1. University of Chicago Lecture 3: Tuning the Models
and Extrapolations to the LHC
Rick Field
University of Florida
Enrico Fermi Institute, University of Chicago
CDF Run 2
Min-Bias and the “Underlying Event”
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

2. Particle Densities Charged Particles pT > 0.5 GeV/c |h| < 1
DhDf = 4p = 12.6
CDF Run 2 “Min-Bias”
CDF Run 2 “Min-Bias”
Observable
Average
Average Density
per unit h-f
Nchg
Number of Charged Particles
(pT > 0.5 GeV/c, |h| < 1)
3.17 +/- 0.31 /
PTsum (GeV/c)
Scalar pT sum of Charged Particles
2.97 +/- 0.23 /
1 charged particle
dNchg/dhdf = 1/4p = 0.08
dNchg/dhdf = 3/4p = 0.24
3 charged particles
1 GeV/c PTsum
dPTsum/dhdf = 1/4p GeV/c = 0.08 GeV/c
dPTsum/dhdf = 3/4p GeV/c = 0.24 GeV/c
3 GeV/c PTsum
Divide by 4p
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.
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

3. “Transverse” Particle Densities
Charged Particles
pT > 0.5 GeV/c |h| < 1
Area = 4p/6
AVE “transverse”
(Trans 1 + Trans 2)/2
1 charged particle in the
“transverse 2” region
dNchg/dhdf = 1/(4p/6) = 0.48
Study the charged particles (pT > 0.5 GeV/c, |h| < 1) in the “Transverse 1” and “Transverse 2” and form the charged particle density, dNchg/dhdf, and the charged scalar pT sum density, dPTsum/dhdf.
The average “transverse” density is the average of “transverse 1” and “transverse 2”.
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

4. 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!
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

5. Evolution of Charged Jets “Underlying Event”
Charged Particle Df Correlations PT > 0.5 GeV/c |h| < 1
Look at the charged particle density in the “transverse” region!
“Transverse” region very sensitive to the “underlying event”!
CDF Run 1 Analysis
Look at charged particle correlations in the azimuthal angle Df relative to the leading charged particle jet.
Define |Df| < 60o as “Toward”, 60o < |Df| < 120o as “Transverse”, and |Df| > 120o as “Away”.
All three regions have the same size in h-f space, DhxDf = 2x120o = 4p/3.
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

6. Run 1 PYTHIA Tune A PYTHIA 6.206 CTEQ5L
CDF Default!
PYTHIA CTEQ5L
Parameter
Tune B
Tune A
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(67)
4.0
Run 1 Analysis
Plot shows the “transverse” charged particle density versus PT(chgjet#1) compared to the QCD hard scattering predictions of two tuned versions of PYTHIA (CTEQ5L, Set B (PARP(67)=1) and Set A (PARP(67)=4)).
Old PYTHIA default
(more initial-state radiation)
Old PYTHIA default
(more initial-state radiation)
New PYTHIA default
(less initial-state radiation)
New PYTHIA default
(less initial-state radiation)
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

7. “Transverse” Charged Particle Density
“Transverse” region as defined by the leading “charged particle jet”
Excellent agreement between Run 1 and 2!
Shows the data on the average “transverse” charge particle density (|h|<1, pT>0.5 GeV) as a function of the transverse momentum of the leading charged particle jet from Run 1.
Compares the Run 2 data (Min-Bias, JET20, JET50, JET70, JET100) with Run 1. The errors on the (uncorrected) Run 2 data include both statistical and correlated systematic uncertainties.
PYTHIA Tune A was tuned to fit the “underlying event” in Run I!
Shows the prediction of PYTHIA Tune A at 1.96 TeV after detector simulation (i.e. after CDFSIM).
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

8. 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).
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

9. 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.
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

10. “Transverse” PTsum Density vs 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 (without MPI) after CDFSIM.
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

11. Latest CDF Run 2 “Underlying Event” Results
The “underlying event” consists of the “beam-beam remnants” and possible multiple parton interactions, but inevitably received contributions from initial and final-state radiation.
“Transverse” region is very sensitive to the “underlying event”!
Latest 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.
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

