The Underlying Event at CDF and CMSReview the CDF Run2 analysis of the underlying event in Leading Jet and Back-to-Back events.Outline of TalkCMS CDF Run 2CMS NOTE-2006/067Discuss using Drell-Yan muon-pair production to study the underlying event at CDF and CMS.Show some extrapolations from CDF CMS.

Discuss the people and the plan.UE&MB@CMS

Proton

AntiProton

Drell-Yan Production

Anti-Lepton

Lepton

Underlying Event

Underlying Event

Initial-State

Radiation

Proton

AntiProton

High PT Jets

PT(hard)

Outgoing Parton

Outgoing Parton

Initial-State Radiation

Final-State Radiation

QCD Monte-Carlo Models:High Transverse Momentum JetsStart with the perturbative 2-to-2 (or sometimes 2-to-3) parton-parton scattering and add initial and final-state gluon radiation (in the leading log approximation or modified leading log approximation). Underlying EventThe underlying event consists of the beam-beam remnants and from particles arising from soft or semi-soft multiple parton interactions (MPI).Of course the outgoing colored partons fragment into hadron jet and inevitably underlying event observables receive contributions from initial and final-state radiation.The underlying event is an unavoidable background to most collider observables and having good understand of it leads to more precise collider measurements!

Hard Scattering

PT(hard)

Outgoing Parton

Outgoing Parton

Initial-State Radiation

Final-State Radiation

Hard Scattering

PT(hard)

Outgoing Parton

Outgoing Parton

Initial-State Radiation

Final-State Radiation

Proton

AntiProton

Underlying Event

Underlying Event

Proton

AntiProton

Underlying Event

Underlying Event

Jet

Jet

Jet

The Transverse Regionsas defined by the Leading JetLook at charged particle correlations in the azimuthal angle Df relative to the leading calorimeter jet (JetClu R = 0.7, |h| < 2).Define |Df| < 60o as Toward, 60o < -Df < 120o and 60o < Df < 120o as Transverse 1 and Transverse 2, and |Df| > 120o as Away. Each of the two transverse regions have area DhDf = 2x60o = 4p/6. The overall transverse region is the sum of the two transverse regions (DhDf = 2x120o = 4p/3).Charged Particle Df Correlations pT > 0.5 GeV/c |h| < 1Transverse region is very sensitive to the underlying event!Look at the charged particle density in the transverse region!

Jet #1 Direction

Toward

Transverse

Transverse

Away

Away-Side Jet

Toward-Side Jet

Jet #1 Direction

Toward

Trans 1

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Leading

Jet

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Region 1

Toward Region

Transverse

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Away Region

Charged Particle Density Df DependenceLook at the transverse region as defined by the leading jet (JetClu R = 0.7, |h| < 2) or by the leading two jets (JetClu R = 0.7, |h| < 2). Back-to-Back events are selected to have at least two jets with Jet#1 and Jet#2 nearly back-to-back (Df12 > 150o) with almost equal transverse energies (ET(jet#2)/ET(jet#1) > 0.8) and with ET(jet#3) < 15 GeV. Shows the Df dependence of the charged particle density, dNchg/dhdf, for charged particles in the range pT > 0.5 GeV/c and |h| < 1 relative to jet#1 (rotated to 270o) for 30 < ET(jet#1) < 70 GeV for Leading Jet and Back-to-Back events.Refer to this as a Leading Jet eventRefer to this as a Back-to-Back eventSubset

Jet #1 Direction

Toward

Transverse

Transverse

Away

Jet #1 Direction

Toward

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Jet #2 Direction

Transverse PTsum Density versus ET(jet#1) Shows the average charged PTsum density, dPTsum/dhdf, in the transverse region (pT > 0.5 GeV/c, |h| < 1) versus ET(jet#1) for Leading Jet and Back-to-Back events.Leading JetBack-to-BackMin-Bias0.24 GeV/c per unit h-fCompares the (uncorrected) data with PYTHIA Tune A and HERWIG (without MPI) after CDFSIM.

Jet #1 Direction

Toward

Transverse

Transverse

Away

Jet #1 Direction

Toward

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The Underlying Event inHigh PT Jet Production (Run 2 vs LHC)Average charged particle density in the Transverse region versus PT(jet#1) at 1.96 TeV for PY Tune AW and HERWIG (without MPI).Average charged particle density in the Transverse region versus PT(jet#1) at 14 TeV for PY Tune AW and HERWIG (without MPI).The Underlying EventCharged particle density versus PT(jet#1)Underlying event much more active at the LHC!

