1. Physics and Techniques of Event Generators
IPPP Durham, April 18-20, 2007
Min-Bias and the Underlying Event
at the TEVATRON and the LHC
Rick Field
University of Florida
(for the CDF & CMS Collaborations)
2nd Lecture
A more detailed study of the “underlying event” in Run 2 at CDF.
and extrapolations to the LHC.
Using lepton-pair production to study the “underlying event” in Run 2 at CDF and the LHC.
CMS at the LHC
CDF Run 2
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

2. The “Transverse” Regions as defined by the Leading Jet
Charged Particle Df Correlations pT > 0.5 GeV/c |h| < 1
Look at the charged particle density in the “transverse” region!
“Transverse” region is very sensitive to the “underlying event”!
Look at charged particle correlations in the azimuthal angle Df relative to the leading calorimeter jet (JetClu R = 0.7, |h| < 2).
Define |Df| < 60o as “Toward”, 60o < -Df < 120o and 60o < Df < 120o as “Transverse 1” and “Transverse 2”, and |Df| > 120o as “Away”. Each of the two “transverse” regions have area DhDf = 2x60o = 4p/6. The overall “transverse” region is the sum of the two transverse regions (DhDf = 2x120o = 4p/3).
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

3. Charged Particle Density Df Dependence
Log Scale!
Leading Jet
Min-Bias
0.25 per unit h-f
Shows the Df dependence of the charged particle density, dNchg/dhdf, for charged particles in the range pT > 0.5 GeV/c and |h| < 1 relative to jet#1 (rotated to 270o) for “leading jet” events 30 < ET(jet#1) < 70 GeV.
Also shows charged particle density, dNchg/dhdf, for charged particles in the range pT > 0.5 GeV/c and |h| < 1 for “min-bias” collisions.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

4. Charged Particle Density Df Dependence
Refer to this as a “Leading Jet” event
Subset
Refer to this as a
“Back-to-Back” event
Look at the “transverse” region as defined by the leading jet (JetClu R = 0.7, |h| < 2) or by the leading two jets (JetClu R = 0.7, |h| < 2). “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 (ET(jet#2)/ET(jet#1) > 0.8) and with ET(jet#3) < 15 GeV.
Shows the Df dependence of the charged particle density, dNchg/dhdf, for charged particles in the range pT > 0.5 GeV/c and |h| < 1 relative to jet#1 (rotated to 270o) for 30 < ET(jet#1) < 70 GeV for “Leading Jet” and “Back-to-Back” events.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

5. Charged Particle Density Df Dependence
“Leading Jet”
“Back-to-Back”
0.5
1.0
1.5
2.0
Polar Plot
Shows the Df dependence of the charged particle density, dNchg/dhdf, for charged particles in the range pT > 0.5 GeV/c and |h| < 1 relative to jet#1 (rotated to 270o) for 30 < ET(jet#1) < 70 GeV for “Leading Jet” and “Back-to-Back” events.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

6. “Transverse” PTsum Density versus ET(jet#1)
“Leading Jet”
Hard Radiation!
“Back-to-Back”
Min-Bias
0.24 GeV/c per unit h-f
Shows the average charged PTsum density, dPTsum/dhdf, in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events.
Compares the (uncorrected) data with PYTHIA Tune A and HERWIG after CDFSIM.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

7. “Transverse” PTsum Density versus ET(jet#1)
30-70 GeV
GeV
Very little dependence on ET(jet#1) in the “transverse” region for “back-to-back” events!
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

8. “TransMIN” PTsum Density versus ET(jet#1)
“Leading Jet”
“Back-to-Back”
“transMIN” is very sensitive to the “beam-beam remnant” component of the “underlying event”!
Use the leading jet to define the MAX and MIN “transverse” regions on an event-by-event basis with MAX (MIN) having the largest (smallest) charged particle density.
Shows the “transMIN” charge particle density, dNchg/dhdf, for pT > 0.5 GeV/c, |h| < 1 versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

