Studying the “Underlying Event” at CDF

1. Studying the “Underlying Event” at CDF Sorry to be so slow!! To be submitted to PRD Rick Field Craig Group Deepak Kar 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 – Florida/CDF/CMS

2. PYTHIA 6.2 Tunes None of the CDF Tunes included any “min-bias” data in the determination of the parameters! All use LO as with L = 192 MeV! UE Parameters Uses CTEQ6L Tune A energy dependence! ISR Parameter Intrinsic KT Rick Field – Florida/CDF/CMS

3. PYTHIA 6.2 Tunes 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”) All use LO as with L = 192 MeV! UE Parameters Tune B Tune AW Tune BW Tune A ATLAS energy dependence! ISR Parameter Tune DW Tune D6 Tune D Tune D6T Intrinsic KT CMS Rick Field – Florida/CDF/CMS

4. “Hard Scattering” Component 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). “Underlying Event” • The “underlying event” consists of the “beam-beam remnants” and from particles arising from soft or semi-soft multiple parton interactions (MPI). The “underlying event” is an unavoidable background to most collider observables and having good understand of it leads to more precise collider measurements! • Of course the outgoing colored partons fragment into hadron “jet” and inevitably “underlying event” observables receive contributions from initial and final-state radiation. Rick Field – Florida/CDF/CMS

5. “Hard Scattering” Component 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. Rick Field – Florida/CDF/CMS

6. “Towards”, “Away”, “Transverse” Look at the charged particle density, the charged PTsum density and the ETsum density in all 3 regions! • Look at correlations in the azimuthal angle Df relative to the leading charged particle jet (|h| < 1) or the leading calorimeter jet (|h| < 2). • Define |Df| < 60o as “Toward”, 60o < |Df| < 120o as “Transverse ”, and |Df| > 120o as “Away”. Each of the three regions have area DhDf = 2×120o = 4p/3. Df Correlations relative to the leading jet Charged particles pT > 0.5 GeV/c |h| < 1 Calorimeter towers ET > 0.1 GeV |h| < 1 “Transverse” region is very sensitive to the “underlying event”! Z-Boson Direction Rick Field – Florida/CDF/CMS

7. “Towards”, “Away”, “Transverse” • Data at 1.96 TeV on the density of charged particles, dN/dhdf, with pT > 0.5 GeV/c and |h| < 1 for “leading jet” events as a function of the leading jet pT 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). “Leading Jet” Factor of ~16 Factor of ~4.5 • Data at 1.96 TeV on the charged particle scalar pT sum density, dPT/dhdf, with pT > 0.5 GeV/c and |h| < 1 for “leading jet” events as a function of the leading jet pT 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). Rick & Craig Rick Field – Florida/CDF/CMS

8. “Towards”, “Away”, “Transverse” • Data at 1.96 TeV on the density of charged particles, dN/dhdf, with pT > 0.5 GeV/c and |h| < 1 for “Z-Boson” events as a function of the leading jet pT 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). “Drell-Yan Producetion” Factor of ~11 Factor of ~3 • Data at 1.96 TeV on the charged particle scalar pT sum density, dPT/dhdf, with pT > 0.5 GeV/c and |h| < 1 for “Z-Boson” events as a function of the leading jet pT 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 Rick Field – Florida/CDF/CMS

9. Charged Particle Multiplicity New • Data at 1.96 TeV on the charged particle multiplicity (pT > 0.4 GeV/c, |h| < 1) for “min-bias” collisions at CDF Run 2. Tune A! No MPI! 7 decades! • The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (pyAnoMPI). Rick Field – Florida/CDF/CMS

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

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

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

13. Min-Bias Correlations New • Data at 1.96 TeV on the average pT of charged particles versus the number of charged particles (pT > 0.4 GeV/c, |h| < 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). Rick Field – Florida/CDF/CMS

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

15. Average PT versus Nchg • Data at 1.96 TeV on the average pT of charged particles versus the number of charged particles (pT > 0.4 GeV/c, |h| < 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 pT of charged particles versus the number of charged particles (pT > 0.5 GeV/c, |h| < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV) at CDF Run 2. Rick Field – Florida/CDF/CMS

16. Average PT versus Nchg No MPI! • Z-boson production (with low pT(Z) and no MPI) produces low multiplicity and small <pT>. • High pT Z-boson production produces large multiplicity and high <pT>. • Z-boson production (with MPI) produces large multiplicity and medium <pT>. = + + Rick Field – Florida/CDF/CMS

17. Average PT(Z) versus Nchg No MPI! • Predictions for the average PT(Z-Boson) versus the number of charged particles (pT > 0.5 GeV/c, |h| < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV) at CDF Run 2. • Data on the average pT of charged particles versus the number of charged particles (pT > 0.5 GeV/c, |h| < 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). Rick Field – Florida/CDF/CMS

18. Average PT versus Nchg It is my fault for being so slow! It is important that we publish this paper now! PT(Z) < 10 GeV/c No MPI! Remarkably similar behavior! Perhaps indicating that MPI playing an important role in both processes. • Predictions for the average pT of charged particles versus the number of charged particles (pT > 0.5 GeV/c, |h| < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV, PT(pair) < 10 GeV/c) at CDF Run 2. • Data the average pT of charged particles versus the number of charged particles (pT > 0.5 GeV/c, |h| < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV, PT(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). Rick Field – Florida/CDF/CMS