1. Toward an Understanding of Hadron-Hadron Collisions
From Feynman-Field to the LHC
Rick Field
University of Florida
Outline of Talk
The early days of Feynman-Field Phenomenology.
Studying “min-bias” collisions and the “underlying event” at CDF.
Rutgers University October 2009
Studying the formation of the “underlying event”.
CDF Run 2
The PYTHIA MPI energy scaling parameter PARP(90).
The “underlying event” at STAR. Extrapolations to RHIC.
LHC predictions!
CMS at the LHC
Summary & Conclusions.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

2. Toward and Understanding of Hadron-Hadron Collisions
Feynman-Field Phenomenology
1st hat!
Feynman
and
Field
From 7 GeV/c p0’s to 600 GeV/c Jets. The early days of trying to understand and simulate hadron-hadron collisions.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

3. Hadron-Hadron Collisions
FF1 1977
What happens when two hadrons collide at high energy?
Feynman quote from FF1
“The model we shall choose is not a popular one,
so that we will not duplicate too much of the
work of others who are similarly analyzing
various models (e.g. constituent interchange
model, multiperipheral models, etc.). We shall
assume that the high PT particles arise from
direct hard collisions between constituent
quarks in the incoming particles, which
fragment or cascade down into several hadrons.”
Most of the time the hadrons ooze through each other and fall apart (i.e. no hard scattering). The outgoing particles continue in roughly the same direction as initial proton and antiproton.
Occasionally there will be a large transverse momentum meson. Question: Where did it come from?
We assumed it came from quark-quark elastic scattering, but we did not know how to calculate it!
“Black-Box Model”
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

4. Quark-Quark Black-Box Model
No gluons!
FF1 1977
Quark Distribution Functions
determined from deep-inelastic
lepton-hadron collisions
Feynman quote from FF1
“Because of the incomplete knowledge of
our functions some things can be predicted
with more certainty than others. Those
experimental results that are not well
predicted can be “used up” to determine
these functions in greater detail to permit
better predictions of further experiments.
Our papers will be a bit long because we
wish to discuss this interplay in detail.”
Quark Fragmentation Functions
determined from e+e- annihilations
Quark-Quark Cross-Section
Unknown! Deteremined from
hadron-hadron collisions.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

5. Quark-Quark Black-Box Model
FF1 1977
Predict
particle ratios
Predict
increase with increasing
CM energy W
“Beam-Beam Remnants”
Predict
overall event topology
(FFF1 paper 1977)
7 GeV/c p0’s!
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

6. Feynman Talk at Coral Gables (December 1976)
1st transparency
Last transparency
“Feynman-Field
Jet Model”
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

7. QCD Approach: Quarks & Gluons
Quark & Gluon Fragmentation Functions
Q2 dependence predicted from QCD
FFF2 1978
Feynman quote from FFF2
“We investigate whether the present
experimental behavior of mesons with
large transverse momentum in hadron-hadron
collisions is consistent with the theory of
quantum-chromodynamics (QCD) with
asymptotic freedom, at least as the theory
is now partially understood.”
Parton Distribution Functions
Q2 dependence predicted from QCD
Quark & Gluon Cross-Sections
Calculated from QCD
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

8. A Parameterization of the Properties of Jets
Field-Feynman 1978
Secondary Mesons
(after decay)
Assumed that jets could be analyzed on a “recursive” principle.
(bk)
(ka)
Let f(h)dh be the probability that the rank 1 meson leaves fractional momentum h to the remaining cascade, leaving quark “b” with momentum P1 = h1P0.
Rank 2
Rank 1
Assume that the mesons originating from quark “b” are distributed in presisely the same way as the mesons which came from quark a (i.e. same function f(h)), leaving quark “c” with momentum P2 = h2P1 = h2h1P0.
Primary Mesons
(cb)
(ba)
cc pair
bb pair
continue
Add in flavor dependence by letting bu = probabliity of producing u-ubar pair, bd = probability of producing d-dbar pair, etc.
Calculate F(z) from f(h) and bi!
Let F(z)dz be the probability of finding a meson (independent of rank) with fractional mementum z of the original quark “a” within the jet.
Original quark with flavor “a” and momentum P0
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