9. “Transverse” PTsum Density PYTHIA Tune A vs HERWIG
“Leading Jet”
“Back-to-Back”
Now look in detail at “back-to-back” events in the region 30 < ET(jet#1) < 70 GeV!
Shows the average charged PTsum density, dPTsum/dhdf, in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events.
Compares the (uncorrected) data with PYTHIA Tune A and HERWIG after CDFSIM.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

10. Charged PTsum Density PYTHIA Tune A vs HERWIG
HERWIG (without multiple parton interactions) does not produces enough PTsum in the “transverse” region for 30 < ET(jet#1) < 70 GeV!
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

11. Charged PTsum Density PYTHIA Tune A vs HERWIG
dPT/dhdf GeV/c
308 MeV in
R = 0.7 cone!
Add 0.2 GeV/c per unit h-f to HERWIG scalar PTsum density, dPTsum/dhdf.
This corresponds to 0.2 × 4p = 2.5 GeV/c in the entire range pT > 0.5 GeV/c, |h| < 1.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

12. “Transverse” PTmax versus ET(jet#1)
“Leading Jet”
Highest pT particle in the “transverse” region!
“Back-to-Back”
Min-Bias
Use the leading jet to define the “transverse” region and look at the maximum pT charged particle in the “transverse” region, PTmaxT.
Shows the average PTmaxT, in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events compared with the average maximum pT particle, PTmax, in “min-bias” collisions (pT > 0.5 GeV/c, |h| < 1).
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

13. Back-to-Back “Associated” Charged Particle Densities
Maximum pT particle in the “transverse” region!
“Associated” densities do not include PTmaxT!
Use the leading jet in “back-to-back” events to define the “transverse” region and look at the maximum pT charged particle in the “transverse” region, PTmaxT.
Look at the Df dependence of the “associated” charged particle and PTsum densities, dNchg/dhdf and dPTsum/dhdf for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmaxT) relative to PTmaxT.
Rotate so that PTmaxT is at the center of the plot (i.e. 180o).
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

14. Back-to-Back “Associated” Charged Particle Densities
“Associated” densities do not include PTmaxT!
Jet#2 Region ??
Log Scale!
Look at the Df dependence of the “associated” charged particle density, dNchg/dhdf for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmaxT) relative to PTmaxT (rotated to 180o) for PTmaxT > 0.5 GeV/c, PTmaxT > 1.0 GeV/c and PTmaxT > 2.0 GeV/c, for “back-to-back” events with 30 < ET(jet#1) < 70 GeV.
Shows “jet structure” in the “transverse” region (i.e. the “birth” of the 3rd & 4th jet).
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

15. Back-to-Back “Associated” Charged Particle Densities
charge density
“Back-to-Back”
“associated” density
0.5
1.0
1.5
2.0
Polar Plot
Shows the Df dependence of the “associated” charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1 (not including PTmaxT) relative to PTmaxT (rotated to 180o) and the charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1 relative to jet#1 (rotated to 270o) for “back-to-back events” with 30 < ET(jet#1) < 70 GeV.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

16. Back-to-Back “Associated” Charged Particle Densities
charge density
“Back-to-Back”
“associated” density
0.5
1.0
1.5
2.0
Polar Plot
Shows the Df dependence of the “associated” charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1, PTmaxT > 2.0 GeV/c (not including PTmaxT) relative to PTmaxT (rotated to 180o) and the charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1, relative to jet#1 (rotated to 270o) for “back-to-back events” with 30 < ET(jet#1) < 70 GeV.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

17. Rick Field – Florida/CDF/CMS
Jet Topologies
QCD Three Jet Topology
QCD Four Jet Topology
0.5
1.0
1.5
2.0
Polar Plot
Shows the Df dependence of the “associated” charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1, PTmaxT > 2.0 GeV/c (not including PTmaxT) relative to PTmaxT (rotated to 180o) and the charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1, relative to jet#1 (rotated to 270o) for “back-to-back events” with 30 < ET(jet#1) < 70 GeV.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

