/c) 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)! Rick Field Florida/CDF/CMS Page 2

dn/dηdφ..2 0.8 0.6 0.0 CDF Data.8 TeV Charged Particle Density: dn/dηdφ 630 GeV PYTHIA Tune A LHC Min-Bias Predictions Pythia 6.206 Set A -6 - -2 0 2 6 Pseudo-Rapidity η all PT TeV PYTHIA was tuned to fit the underlying event in hard-scattering processes at.8 TeV and 630 GeV. Charged density dn/dηdφ..2 0.8 0.6 0.0 Charged Particle Density: dn/dηdφ Pythia 6.206 Set A CDF Data UA5 Data Fit 2 Fit 0 00,000 0,000 00,000 CM Energy W (GeV) Shows the center-of-mass energy dependence of the charged particle density, dn chg /dηdφ, for Min-Bias collisions compared with PYTHIA Tune A with P T (hard) > 0. η = 0 LHC? PYTHIA Tune A predicts a 2% rise in dn chg /dηdφ at η = 0 in going from the Tevatron (.8 TeV) to the LHC ( TeV). Similar to HERWIG soft min-bias, charged particles per unit η becomes 6. Rick Field Florida/CDF/CMS Page 3

UE Parameters ISR Parameters CDF Run P (Z) T PYTHIA 6.2 CTEQ5L Parameter MSTP(8) MSTP(82) PARP(82) PARP(83) PARP(8) PARP(85) PARP(86) PARP(89) PARP(90) PARP(62) PARP(6) PARP(67) MSTP(9) PARP(9) Tune A 2.0 GeV 0.9 0.95.8 TeV 5.0 Tune AW 2.0 GeV 0.9 0.95.8 TeV 5.25.0 2. Tune used by the CDF-EWK group! PT Distribution /N dn/dpt 0.08 0.0 0.00 Z-Boson Transverse Momentum CDF Run Data PYTHIA Tune A PYTHIA Tune AW 0 2 6 8 0 2 6 8 20 Z-Boson PT (GeV/c) CDF Run published.8 TeV Normalized to Shows the Run Z-boson p T distribution (<p T (Z)>.5 GeV/c) compared with PYTHIA Tune A (<p T (Z)> = 9.7 GeV/c), and PYTHIA Tune AW (<p T (Z)> =.7 GeV/c). Intrensic KT PARP(93) 5.0 5.0 Effective Q cut-off, below which space-like showers are not evolved. The Q 2 = k T 2 in α s for space-like showers is scaled by PARP(6)! Rick Field Florida/CDF/CMS Page

Jet-Jet Correlations (DØ) Jet#-Jet#2 φ Distribution φ Jet#-Jet#2 MidPoint Cone Algorithm (R = 0.7, f merge = ) L = 50 pb - (Phys. Rev. Lett. 9 2280 (2005)) Data/NLO agreement good. Data/HERWIG agreement good. Data/PYTHIA agreement good provided PARP(67) =.0 (i.e. like Tune A, best fit 2.5). Rick Field Florida/CDF/CMS Page 5

UE Parameters ISR Parameters PYTHIA Tune DW PYTHIA 6.2 CTEQ5L Parameter MSTP(8) MSTP(82) PARP(82) PARP(83) PARP(8) PARP(85) PARP(86) PARP(89) PARP(90) PARP(62) PARP(6) PARP(67) MSTP(9) Tune DW.9 GeV.8 TeV 5.25 2.5 Tune AW 2.0 GeV 0.9 0.95.8 TeV 5.25.0 PT Distribution /N dn/dpt 0.08 0.0 0.00 Z-Boson Transverse Momentum CDF Run Data PYTHIA Tune DW HERWIG 0 2 6 8 0 2 6 8 20 Z-Boson PT (GeV/c) CDF Run published.8 TeV Normalized to Shows the Run Z-boson p T distribution (<p T (Z)>.5 GeV/c) compared with PYTHIA Tune DW, and HERWIG. PARP(9) PARP(93) 2. 5.0 2. 5.0 Intrensic KT Tune DW uses DØ s perfered value of PARP(67)! Tune DW has a lower value of PARP(67) and slightly more MPI! Rick Field Florida/CDF/CMS Page 6

