1. Lake Louise Winter Institute
Extrapolating from the Tevatron to the LHC
Rick Field
University of Florida
Chateau Lake Louise
February 2010
Outline of Talk 2
The latest “underlying event” studies at CDF for “leading Jet” and Z-boson events. Data corrected to the particle level.
CDF Run 2
Min-Bias and the “underlying event”.
Studying <pT> versus Nchg in “min-bias” collisions and in Drell-Yan.
CMS at the LHC
UE studies at 900 GeV from CMS and ATLAS coming soon!
LHC predictions!
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

2. QCD Monte-Carlo Models: High Transverse Momentum Jets
“Hard Scattering” Component
“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).
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!
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

3. QCD Monte-Carlo Models: Lepton-Pair Production
“Hard Scattering” Component
“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.
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

4. “Towards”, “Away”, “Transverse”
Look at the charged particle density, the charged PTsum density and the ETsum density in all 3 regions!
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
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.
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

5. Rick Field – Florida/CDF/CMS
Event Topologies
“Leading Jet” events correspond to the leading calorimeter jet (MidPoint R = 0.7) in the region |h| < 2 with no other conditions.
“Leading Jet”
subset
“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” (Df12 > 150o) with almost equal transverse energies (PT(jet#2)/PT(jet#1) > 0.8) with no other conditions .
“Inc2J Back-to-Back”
subset
“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” (Df12 > 150o) with almost equal transverse energies (PT(jet#2)/PT(jet#1) > 0.8) and PT(jet#3) < 15 GeV/c.
“Exc2J Back-to-Back”
“Charged Jet”
“Leading ChgJet” events correspond to the leading charged particle jet (R = 0.7) in the region |h| < 1 with no other conditions.
“Z-Boson” events are Drell-Yan events with 70 < M(lepton-pair) < 110 GeV with no other conditions.
Z-Boson
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

6. “transMAX” & “transMIN”
“transMIN” very sensitive to the “beam-beam remnants”!
Z-Boson Direction
Area = 4p/6
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 h-f space of 4p/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).
The overall “transverse” density is the average of the “transMAX” and “transMIN” densities.
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

7. Observables at the Particle and Detector Level
“Leading Jet”
Observable
Particle Level
Detector Level
dNchg/dhdf
Number of charged particles
per unit h-f
(pT > 0.5 GeV/c, |h| < 1)
Number of “good” charged tracks
dPTsum/dhdf
Scalar pT sum of charged particles per unit h-f
Scalar pT sum of “good” charged tracks per unit h-f
<pT>
Average pT of charged particles
Average pT of “good” charged tracks
PTmax
Maximum pT charged particle
Require Nchg ≥ 1
Maximum pT “good” charged tracks
dETsum/dhdf
Scalar ET sum of all particles
(all pT, |h| < 1)
Scalar ET sum of all calorimeter towers
(ET > 0.1 GeV, |h| < 1)
PTsum/ETsum
Scalar pT sum of charged particles
divided by the scalar ET sum of
all particles (all pT, |h| < 1)
Scalar pT sum of “good” charged tracks
calorimeter towers (ET > 0.1 GeV, |h| < 1)
“Back-to-Back”
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

8. Overall Totals (|h| < 1)
ETsum = 775 GeV!
“Leading Jet”
ETsum = 330 GeV
PTsum = 190 GeV/c
Nchg = 30
Data at 1.96 TeV on the overall number of charged particles (pT > 0.5 GeV/c, |h| < 1) and the overall scalar pT sum of charged particles (pT > 0.5 GeV/c, |h| < 1) and the overall scalar ET sum of all particles (|h| < 1) for “leading jet” events as a function of the leading jet pT. 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)..
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

9. “Towards”, “Away”, “Transverse”
“Leading Jet”
Factor of ~13
Factor of ~16
Factor of ~4.5
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).
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).
Data at 1.96 TeV on the particle scalar ET sum density, dET/dhdf, for |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).
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

10. Charged Particle Density
HERWIG + JIMMY
Tune (PTJIM = 3.6)
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” and “Leading Jet” events as a function of the leading jet pT or PT(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).
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

11. The “TransMAX/MIN” Regions
Data at 1.96 TeV on the charged particle density, dN/dhdf, with pT > 0.5 GeV/c and |h| < 1 for “Z-Boson” and “Leading Jet” events as a function of PT(Z) or the leading jet pT 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/dhdf, with pT > 0.5 GeV/c and |h| < 1 for “leading jet” events as a function of the leading jet pT and for Z-Boson events as a function of PT(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).
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

12. Charged Particle <pT>
Data at 1.96 TeV on the charged particle average pT, with pT > 0.5 GeV/c and |h| < 1 for the “toward” region for “Z-Boson” and the “transverse” region for “Leading Jet” events as a function of the leading jet pT or PT(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)
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

13. Z-Boson: “Towards”, Transverse”, & “TransMIN” Charge Density
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 PT(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).
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