9. Feynman-Field Jet Model
R. P. Feynman
ISMD, Kaysersberg, France, June 12, 1977
Feynman quote from FF2
“The predictions of the model are reasonable
enough physically that we expect it may
be close enough to reality to be useful in
designing future experiments and to serve
as a reasonable approximation to compare
to data. We do not think of the model
as a sound physical theory, ....”
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

10. High PT Jets CDF (2006) Feynman, Field, & Fox (1978) 30 GeV/c! Predict
large “jet” cross-section
30 GeV/c!
Feynman quote from FFF
“At the time of this writing, there is
still no sharp quantitative test of QCD.
An important test will come in connection
with the phenomena of high PT discussed here.”
600 GeV/c Jets!
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

11. Monte-Carlo Simulation of Hadron-Hadron Collisions
FF1-FFF1 (1977) “Black-Box” Model
FF2 (1978)
Monte-Carlo simulation of “jets”
F1-FFF2 (1978) QCD Approach
FFFW “FieldJet” (1980)
QCD “leading-log order” simulation
of hadron-hadron collisions
“FF” or “FW” Fragmentation
my early days
yesterday
ISAJET
(“FF” Fragmentation)
HERWIG
(“FW” Fragmentation)
PYTHIA
(“String” Fragmentation)
today
SHERPA
PYTHIA 6.4
HERWIG++
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

12. 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!
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

13. 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.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

14. 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
The “hard core” component contains both “hard” and “soft” collisions.
CDF “Min-Bias” trigger
1 charged particle in forward BBC
AND
1 charged particle in backward BBC
“Inelastic Non-Diffractive Component”
Beam-Beam Counters
3.2 < |h| < 5.9
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

15. Inelastic Non-Diffractive Cross-Section
My guess!
Lots of events!
Linear scale!
Log scale!
stot = sEL + sSD + sDD + sHC
The inelastic non-diffractive cross section versus center-of-mass energy from PYTHIA (×1.2).
sHC varies slowly. Only a 13% increase between 7 TeV (≈ 58 mb) and 14 teV (≈ 66 mb). Linear on a log scale!
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

16. 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.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

17. CDF Run 1 “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).
0.25
0.67
There are about 0.25 charged particles per unit h-f in “Min-Bias” collisions at 1.96 TeV (|h| < 1, pT > 0.5 GeV/c). <dNchg/dh> = 1.6!
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

18. CDF Run 1: 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.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

19. PYTHIA default parameters
PYTHIA Defaults
MPI constant
probability
scattering
PYTHIA default parameters
Parameter
6.115
6.125
6.158
6.206
MSTP(81) 1
MSTP(82)
PARP(81)
1.4
1.9
PARP(82)
1.55
2.1
PARP(89)
1,000
PARP(90)
0.16
PARP(67)
4.0
1.0
Plot shows the “Transverse” charged particle density versus PT(chgjet#1) compared to the QCD hard scattering predictions of PYTHIA (PT(hard) > 0) using the default parameters for multiple parton interactions and CTEQ3L, CTEQ4L, and CTEQ5L.
Default parameters give very poor description of the “underlying event”!
Note Change
PARP(67) = 4.0 (< 6.138)
PARP(67) = 1.0 (> 6.138)
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

20. 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)
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

21. Run 1 Charged Particle Density “Transverse” pT Distribution
Factor of 2!
PT(charged jet#1) > 30 GeV/c
“Transverse” <dNchg/dhdf> = 0.56
“Min-Bias”
CDF Run 1 Min-Bias data
<dNchg/dhdf> = 0.25
Compares the average “transverse” charge particle density with the average “Min-Bias” charge particle density (|h|<1, pT>0.5 GeV). Shows how the “transverse” charge particle density and the Min-Bias charge particle density is distributed in pT.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