PYTHIA 6.2 Tunes PYTHIA 6.2 CTEQ5L σ(mpi) at.96 TeV σ(mpi) at TeV Parameter Tune A Tune DW Tune DWT ATLAS Tune A 309.7 mb 8.0 mb MSTP(8) Tune DW 35.7 mb 59.2 mb MSTP(82) Tune DWT 35.7 mb 829. mb PARP(82) PARP(83) 2.0 GeV.9 GeV.909 GeV.8 GeV ATLAS 32.5 mb 768.0 mb PARP(8) PARP(85) PARP(86) PARP(89) PARP(90) PARP(62) PARP(6) PARP(67) MSTP(9) PARP(9) PARP(93) 0.9 0.95.8 TeV 5.0 5.0.8 TeV 5.25 2.5 2. 5.0.96 TeV 0.6.25 2.5 2. 5.0 0.33 0.66 TeV 0.6 5.0 "Transverse" Charged Density 0.8 0.6 0.0 "Transverse" Charged Particle Density: dn/dηdφ RDF Preliminary generator level HERWIG PY Tune DW PY-ATLAS.96 TeV Leading Jet ( η <2.0) Charged Particles ( η <, PT> GeV/c) 0 50 00 50 200 250 300 350 00 50 500 PT(particle jet#) (GeV/c) Shows the transverse charged particle density, dn/dηdφ, versus P T (jet#) for leading jet events at.96 TeV for Tune DW, ATLAS, and HERWIG (without MPI). Rick Field Florida/CDF/CMS Page 7

Charged Particle Density 0 8 6 2 0 Generator Level TeV PYTHIA 6.2 Tunes LHC HC Min-Bias Predictions Charged Particle Density: dn/dη -0-8 -6 - -2 0 2 6 8 0 Hard Core (HC) Min-Bias Charged Particles (all p T ) PseudoRapidity η pya pydw pydwt ATLAS Charged Particle Density 2 0 8 6 2 0 Generator Level TeV Charged Particle Density: dn/dy -0-8 -6 - -2 0 2 6 8 0 Hard Core (HC) Min-Bias Charged Particles (all p T ) Rapidity Y pya pydw pydwt ATLAS Shows the predictions of PYTHIA Tune A, Tune DW, Tune DWT, and the ATLAS tune for the charged particle density dn/dη and dn/dy for hard core (HC) Min-Bias at TeV (all p T ). PYTHIA Tune A and Tune DW predict about 6 charged particles per unit η at η = 0, while the ATLAS tune predicts around 9. PYTHIA Tune DWT is identical to Tune DW at.96 TeV, but extrapolates to the LHC using the ATLAS energy dependence. Rick Field Florida/CDF/CMS Page 8

PYTHIA 6.2 Tunes LHC HC Min-Bias Predictions /Nev dn/dpt (/GeV/c) 00.0 0.0 Charged PT Distribution Generator Level Min-Bias TeV Charged Particles ( η <) pya <PT> = 6 MeV/c pydw <PT> = 665 MeV/c pydwt <PT> = 693 MeV/c ATLAS <PT> = 58 MeV/c <Nchg> 20 5 0 5 0 Average Number of Charged Particles vs PTmin Charged Particles ( η <, PT>PTmin) 0.0 0. 0.3 0.6 0.7 0.8 0.9 Hard Core (HC) Min-Bias Minimum P T (GeV/c) Generator Level Min-Bias TeV pya pydw pydwt ATLAS 0. 0.0.5 2.0 2.5 3.0 Charged Particle P T (GeV/c) Shows the predictions of PYTHIA Tune A, Tune DW, Tune DWT, and the ATLAS tune for the charged particle p T distribution for hard core (HC) Min-Bias at TeV ( η < ) and the average number of charged particles with p T > p T min ( η < ). The ATLAS tune has many more soft particles than does any of the CDF Tunes. The ATLAS tune has <p T > = 58 MeV/c while Tune A has <p T > = 6 MeV/c (00 MeV/c more per particle)! Rick Field Florida/CDF/CMS Page 9

PYTHIA 6.2 Tunes LHC HC Min-Bias Predictions Fraction of Events 0.00 0.00 Charged Multiplicity Distribution Generator Level Min-Bias TeV Charged Particles ( η <, All p T ) pya <Nchg> =.93 pydw <Nchg> =.76 pydwt <Nchg> = 2.95 ATLAS <Nchg> = 8. <Nchg> 20 5 0 5 0 Average Number of Charged Particles vs PTmin Charged Particles ( η <, PT>PTmin) 0.0 0. 0.3 0.6 0.7 0.8 0.9 Hard Core (HC) Min-Bias Minimum P T (GeV/c) Generator Level Min-Bias TeV pya pydw pydwt ATLAS 0.00 0 5 0 5 20 25 30 35 0 5 50 Number of Charged Particles Shows the predictions of PYTHIA Tune A, Tune DW, Tune DWT, and the ATLAS tune for the charged particle multiplicity distribution for hard core (HC) Min-Bias at TeV ( η < ) and the average number of charged particles with p T > p T min ( η < ). The ATLAS tune has many more soft particles than does any of the CDF Tunes. The ATLAS tune has <N chg > = 8. ( η < ) while Tune A has <N chg > =.93 ( η < ). Rick Field Florida/CDF/CMS Page 0