14. Z-Boson: “Towards” Region
DWT
HW without MPI
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 PT(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).
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

15. Z-Boson: “Towards” Region
DWT
HW (without MPI)
almost no change!
Data at 1.96 TeV on the average pT of charged particles with pT > 0.5 GeV/c and |h| < 1 for “Z-Boson” events as a function of PT(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).
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

16. Z-Boson: “Towards” Region
RDF LHC Prediction!
Tevatron
LHC
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 PT(Z) for the “toward” region from PYTHIA Tune AW, Tune DW, Tune S320, and Tune P329 at the particle level (i.e. generator level).
Extrapolations of PYTHIA Tune AW, Tune DW, Tune DWT, Tune S320, and Tune P329 to the LHC.
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

17. Z-Boson: “Towards” Region
RDF LHC Prediction!
Tevatron
LHC
Data at 1.96 TeV on the charged PTsum density, dPT/dhdf, with pT > 0.5 GeV/c and |h| < 1 for “Z-Boson” events as a function of PT(Z) for the “toward” region from PYTHIA Tune AW, Tune DW, Tune S320, and Tune P329 at the particle level (i.e. generator level).
Extrapolations of PYTHIA Tune AW, Tune DW, Tune DWT, Tune S320, and Tune P329 to the LHC.
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

18. Charged Particle Multiplicity
New
No MPI!
Tune A!
7 decades!
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.
The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (pyAnoMPI).
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

19. PYTHIA Tune A Min-Bias “Soft” + ”Hard”
Tuned to fit the CDF Run 1 “underlying event”!
PYTHIA Tune A
CDF Run 2 Default
12% of “Min-Bias” events have PT(hard) > 5 GeV/c!
1% of “Min-Bias” events have PT(hard) > 10 GeV/c!
PYTHIA regulates the perturbative 2-to-2 parton-parton cross sections with cut-off parameters which allows one to run with PT(hard) > 0. One can simulate both “hard” and “soft” collisions in one program.
Lots of “hard” scattering in “Min-Bias” at the Tevatron!
The relative amount of “hard” versus “soft” depends on the cut-off and can be tuned.
This PYTHIA fit predicts that 12% of all “Min-Bias” events are a result of a hard 2-to-2 parton-parton scattering with PT(hard) > 5 GeV/c (1% with PT(hard) > 10 GeV/c)!
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

20. PYTHIA Tune A LHC Min-Bias Predictions
12% of “Min-Bias” events have PT(hard) > 10 GeV/c!
LHC?
Shows the center-of-mass energy dependence of the charged particle density, dNchg/dhdfdPT, for “Min-Bias” collisions compared with PYTHIA Tune A with PT(hard) > 0.
1% of “Min-Bias” events have PT(hard) > 10 GeV/c!
PYTHIA Tune A predicts that 1% of all “Min-Bias” events at 1.8 TeV are a result of a hard 2-to-2 parton-parton scattering with PT(hard) > 10 GeV/c which increases to 12% at 14 TeV!
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

21. Charged Particle Multiplicity
Tune A!
No MPI!
Tune S320!
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.
The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (pyAnoMPI).
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

22. 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)!
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

23. 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)!
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

24. 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)!
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

25. 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).
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

26. 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!
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

27. QCD Monte-Carlo Models: Lepton-Pair Production
“Hard Scattering” Component
“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.
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

28. Rick Field – Florida/CDF/CMS
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.
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

29. Rick Field – Florida/CDF/CMS
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>. = + +
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

30. 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).
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

31. Rick Field – Florida/CDF/CMS
Average PT versus Nchg
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).
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

32. Charged Particle Multiplicity
Tune A prediction at 900 GeV!
No MPI!
Tune A!
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.
The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (pyAnoMPI).
Prediction from PYTHIA Tune A for proton-proton collisions at 900 GeV.
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

33. Rick Field – Florida/CDF/CMS
LHC Predictions: 900 GeV
Charged multiplicity distributions for proton-proton collisions at 900 GeV (|h| < 2) from PYTHIA Tune A, Tune DW, Tune S320, and Tune P329.
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

34. Rick Field – Florida/CDF/CMS
LHC Predictions: 900 GeV
Compares the 900 GeV data with my favorite PYTHIA Tunes (Tune DW and Tune S320 Perugia 0). Tune DW uses the old Q2-ordered parton shower and the old MPI model. Tune S320 uses the new pT-ordered parton shower and the new MPI model. The numbers in parentheses are the average value of dN/dh for the region |h| < 0.6.
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

35. Rick Field – Florida/CDF/CMS
LHC Predictions: 900 GeV
Off by 11%!
CMS dN/dh
Shows the individual HC, DD, and SD predictions of PYTHIA Tune DW and Tune S320 Perugia 0. The numbers in parentheses are the average value of dN/dh for the region |h| < I do not trust PYTHIA to model correctly the DD and SD contributions! I would like to know how well these tunes model the HC component. We need to look at observables where only HC contributes!
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