18. “Back-to-Back” vs “Min-Bias” “Associated” Charge Density
“Birth” of jet#3 in the “transverse” region!
“Back-to-Back”
“Associated” Density
“Min-Bias”
“Associated” Density
Log Scale!
“Birth” of jet#1 in “min-bias” collisions!
Shows the Df dependence of the “associated” charged particle density, dNchg/dhdf for pT > 0.5 GeV/c, |h| < 1 (not including PTmaxT) relative to PTmaxT (rotated to 180o) for PTmaxT > 2.0 GeV/c, for “back-to-back” events with 30 < ET(jet#1) < 70 GeV.
Shows the data on the Df dependence of the “associated” charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1 (not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” events with PTmax > 2.0 GeV/c.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

19. “Associated” PTsum Density PYTHIA Tune A vs HERWIG
HERWIG (without multiple parton interactions) does not produce enough “associated” PTsum in the direction of PTmaxT!
PTmaxT > 0.5 GeV/c
And HERWIG (without multiple parton interactions) does not produce enough PTsum in the direction opposite of PTmaxT!
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

20. “Associated” PTsum Density PYTHIA Tune A vs HERWIG
For PTmaxT > 2.0 GeV both PYTHIA and HERWIG produce slightly too much “associated” PTsum in the direction of PTmaxT!
PTmaxT > 2 GeV/c
But HERWIG (without multiple parton interactions) produces too few particles in the direction opposite of PTmaxT!
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

21. Jet Multiplicity
Max pT in the “transverse” region!
HERWIG (without multiple parton interactions) does not have equal amounts of 3 and 4 jet topologies!
Data have about equal amounts of 3 and 4 jet topologies!
Shows the data on the number of jets (JetClu, R = 0.7, |h| < 2, ET(jet) > 3 GeV) for “back-to-back” events with 30 < ET(jet#1) < 70 GeV and PTmaxT > 2.0 GeV/c.
Compares the (uncorrected) data with HERWIG after CDFSIM.
Compares the (uncorrected) data with PYTHIA Tune A after CDFSIM.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

22. “Transverse” <pT> versus “Transverse” Nchg
“Leading Jet”
“Back-to-Back”
Min-Bias
Look at the <pT> of particles in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) versus the number of particles in the “transverse” region: <pT> vs Nchg.
Shows <pT> versus Nchg in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) for “Leading Jet” and “Back-to-Back” events with 30 < ET(jet#1) < 70 GeV compared with “min-bias” collisions.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

23. “Transverse 1” Region vs “Transverse 2” Region
“Leading Jet”
“Back-to-Back”
Use the leading jet to define two “transverse” regions and look at the correlations between “transverse 1” and “transverse 2”.
Shows the average number of charged particles in the “transverse 2” region versus the number of charged particles in the “transverse 1” region for pT > 0.5 GeV/c and |h| < 1 for “Leading Jet” and “Back-to-Back” events.
Shows the average pT of charged particles in the “transverse 2” region versus the number of charged particles in the “transverse 1” region for pT > 0.5 GeV/c and |h| < 1 for “Leading Jet” and “Back-to-Back” events.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

24. “Transverse 1” Region vs “Transverse 2” Region
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

25. Recent CDF Run 2 “Underlying Event” Results
The “underlying event” consists of hard initial & final-state radiation plus the “beam-beam remnants” and possible multiple parton interactions.
“Transverse” region is very sensitive to the “underlying event”!
New CDF Run 2 results (L = 385 pb-1) :
Two Classes of Events: “Leading Jet” and “Back-to-Back”.
Two “Transverse” regions: “transMAX”, “transMIN”, “transDIF”.
Data Corrected to the Particle Level: unlike our previous CDF Run 2 “underlying event” analysis which used JetClu to define “jets” and compared uncorrected data with the QCD Monte-Carlo models after detector simulation, this analysis uses the MidPoint jet algorithm and corrects the observables to the particle level. The corrected observables are then compared with the QCD Monde-Carlo models at the particle level.
For the 1st time we study the energy density in the “transverse” region.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

26. “Transverse” Observables 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
PTmax = 0 for no charged particle
Maximum pT “good” charged tracks
PTmax = 0 for no “good” charged track
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”
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