12. “TransMAX/MIN” PTsum Density PYTHIA Tune A vs HERWIG
PYTHIA Tune A does a fairly good job fitting the PTsum density in the “transverse” region!
HERWIG does a poor job!
“Leading Jet”
“Back-to-Back”
Shows the charged particle PTsum density, dPTsum/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.
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

13. “TransMAX/MIN” ETsum Density PYTHIA Tune A vs HERWIG
“Leading Jet”
“Back-to-Back”
Neither PY Tune A or HERWIG fits the ETsum density in the “transferse” region!
HERWIG does slightly better than Tune A!
Shows the data on the tower ETsum density, dETsum/dhdf, in the “transMAX” and “transMIN” region (ET > 100 MeV, |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 (all particles, |h| < 1).
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

14. “TransDIF” ETsum Density PYTHIA Tune A vs HERWIG
“Leading Jet”
“Back-to-Back”
“transDIF” is more 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.
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

15. Rick Field – Florida/CDF
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.
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

16. “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!
JIMMY: MPI
J. M. Butterworth
J. R. Forshaw
M. H. Seymour
“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) at the particle level.
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

17. “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.
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

18. “Transverse” <PT> PYTHIA Tune A vs JIMMY
“Leading Jet”
“Back-to-Back”
Shows the charged particle <PT> in the “transverse” (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.
Both JIMMY and HERWIG are too “soft” for pT > 0.5 GeV/c!
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

19. Rick Field – Florida/CDF
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
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

20. CDF Run 1 PT(Z) PYTHIA 6.2 CTEQ5L
Tune used by the
CDF-EWK group!
PYTHIA 6.2 CTEQ5L
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)!
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

21. 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).
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

22. 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!
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

23. “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!
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

24. “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!
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

25. 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 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).
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).
Identical to DW at 1.96 TeV but uses
ATLAS extrapolation to the LHC!
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

26. MIT Search Scheme 12 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
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

27. The data have more 3 jet events with small R(j2,j3)!?
3Jexc 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
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

28. 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
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

29. 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).
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

30. 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.
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

31. 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.
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

32. 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).
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

33. 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).
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

34. 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).
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

35. 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).
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

36. 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).
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

37. Proton-AntiProton Collisions at the Tevatron
The CDF “Min-Bias” trigger picks up most of the “hard core” cross-section plus a small amount of single & double diffraction.
stot = sEL + sIN
stot = sEL + sSD + sDD + sHC
1.8 TeV: 78mb = 18mb mb (4-7)mb + (47-44)mb
CDF “Min-Bias” trigger
1 charged particle in forward BBC
AND
1 charged particle in backward BBC
The “hard core” component contains both “hard” and “soft” collisions.
Beam-Beam Counters
3.2 < |h| < 5.9
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

38. CDF “Min-Bias” Data Charged Particle Density
<dNchg/dh> = 4.2
<dNchg/dhdf> = 0.67
Shows CDF “Min-Bias” data on the number of charged particles per unit pseudo-rapidity at 630 and 1,800 GeV. There are about 4.2 charged particles per unit h in “Min-Bias” collisions at 1.8 TeV (|h| < 1, all PT).
Convert to charged particle density, dNchg/dhdf, by dividing by 2p. There are about 0.67 charged particles per unit h-f in “Min-Bias” collisions at 1.8 TeV (|h| < 1, all PT).
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

39. CDF “Min-Bias” Data Energy Dependence
LHC?
<dNchg/dhdf> = 0.51
h = GeV
24% increase
<dNchg/dhdf> = 0.63
h = TeV
Shows the center-of-mass energy dependence of the charged particle density, dNchg/dhdf, for “Min-Bias” collisions at h = 0. Also show a log fit (Fit 1) and a (log)2 fit (Fit 2) to the CDF plus UA5 data.
What should we expect for the LHC?
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

40. PYTHIA Tune A Min-Bias “Soft” + ”Hard”
Tuned to fit the “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”!
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)!
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