22. 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)!
Rutgers High Energy Physics Seminar October 13, 2009
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)!
Rutgers High Energy Physics Seminar October 13, 2009
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)!
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

25. CDF Run 1 Min-Bias “Associated” Charged Particle Density
Highest pT charged particle!
“Associated” densities do not include PTmax!
Use the maximum pT charged particle in the event, PTmax, to define a direction and look at the the “associated” density, dNchg/dhdf, in “min-bias” collisions (pT > 0.5 GeV/c, |h| < 1).
It is more probable to find a particle accompanying PTmax than it is to find a particle in the central region!
Shows the data on the Df dependence of the “associated” charged particle density, dNchg/dhdf, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” events. Also shown is the average charged particle density, dNchg/dhdf, for “min-bias” events.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

26. CDF Run 1 Min-Bias “Associated” Charged Particle Density
Rapid rise in the particle density in the “transverse” region as PTmax increases!
PTmax > 2.0 GeV/c
Transverse Region
Transverse Region
Ave Min-Bias
0.25 per unit h-f
PTmax > 0.5 GeV/c
Shows the data on the Df dependence of the “associated” charged particle density, dNchg/dhdf, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” events with PTmax > 0.5, 1.0, and 2.0 GeV/c.
Shows “jet structure” in “min-bias” collisions (i.e. the “birth” of the leading two jets!).
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

27. Min-Bias “Associated” Charged Particle Density
“Toward” Region
“Transverse”
“Transverse”
~ factor of 2!
Shows the Df dependence of the “associated” charged particle density, dNchg/dhdf, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” events at 1.96 TeV with PTmax > 0.5, 1.0, 2.0, 5.0, and 10.0 GeV/c from PYTHIA Tune A (generator level).
Shows the “associated” charged particle density in the “toward”, “away” and “transverse” regions as a function of PTmax for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for “min-bias” events at 1.96 TeV from PYTHIA Tune A (generator level).
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

28. “Transverse” Charged Density
0.6
Shows the charged particle density in the “transverse” region for charged particles (pT > 0.5 GeV/c, |h| < 1) at 1.96 TeV as defined by PTmax, PT(chgjet#1), and PT(jet#1) from PYTHIA Tune A at the particle level (i.e. generator level).
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

29. Tuning PYTHIA: Multiple Parton Interaction Parameters
Default
Description
PARP(83)
0.5
Double-Gaussian: Fraction of total hadronic matter within PARP(84)
PARP(84)
0.2
Double-Gaussian: Fraction of the overall hadron radius containing the fraction PARP(83) of the total hadronic matter.
PARP(85)
0.33
Probability that the MPI produces two gluons with color connections to the “nearest neighbors.
PARP(86)
0.66
Probability that the MPI produces two gluons either as described by PARP(85) or as a closed gluon loop. The remaining fraction consists of quark-antiquark pairs.
PARP(89)
1 TeV
Determines the reference energy E0.
PARP(82)
1.9 GeV/c
The cut-off PT0 that regulates the 2-to-2 scattering divergence 1/PT4→1/(PT2+PT02)2
PARP(90)
0.16
Determines the energy dependence of the cut-off
PT0 as follows PT0(Ecm) = PT0(Ecm/E0)e with e = PARP(90)
PARP(67)
1.0
A scale factor that determines the maximum parton virtuality for space-like showers. The larger the value of PARP(67) the more initial-state radiation.
Hard Core
Determines the energy dependence of the MPI!
Determine by comparing
with 630 GeV data!
Affects the amount of
initial-state radiation!
Take E0 = 1.8 TeV
Reference point
at 1.8 TeV
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

30. “Transverse” Cones vs “Transverse” Regions
“Cone Analysis”
(Tano, Kovacs, Huston, Bhatti)
Transverse Cone:
p(0.7)2=0.49p
Transverse Region:
2p/3=0.67p
Sum the PT of charged particles in two cones of radius 0.7 at the same h as the leading jet but with |DF| = 90o.
Plot the cone with the maximum and minimum PTsum versus the ET of the leading (calorimeter) jet.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

