1. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 1 Sorry to be so slow!! Studying the “Underlying Event” at CDF CDF Run 2 “Leading Jet” The goal is to produce data (corrected to the particle level) that can be used by the theorists to tune and improve the QCD Monte-Carlo models that are used to simulate hadron-hadron collisions. Rick Field Craig Group Deepak Kar To be submitted to PRD

2. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 2 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! None of the CDF Tunes included any “min-bias” data in the determination of the parameters!

3. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 3 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! Tune A Tune AW Tune B Tune BW Tune D Tune DW Tune D6 Tune D6T These are “old” PYTHIA 6.2 tunes! There are new 6.420 tunes by Peter Skands (Tune S320, update of S0) Peter Skands (Tune N324, N0CR) Hendrik Hoeth (Tune P329, “Professor”) CMS

4. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 4 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!

5. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 5 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

6. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 6 “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

7. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 7 “Leading Jet” “Towards”, “Away”, “Transverse”  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 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 A at the particle level (i.e. generator level).  Data at 1.96 TeV on the charged particle scalar p T sum 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 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 A at the particle level (i.e. generator level). Factor of ~4.5 Factor of ~16 Rick & Craig

8. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 8 “Drell-Yan Producetion” “Towards”, “Away”, “Transverse”  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 the leading jet p T 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 at the particle level (i.e. generator level).  Data at 1.96 TeV on the charged particle scalar p T sum density, dPT/d  d , with p T > 0.5 GeV/c and |  | < 1 for “Z-Boson” events as a function of the leading jet p T 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 at the particle level (i.e. generator level). Deepak Kar’s Thesis Factor of ~3 Factor of ~11

9. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 9 Charged Particle Multiplicity  Data at 1.96 TeV on the charged particle multiplicity (p T > 0.4 GeV/c, |  | < 1) for “min-bias” collisions at CDF Run 2.  The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (pyAnoMPI). No MPI! Tune A! 7 decades!

10. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 10 The “Underlying Event” Select inelastic non-diffractive events that contain a hard scattering + + + … “Semi-hard” parton- parton collision (p T < ≈2 GeV/c) Hard parton-parton collisions is hard (p T > ≈2 GeV/c) The “underlying-event” (UE)! Multiple-parton interactions (MPI)! Given that you have one hard scattering it is more probable to have MPI! Hence, the UE has more activity than “min-bias”.

11. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 11 The Inelastic Non-Diffractive Cross-Section + + + + … “Semi-hard” parton- parton collision (p T < ≈2 GeV/c) Occasionally one of the parton-parton collisions is hard (p T > ≈2 GeV/c) Majority of “min- bias” events! Multiple-parton interactions (MPI)!

12. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 12 The “Underlying Event” Select inelastic non-diffractive events that contain a hard scattering + + + … “Semi-hard” parton- parton collision (p T < ≈2 GeV/c) Hard parton-parton collisions is hard (p T > ≈2 GeV/c) The “underlying-event” (UE)! Multiple-parton interactions (MPI)! Given that you have one hard scattering it is more probable to have MPI! Hence, the UE has more activity than “min-bias”.

13. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 13 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).

14. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 14 Min-Bias: Average PT versus Nchg =+ +  Beam-beam remnants (i.e. soft hard core) produces low multiplicity and small with independent of the multiplicity.  Hard scattering (with no MPI) produces large multiplicity and large.  Hard scattering (with MPI) produces large multiplicity and medium. The CDF “min-bias” trigger picks up most of the “hard core” component! This observable is sensitive to the MPI tuning!

15. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 15 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.

16. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 16 Average PT versus Nchg =+  Z-boson production (with low p T (Z) and no MPI) produces low multiplicity and small. +  High p T Z-boson production produces large multiplicity and high.  Z-boson production (with MPI) produces large multiplicity and medium. No MPI!

17. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 17 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.

18. CDF Paper Seminar Fermilab - March 11, 2010 Rick Field – Florida/CDF/CMSPage 18 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. It is my fault for being so slow! It is important that we publish this paper now!