Proton

AntiProton

High PT Jet Production

PT(hard)

Outgoing Parton

Outgoing Parton

Underlying Event

Underlying Event

Final-State Radiation

Initial-State Radiation

Extrapolations to the LHC:High PT Jet ProductionAverage charged particle density in the Transverse region versus PT(jet#1) at 14 TeV for PY Tune AW, Tune DWT, ATLAS, and HERWIG (without MPI).Average charged particle density in the Transverse region versus PT(jet#1) at 14 TeV for PY Tune AW, Tune DWT, ATLAS, and HERWIG (without MPI).The Underlying EventTransverse Charged particle density and charged PTsum density versus PT(jet#1)Tune DW and DWT are identical at 1.96 TeV, but have different MPI energy dependence!The ATLAS tune has a much softer distribution of charged particles than the CDF Run 2 Tunes!

Proton

AntiProton

High PT Jet Production

PT(hard)

Outgoing Parton

Outgoing Parton

Underlying Event

Underlying Event

Final-State Radiation

Initial-State Radiation

The Underlying Event inHigh PT Charged Jet Production (LHC)Average charged particle density in the Transverse region versus PT(jet#1) versus PT(charged jet#1) at 14 TeV for PY Tune DW.The calorimeter jet belonging to the charged particle jet has more transverse momentum!Average charged PTsum density in the Transverse region versus PT(jet#1) versus PT(charged jet#1) at 14 TeV for PY Tune DW.The Underlying EventCharged densities versus PT(jet#1) and PT(charged jet#1)You can study the underlying event with either charged particle jets or calorimeter jets!

Proton

AntiProton

High PT Charged Jet Production

PT(hard)

Outgoing Parton

Outgoing Parton

Underlying Event

Underlying Event

Final-State Radiation

Initial-State Radiation

QCD Monte-Carlo Models:Lepton-Pair ProductionStart with the perturbative Drell-Yan muon pair production and add initial-state gluon radiation (in the leading log approximation or modified leading log approximation). Underlying EventThe underlying event consists of the beam-beam remnants and from particles arising from soft or semi-soft multiple parton interactions (MPI).Of course the outgoing colored partons fragment into hadron jet and inevitably underlying event observables receive contributions from initial and final-state radiation.

Proton

AntiProton

Underlying Event

Underlying Event

Proton

AntiProton

Underlying Event

Underlying Event

Lepton-Pair Production

Lepton

Anti-Lepton

Initial-State Radiation

Lepton-Pair Production

Lepton

Anti-Lepton

Initial-State Radiation

Jet

The Central Regionin Drell-Yan ProductionLook at the central region after removing the lepton-pair. Study the charged particles (pT > 0.5 GeV/c, |h| < 1) and form the charged particle density, dNchg/dhdf, and the charged scalar pT sum density, dPTsum/dhdf, by dividing by the area in h-f space.Charged Particles (pT > 0.5 GeV/c, |h| < 1)After removing the lepton-pair everything else is the underlying event!Look at the charged particle density and the PTsum density in the central region!

Proton

AntiProton

Drell-Yan Production

Anti-Lepton

Lepton

Underlying Event

Underlying Event

Initial-State

Radiation

Proton

AntiProton

Multiple Parton Interactions

Anti-Lepton

Lepton

Underlying Event

Underlying Event

-1

+1

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0

Central Region

Drell-Yan Production (Run2 vs LHC)Average Lepton-Pair transverse momentum at the Tevatron and the LHC for PYTHIA Tune DW and HERWIG (without MPI).Shape of the Lepton-Pair pT distribution at the Z-boson mass at the Tevatron and the LHC for PYTHIA Tune DW and HERWIG (without MPI).Lepton-Pair Transverse MomentumShapes of the pT(m+m-) distribution at the Z-boson mass. is much larger at the LHC!Z

Proton

AntiProton

Drell-Yan Production

Anti-Lepton

Lepton

Underlying Event

Underlying Event

Initial-State

Radiation

The Underlying Event inDrell-Yan Production (Run2 vs LHC)Charged particle density versus the lepton-pair invariant mass at 1.96 TeV for PYTHIA Tune AW and HERWIG (without MPI).Charged particle density versus the lepton-pair invariant mass at 14 TeV for PYTHIA Tune AW and HERWIG (without MPI).The Underlying EventCharged particle density versus M(pair)Underlying event much more active at the LHC!HERWIG (without MPI) is much less active than PY Tune AW (with MPI)!ZZ