27. “TransMAX/MIN” Nchg Density PYTHIA Tune A vs HERWIG
“Leading Jet”
“Back-to-Back”
Shows the charged particle density, dNchg/dhdf, in the “transMAX” and “transMIN” region (pT > 0.5 GeV/c, |h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events.
Compares the (corrected) data with PYTHIA Tune A (with MPI) and HERWIG (without MPI) at the particle level.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

28. “Transverse” <PT> and <PTmax> PYTHIA Tune A vs HERWIG
“Leading Jet”
“Back-to-Back”
Shows the average transverse momentum, <PT>, and <PTmax> for charged particles in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events.
Compares the (corrected) data with PYTHIA Tune A (with MPI) and HERWIG (without MPI) at the particle level.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

29. “TransMAX/MIN” ETsum Density PYTHIA Tune A vs HERWIG
“Leading Jet”
“Back-to-Back”
Shows the ETsum density, dETsum/dhdf, in the “transMAX” and “transMIN” region (all particles |h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events.
Compares the (corrected) data with PYTHIA Tune A (with MPI) and HERWIG (without MPI) at the particle level.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

30. “TransDIF” ETsum Density PYTHIA Tune A vs HERWIG
“Leading Jet”
“Back-to-Back”
“transDIF” is very sensitive to the “hard scattering” component of the “underlying event”!
Use the leading jet to define the MAX and MIN “transverse” regions on an event-by-event basis with MAX (MIN) having the largest (smallest) charged PTsum density.
Shows the “transDIF” = MAX-MIN ETsum density, dETsum/dhdf, for all particles (|h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

31. “TransMAX/MIN” ETsum Density PYTHIA Tune A vs JIMMY
JIMMY was tuned to fit the energy density in the “transverse” region for “leading jet” events!
“Leading Jet”
“Back-to-Back”
Shows the ETsum density, dETsum/dhdf, in the “transMAX” and “transMIN” region (all particles |h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events.
Compares the (corrected) data with PYTHIA Tune A (with MPI) and a tuned version of JIMMY (with MPI, PTJIM = 3.25 GeV/c, default = 2.5 GeV/c) at the particle level.
JIMMY: MPI
J. M. Butterworth
J. R. Forshaw
M. H. Seymour
JIMMY
Runs with HERWIG and adds multiple parton interactions!
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

32. “TransMAX/MIN” PTsum Density PYTHIA Tune A vs JIMMY
“Leading Jet”
“Back-to-Back”
Shows the charged PTsum density, dETsum/dhdf, in the “transMAX” and “transMIN” region (pT > 0.5 GeV/c, |h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events.
Compares the (corrected) data with PYTHIA Tune A (with MPI) and a tuned version of JIMMY (with MPI, PTJIM = 3.25 GeV/c) at the particle level.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

33. “TransMAX/MIN” Nchg Density PYTHIA Tune A vs JIMMY
“Leading Jet”
“Back-to-Back”
Shows the charged particle density, dNchg/dhdf, in the “transMAX” and “transMIN” region (pT > 0.5 GeV/c, |h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events.
Compares the (corrected) data with PYTHIA Tune A (with MPI) and a tuned version of JIMMY (with MPI, PTJIM = 3.25 GeV/c) at the particle level.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

34. “Transverse” <PT> PYTHIA Tune A vs JIMMY
“Leading Jet”
“Back-to-Back”
Shows the charged particle <PT> in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events.
Compares the (corrected) data with PYTHIA Tune A (with MPI) and HERWIG and a tuned version of JIMMY (with MPI, PTJIM = 3.25 GeV/c) at the particle level.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

35. Rick Field – Florida/CDF/CMS
Possible Scenario??
PYTHIA Tune A fits the charged particle PTsum density for pT > 0.5 GeV/c, but it does not produce enough ETsum for towers with ET > 0.1 GeV.
It is possible that there is a sharp rise in the number of particles in the “underlying event” at low pT (i.e. pT < 0.5 GeV/c).
Perhaps there are two components, a vary “soft” beam-beam remnant component (Gaussian or exponential) and a “hard” multiple interaction component.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