31. Energy Dependence of the “Underlying Event”
“Cone Analysis”
(Tano, Kovacs, Huston, Bhatti)
630 GeV
1,800 GeV
PYTHIA 6.115
PT0 = 1.4 GeV
PYTHIA 6.115
PT0 = 2.0 GeV
Sum the PT of charged particles (pT > 0.4 GeV/c) in two cones of radius 0.7 at the same h as the leading jet but with |DF| = 90o. Plot the cone with the maximum and minimum PTsum versus the ET of the leading (calorimeter) jet.
Note that PYTHIA is tuned at 630 GeV with PT0 = 1.4 GeV and at 1,800 GeV with PT0 = 2.0 GeV. This implies that e = PARP(90) should be around 0.30 instead of the 0.16 (default).
For the MIN cone 0.25 GeV/c in radius R = 0.7 implies a PTsum density of dPTsum/dhdf = 0.16 GeV/c and 1.4 GeV/c in the MAX cone implies dPTsum/dhdf = 0.91 GeV/c (average PTsum density of 0.54 GeV/c per unit h-f).
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

32. “Transverse” Charged Densities Energy Dependence
Increasing e produces less energy dependence for the UE resulting in less UE activity at the LHC!
Lowering PT0 at 630 GeV (i.e. increasing e) increases UE activity resulting in less energy dependence.
Shows the “transverse” charged PTsum density (|h|<1, PT>0.4 GeV) versus PT(charged jet#1) at 630 GeV predicted by HERWIG 6.4 (PT(hard) > 3 GeV/c, CTEQ5L) and a tuned version of PYTHIA (PT(hard) > 0, CTEQ5L, Set A, e = 0, e = 0.16 (default) and e = 0.25 (preferred)).
Also shown are the PTsum densities (0.16 GeV/c and 0.54 GeV/c) determined from the Tano, Kovacs, Huston, and Bhatti “transverse” cone analysis at 630 GeV.
Rick Field Fermilab MC Workshop
October 4, 2002!
Reference point
E0 = 1.8 TeV
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

33. 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)!
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

34. 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).
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

35. 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!
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

36. Tune A energy dependence!
PYTHIA 6.2 Tunes
All use LO as
with L = 192 MeV!
Parameter
Tune AW
Tune DW
Tune D6
PDF
CTEQ5L
CTEQ6L
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)
2.1
PARP(93)
15.0
UE Parameters
Uses CTEQ6L
Tune A energy dependence!
(not the default)
ISR Parameter
Intrinsic KT
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

37. PYTHIA 6.2 Tunes These are “old” PYTHIA 6.2 tunes!
There are new tunes by
Peter Skands (Tune S320, update of S0)
Peter Skands (Tune N324, N0CR)
Hendrik Hoeth (Tune P329, “Professor”)
All use LO as
with L = 192 MeV!
Parameter
Tune DWT
Tune D6T
ATLAS
PDF
CTEQ5L
CTEQ6L
MSTP(81) 1
MSTP(82) 4
PARP(82)
GeV
GeV
1.8 GeV
PARP(83)
0.5
PARP(84)
0.4
PARP(85)
1.0
0.33
PARP(86)
0.66
PARP(89)
1.96 TeV
1.0 TeV
PARP(90)
0.16
PARP(62)
1.25
PARP(64)
0.2
PARP(67)
2.5
MSTP(91)
PARP(91)
2.1
PARP(93)
15.0
5.0
UE Parameters
Tune B
Tune AW
Tune A
ATLAS energy dependence!
(PYTHIA default)
Tune BW
ISR Parameter
Tune DW
Tune D6
Tune D
Tune D6T
Intrinsic KT
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

38. Peter’s Pythia Tunes WEBsite
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

39. Min-Bias “Associated” Charged Particle Density
35% more at RHIC means 26% less at the LHC!
~1.35
~1.35
0.2 TeV → 14 TeV
(~factor of 70 increase)
RHIC
LHC
Shows the “associated” charged particle density in the “transverse” regions 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 and 14 TeV from PYTHIA Tune DW and Tune DWT at the particle level (i.e. generator level). The STAR data from RHIC favors Tune DW!
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

