XXXIV International Meeting on Fundamental Physics From HERA and the TEVATRON to the LHC Physics at the Tevatron Rick Field University of Florida (for the CDF & D0 Collaborations) Real Colegio Maria Cristina, El Escorial, Spain 4th Lecture Detailed Study of the “Underlying Event” at the Tevatron CDF Run 2 IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

The “Underlying Event” in Run 2 (CDF) The “underlying event” consists of hard initial & final-state radiation plus the “beam-beam remnants” and possible multiple parton interactions. Studying the “Underlying Event” Two Classes of Events: “Leading Jet” and “Back-to-Back”. Two “Transverse” regions: “transMAX”, “transMIN”, “transDIF”. PTmax and PTmaxT distributions and averages. Df Distributions: “Density” and “Associated Density”. <pT> versus charged multiplicity: “min-bias” and the “transverse” region. Correlations between the two “transverse” regions: “trans1” vs “trans2”. Studying the “Underlying Event” in Drell-Yan Production. Extrapolations to the LHC. UE&MB@CMS Florida-Perugia CMS at the LHC IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

The “Transverse” Regions as defined by the Leading Jet Charged Particle Df Correlations pT > 0.5 GeV/c |h| < 1 Look at the charged particle density in the “transverse” region! “Transverse” region is very sensitive to the “underlying event”! Look 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). IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Particle Densities Charged Particles pT > 0.5 GeV/c |h| < 1 DhDf = 4p = 12.6 CDF Run 2 “Min-Bias” CDF Run 2 “Min-Bias” Observable Average Average Density per unit h-f Nchg Number of Charged Particles (pT > 0.5 GeV/c, |h| < 1) 3.17 +/- 0.31 0.252 +/- 0.025 PTsum (GeV/c) Scalar pT sum of Charged Particles 2.97 +/- 0.23 0.236 +/- 0.018 1 charged particle dNchg/dhdf = 1/4p = 0.08 dNchg/dhdf = 3/4p = 0.24 3 charged particles 1 GeV/c PTsum dPTsum/dhdf = 1/4p GeV/c = 0.08 GeV/c dPTsum/dhdf = 3/4p GeV/c = 0.24 GeV/c 3 GeV/c PTsum Divide by 4p 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. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

“Transverse” Particle Densities Charged Particles pT > 0.5 GeV/c |h| < 1 Area = 4p/6 AVE “transverse” (Trans 1 + Trans 2)/2 1 charged particle in the “transverse 2” region dNchg/dhdf = 1/(4p/6) = 0.48 Study the charged particles (pT > 0.5 GeV/c, |h| < 1) in the “Transverse 1” and “Transverse 2” and form the charged particle density, dNchg/dhdf, and the charged scalar pT sum density, dPTsum/dhdf. The average “transverse” density is the average of “transverse 1” and “transverse 2”. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Charged Particle Density Df Dependence Log Scale! Leading Jet Min-Bias 0.25 per unit h-f 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 “leading jet” events 30 < ET(jet#1) < 70 GeV. Also shows charged particle density, dNchg/dhdf, for charged particles in the range pT > 0.5 GeV/c and |h| < 1 for “min-bias” collisions. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Charged Particle Density Df Dependence Refer to this as a “Leading Jet” event Subset Refer to this as a “Back-to-Back” event Look 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. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Charged Particle Density Df Dependence “Leading Jet” “Back-to-Back” 0.5 1.0 1.5 2.0 Polar Plot 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. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

“Transverse” PTsum Density versus ET(jet#1) “Leading Jet” Hard Radiation! “Back-to-Back” Min-Bias 0.24 GeV/c per unit h-f 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. Compares the (uncorrected) data with PYTHIA Tune A and HERWIG after CDFSIM. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

“Transverse” PTsum Density versus ET(jet#1) 30-70 GeV 95-130 GeV Very little dependence on ET(jet#1) in the “transverse” region for “back-to-back” events! IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

“TransDIF” PTsum Density versus ET(jet#1) “Leading Jet” Hard Radiation! “Back-to-Back” “MAX-MIN” is very sensitive to the “hard scattering” component of the “underlying event”! Use the leading jet to define the MAX and MIN “transverse” regions on an event-by-event basis with MAX (MIN) having the largest (smallest) charged PTsum density. Shows the “transDIF” = MAX-MIN charge PTsum density, dPTsum/dhdf, for pT > 0.5 GeV/c, |h| < 1 versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