36. Rick Field – Florida/CDF/CMS
CDF Run 1 PT(Z)
PYTHIA 6.2 CTEQ5L
UE Parameters
Parameter
Tune A
Tune A25
Tune A50
MSTP(81) 1
MSTP(82) 4
PARP(82)
2.0 GeV
PARP(83)
0.5
PARP(84)
0.4
PARP(85)
0.9
PARP(86)
0.95
PARP(89)
1.8 TeV
PARP(90)
0.25
PARP(67)
4.0
MSTP(91)
PARP(91)
1.0
2.5
5.0
PARP(93)
15.0
25.0
ISR Parameter
Shows the Run 1 Z-boson pT distribution (<pT(Z)> ≈ 11.5 GeV/c) compared with PYTHIA Tune A (<pT(Z)> = 9.7 GeV/c), Tune A25 (<pT(Z)> = 10.1 GeV/c), and Tune A50 (<pT(Z)> = 11.2 GeV/c).
Vary the intrensic KT!
Intrensic KT
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

37. CDF Run 1 PT(Z) PYTHIA 6.2 CTEQ5L
Tune used by the
CDF-EWK group!
Parameter
Tune A
Tune AW
MSTP(81) 1
MSTP(82) 4
PARP(82)
2.0 GeV
PARP(83)
0.5
PARP(84)
0.4
PARP(85)
0.9
PARP(86)
0.95
PARP(89)
1.8 TeV
PARP(90)
0.25
PARP(62)
1.0
1.25
PARP(64)
0.2
PARP(67)
4.0
MSTP(91)
PARP(91)
2.1
PARP(93)
5.0
15.0
UE Parameters
ISR Parameters
Shows the Run 1 Z-boson pT distribution (<pT(Z)> ≈ 11.5 GeV/c) compared with PYTHIA Tune A (<pT(Z)> = 9.7 GeV/c), and PYTHIA Tune AW (<pT(Z)> = 11.7 GeV/c).
Effective Q cut-off, below which space-like showers are not evolved.
Intrensic KT
The Q2 = kT2 in as for space-like showers is scaled by PARP(64)!
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

38. Jet-Jet Correlations (DØ)
Df Jet#1-Jet#2
Jet#1-Jet#2 Df Distribution
MidPoint Cone Algorithm (R = 0.7, fmerge = 0.5)
L = 150 pb-1 (Phys. Rev. Lett (2005))
Data/NLO agreement good. Data/HERWIG agreement good.
Data/PYTHIA agreement good provided PARP(67) = 1.0→4.0 (i.e. like Tune A, best fit 2.5).
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

39. CDF Run 1 PT(Z) PYTHIA 6.2 CTEQ5L
Parameter
Tune DW
Tune AW
MSTP(81) 1
MSTP(82) 4
PARP(82)
1.9 GeV
2.0 GeV
PARP(83)
0.5
PARP(84)
0.4
PARP(85)
1.0
0.9
PARP(86)
0.95
PARP(89)
1.8 TeV
PARP(90)
0.25
PARP(62)
1.25
PARP(64)
0.2
PARP(67)
2.5
4.0
MSTP(91)
PARP(91)
2.1
PARP(93)
15.0
UE Parameters
ISR Parameters
Shows the Run 1 Z-boson pT distribution (<pT(Z)> ≈ 11.5 GeV/c) compared with PYTHIA Tune DW, and HERWIG.
Tune DW uses D0’s perfered value of PARP(67)!
Intrensic KT
Tune DW has a lower value of PARP(67) and slightly more MPI!
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

