Physics of the Underlying Event Rick Field University of Florida - PowerPoint PPT Presentation

High Energy QCD after the start of the LHC Physics of the Underlying Event Rick Field University of Florida CMS Outline � How well did we do at predicting the behavior of the “underlying event” at the LHC (900 GeV and 7 TeV)? � How universal are the QCD Monte-Carlo model tunes? � Examine the connection between the “underlying event” in a hard ATLAS scattering process (UE) and “min-bias” collisions (MB). � How well can we predict “min-bias” collisions at the LHC? � Strange particle and baryon production at the LHC. Outgoing Parton “Minimum Bias” Collisions p PT(hard) K + K short Initial-State Radiation u u d Proton Proton Proton Proton d s d s u s + Λ Λ Underlying Event Λ Λ Underlying Event Ξ − − − − Ξ Ξ Ξ K - u d s u s UE&MB@CMS d s s UE&MB@CMS Final-State Radiation Outgoing Parton GGI Florence, Italy Rick Field – Florida/CDF/CMS Page 1 September 14, 2011

QCD Monte- -Carlo Models: Carlo Models: QCD Monte High Transverse Momentum Jets High Transverse Momentum Jets Hard Scattering Outgoing Parton PT(hard) Initial-State Radiation Hard Scattering Outgoing Parton “Jet” “Hard Scattering” Component PT(hard) Initial-State Radiation “Jet” Proton AntiProton Final-State Radiation Outgoing Parton Underlying Event Underlying Event Proton AntiProton “Jet” Final-State Radiation Underlying Event Underlying Event Outgoing Parton “Underlying Event” � 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). � 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 � Of course the outgoing colored partons fragment into hadron “jet” and inevitably “underlying event” background to most collider observables observables receive contributions from initial and final-state radiation. and having good understand of it leads to more precise collider measurements! GGI Florence, Italy Rick Field – Florida/CDF/CMS Page 2 September 14, 2011

QCD Monte- -Carlo Models: Carlo Models: QCD Monte Lepton- -Pair Production Pair Production Lepton Lepton-Pair Production High P T Z-Boson Production Anti-Lepton Outgoing Parton Initial-State Radiation Initial-State Radiation High P T Z-Boson Production Final-State Radiation Lepton-Pair Production Outgoing Parton Anti-Lepton Final-State Radiation “Hard Scattering” Component “Jet” Initial-State Radiation Initial-State Radiation Proton Proton AntiProton AntiProton Lepton Z-boson Underlying Event Underlying Event Proton AntiProton Z-boson Lepton Underlying Event Underlying Event “Underlying Event” � 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). � 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. GGI Florence, Italy Rick Field – Florida/CDF/CMS Page 3 September 14, 2011

“Towards Towards” ”, , “ “Away Away” ”, , “ “Transverse Transverse” ” “ “Leading Jet” Charged Particle Density: dN/d η η d φ φ η η φ φ 5 CDF Run 2 Preliminary "Away" data corrected Average Charged Density 4 Jet #1 Direction pyA generator level ∆φ ∆φ ∆φ ∆φ "Toward" 3 “Toward” "Leading Jet" 2 Factor of ~4.5 MidPoint R=0.7 | η η (jet#1)|<2 η η “Transverse” “Transverse” "Transverse" 1 “Away” Charged Particles (| η η |<1.0, PT>0.5 GeV/c) η η 0 0 50 100 150 200 250 300 350 400 PT(jet#1) (GeV/c) � CDF data at 1.96 TeV on the density of charged particles, dN/d η η d φ φ , with p T > 0.5 GeV/c and | η η | < 1 for η η φ φ η η “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). GGI Florence, Italy Rick Field – Florida/CDF/CMS Page 4 September 14, 2011