“TransMIN” PTsum Density versus ET(jet#1) “Leading Jet” “Back-to-Back” “transMIN” is very sensitive to the “beam-beam remnant” component of the “underlying event”! Use the leading jet to define the MAX and MIN “transverse” regions on an event-by-event basis with MAX (MIN) having the largest (smallest) charged particle density. Shows the “transMIN” charge particle density, dNchg/dhdf, for pT > 0.5 GeV/c, |h| < 1 versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

“Transverse” PTsum Density PYTHIA Tune A vs HERWIG “Leading Jet” “Back-to-Back” Now look in detail at “back-to-back” events in the region 30 < ET(jet#1) < 70 GeV! 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. Compares the (uncorrected) data with PYTHIA Tune A and HERWIG after CDFSIM. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Charged PTsum Density PYTHIA Tune A vs HERWIG HERWIG (without multiple parton interactions) does not produces enough PTsum in the “transverse” region for 30 < ET(jet#1) < 70 GeV! IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Min-Bias “Associated” Charged Particle Density Highest pT charged particle! “Associated” densities do not include PTmax! Use the maximum pT charged particle in the event, PTmax, to define a direction and look at the the “associated” density, dNchg/dhdf, in “min-bias” collisions (pT > 0.5 GeV/c, |h| < 1). It is more probable to find a particle accompanying PTmax than it is to find a particle in the central region! Shows the data on the Df dependence of the “associated” charged particle density, dNchg/dhdf, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” events. Also shown is the average charged particle density, dNchg/dhdf, for “min-bias” events. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Min-Bias “Associated” Charged Particle Density Rapid rise in the particle density in the “transverse” region as PTmax increases! PTmax > 2.0 GeV/c Transverse Region Transverse Region Ave Min-Bias 0.25 per unit h-f PTmax > 0.5 GeV/c Shows the data on the Df dependence of the “associated” charged particle density, dNchg/dhdf, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” events with PTmax > 0.5, 1.0, and 2.0 GeV/c. Shows “jet structure” in “min-bias” collisions (i.e. the “birth” of the leading two jets!). IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

“Transverse” PTmax versus ET(jet#1) “Leading Jet” Highest pT particle in the “transverse” region! “Back-to-Back” Min-Bias Use the leading jet to define the “transverse” region and look at the maximum pT charged particle in the “transverse” region, PTmaxT. Shows the average PTmaxT, in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events compared with the average maximum pT particle, PTmax, in “min-bias” collisions (pT > 0.5 GeV/c, |h| < 1). IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Back-to-Back “Associated” Charged Particle Densities Maximum pT particle in the “transverse” region! “Associated” densities do not include PTmaxT! Use the leading jet in “back-to-back” events to define the “transverse” region and look at the maximum pT charged particle in the “transverse” region, PTmaxT. Look at the Df dependence of the “associated” charged particle and PTsum densities, dNchg/dhdf and dPTsum/dhdf for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmaxT) relative to PTmaxT. Rotate so that PTmaxT is at the center of the plot (i.e. 180o). IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Back-to-Back “Associated” Charged Particle Densities “Associated” densities do not include PTmaxT! Jet#2 Region ?? Log Scale! Look at the Df dependence of the “associated” charged particle density, dNchg/dhdf for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmaxT) relative to PTmaxT (rotated to 180o) for PTmaxT > 0.5 GeV/c, PTmaxT > 1.0 GeV/c and PTmaxT > 2.0 GeV/c, for “back-to-back” events with 30 < ET(jet#1) < 70 GeV. Shows “jet structure” in the “transverse” region (i.e. the “birth” of the 3rd & 4th jet). IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Back-to-Back “Associated” Charged Particle Densities charge density “Back-to-Back” “associated” density Shows the Df dependence of the “associated” charged particle density, dNchg/dhdf for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmaxT) relative to PTmaxT (rotated to 180o) for PTmaxT > 0.5 GeV/c, PTmaxT > 1.0 GeV/c and PTmaxT > 2.0 GeV/c, for “back-to-back” events with 30 < ET(jet#1) < 70 GeV. It is more probable to find a particle accompanying PTmaxT than it is to find a particle in the “transverse” region! Shows Df dependence of the charged particle density, dNchg/dhdf for charged particles (pT > 0.5 GeV/c, |h| < 1) relative to jet#1 (rotated to 270o) for “back-to-back events” with 30 < ET(jet#1) < 70 GeV. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Back-to-Back “Associated” Charged Particle Densities charge density “Back-to-Back” “associated” density 0.5 1.0 1.5 2.0 Polar Plot Shows the Df dependence of the “associated” charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1 (not including PTmaxT) relative to PTmaxT (rotated to 180o) and the charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1 relative to jet#1 (rotated to 270o) for “back-to-back events” with 30 < ET(jet#1) < 70 GeV. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Back-to-Back “Associated” Charged Particle Densities charge density “Back-to-Back” “associated” density 0.5 1.0 1.5 2.0 Polar Plot Shows the Df dependence of the “associated” charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1, PTmaxT > 2.0 GeV/c (not including PTmaxT) relative to PTmaxT (rotated to 180o) and the charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1, relative to jet#1 (rotated to 270o) for “back-to-back events” with 30 < ET(jet#1) < 70 GeV. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Rick Field – Florida/CDF/CMS Jet Topologies QCD Four Jet Topology QCD Three Jet Topology 0.5 1.0 1.5 2.0 Polar Plot Shows the Df dependence of the “associated” charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1, PTmaxT > 2.0 GeV/c (not including PTmaxT) relative to PTmaxT (rotated to 180o) and the charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1, relative to jet#1 (rotated to 270o) for “back-to-back events” with 30 < ET(jet#1) < 70 GeV. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Back-to-Back “Associated” Charged Particle Density Jet#2 Region Log Scale! Look at the Df dependence of the “associated” charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1 (not including PTmaxT) relative to PTmaxT (rotated to 180o) for PTmaxT > 2.0 GeV/c for “back-to-back” events with 30 < ET(jet#1) < 70 GeV and 95 < ET(jet#1) < 130 GeV. Very little dependence on ET(jet#1) in the “transverse” region for “back-to-back” events! IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