40. Min-Bias “Associated” Charged Particle Density
~1.9
~2.7
0.2 TeV → 1.96 TeV
(UE increase ~2.7 times)
1.96 TeV → 14 TeV
(UE increase ~1.9 times)
RHIC
Tevatron
LHC
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, 1.96 TeV and 14 TeV predicted by PYTHIA Tune DW at the particle level (i.e. generator level).
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

41. The “Underlying Event” at STAR
At STAR they have measured the “underlying event at W = 200 GeV (|h| < 1, pT > 0.2 GeV) and compared their uncorrected data with PYTHIA Tune A + STAR-SIM.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

42. Min-Bias “Associated” Charged Particle Density
If the LHC data are not in
the range shown here then
we learn new (QCD) physics!
RDF LHC Prediction!
Tevatron
LHC
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 1.96 TeV from PYTHIA Tune A, Tune S320, Tune N324, and Tune P329 at the particle level (i.e. generator level).
Extrapolations of PYTHIA Tune A, Tune DW, Tune DWT, Tune S320, Tune P329, and pyATLAS to the LHC.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

43. “Transverse” Charged Density
Shows the charged particle density in the “transverse” region for charged particles (pT > 0.5 GeV/c, |h| < 1) at 7 TeV as defined by PTmax, PT(chgjet#1), and PT(muon-pair) from PYTHIA Tune DW at the particle level (i.e. generator level). Charged particle jets are constructed using the Anti-KT algorithm with d = 0.5.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

44. Min-Bias “Associated” Charged Particle Density
LHC14
LHC10
LHC7
Tevatron
900 GeV
RHIC
0.2 TeV → 1.96 TeV
(UE increase ~2.7 times)
1.96 TeV → 14 TeV
(UE increase ~1.9 times)
RHIC
Tevatron
LHC
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).
Linear scale!
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

45. 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!
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

46. Rick Field – Florida/CDF/CMS
sHC: PTmax > 5 GeV/c
Still lots of events!
Linear scale!
Log scale!
stot = sEL + sSD + sDD + sHC
The inelastic non-diffractive PTmax > 5 GeV/c cross section 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!
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

47. “Transverse” Charged Density
With 1/nb of “min-bias” data at 7 TeV we could study the UE out to PTmax = 25 GeV/c or PT(chgjet#1) = 45 GeV/c !
Shows the charged particle density in the “transverse” region for charged particles (pT > 0.5 GeV/c, |h| < 1) at 7 TeV as defined by PTmax and PT(chgjet#1) from PYTHIA Tune DW at the particle level (i.e. generator level). Charged particle jet are constructed using the Anti-KT algorithm with d = 0.5.
Shows the leading charged particle jet, chgjet#1, and the leading charged particle, PTmax, differential cross section, ds/dPT (pT > 0.5 GeV/c, |h| < 1) from PYTHIA Tune DW at the particle level (i.e. generator level). Charged particle jet are constructed using the Anti-KT algorithm with d = 0.5.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

48. Drell-Yan Muon-Pair Cross-Section
Linear scale!
The Drell-Yan muon-pair cross section 70 < M(pair) < 110 GeV versus center-of-mass energy from PYTHIA (×1.3).
The Drell-Yan cross-section varies rapidly. Factor of 2.2 increase between 7 TeV (≈ 0.9 nb) and 14 teV (≈ 2 nb). Linear on a linear scale!
Note nb not mb!
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

49. Drell-Yan Muon-Pair Cross-Section
Linear scale!
4,700 events in 10/pb!
CMS acceptance!
The Drell-Yan muon-pair cross section 70 < M(pair) < 110 GeV (|h(m)| < 2.4, pT(m) > 5 GeV/c) versus center-of-mass energy from PYTHIA (×1.3).
The CMS Drell-Yan cross-section varies rapidly. Factor of 1.9 increase between 7 TeV (≈ 0.5 nb) and 14 TeV (≈ 0.9 nb). Linear on a linear scale!
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