41. PYTHIA Tune A LHC Min-Bias Predictions
Shows the center-of-mass energy dependence of the charged particle density, dNchg/dhdf, for “Min-Bias” collisions compared with PYTHIA Tune A with PT(hard) > 0.
PYTHIA was tuned to fit the “underlying event” in hard-scattering processes at 1.8 TeV and 630 GeV.
PYTHIA Tune A predicts a 42% rise in dNchg/dhdf at h = 0 in going from the Tevatron (1.8 TeV) to the LHC (14 TeV). Similar to HERWIG “soft” min-bias, 4 charged particles per unit h becomes 6.
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

42. 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!
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

43. PYTHIA 6.2 Tunes LHC Min-Bias Predictions
Shows the predictions of PYTHIA Tune A, Tune DW, Tune DWT, and the ATLAS tune for the charged particle density dN/dh and dN/dY at 14 TeV (all pT).
PYTHIA Tune A and Tune DW predict about 6 charged particles per unit h at h = 0, while the ATLAS tune predicts around 9.
PYTHIA Tune DWT is identical to Tune DW at 1.96 TeV, but extrapolates to the LHC using the ATLAS energy dependence.
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

44. PYTHIA 6.2 Tunes LHC Min-Bias Predictions
Shows the predictions of PYTHIA Tune A, Tune DW, Tune DWT, and the ATLAS tune for the charged particle pT distribution at 14 TeV (|h| < 1) and the average number of charged particles with pT > pTmin (|h| < 1).
The ATLAS tune has many more “soft” particles than does any of the CDF Tunes. The ATLAS tune has <pT> = 548 MeV/c while Tune A has <pT> = 641 MeV/c (100 MeV/c more per particle)!
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

45. Summary Tevatron LHC More work needs to be done in
comparing the various tunes at the LHC.
The ATLAS tune cannot be right
because it does not fit the Tevatron
data. Right now I like Tune DW.
Probably no tune will fit the LHC data.
That is why we plan to measure MB&UE
at CMS and retune the Monte-Carlo
models!
Tevatron LHC
PYTHIA Tune A does not produce enough “soft” energy in the “underlying event”! JIMMY 325 (PTJIM = 3.25 GeV/c) fits the energy in the “underlying event” but does so by producing too many particles (i.e. it is too soft).
The ATLAS tune is “goofy”! It produces too many “soft” particles. The charged particle <pT> is too low and does not agree with the CDF Run 2 data. The ATLAS tune agrees with <Nchg> but not with <PTsum> at the Tevatron.
PYTHIA Tune DW is very similar to Tune A except that it fits the CDF PT(Z) distribution and it uses the DØ prefered value of PARP(67) = 2.5 (determined from the dijet Df distribution).
PYTHIA Tune DWT is identical to Tune DW at 1.96 TeV but uses the ATLAS energy extrapolation to the LHC (i.e. PARP(90) = 0.16).
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF

46. Conclusions Tevatron LHC I think more work needs to be done
in comparing the various tunes.
The ATLAS tune cannot be right
because it does not fit the Tevatron
data. Right now I like Tune DW.
Probably no tune will fit the CMS data.
That is why we want to measure MB&UE
at CMS and retune the Monte-Carlo
models!
Tevatron LHC
We cannot use the new underlying event model in PYTHIA It has not been studied (and tuned) well enough yet!
The ATLAS tune is “goofy”! It produces too many “soft” particles. The charged particle <pT> is too low and does not agree with the CDF Run 2 data. The ATLAS tune agrees with <Nchg> but not with <PTsum> at the Tevatron.
PYTHIA Tune DW is very similar to Tune A except that it fits the CDF PT(Z) distribution and it uses the DØ prefered value of PARP(67) = 2.5 (determined from the dijet Df distribution).
PYTHIA Tune DWT is identical to Tune DW at 1.96 TeV but uses the ATLAS energy extrapolation to the LHC (i.e. PARP(90) = 0.16).
Lecture 3: University of Chicago July 11, 2006
Rick Field – Florida/CDF