“Back-to-Back” vs “Min-Bias” “Associated” Charge Density “Birth” of jet#3 in the “transverse” region! “Back-to-Back” “Associated” Density “Min-Bias” “Associated” Density Log Scale! “Birth” of jet#1 in “min-bias” collisions! Shows the Df dependence of the “associated” charged particle density, dNchg/dhdf for pT > 0.5 GeV/c, |h| < 1 (not including PTmaxT) relative to PTmaxT (rotated to 180o) for PTmaxT > 2.0 GeV/c, for “back-to-back” events with 30 < ET(jet#1) < 70 GeV. Shows the data on the Df dependence of the “associated” charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1 (not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” events with PTmax > 2.0 GeV/c. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

“Associated” PTsum Density PYTHIA Tune A vs HERWIG HERWIG (without multiple parton interactions) does not produce enough “associated” PTsum in the direction of PTmaxT! PTmaxT > 0.5 GeV/c And HERWIG (without multiple parton interactions) does not produce enough PTsum in the direction opposite of PTmaxT! IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

“Associated” PTsum Density PYTHIA Tune A vs HERWIG For PTmaxT > 2.0 GeV both PYTHIA and HERWIG produce slightly too much “associated” PTsum in the direction of PTmaxT! PTmaxT > 2 GeV/c But HERWIG (without multiple parton interactions) produces too few particles in the direction opposite of PTmaxT! IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Jet Multiplicity Max pT in the “transverse” region! HERWIG (without multiple parton interactions) does not have equal amounts of 3 and 4 jet topologies! Data have about equal amounts of 3 and 4 jet topologies! Shows the data on the number of jets (JetClu, R = 0.7, |h| < 2, ET(jet) > 3 GeV) for “back-to-back” events with 30 < ET(jet#1) < 70 GeV and PTmaxT > 2.0 GeV/c. Compares the (uncorrected) data with HERWIG after CDFSIM. Compares the (uncorrected) data with PYTHIA Tune A after CDFSIM. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