Proton

AntiProton

Drell-Yan Production

Anti-Lepton

Lepton

Underlying Event

Underlying Event

Initial-State

Radiation

Extrapolations to the LHC:Drell-Yan ProductionAverage charged particle density versus the lepton-pair invariant mass at 14 TeV for PYTHIA Tune DW, Tune DWT, ATLAS and HERWIG (without MPI).Average charged PTsum density versus the lepton-pair invariant mass at 14 TeV for PYTHIA Tune DW, Tune DWT, ATLAS and HERWIG (without MPI).The Underlying EventCharged particle density and charged PTsum density versus M(pair)The ATLAS tune has a much softer distribution of charged particles than the CDF Run 2 Tunes!Tune DW and DWT are identical at 1.96 TeV, but have different MPI energy dependence!ZZ

Proton

AntiProton

Drell-Yan Production

Anti-Lepton

Lepton

Underlying Event

Underlying Event

Initial-State

Radiation

Extrapolations to the LHC:Drell-Yan ProductionAverage charged particle density (pT > 0.5 GeV/c) versus the lepton-pair invariant mass at 14 TeV for PYTHIA Tune DW, Tune DWT, ATLAS and HERWIG (without MPI).Average charged particle density (pT > 0.9 GeV/c) versus the lepton-pair invariant mass at 14 TeV for PYTHIA Tune DW, Tune DWT, ATLAS and HERWIG (without MPI).The Underlying EventCharged particle density versus M(pair)Charged Particles (|h| 0.5 GeV/c)ZZCharged Particles (|h| 0.9 GeV/c)The ATLAS tune has a much softer distribution of charged particles than the CDF Run 2 Tunes!

Proton

AntiProton

Drell-Yan Production

Anti-Lepton

Lepton

Underlying Event

Underlying Event

Initial-State

Radiation

UE&MB@CMSMeasure Min-Bias and the Underlying Event at CMSThe plan involves two phases. Phase 1 would be to measure min-bias and the underlying event as soon as possible (when the luminosity is low), perhaps during commissioning. We would then tune the QCD Monte-Carlo models for all the other CMS analyses. Phase 1 would be a service to the rest of the collaboration. As the measurements become more reliable we would re-tune the QCD Monte-Carlo models if necessary and begin Phase 2. Phase 2 is physics and would include comparing the min-bias and underlying event measurements at the LHC with the measurements we have done (and are doing now) at CDF and then writing a physics publication.PaoloUE&MB@CMSRick Field (Florida)Darin Acosta (Florida) Paolo Bartalini (Florida)Albert De Roeck (CERN)Livio Fano' (INFN/Perugia at CERN)Filippo Ambroglini (INFN/Perugia at CERN)Khristian Kotov (UF Student, Acosta)UE&MB@CMSPerugia, Italy, March 2006FilippoLivioUniversity of PerugiaFlorida-Perugia

UE&MB@CMSUnderlying Event Studies: The transverse region in leading Jet and back-to-back charged particle jet production and the central region in Drell-Yan production. (requires charged tracks and muons for Drell-Yan)Drell-Yan Studies: Transverse momentum distribution of the lepton-pair versus the mass of the lepton-pair, , , ds/dpT(pair) (only requires muons). Event structure for large lepton-pair pT (i.e. mm +jets, requires muons). Min-Bias Studies: Charged particle distributions and correlations. Construct charged particle jets and look at mini-jet structure and the onset of the underlying event. (requires only charged tracks)UE&MB@CMSStudy the underlying event by using charged particles and muons!(start during the pilot run)

Proton

Proton

High PT Jet Production

PT(hard)

Outgoing Parton

Outgoing Parton

Underlying Event

Underlying Event

Final-State Radiation

Initial-State Radiation

Proton

Proton

Drell-Yan Production

Anti-Lepton

Lepton

Underlying Event

Underlying Event

Initial-State

Radiation

Proton

Proton

Minimum-Bias Collisions

Proton

Proton

Drell-Yan Production

PT(pair)

Lepton-Pair

Outgoing Parton

Underlying Event

Underlying Event

Initial-State

Radiation

Final-State

Radiation