“Towards Towards” ”, , “ “Away Away” ”, , “ “Transverse Transverse” ” “ “Leading Jet” Charged Particle Density: dN/d η η d φ φ η η φ φ Charged PTsum Density: dPT/d η η d φ η η φ φ φ 5 100.0 CDF Run 2 Preliminary Charged PTsum Density (GeV/c) CDF Run 2 Preliminary "Away" data corrected Average Charged Density data corrected 4 Jet #1 Direction pyA generator level pyA generator level ∆φ ∆φ ∆φ ∆φ 10.0 "Toward" "Toward" 3 "Away" Factor of ~16 “Toward” "Leading Jet" "Transverse" 2 Factor of ~4.5 MidPoint R=0.7 | η η (jet#1)|<2 η η 1.0 “Transverse” “Transverse” "Transverse" "Leading Jet" 1 MidPoint R=0.7 | η η η (jet#1)|<2 η “Away” Charged Particles (| η η |<1.0, PT>0.5 GeV/c) Charged Particles (| η η η η |<1.0, PT>0.5 GeV/c) η η 0 0.1 0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 300 350 400 PT(jet#1) (GeV/c) PT(jet#1) (GeV/c) � CDF data at 1.96 TeV on the density of charged particles, dN/d η η d φ φ , with p T > 0.5 GeV/c and | η η | < 1 for η η φ φ η η � CDF data at 1.96 TeV on the charged particle scalar p T sum density, dPT/d η η η η d φ φ , with p T > 0.5 GeV/c and φ φ “leading jet” events as a function of the leading jet p T for the “toward”, “away”, and “transverse” | η η | < 1 for “leading jet” events as a function of the leading jet p T for the “toward”, “away”, and η η regions. The data are corrected to the particle level ( with errors that include both the statistical error and “transverse” regions. The data are corrected to the particle level ( with errors that include both the the systematic uncertainty ) and are compared with PYTHIA Tune A at the particle level ( i.e. generator statistical error and the systematic uncertainty ) and are compared with PYTHIA Tune A at the particle level). level ( i.e. generator level). GGI Florence, Italy Rick Field – Florida/CDF/CMS Page 5 September 14, 2011

Charged Particle Density Charged Particle Density Charged Particle Density: dN/d η η d φ Charged Particle Density: dN/d η η d φ η η φ φ φ η η φ φ φ 3 4 CDF Run 2 Preliminary CDF Run 2 Preliminary data corrected Average Charged Density Average Charged Density data corrected "Away" "Away" pyA generator level pyAW generator level 3 2 "Drell-Yan Production" "Toward" 70 < M(pair) < 110 GeV 2 "Leading Jet" MidPoint R=0.7 | η η (jet#1)|<2 η η 1 "Transverse" 1 "Transverse" Charged Particles (| η η η |<1.0, PT>0.5 GeV/c) η "Toward" Charged Particles (| η η |<1.0, PT>0.5 GeV/c) η η excluding the lepton-pair 0 0 0 20 40 60 80 100 120 140 160 180 200 0 20 40 60 80 100 PT(jet#1) (GeV/c) PT(Z-Boson) (GeV/c) Jet #1 Direction Z-Boson Direction High P T Z-Boson Production ∆φ ∆φ ∆φ ∆φ Outgoing Parton Outgoing Parton ∆φ ∆φ ∆φ ∆φ PT(hard) Initial-State Radiation “Toward” “Toward” Initial-State Radiation Proton Proton AntiProton AntiProton “Transverse” “Transverse” “Transverse” “Transverse” Underlying Event Underlying Event “Away” “Away” Final-State Radiation Outgoing Parton Z-boson � CDF data at 1.96 TeV on the density of charged particles, dN/d η η d φ φ , with p T > 0.5 GeV/c and | η η | < 1 for “Z- η η φ φ η η 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 and are compared with PYTHIA Tune AW and Tune A, respectively, at the particle level ( i.e. generator level). GGI Florence, Italy Rick Field – Florida/CDF/CMS Page 6 September 14, 2011