40. “Transverse” Nchg Density
PYTHIA 6.2 CTEQ5L
Three different amounts of MPI!
UE Parameters
Parameter
Tune AW
Tune DW
Tune BW
MSTP(81) 1
MSTP(82) 4
PARP(82)
2.0 GeV
1.9 GeV
1.8 GeV
PARP(83)
0.5
PARP(84)
0.4
PARP(85)
0.9
1.0
PARP(86)
0.95
PARP(89)
1.8 TeV
PARP(90)
0.25
PARP(62)
1.25
PARP(64)
0.2
PARP(67)
4.0
2.5
MSTP(91)
PARP(91)
2/5
PARP(93)
15.0
ISR Parameter
Shows the “transverse” charged particle density, dN/dhdf, versus PT(jet#1) for “leading jet” events at 1.96 TeV for PYTHIA Tune A, Tune AW, Tune DW, Tune BW, and HERWIG (without MPI).
Shows the “transverse” charged particle density, dN/dhdf, versus PT(jet#1) for “leading jet” events at 1.96 TeV for Tune DW, ATLAS, and HERWIG (without MPI).
Intrensic KT
Three different amounts of ISR!
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

41. “Transverse” PTsum Density
PYTHIA 6.2 CTEQ5L
Three different amounts of MPI!
UE Parameters
Parameter
Tune AW
Tune DW
Tune BW
MSTP(81) 1
MSTP(82) 4
PARP(82)
2.0 GeV
1.9 GeV
1.8 GeV
PARP(83)
0.5
PARP(84)
0.4
PARP(85)
0.9
1.0
PARP(86)
0.95
PARP(89)
1.8 TeV
PARP(90)
0.25
PARP(62)
1.25
PARP(64)
0.2
PARP(67)
4.0
2.5
MSTP(91)
PARP(91)
2/5
PARP(93)
15.0
ISR Parameter
Shows the “transverse” charged PTsum density, dPT/dhdf, versus PT(jet#1) for “leading jet” events at 1.96 TeV for PYTHIA Tune A, Tune AW, Tune DW, Tune BW, and HERWIG (without MPI).
Shows the “transverse” charged PTsum density, dPT/dhdf, versus PT(jet#1) for “leading jet” events at 1.96 TeV for Tune DW, ATLAS, and HERWIG (without MPI).
Intrensic KT
Three different amounts of ISR!
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

42. Identical to DW at 1.96 TeV but uses ATLAS extrapolation to the LHC!
PYTHIA 6.2 Tunes
PYTHIA 6.2 CTEQ5L
s(MPI) at 1.96 TeV
s(MPI) at 14 TeV
Tune A
309.7 mb
484.0 mb
Tune DW
351.7 mb
549.2 mb
Tune DWT
829.1 mb
ATLAS
324.5 mb
768.0 mb
Parameter
Tune A
Tune DW
Tune DWT
ATLAS
MSTP(81) 1
MSTP(82) 4
PARP(82)
2.0 GeV
1.9 GeV
GeV
1.8 GeV
PARP(83)
0.5
PARP(84)
0.4
PARP(85)
0.9
1.0
0.33
PARP(86)
0.95
0.66
PARP(89)
1.8 TeV
1.96 TeV
1.0 TeV
PARP(90)
0.25
0.16
PARP(62)
1.25
PARP(64)
0.2
PARP(67)
4.0
2.5
MSTP(91)
PARP(91)
2.1
PARP(93)
5.0
15.0
CDF Run 2 Data!
Shows the “transverse” charged PTsum density, dPT/dhdf, versus PT(jet#1) for “leading jet” events at 1.96 TeV for Tune A, DW, ATLAS, and HERWIG (without MPI).
Shows the “transverse” charged average pT, versus PT(jet#1) for “leading jet” events at 1.96 TeV for Tune A, DW, ATLAS, and HERWIG (without MPI).
Shows the “transverse” charged particle density, dN/dhdf, versus PT(jet#1) for “leading jet” events at 1.96 TeV for Tune A, DW, ATLAS, and HERWIG (without MPI).
Identical to DW at 1.96 TeV but uses
ATLAS extrapolation to the LHC!
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

43. The “Underlying Event” in High PT Jet Production (LHC)
Charged particle density versus PT(jet#1)
The “Underlying Event”
“Underlying event” much more active at the LHC!
Charged particle density in the “Transverse” region versus PT(jet#1) at 1.96 TeV for PY Tune AW and HERWIG (without MPI).
Charged particle density in the “Transverse” region versus PT(jet#1) at 14 TeV for PY Tune AW and HERWIG (without MPI).
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

