1. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 1 Early LHC Measurements Rick Field University of Florida Outline of Talk  “Min-bias” Summary.  UE Summary.  LHC “min-bias” data at 7 TeV. UE&MB@CMS MC Tunes: What have we learned?  The new ATLAS & CMS “underlying event” results. PARP(90) Color Connections PARP(82) Diffraction

2. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 2 ATLAS & CMS UE Analyses  Uncorrected data on the “transverse” region as defined by the leading track, PTmax, and the leading charged particle jet, PT(chgjet#1) at 900 GeV (p T > 0.5 GeV/c, |  | < 2.0) compared with several QCD Monte-Carlo models after detector simulation.  Corrected data on the “towards”, “away”, and “transverse” regions as defined by the leading track, PTmax, at 7 TeV and 900 GeV (p T > 0.5 GeV/c, |  | < 2.5) compared with several QCD Monte-Carlo models at the generator level. UE&MB@CMS

3. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 3 ATLAS & CMS UE Analyses  Uncorrected data on the “transverse” region as defined by the leading track, PTmax, and the leading charged particle jet, PT(chgjet#1) at 900 GeV (p T > 0.5 GeV/c, |  | < 2.0) compared with several QCD Monte-Carlo models after detector simulation.  Corrected data on the “towards”, “away”, and “transverse” regions as defined by the leading track, PTmax, at 7 TeV and 900 GeV (p T > 0.5 GeV/c, |  | < 2.5) compared with several QCD Monte-Carlo models at the generator level. UE&MB@CMS Please note that I have read the ATLAS and CMS data points off these papers with a ruler so that I can plot the data and make comparisons! Please refer to these papers (not my plots) for the true data points! None of my plots are the original figures from the papers!

4. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 4 “Transverse” Charged Particle Density  Fake data (from MC) at 900 GeV on the “transverse” charged particle density, dN/d  d , as defined by the leading charged particle (PTmax) and the leading charged particle jet (chgjet#1) for charged particles with p T > 0.5 GeV/c and |  | < 2. The fake data (from PYTHIA Tune DW) are generated at the particle level (i.e. generator level) assuming 0.5 M min-bias events at 900 GeV (361,595 events in the plot). Rick Field MB&UE@CMS Workshop CERN, November 6, 2009

5. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 5 “Transverse” Charged Particle Density  Fake data (from MC) at 900 GeV on the “transverse” charged particle density, dN/d  d , as defined by the leading charged particle (PTmax) and the leading charged particle jet (chgjet#1) for charged particles with p T > 0.5 GeV/c and |  | < 2. The fake data (from PYTHIA Tune DW) are generated at the particle level (i.e. generator level) assuming 0.5 M min-bias events at 900 GeV (361,595 events in the plot).  CMS preliminary data at 900 GeV on the “transverse” charged particle density, dN/d  d , as defined by the leading charged particle (PTmax) and the leading charged particle jet (chgjet#1) for charged particles with p T > 0.5 GeV/c and |  | < 2. The data are uncorrected and compared with PYTHIA Tune DW after detector simulation (216,215 events in the plot).

6. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 6 “Transverse” Charged PTsum Density  Fake data (from MC) at 900 GeV on the “transverse” charged PTsum density, dPT/d  d , as defined by the leading charged particle (PTmax) and the leading charged particle jet (chgjet#1) for charged particles with p T > 0.5 GeV/c and |  | < 2. The fake data (from PYTHIA Tune DW) are generated at the particle level (i.e. generator level) assuming 0.5 M min-bias events at 900 GeV (361,595 events in the plot).  CMS preliminary data at 900 GeV on the “transverse” charged PTsum density, dPT/d  d , as defined by the leading charged particle (PTmax) and the leading charged particle jet (chgjet#1) for charged particles with p T > 0.5 GeV/c and |  | < 2. The data are uncorrected and compared with PYTHIA Tune DW after detector simulation (216,215 events in the plot).

7. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 7 PYTHIA Tune CW  CMS preliminary data at 900 GeV on the “transverse” charged PTsum density, dPT/d  d , as defined by the leading charged particle (PTmax) and the leading charged particle jet (chgjet#1) for charged particles with p T > 0.5 GeV/c and |  | < 2. The data are uncorrected and compared with PYTHIA Tune CW after detector simulation.  CMS preliminary data at 900 GeV on the “transverse” charged particle density, dN/d  d , as defined by the leading charged particle (PTmax) and the leading charged particle jet (chgjet#1) for charged particles with p T > 0.5 GeV/c and |  | < 2. The data are uncorrected and compared with PYTHIA Tune CW after detector simulation. Tune DW → Tune CW PARP(82) = 1.9 → 1.8 PARP(90) = 0.25 → 0.30 PARP(85) = 1.0 → 0.9 PARP(86) = 1.0 → 0.95

8. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 8 “Transverse” Charge Density LHC 900 GeV LHC 7 TeV 900 GeV → 7 TeV (UE increase ~ factor of 2)  Shows the charged particle density in the “transverse” region for charged particles (p T > 0.5 GeV/c, |  | < 2) at 900 GeV and 7 TeV as defined by PTmax from PYTHIA Tune DW and at the particle level (i.e. generator level). factor of 2! ~0.4 → ~0.8 Rick Field MB&UE@CMS Workshop CERN, November 6, 2009

9. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 9 “Transverse” Charge Density LHC 900 GeV LHC 7 TeV 900 GeV → 7 TeV (UE increase ~ factor of 2)  ATLAS preliminary data on the charged particle density in the “transverse” region for charged particles (p T > 0.5 GeV/c, |  | < 2.5) at 900 GeV and 7 TeV as defined by PTmax. factor of 2! ~0.4 → ~0.8

10. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 10 “Transverse” Charge Density LHC 900 GeV LHC 7 TeV 900 GeV → 7 TeV (UE increase ~ factor of 2)  Ratio of the ATLAS preliminary data on the charged particle density in the “transverse” region for charged particles (p T > 0.5 GeV/c, |  | < 2.5) at 900 GeV and 7 TeV as defined by PTmax compared with PYTHIA Tune CW, DW, and ATLAS MC08. ~0.4 → ~0.8 PARP(90) = 0.16 PARP(90) = 0.25 PARP(90) = 0.30

11. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 11 PYTHIA Tune DW  ATLAS preliminary data at 900 GeV and 7 TeV on the “transverse” charged PTsum density, dPT/d  d , as defined by the leading charged particle (PTmax) for charged particles with p T > 0.5 GeV/c and |  | < 2.5. The data are corrected and compared with PYTHIA Tune DW at the generrator level.  ATLAS preliminary data at 900 GeV and 7 TeV on the “transverse” charged particle density, dN/d  d , as defined by the leading charged particle (PTmax) for charged particles with p T > 0.5 GeV/c and |  | < 2.5. The data are corrected and compared with PYTHIA Tune DW at the generator level.

12. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 12 Tuning the Color Connections  Shows the charged particle and PTsum density in the “transverse” region for charged particles (p T > 0.5 GeV/c, |  | < 2.5) at 7 TeV as defined by the leading charged particle, PTmax, for pyX18GG8, pyX18GG1, and pyX18QQ at the particle level (i.e. generator level).

13. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 13 Tuning the Color Connections  Shows the charged particle average pT in the “transverse” region for charged particles (p T > 0.5 GeV/c, |  | < 2.5) at 7 TeV as defined by the leading charged particle, PTmax, for pyX18GG8, pyX18GG1, and pyX18QQ at the particle level (i.e. generator level). Tune A has 90% GG8 and Tune DW and D6T have 100% GG8 in order to fit the and PTsum/Nchg at the Tevatron! GG8 has larger !

14. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 14 Tuning the Color Connections  Shows the charged particle average pT in the “transverse” region for charged particles (p T > 0.5 GeV/c, |  | < 2.5) at 7 TeV as defined by the leading charged particle, PTmax, for pyX18GG8, pyX18GG1, and pyX18QQ at the particle level (i.e. generator level). Tune A has 90% GG8 and Tune DW and D6T have 100% GG8 in order to fit the and PTsum/Nchg at the Tevatron! GG8 has larger !

15. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 15 Tuning the Color Connections  Shows the charged particle ratio PTsum/Nchg in the “transverse” region for charged particles (p T > 0.5 GeV/c, |  | < 2.5) at 7 TeV as defined by the leading charged particle, PTmax, for pyX18GG8, pyX18GG1, and pyX18QQ at the particle level (i.e. generator level). GG8 has larger PTsum/Nchg!

16. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 16 PYTHIA Tune X1  ATLAS preliminary data at 900 GeV and 7 TeV on the “transverse” charged PTsum density, dPT/d  d , as defined by the leading charged particle (PTmax) for charged particles with p T > 0.5 GeV/c and |  | < 2.5. The data are corrected and compared with PYTHIA Tune X1 at the generrator level.  ATLAS preliminary data at 900 GeV and 7 TeV on the “transverse” charged particle density, dN/d  d , as defined by the leading charged particle (PTmax) for charged particles with p T > 0.5 GeV/c and |  | < 2.5. The data are corrected and compared with PYTHIA Tune X1 at the generator level. Tune DW → Tune X1 PARP(82) = 1.9 → 1.8 PARP(85) = 1.0 → 0.8 PARP(86) = 1.0 → 0.9

17. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 17 PYTHIA Tune X1  Ratio of the ATLAS preliminary data on the charged PTsum density in the “transverse” region for charged particles (p T > 0.5 GeV/c, |  | < 2.5) at 900 GeV and 7 TeV as defined by PTmax compared with PYTHIA Tune X1 at the generator level.  Ratio of the ATLAS preliminary data on the charged particle density in the “transverse” region for charged particles (p T > 0.5 GeV/c, |  | < 2.5) at 900 GeV and 7 TeV as defined by PTmax compared with PYTHIA Tune X1 at the generator level. Tune DW → Tune X1 PARP(82) = 1.9 → 1.8 PARP(85) = 1.0 → 0.8 PARP(86) = 1.0 → 0.9

18. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 18 PYTHIA Tune X1  Ratio of the ATLAS preliminary data on the charged PTsum density in the “transverse” region for charged particles (p T > 0.5 GeV/c, |  | < 2.5) at 900 GeV and 7 TeV as defined by PTmax compared with PYTHIA Tune X1 at the generator level.  Ratio of the ATLAS preliminary data on the charged particle density in the “transverse” region for charged particles (p T > 0.5 GeV/c, |  | < 2.5) at 900 GeV and 7 TeV as defined by PTmax compared with PYTHIA Tune X1 at the generator level. Tune DW → TuneX1 PARP(82) = 1.9 → 1.8 PARP(85) = 1.0 → 0.8 PARP(86) = 1.0 → 0.9

19. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 19  Shows the data on the  dependence of the “associated” charged particle density, dN chg /d  d , for charged particles (p T > 0.5 GeV/c, |  | 0.5 GeV/c and PTmax > 2.0 GeV/c compared with PYTHIA Tune A (after CDFSIM).  PYTHIA Tune A predicts a larger correlation than is seen in the “min-bias” data (i.e. Tune A “min-bias” is a bit too “jetty”). PTmax > 2.0 GeV/c PTmax > 0.5 GeV/c Transverse Region PY Tune A CDF Run 2 Min-Bias “Associated” Charged Particle Density

20. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 20  Shows the data on the  dependence of the “associated” charged particle density, dN chg /d  d , for charged particles (p T > 0.5 GeV/c, |  | 0.5 GeV/c and PTmax > 2.0 GeV/c compared with PYTHIA Tune A (after CDFSIM).  PYTHIA Tune A predicts a larger correlation than is seen in the “min-bias” data (i.e. Tune A “min-bias” is a bit too “jetty”). PTmax > 2.0 GeV/c PTmax > 0.5 GeV/c Transverse Region PY Tune A CDF Run 2 Min-Bias “Associated” Charged Particle Density The problem in fitting the “toward” associated particle density seen 10 years ago at CDF also appears at 900 GeV and 7 TeV in the ATLAS & CMS data!

21. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 21 UE Summary  The “underlying event” at 7 TeV and 900 GeV is almost what we expected! I expect that a PYTHIA 6 tune just slightly different than Tune DW will fit the UE data perfectly including the energy dependence (Tune X1 is not bad!). I also expect to see good PYTHIA 8 tune soon!  “Min-Bias” is a whole different story! Much more complicated due to diffraction!  I will quickly show you some of my attempts (all failures) to fit the LHC “min-bias” data. PARP(90) Color Connections PARP(82) Diffraction

22. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 22 versus Nchg versus Nchg  Shows how changing the color connections affects the versus Nchg. Here the data and theory are non-diffractive (ND). Here you can understand why Tune DW rises faster than the data and why the ATLAS tunes does so poorly. The CDF “min-bias” data are telling us that the correct tune must be largely GG8! Okay Tune A and DW have a little to much GG8!  CDF ND data on the versus Nchg compared with Tune A(ND), Tune DW(ND) and Tune ATLAS MC08(ND). This is why no one likes the ATLAS MC08 Tune!

23. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 23 versus Nchg versus Nchg  Shows how changing the color connections affects the versus Nchg. Here the data and theory are non-diffractive (ND). Here you can understand why Tune DW rises faster than the data and why the ATLAS tunes does so poorly. The CDF “min-bias” data are telling us that the correct tune must be largely GG8! Okay Tune A and DW have a little to much GG8!  CDF ND data on the versus Nchg compared with Tune A(ND), Tune DW(ND) and Tune ATLAS MC08(ND). This is why no one likes the ATLAS MC08 Tune! Tune X1!

24. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 24 PYTHIA Tune X2  Tune X2 uses the PYTHIA HC, SD, DD fractions for INEL (above left) and HC, DD fractions for NSD (above right). PYTHIA is thought to predict to much SD and DD. Tune X3 (not ready yet) will use the ALICE DD and SD fractions (see above). For now I will try and do the best possible using the PYTHIA SD and DD fractions.  For Tune X2 I will attempt to produce enough charged particles (all pT) at 7 TeV (i.e. fit the CMS NSD dN/d  distribution). It is important to have a tune that gets the average multiplicity right! I will only look at 7 TeV “min-bias” data. Tune X2 does fit the “underlying event” data!

25. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 25 Color Connections  Shows how changing the color connections affects the average number of charged particles. Also shows the SD and ND contributions. CMS sees about ~24 charged particles (all pT, |  | < 2). CMS

26. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 26 Color Connections  Generator level dN/d  (all pT). Shows the HC contribution for the three color connections GG8, GG1, and QQbar. Also shows the CMS NSD data. DW, DWT, and D6T are 100% GG8! pyATLAS is equal mixtures of all three!

27. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 27 PYTHIA Tune X2  Generator level dN/d  (all pT). Shows the NSD = HC + DD, HC = ND, and DD contributions for Tune X2. Also shows the CMS NSD data.

28. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 28 PYTHIA Tune X2  Shows the CMS NSD data for dN/d  (all pT) and the ATLAS INEL data for dN/d  (pT > 0.5 GeV/c, Nchg ≥ 1) compared with Tune X2 (generator level). SD = 9.4%, DD = 6.8%!

29. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 29 Color Connections Tune X2 gives the right average number of charged particles but = 0.501 is a long way off on the the observed average pT (i.e. too small)!  Shows how changing the color connections affects the average transverse momentum of charged particles. Also shows the SD and ND contributions. CMS sees ~ 0.545 GeV/c (all pT, |  | < 2). CMS

30. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 30 PYTHIA Tune X2  Shows the CMS NSD data for versus Nchg (all pT) and the ATLAS INEL data for versus Nchg (pT > 0.5 GeV/c, Nchg ≥ 1) compared with Tune X2 (generator level).

31. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 31 Color Connections  Shows the ATLAS INEL data for versus Nchg (pT > 0.5 GeV/c, Nchg ≥ 1) compared with Tune X18GG8, X18GG1, and X18QQ (left) and PYTHIA Tune X1844 (INEL, right). Gives the right !

32. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 32 Color Connections  Shows the ATLAS INEL data for versus Nchg (pT > 0.5 GeV/c, Nchg ≥ 1) compared with Tune X18GG8, X18GG1, and X18QQ (left) and PYTHIA Tune X1844 (INEL, right).

33. UE&MB Working Group Meeting LPCC May 31, 2010 Rick Field – Florida/CDF/CMSPage 33 Min-Bias Summary  I think the problem is that we do not understand diffraction well enough yet!  We are a long way from having a model that will fit all the features of the LHC min-bias data!  We are learning a lot about how nature works! PARP(90) Color Connections PARP(82) Diffraction