50. “Transverse” Charged Density
Note at CMS “min-bias” is pre-scaled by a factor of 5,000 so this really corresponds to 5/pb delivered !
With 10/pb of data at 7 TeV we could study the UE in Drell-Yan production out to PT(pair) = 15 GeV/c !
Shows the charged particle density in the “transverse” region for charged particles (pT > 0.5 GeV/c, |h| < 1) at 7 TeV as defined by PTmax, PT(chgjet#1), and PT(muon-pair) for PYTHIA Tune DW at the particle level (i.e. generator level). Charged particle jet are constructed using the Anti-KT algorithm with d = 0.5.
Shows the leading charged particle jet, chgjet#1, and the leading charged particle, PTmax, differential cross section, ds/dPT (pT > 0.5 GeV/c, |h| < 1), and the Drell-Yan differential cross-section (70 < M(pair) < 110 GeV) from PYTHIA Tune DW at the particle level (i.e. generator level). Charged particle jet are constructed using the Anti-KT algorithm with d = 0.5.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

51. Charged Particle Density: dN/dh
Charged particle (all pT) pseudo-rapidity distribution, dNchg/dhdf, at 1.96 TeV for inelastic non-diffractive collisions from PYTHIA Tune A, Tune DW, Tune S320, and Tune P324.
Charged particle (pT>0.5 GeV/c) pseudo-rapidity distribution, dNchg/dhdf, at 1.96 TeV for inelastic non-diffractive collisions from PYTHIA Tune A, Tune DW, Tune S320, and Tune P324.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

52. Charged Particle Density: dN/dh
If the LHC data are not in
the range shown here then
we learn new (QCD) physics!
RDF LHC Prediction!
Tevatron
LHC
Charged particle (all pT) pseudo-rapidity distribution, dNchg/dhdf, at 1.96 TeV for inelastic non-diffractive collisions from PYTHIA Tune A, Tune DW, Tune S320, and Tune P324.
Extrapolations (all pT) of PYTHIA Tune A, Tune DW, Tune S320, Tune P324. and ATLAS to the LHC.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

53. Charged Particle Density: dN/dh
If the LHC data are not in
the range shown here then
we learn new (QCD) physics!
RDF LHC Prediction!
Tevatron
LHC
Charged particle (pT > 0.5 GeV/c) pseudo-rapidity distribution, dNchg/dhdf, at 1.96 TeV for inelastic non-diffractive collisions from PYTHIA Tune A, Tune DW, Tune S320, and Tune P324.
Extrapolations (pT > 0.5 GeV/c) of PYTHIA Tune A, Tune DW, Tune S320, Tune P324. and ATLAS to the LHC.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

54. LHC Predictions If the LHC data are not in the range shown here then
we learn new (QCD) physics!
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.
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS

55. Rick Field – Florida/CDF/CMS
Summary & Conclusions
We are making good progress in understanding and modeling the “underlying event”. RHIC data at 200 GeV are very important!
The new Pythia pT ordered tunes (py64 S320 and py64 P329) are very similar to Tune A, Tune AW, and Tune DW. At present the new tunes do not fit the data better than Tune AW and Tune DW. However, the new tune are theoretically preferred!
Py64 S320 = LHC “Reference Tune”!
It is clear now that the default value PARP(90) = 0.16 is not correct and the value should be closer to the Tune A value of 0.25.
The new and old PYTHIA tunes are beginning to converge and I believe we are finally in a position to make some legitimate predictions at the LHC!
All tunes with the default value PARP(90) = 0.16 are wrong and are overestimating the activity of min-bias and the underlying event at the LHC! This includes all my “T” tunes and the ATLAS tunes!
Need to measure “Min-Bias” and the “underlying event” at the LHC as soon as possible to see if there is new QCD physics to be learned!
Rutgers High Energy Physics Seminar October 13, 2009
Rick Field – Florida/CDF/CMS