The “Central” Region in Drell-Yan Production Look at the charged particle density and the PTsum density in the “central” region! Charged Particles (pT > 0.5 GeV/c, |h| < 1) After removing the lepton-pair everything else is the “underlying event”! Look 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. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Rick Field – Florida/CDF/CMS CDF Run 1 PT(Z) PYTHIA 6.2 CTEQ5L Parameter Tune A Tune A25 Tune A50 MSTP(81) 1 MSTP(82) 4 PARP(82) 2.0 GeV PARP(83) 0.5 PARP(84) 0.4 PARP(85) 0.9 PARP(86) 0.95 PARP(89) 1.8 TeV PARP(90) 0.25 PARP(67) 4.0 MSTP(91) PARP(91) 1.0 2.5 5.0 PARP(93) 15.0 25.0 UE Parameters ISR Parameter Shows the Run 1 Z-boson pT distribution (<pT(Z)> ≈ 11.5 GeV/c) compared with PYTHIA Tune A (<pT(Z)> = 9.7 GeV/c), Tune A25 (<pT(Z)> = 10.1 GeV/c), and Tune A50 (<pT(Z)> = 11.2 GeV/c). Intrensic KT IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

CDF Run 1 PT(Z) PYTHIA 6.2 CTEQ5L Parameter Tune A Tune AW MSTP(81) 1 MSTP(82) 4 PARP(82) 2.0 GeV PARP(83) 0.5 PARP(84) 0.4 PARP(85) 0.9 PARP(86) 0.95 PARP(89) 1.8 TeV PARP(90) 0.25 PARP(62) 1.0 1.25 PARP(64) 0.2 PARP(67) 4.0 MSTP(91) PARP(91) 2.1 PARP(93) 5.0 15.0 UE Parameters ISR Parameters Shows the Run 1 Z-boson pT distribution (<pT(Z)> ≈ 11.5 GeV/c) compared with PYTHIA Tune AW (<pT(Z)> = 11.7 GeV/c). Effective Q cut-off, below which space-like showers are not evolved. The Q2 = kT2 in as for space-like showers is scaled by PARP(64)! Intrensic KT IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Drell-Yan Production at the Tevatron Lepton-Pair Transverse Momentum <PT(pair)> versus M(pair) Z Z Shows the lepton-pair average PT versus the lepton-pair invariant mass at 1.96 TeV for PYTHIA Tune AW and PYTHIA Tune A. Shows the lepton-pair average PT versus the lepton-pair invariant mass at 1.96 TeV for PYTHIA Tune AW and HERWIG. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

Drell-Yan Production at the LHC Lepton-Pair Transverse Momentum <PT(pair)> versus M(pair) The lepton-pair <PT> much larger at the LHC! Z Z Shows the lepton-pair average PT versus the lepton-pair invariant mass at 1.96 TeV for PYTHIA Tune AW and HERWIG. Shows the lepton-pair average PT versus the lepton-pair invariant mass at 14 TeV for PYTHIA Tune AW and HERWIG. IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

The “Underlying Event” in Drell-Yan Production (Tevatron) Charged particle density versus M(pair) The “Underlying Event” HERWIG (without MPI) is much less active than PY Tune AW (with MPI)! Z Z Shows the charged particle density versus the lepton-pair invariant mass at 1.96 TeV for PYTHIA Tune AW and PYTHIA Tune A. Shows the charged particle density versus the lepton-pair invariant mass at 1.96 TeV for PYTHIA Tune AW and HERWIG (with no MPI). IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

The “Underlying Event” in Drell-Yan Production (LHC) Charged particle density versus M(pair) The “Underlying Event” HERWIG (without MPI) is much less active than PY Tune AW (with MPI)! “Underlying event” much more active at the LHC! Z Z 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). IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

The “Underlying Event” in High PT Jet Production (LHC) Charged particle density versus PT(jet#1) The “Underlying Event” “Underlying event” much more active at the LHC! Charged particle density in the “Transverse” region versus PT(jet#1) at 1.96 TeV for PY Tune AW and HERWIG (without MPI). Charged particle density in the “Transverse” region versus PT(jet#1) at 14 TeV for PY Tune AW and HERWIG (without MPI). IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

UE&MB@CMS UE&MB@CMS UE&MB@CMS Rick 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) Me at CMS! Measure Min-Bias and the “Underlying Event” at CMS The 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 am doing now) at CDF and then writing a physics publication. Darin UE&MB@CMS IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS

UE&MB@CMS UE&MB@CMS Study charged particles and muons using the CMS detector at the LHC (during the pilot run)! 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) “Underlying 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, <pT(pair)>, <pT2(pair)>, ds/dpT(pair) (only requires muons). Event structure for large lepton-pair pT (i.e. mm +jets, requires muons). IMFP2006 - Day 4 April 6, 2006 Rick Field – Florida/CDF/CMS