Charged Particle Density 8 6 2 Charged Particles (all p T ) HC Charged Particle Density: dn/dη DD PYTHIA Tune DWT LHC Min-Bias Predictions HC + SD + DD pydwt Generator Level Min-Bias TeV SD <Nchg> 5 0 5 Average Number of Charged Particles vs PTmin SD HC HC + SD + DD DD pydwt Generator Level Min-Bias TeV Charged Particles ( η <, PT>PTmin) 0-0 -8-6 - -2 0 2 6 8 0 PseudoRapidity η 0 0.0 0. 0.3 0.6 0.7 0.8 0.9 Minimum P T (GeV/c) Shows the predictions of PYTHIA Tune DWT for the charged particle density dn/dη (all p T ) and the average number of charged particles with p T > p T min ( η < ) for Min-Bias at TeV. Shows the contributions from the hard core (HC), Single-Diffraction (SD), and doublediffraction (DD) components of Min-Bias collisions. Also shows the sum (HC + SD + DD). Note the sum is actually (MB = 0.697HC + 0.8SD + 2DD) For p T > GeV/c and η < one is simply adding in zero N chg for SD and DD. Rick Field Florida/CDF/CMS Page

Components HC SD DD Total Cross-Section ( TeV) 55.22 mb.30 mb 9.69 mb 79.2 mb Shows the cross-sections (in mb) the hard core (HC), Single-Diffraction (SD), and double-diffraction (DD) components of Min- Bias collisions from PYTHIA. PYTHIA Tune DWT LHC Min-Bias Predictions % Total 69.7% 8.% 2.2% 00% P T min 0.0 0. 0.3 0.6 0.7 0.8 0.9 Average Number of charged particles with p T > p T min and η < HC (pydwt) 2.95 2.5 0.90 9.09 7.8 6.6 5.09.2 3.56 3.0 2.57 SD.57.8.7 0.82 0.33 0.9 0.0 0.05 0.03 0.0 DD.60.50.9 0.83 0.33 0.9 0.0 0.05 0.03 0.0 Total 9.50 9.3 7.9 6.58 5.37.38 3.60 2.98 2.9 2.0.79 Shows the predictions of PYTHIA Tune DWT for the average umber of charged particles with p T > p T min ( η < ) for Min-Bias at TeV. Rick Field Florida/CDF/CMS Page 2

Conclusions Minumum Bias Collisions Tevatron LHC Outgoing Parton PT(hard) Proton AntiProton Proton Initial-State Radiation AntiProton Underlying Event Underlying Event We cannot use the new underlying event model in PYTHIA 6.3. It has not been studied (and tuned) well enough yet! Outgoing Parton Final-State Radiation The ATLAS tune is goofy! It produces too many soft particles. The charged particle <pt> is too low and does not agree with the CDF Run 2 data. The ATLAS tune agrees with <Nchg> but not with <PTsum> at the Tevatron. PYTHIA Tune DW is very similar to Tune A except that it fits the CDF P T (Z) distribution and it uses the DØ prefered value of PARP(67) = 2.5 (determined from the dijet φ distribution). PYTHIA Tune DWT is identical to Tune DW at.96 TeV but uses the ATLAS energy extrapolation to the LHC (i.e. PARP(90) = 0.6). Rick Field Florida/CDF/CMS Page 3

Conclusions Proton Minumum Bias Collisions Tevatron AntiProton Proton LHC Outgoing Parton PT(hard) Initial-State Radiation AntiProton Underlying Event Underlying Event We cannot use the new underlying I think more event work model needs in to be done Final-State Outgoing Parton Radiation PYTHIA 6.3. It has not been in studied comparing (and the tuned) various tunes. well enough yet! The ATLAS tune cannot be right because it does not fit the Tevatron The ATLAS tune is goofy! data. It produces Right now too I many like Tune soft DW. particles. The charged particle <pt> is too low and Probably does not tune agree will with fit the the CDF CMS Run data. 2 data. The ATLAS tune agrees with <Nchg> but That not with is why <PTsum> we want at to the measure Tevatron. MB&UE at CMS and retune the Monte-Carlo PYTHIA Tune DW is very similar to Tune models! A except that it fits the CDF P T (Z) distribution and it uses the DØ prefered value of PARP(67) = 2.5 (determined from the dijet φ distribution). PYTHIA Tune DWT is identical to Tune DW at.96 TeV but uses the ATLAS energy extrapolation to the LHC (i.e. PARP(90) = 0.6). Rick Field Florida/CDF/CMS Page