44. MIT Search Scheme: Vista/Sleuth
Exclusive 3 Jet Final State Challenge
CDF Data
At least 1 Jet (“trigger” jet)
(PT > 40 GeV/c, |h| < 1.0)
Bruce Knuteson
Normalized to 1
PYTHIA Tune A
Exactly 3 jets
(PT > 20 GeV/c, |h| < 2.5)
Order Jets by PT
Jet1 highest PT, etc.
R(j2,j3)
Khaldoun Makhoul
Georgios Choudalakis
Markus Klute
Conor Henderson
Ray Culbertson
Gene Flanagan
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

45. Exc3J: R(j2,j3) Normalized
The data have more 3 jet events with small R(j2,j3)!?
Let Ntrig40 equal the number of events with at least one jet with PT > 40 geV and |h| < 1.0 (this is the “offline” trigger).
Let N3Jexc20 equal the number of events with exactly three jets with PT > 20 GeV/c and |h| < 2.5 which also have at least one jet with PT > 40 GeV/c and |h| < 1.0.
Normalized to N3JexcFr
Let N3JexcFr = N3Jexc20/Ntrig40. The is the fraction of the “offline” trigger events that are exclusive 3-jet events.
The CDF data on dN/dR(j2,j3) at 1.96 TeV compared with PYTHIA Tune AW (PARP(67)=4), Tune DW (PARP(67)=2.5), Tune BW (PARP(67)=1).
PARP(67) affects the initial-state radiation which contributes primarily to the region R(j2,j3) > 1.0.
R > 1.0
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

46. excess number of events Perhaps this is related to the
3Jexc R(j2,j3) Normalized
I do not understand the
excess number of events
with R(j2,j3) < 1.0.
Perhaps this is related to the
“soft energy” problem??
For now the best tune is
PYTHIA Tune DW.
Let Ntrig40 equal the number of events with at least one jet with PT > 40 geV and |h| < 1.0 (this is the “offline” trigger).
Let N3Jexc20 equal the number of events with exactly three jets with PT > 20 GeV/c and |h| < 2.5 which also have at least one jet with PT > 40 GeV/c and |h| < 1.0.
Normalized to N3JexcFr
Let N3JexcFr = N3Jexc20/Ntrig40. The is the fraction of the “offline” trigger events that are exclusive 3-jet events.
The CDF data on dN/dR(j2,j3) at 1.96 TeV compared with PYTHIA Tune DW (PARP(67)=2.5) and HERWIG (without MPI).
Final-State radiation contributes to the region R(j2,j3) < 1.0.
If you ignore the normalization and normalize all the distributions to one then the data prefer Tune BW, but I believe this is misleading.
R < 1.0
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

47. 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 and final-state radiation.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

48. The “Central” Region in Drell-Yan Production
Look at the charged particle density and the PTsum density in the “central” region!
Charged Particles (pT > 0.5 GeV/c, |h| < 1)
After removing the lepton-pair everything else is the “underlying event”!
Look at the “central” region after removing the lepton-pair.
Study the charged particles (pT > 0.5 GeV/c, |h| < 1) and form the charged particle density, dNchg/dhdf, and the charged scalar pT sum density, dPTsum/dhdf, by dividing by the area in h-f space.
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

49. Drell-Yan Production (Run 2 vs LHC)
Lepton-Pair Transverse Momentum
<pT(m+m-)> is much larger at the LHC!
Shapes of the pT(m+m-) distribution at the Z-boson mass. Z
Average Lepton-Pair transverse momentum at the Tevatron and the LHC for PYTHIA Tune DW and HERWIG (without MPI).
Shape of the Lepton-Pair pT distribution at the Z-boson mass at the Tevatron and the LHC for PYTHIA Tune DW and HERWIG (without MPI).
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

