1. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 1 Studying the Underlying Event at CDF and the LHC Rick Field University of Florida Outline of Talk CMS at the LHC CDF Run 2 Perugia, Italy October 27. 2008 “Leading Jet” vs Z-Boson Rick Field Craig Group Deepak Kar  The “Towards”, “Away”, and “Transverse” regions of  -  space.  Four Jet Topologies plus Drell-Yan.  The “transMAX” and “transMIN” regions.  Look at versus Nchg in “min-bias” and Drell-Yan.  Show some extrapolations of Drell-Yan to the LHC.  The observables: First look at average quantities. Then do distributions.

2. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 2 UE&MB@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 are doing now) at CDF and then writing a physics publication. Initial Group Members 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) UE&MB@CMS Perugia, Italy, March 2006 University of Perugia Florida-Perugia-CERN PTDR Volume 2 Section 3.3.2 See the talks by Filippo Ambroglini and Florian Bechtel tomorrow morning!

3. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 3 QCD Monte-Carlo Models: High Transverse Momentum Jets  Start 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). “Hard Scattering” Component “Underlying Event”  The “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!

4. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 4 QCD Monte-Carlo Models: Lepton-Pair Production  Start 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 Event”  The “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-state radiation. “Hard Scattering” Component

5. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 5 “Towards”, “Away”, “Transverse”  Look at correlations in the azimuthal angle  relative to the leading charged particle jet (|  | < 1) or the leading calorimeter jet (|  | < 2).  Define |  | 120 o as “Away”. Each of the three regions have area  = 2×120 o = 4  /3.  Correlations relative to the leading jet Charged particles p T > 0.5 GeV/c |  | < 1 Calorimeter towers E T > 0.1 GeV |  | < 1 “Transverse” region is very sensitive to the “underlying event”! Look at the charged particle density, the charged PTsum density and the ETsum density in all 3 regions! Z-Boson Direction

6. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 6 Event Topologies  “Leading Jet” events correspond to the leading calorimeter jet (MidPoint R = 0.7) in the region |  | < 2 with no other conditions. “Leading Jet”  “Leading ChgJet” events correspond to the leading charged particle jet (R = 0.7) in the region |  | < 1 with no other conditions. “Charged Jet” “Inc2J Back-to-Back” “Exc2J Back-to-Back”  “Inclusive 2-Jet Back-to-Back” events are selected to have at least two jets with Jet#1 and Jet#2 nearly “back- to-back” (  12 > 150 o ) with almost equal transverse energies (P T (jet#2)/P T (jet#1) > 0.8) with no other conditions.  “Exclusive 2-Jet Back-to-Back” events are selected to have at least two jets with Jet#1 and Jet#2 nearly “back- to-back” (  12 > 150 o ) with almost equal transverse energies (P T (jet#2)/P T (jet#1) > 0.8) and P T (jet#3) < 15 GeV/c. subset Z-Boson  “Z-Boson” events are Drell-Yan events with 70 < M(lepton-pair) < 110 GeV with no other conditions.

7. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 7 “transMAX” & “transMIN”  Define the MAX and MIN “transverse” regions (“transMAX” and “transMIN”) on an event-by-event basis with MAX (MIN) having the largest (smallest) density. Each of the two “transverse” regions have an area in  -  space of 4  /6.  The “transMIN” region is very sensitive to the “beam-beam remnant” and the soft multiple parton interaction components of the “underlying event”.  The difference, “transDIF” (“transMAX” minus “transMIN”), is very sensitive to the “hard scattering” component of the “underlying event” (i.e. hard initial and final-state radiation). Area = 4  /6 “transMIN” very sensitive to the “beam-beam remnants”!  The overall “transverse” density is the average of the “transMAX” and “transMIN” densities. Z-Boson Direction

8. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 8 “Back-to-Back” ObservableParticle LevelDetector Level dN chg /d  d  Number of charged particles per unit  -  (p T > 0.5 GeV/c, |  | < 1) Number of “good” charged tracks per unit  -  (p T > 0.5 GeV/c, |  | < 1) dPT sum /d  d  Scalar p T sum of charged particles per unit  -  (p T > 0.5 GeV/c, |  | < 1) Scalar p T sum of “good” charged tracks per unit  -  (p T > 0.5 GeV/c, |  | < 1) Average p T of charged particles (p T > 0.5 GeV/c, |  | < 1) Average p T of “good” charged tracks (p T > 0.5 GeV/c, |  | < 1) PT max Maximum p T charged particle (p T > 0.5 GeV/c, |  | < 1) Require Nchg ≥ 1 Maximum p T “good” charged tracks (p T > 0.5 GeV/c, |  | < 1) Require Nchg ≥ 1 dET sum /d  d  Scalar E T sum of all particles per unit  -  (all p T, |  | < 1) Scalar E T sum of all calorimeter towers per unit  -  (E T > 0.1 GeV, |  | < 1) PT sum /ET sum Scalar p T sum of charged particles (p T > 0.5 GeV/c, |  | < 1) divided by the scalar E T sum of all particles (all p T, |  | < 1) Scalar p T sum of “good” charged tracks (p T > 0.5 GeV/c, |  | < 1) divided by the scalar E T sum of calorimeter towers (E T > 0.1 GeV, |  | < 1) “Leading Jet” Observables at the Particle and Detector Level

9. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 9 CDF Run 1 P T (Z)  Shows the Run 1 Z-boson p T distribution ( ≈ 11.5 GeV/c) compared with PYTHIA Tune A ( = 9.7 GeV/c), and PYTHIA Tune AW ( = 11.7 GeV/c). ParameterTune ATune AW MSTP(81)11 MSTP(82)44 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)1.01.25 PARP(64)1.00.2 PARP(67)4.0 MSTP(91)11 PARP(91)1.02.1 PARP(93)5.015.0 The Q 2 = k T 2 in  s for space-like showers is scaled by PARP(64)! Effective Q cut-off, below which space-like showers are not evolved. UE Parameters ISR Parameters Intrensic KT PYTHIA 6.2 CTEQ5L Tune used by the CDF-EWK group!

10. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 10 Jet-Jet Correlations (DØ) Jet#1-Jet#2  Distribution  Jet#1-Jet#2  MidPoint Cone Algorithm (R = 0.7, f merge = 0.5)  L = 150 pb -1 (Phys. Rev. Lett. 94 221801 (2005))  Data/NLO agreement good. Data/HERWIG agreement good.  Data/PYTHIA agreement good provided PARP(67) = 1.0→4.0 (i.e. like Tune A, best fit 2.5).

11. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 11 CDF Run 1 P T (Z)  Shows the Run 1 Z-boson p T distribution ( ≈ 11.5 GeV/c) compared with PYTHIA Tune DW, and HERWIG. ParameterTune DWTune AW MSTP(81)11 MSTP(82)44 PARP(82)1.9 GeV2.0 GeV PARP(83)0.5 PARP(84)0.4 PARP(85)1.00.9 PARP(86)1.00.95 PARP(89)1.8 TeV PARP(90)0.25 PARP(62)1.25 PARP(64)0.2 PARP(67)2.54.0 MSTP(91)11 PARP(91)2.1 PARP(93)15.0 UE Parameters ISR Parameters Intrensic KT PYTHIA 6.2 CTEQ5L Tune DW has a lower value of PARP(67) and slightly more MPI! Tune DW uses D0’s perfered value of PARP(67)!

12. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 12 PYTHIA 6.2 Tunes ParameterTune AWTune DWTune D6 PDFCTEQ5L CTEQ6L MSTP(81)111 MSTP(82)444 PARP(82)2.0 GeV1.9 GeV1.8 GeV PARP(83)0.5 PARP(84)0.4 PARP(85)0.91.0 PARP(86)0.951.0 PARP(89)1.8 TeV PARP(90)0.25 PARP(62)1.25 PARP(64)0.2 PARP(67)4.02.5 MSTP(91)111 PARP(91)2.1 PARP(93)15.0 Intrinsic KT ISR Parameter UE Parameters Uses CTEQ6L All use LO  s with  = 192 MeV! Tune A energy dependence!

13. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 13 PYTHIA 6.2 Tunes ParameterTune DWTTune D6TATLAS PDFCTEQ5LCTEQ6LCTEQ5L MSTP(81)111 MSTP(82)444 PARP(82)1.9409 GeV1.8387 GeV1.8 GeV PARP(83)0.5 PARP(84)0.4 0.5 PARP(85)1.0 0.33 PARP(86)1.0 0.66 PARP(89)1.96 TeV 1.0 TeV PARP(90)0.16 PARP(62)1.25 1.0 PARP(64)0.2 1.0 PARP(67)2.5 1.0 MSTP(91)111 PARP(91)2.1 1.0 PARP(93)15.0 5.0 Intrinsic KT ISR Parameter UE Parameters All use LO  s with  = 192 MeV! ATLAS energy dependence! These are “old” PYTHIA 6.2 tunes! See the talks by Arthur Moraes and Hendrik Hoeth for “new” tunes!

14. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 14 JIMMY at CDF The Energy in the “Underlying Event” in High P T Jet Production “Transverse” vs P T (jet#1) JIMMY: MPI J. M. Butterworth J. R. Forshaw M. H. Seymour JIMMY was tuned to fit the energy density in the “transverse” region for “leading jet” events! JIMMY Runs with HERWIG and adds multiple parton interactions! PT(JIM)= 2.5 GeV/c. PT(JIM)= 3.25 GeV/c. The Drell-Yan JIMMY Tune PTJIM = 3.6 GeV/c, JMRAD(73) = 1.8 JMRAD(91) = 1.8

15. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 15 Charged Particle Density  Data at 1.96 TeV on the density of charged particles, dN/d  d , with p T > 0.5 GeV/c and |  | < 1 for “Z-Boson” and “Leading Jet” events as a function of the leading jet p T or P T (Z) for the “toward”, “away”, and “transverse” regions. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune AW and Tune A, respectively, at the particle level (i.e. generator level). HERWIG + JIMMY Tune (PTJIM = 3.6)

16. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 16 Charged PTsum Density  Data at 1.96 TeV on the charged scalar PTsum density, dPT/d  d , with p T > 0.5 GeV/c and |  | < 1 for “Z- Boson” and “Leading Jet” events as a function of the leading jet p T or P T (Z) for the “toward”, “away”, and “transverse” regions. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune AW and Tune A, respectively, at the particle level (i.e. generator level).

17. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 17 The “TransMAX/MIN” Regions  Data at 1.96 TeV on the charged particle density, dN/d  d , with p T > 0.5 GeV/c and |  | < 1 for “Z-Boson” and “Leading Jet” events as a function of P T (Z) or the leading jet p T for the “transMAX”, and “transMIN” regions. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune AW and Tune A, respectively, at the particle level (i.e. generator level).  Data at 1.96 TeV on the density of charged particles, dN/d  d , with p T > 0.5 GeV/c and |  | < 1 for “leading jet” events as a function of the leading jet p T and for Z-Boson events as a function of P T (Z) for “TransDIF” = “transMAX” minus “transMIN” regions. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune A and HERWIG (without MPI) at the particle level (i.e. generator level).

18. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 18 The “TransMAX/MIN” Regions  Data at 1.96 TeV on the charged scalar PTsum density, dPT/d  d , with p T > 0.5 GeV/c and |  | < 1 for “Z- Boson” and “Leading Jet” events as a function of P T (Z) or the leading jet p T for the “transMAX”, and “transMIN” regions. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune AW and Tune A, respectively, at the particle level (i.e. generator level).  Data at 1.96 TeV on the charged scalar PTsum density, dPT/d  d , with p T > 0.5 GeV/c and |  | < 1 for “leading jet” events as a function of the leading jet p T and for Z-Boson events as a function of P T (Z) for “TransDIF” = “transMAX” minus “transMIN” regions. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune A and HERWIG (without MPI) at the particle level (i.e. generator level).

19. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 19 Charged Particle Charged Particle  Data at 1.96 TeV on the charged particle average p T, with p T > 0.5 GeV/c and |  | < 1 for the “toward” region for “Z-Boson” and the “transverse” region for “Leading Jet” events as a function of the leading jet p T or P T (Z). The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune AW and Tune A, respectively, at the particle level (i.e. generator level). The Z-Boson data are also compared with PYTHIA Tune DW, the ATLAS tune, and HERWIG (without MPI)

20. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 20 Z-Boson: “Towards”, Transverse”, & “TransMIN” Charge Density  Data at 1.96 TeV on the density of charged particles, dN/d  d , with p T > 0.5 GeV/c and |  | < 1 for “Z- Boson” events as a function of P T (Z) for the “toward” and “transverse” regions. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune AW and HERWIG (without MPI) at the particle level (i.e. generator level).

21. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 21 Z-Boson: “Towards”, Transverse”, & “TransMIN” Charge Density  Data at 1.96 TeV on the charged scalar PTsum density, dPT/d  d , with p T > 0.5 GeV/c and |  | < 1 for “Z-Boson” events as a function of P T (Z) for the “toward” and “transverse” regions. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune AW and HERWIG (without MPI) at the particle level (i.e. generator level).

22. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 22 Z-Boson: “Towards” Region  Data at 1.96 TeV on the density of charged particles, dN/d  d , with p T > 0.5 GeV/c and |  | < 1 for “Z- Boson” events as a function of P T (Z) for the “toward” region. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune AW and HERWIG (without MPI) at the particle level (i.e. generator level). HW without MPI DWT

23. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 23 Z-Boson: “Towards” Region  Data at 1.96 TeV on the average p T of charged particles with p T > 0.5 GeV/c and |  | < 1 for “Z- Boson” events as a function of P T (Z) for the “toward” region. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune AW and HERWIG (without MPI) at the particle level (i.e. generator level). DWT HW (without MPI) almost no change!

24. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 24  Shows the average transverse momentum of charged particles (|  | 0.5 GeV) versus the number of charged particles, N chg, at the detector level for the CDF Run 2 Min-Bias events. The charged rises with Nchg! Charged versus N chg See the talk by Peter Skands on Thursday morning!

25. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 25 Min-Bias Correlations  Data at 1.96 TeV on the average p T of charged particles versus the number of charged particles (p T > 0.4 GeV/c, |  | < 1) for “min-bias” collisions at CDF Run 2. The data are corrected to the particle level and are compared with PYTHIA Tune A at the particle level (i.e. generator level). See the talk by Niccolo Moggi this afternoon!

26. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 26 Average PT versus Nchg  Data at 1.96 TeV on the average p T of charged particles versus the number of charged particles (p T > 0.4 GeV/c, |  | < 1) for “min-bias” collisions at CDF Run 2. The data are corrected to the particle leveland are compared with PYTHIA Tune A, Tune DW, and the ATLAS tune at the particle level (i.e. generator level).  Particle level predictions for the average p T of charged particles versus the number of charged particles (p T > 0.5 GeV/c, |  | < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV) at CDF Run 2.

27. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 27 Average PT(Z) versus Nchg  Data on the average p T of charged particles versus the number of charged particles (p T > 0.5 GeV/c, |  | < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV) at CDF Run 2. The data are corrected to the particle level and are compared with various Monte-Carlo tunes at the particle level (i.e. generator level). No MPI!  Predictions for the average P T (Z-Boson) versus the number of charged particles (p T > 0.5 GeV/c, |  | < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV) at CDF Run 2.

28. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 28 Average PT versus Nchg  Predictions for the average p T of charged particles versus the number of charged particles (p T > 0.5 GeV/c, |  | < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV, P T (pair) < 10 GeV/c) at CDF Run 2.  Data the average p T of charged particles versus the number of charged particles (p T > 0.5 GeV/c, |  | < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV, P T (pair) < 10 GeV/c) at CDF Run 2. The data are corrected to the particle level and are compared with various Monte-Carlo tunes at the particle level (i.e. generator level). P T (Z) < 10 GeV/c No MPI! Remarkably similar behavior! Perhaps indicating that MPI playing an important role in both processes.

29. MPI@LHC08, Perugia, Italy October 27, 2008 Rick Field – Florida/CDF/CMSPage 29 Summary  It is important to produce a lot of plots (corrected to the particle level) so that the theorists can tune and improve the QCD Monte-Carlo models. If they improve the “transverse” region they might miss-up the “toward” region etc.. We need to show the whole story!  There are over 128 plots to get “blessed” and then to published. So far we have only looked at average quantities. We plan to also produce distributions and flow plots.  We are making good progress in understanding and modeling the “underlying event” in jet production and in Drell-Yan. Tune A and Tune AW describe the data very well, although not perfect. However, we do not yet have a perfect fit to all the features of the CDF “underlying event” data!  I plan to construct a “CDF-QCD Data for Theory” WEBsite with the “blessed” plots together with tables of the data points and errors so that people can have access to the results. CDF-QCD Data for Theory  Looking at versus Nchg in Drell-Yan with 70 < Mpair) < 110 GeV and P T (pair) < 5 GeV is a good way to look at MPI and the color connections. The data show the correlations expected from MPI! CDF Run 2 publication. Should be out by the end of the year!