36. “Transverse” Charged Density
PTmax > 5 GeV/c!
Shows the charged particle density in the “transverse” region for charged particles (pT > 0.5 GeV/c, |h| < 2) at 900 GeV as defined by PTmax from PYTHIA Tune DW and Tune S320 at the particle level (i.e. generator level).
Shows the charged particle multiplicity distribution in the “transverse” region (pT > 0.5 GeV/c, |h| < 2) at 900 GeV as defined by PTmax from PYTHIA Tune DW and Tune S320 at the particle level (i.e. generator level).
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

37. Charged Particle Multiplicity
The “underlying event” is twice as active as an average HC collision!
NchgDen = 0.21
Shows the charged particle multiplicity distribution in the “transverse” region (pT > 0.5 GeV/c, |h| < 2) at 900 GeV as defined by PTmax from PYTHIA Tune DW and Tune S320 at the particle level (i.e. generator level).
Shows the charged particle multiplicity distribution in HC collisions (pT > 0.5 GeV/c, |h| < 2) at 900 GeV PYTHIA Tune A, Tune DW, Tune S320, and Tune P329 at the particle level (i.e. generator level).
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

38. Min-Bias “Associated” Charged Particle Density
LHC14
LHC10
LHC7
Tevatron
900 GeV
RHIC
7 TeV → 14 TeV
(UE increase ~20%)
LHC7
LHC14
Linear on a log plot!
Shows the “associated” charged particle density in the “transverse” region as a function of PTmax for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for “min-bias” events at 0.2 TeV, 0.9 TeV, 1.96 TeV, 7 TeV, 10 TeV, 14 TeV predicted by PYTHIA Tune DW at the particle level (i.e. generator level).
Log scale!
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

39. “Transverse” Charge Density
factor of 2!
900 GeV → 7 TeV
(UE increase ~ factor of 2.1)
LHC
900 GeV
LHC
7 TeV
Shows the charged particle density in the “transverse” region for charged particles (pT > 0.5 GeV/c, |h| < 2) at 900 GeV as defined by PTmax from PYTHIA Tune DW and Tune S320 at the particle level (i.e. generator level).
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

40. Rick Field – Florida/CDF/CMS
sHC: PTmax > 5 GeV/c
Still lots of events!
Linear scale!
Log scale!
stot = sEL + sSD + sDD + sHC
In 1,000,000 HC collisions at 900 GeV you get 940 with PTmax > 5 GeV/c!
The inelastic non-diffractive PTmax > 5 GeV/c cross section (|h| < 1) versus center-of-mass energy from PYTHIA (×1.2).
sHC(PTmax > 5 GeV/c) varies more rapidly. Factor of 2.3 increase between 7 TeV (≈ 0.56 mb) and 14 teV (≈ 1.3 mb). Linear on a linear scale!
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

41. PTmax Cross-Section 900 GeV
stot = sEL + sSD + sDD + sHC
In 1,000,000 HC collisions at 900 GeV you get ~3,000 with PTmax > 5 GeV/c!
The inelastic non-diffractive PTmax > 5 GeV/c cross section (|h| < 2) at 900 GeV from PYTHIA Tune DW and Tune S320.
Number of events with PTmax > PT0 (|h| < 2) for 1,000,000 HC collisions at 900 GeV from PYTHIA Tune DW and Tune S320.
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

42. “Transverse” Charged Particle Density
361,595 events
Fake data (from MC) at 900 GeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle (PTmax) and the leading charged particle jet (chgjet#1) for charged particles with pT > 0.5 GeV/c and |h| < 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).
Fake data (from MC) at 900 GeV on the “transverse” charged PTsum density, dPT/dhdf, as defined by the leading charged particle (PTmax) and the leading charged particle jet (chgjet#1) for charged particles with pT > 0.5 GeV/c and |h| < 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).
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

43. “Transverse” Distributions
Stay tuned! UE studies
at 900 GeV coming soon
from CMS and ATLAS.
43, 855 events
Fake data (from MC) at 900 GeV on the “transverse” charged particle multiplicity as defined by the leading charged particle (PTmax) with PTmax > 2 GeV/c for charged particles with pT > 0.5 GeV/c and |h| < 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 (43,855 events in the plot).
Fake data (from MC) at 900 GeV on the “transverse” charged PT distribution as defined by the leading charged particle (PTmax) with PTmax > 2 GeV/c for charged particles with pT > 0.5 GeV/c and |h| < 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.
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS

44. LHC Predictions Stay tuned! UE studies at 900 GeV and 7 TeV
coming soon!
I believe because of the STAR analysis we are now
in a position to make some predictions at the LHC!
The amount of activity in “min-bias” collisions.
The amount of activity in the “underlying event” in hard scattering events.
The amount of activity in the “underlying event” in Drell-Yan events.
Lake Louise Winter Institute February 16, 2010
Rick Field – Florida/CDF/CMS