50. The “Underlying Event” in Drell-Yan Production
Charged particle density versus M(pair)
HERWIG (without MPI) is much less active than PY Tune AW (with MPI)!
“Underlying event” much more active at the LHC! Z Z
Charged particle density versus the lepton-pair invariant mass at 1.96 TeV for PYTHIA Tune AW and HERWIG (without MPI).
Charged particle density versus the lepton-pair invariant mass at 14 TeV for PYTHIA Tune AW and HERWIG (without MPI).
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

51. Extrapolations to the LHC: Drell-Yan Production
Charged particle density versus M(pair)
The “Underlying Event”
Tune DW and DWT are identical at 1.96 TeV, but have different MPI energy dependence! Z Z
Average charged particle density versus the lepton-pair invariant mass at 1.96 TeV for PYTHIA Tune A, Tune AW, Tune BW, Tune DW and HERWIG (without MPI).
Average charged particle density versus the lepton-pair invariant mass at 14 TeV for PYTHIA Tune DW, Tune DWT, ATLAS and HERWIG (without MPI).
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

52. Extrapolations to the LHC: Drell-Yan Production
Charged particle charged PTsum density versus M(pair)
The “Underlying Event”
The ATLAS tune has a much “softer” distribution of charged particles than the CDF Run 2 Tunes! Z Z
Average charged PTsum density versus the lepton-pair invariant mass at 1.96 TeV for PYTHIA Tune A, Tune AW, Tune BW, Tune DW and HERWIG (without MPI).
Average charged PTsum density versus the lepton-pair invariant mass at 14 TeV for PYTHIA Tune DW, Tune DWT, ATLAS and HERWIG (without MPI).
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

53. Extrapolations to the LHC: Drell-Yan Production
Charged particle density versus M(pair)
The “Underlying Event”
The ATLAS tune has a much “softer” distribution of charged particles than the CDF Run 2 Tunes!
Charged Particles (|h|<1.0, pT > 0.5 GeV/c)
Charged Particles (|h|<1.0, pT > 0.9 GeV/c) Z Z
Average charged particle density (pT > 0.5 GeV/c) versus the lepton-pair invariant mass at 14 TeV for PYTHIA Tune DW, Tune DWT, ATLAS and HERWIG (without MPI).
Average charged particle density (pT > 0.9 GeV/c) versus the lepton-pair invariant mass at 14 TeV for PYTHIA Tune DW, Tune DWT, ATLAS and HERWIG (without MPI).
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

54. Summary and Conclusions
“Min-Bias” is not well defined. What you see depends on what you trigger on! Every trigger produces some biases.
We have learned a lot about “Min-Bias” at the Tevatron, but we do not know what to expect at the LHC.
This will depend on the Min-Bias Trigger!
I must double check my analysis and get it “blessed” before you can trust what I have shown!
Very preliminary results seem to show that pile-up conspires to help give you what you ask for (i.e. satisfy your “trigger” or your event selection)!
If true this means the pile-up is not the same for all processes. It is process (i.e. trigger) dependent!
We are making good progress in understanding and modeling the “underlying event”. However, we do not yet have a perfect fit to all the features of the CDF “underlying event” data!
Need to measure “Min-Bias” and the “underlying event” at the LHC as soon as possible and tune the Monte-Carlo modles and compare with CDF!
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS

55.
Study charged particles
and muons using the CMS detector
at the LHC (as soon as possible)!
Min-Bias Studies: Charged particle distributions and correlations. Construct “charged particle jets” and look at “mini-jet” structure and the onset of the “underlying event”. (requires only charged tracks)
“Underlying Event” Studies: The “transverse region” in “leading Jet” and “back-to-back” charged particle jet production and the “central region” in Drell-Yan production. (requires charged tracks and muons for Drell-Yan)
Drell-Yan Studies: Transverse momentum distribution of the lepton-pair versus the mass of the lepton-pair, <pT(pair)>, <pT2(pair)>, ds/dpT(pair) (only requires muons). Event structure for large lepton-pair pT (i.e. mm +jets, requires muons).
MCnet07 - Durham - Part April 18-20, 2007
Rick Field – Florida/CDF/CMS