PHZ 6358 Fall 2011
The Modeling of the Underlying Event
Rick Field
University of Florida
Outline of Talk
 Studying the “underlying event” at the Tevatron. The
CDF PYTHIA 6.2 tunes.
University of Florida November 2011
 How well did we do at predicting the behavior of the
“underlying event” at 900 GeV and 7 TeV?
High PT Z-Boson Production
Initial-State Radiation
 The “underlying event” in Z-boson production
at the Tevatron and the LHC.
OutgoingParton
Parton
Outgoing
PT(hard)
Initial-State Radiation
Proton
Proton
Underlying Event
Underlying Event
 Homework Assignment (optional).
Outgoing
Parton
Z-boson
Final-State
Radiation
www.phys.ufl.edu/~rfield/cdf/UF-SM_RickField_11-7-11.ppt
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 1
QCD Monte-Carlo Models:
High Transverse Momentum Jets
Hard Scattering
Initial-State Radiation
Hard Scattering “Jet”
Initial-State Radiation
“Jet”
Outgoing Parton
PT(hard)
Outgoing Parton
PT(hard)
Proton
“Hard Scattering” Component
AntiProton
Final-State Radiation
Outgoing Parton
Underlying Event
Underlying Event
Proton
“Jet”
Final-State Radiation
AntiProton
Underlying Event
Outgoing Parton
Underlying Event
“Underlying Event”
 Start with the perturbative 2-to-2 (or sometimes 2-to-3) parton-parton scattering and add initial and finalstate 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).
The “underlying
event” is“jet”
an unavoidable
 Of course the outgoing colored partons fragment
into hadron
and inevitably “underlying event”
background to most collider observables
observables receive contributions from initial
and final-state radiation.
and having good understand of it leads to
more precise collider measurements!
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 2
Proton-Proton Collisions
Elastic Scattering
Single Diffraction
Double Diffraction
M2
M
M1
stot = sEL + sSD
IN +sDD +sHC
ND
“Inelastic Non-Diffractive Component”
Hard Core
The “hard core” component
contains both “hard” and
“soft” collisions.
“Hard” Hard Core (hard scattering)
Outgoing Parton
“Soft” Hard Core (no hard scattering)
Proton
PT(hard)
Proton
Proton
Proton
Underlying Event
Underlying Event
Initial-State
Radiation
Final-State
Radiation
Outgoing Parton
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 3
The Inelastic Non-Diffractive
Cross-Section
Occasionally one of
the parton-parton
collisions is hard
(pT > ≈2 GeV/c)
Proton
Proton
Majority of “minbias” events!
Proton
“Semi-hard” partonparton collision
(pT < ≈2 GeV/c)
Proton
+
Proton
+
Proton
Proton
Proton
+
Proton
Proton
+…
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Multiple-parton
interactions (MPI)!
Page 4
The “Underlying Event”
Select inelastic non-diffractive events
that contain a hard scattering
Proton
Hard parton-parton
collisions is hard
(pT > ≈2 GeV/c)
Proton
1/(pT)4→ 1/(pT2+pT02)2
The “underlying-event” (UE)!
Proton
Given that you have one hard
scattering it is more probable to
have MPI! Hence, the UE has
more activity than “min-bias”.
PHZ 6358 University of Florida
November 7, 2011
Proton
+
+
Proton
Proton
Rick Field – Florida/CDF/CMS
“Semi-hard” partonparton collision
(pT < ≈2 GeV/c)
Proton
Proton
+…
Multiple-parton
interactions (MPI)!
Page 5
Allow leading hard
scattering to go to
zero pT with same
cut-off as the MPI!
Model of sND
Proton
Proton
Proton
Proton
Proton
+
Proton
“Semi-hard” partonparton collision
(pT < ≈2 GeV/c)
1/(pT)4→ 1/(pT2+pT02)2
Model of the inelastic nondiffractive cross section!
+
Proton
Proton
Proton
+
Proton
Proton
+…
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Multiple-parton
interactions (MPI)!
Page 6
MPI, Pile-Up, and Overlap
MPI: Multiple Parton Interactions
Outgoing Parton
PT(hard)
Initial-State Radiation
Proton
Proton
Underlying Event
 MPI: Additional 2-to-2 parton-parton
scatterings within a single hadron-hadron
collision.
Underlying Event
Outgoing Parton
Final-State
Radiation
Proton
Pile-Up
Pile-Up
Proton
Proton
Proton
Primary
Interaction Region Dz
 Pile-Up: More than one hadron-hadron collision in the beam
crossing.
Overlap
 Overlap: An experimental timing issue where a hadron-hadron
collision from the next beam crossing gets included in the hadronhadron collision from the current beam crossing because the next
crossing happened before the event could be read out.
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 7
Traditional Approach
CDF Run 1 Analysis Charged Particle Df Correlations
Leading Calorimeter Jet or
Charged Jet #1
Leading Charged Particle Jet or
PT > PTmin |h| < hcut
Direction
Leading Charged Particle or
2
“Transverse” region
very sensitive to the
“underlying event”!
Away RegionZ-Boson
“Toward-Side” Jet
Df
“Toward”
“Transverse”
“Transverse”
“Away”
Leading Object
Direction
Df
“Toward”
“Transverse”
“Transverse”
Transverse
Region
f
Leading
Object
Toward Region
Transverse
Region
“Away”
Away Region
0
-hcut
“Away-Side” Jet
h
+hcut
 Look at charged particle correlations in the azimuthal angle Df relative to a leading object (i.e.
CaloJet#1, ChgJet#1, PTmax, Z-boson). For CDF PTmin = 0.5 GeV/c hcut = 1.
 Define |Df| < 60o as “Toward”, 60o < |Df| < 120o as “Transverse”, and |Df| > 120o as
“Away”.
 All three regions have the same area in h-f space, Dh×Df = 2hcut×120o = 2hcut×2/3. Construct
densities by dividing by the area in h-f space.
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 8
ISAJET 7.32 (without MPI)
“Transverse” Density
ISAJET uses a naïve leading-log
parton shower-model which does
not agree with the data!
Charged Jet #1
Direction
"Transverse" Charged Particle Density: dN/dhdf
1.00
Df
“Transverse”
“Transverse”
“Away”
Beam-Beam
Remnants
CDF Run 1Data
"Transverse" Charged Density
“Toward”
ISAJET
Isajet
data uncorrected
theory corrected
0.75
"Hard"
0.50
0.25
"Remnants"
February 25, 2000
“Hard”
Component
1.8 TeV |h|<1.0 PT>0.5 GeV
0.00
0
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1) (GeV/c)
 Plot shows average “transverse” charge particle density (|h|<1, pT>0.5 GeV) versus PT(charged jet#1)
compared to the QCD hard scattering predictions of ISAJET 7.32 (default parameters with
PT(hard)>3 GeV/c) .
 The predictions of ISAJET are divided into two categories: charged particles that arise from the
break-up of the beam and target (beam-beam remnants); and charged particles that arise from the
outgoing jet plus initial and final-state radiation (hard scattering component).
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 9
HERWIG 6.4 (without MPI)
“Transverse” Density
Df
“Toward”
“Transverse”
“Transverse”
“Away”
1.00
1.00
CDF Run 1Data
CDF
"Transverse" Charged Density
Charged Jet #1
Direction
HERWIG uses a modified leadinglog parton shower-model which
does agrees better with the data!
"Transverse"
"Transverse"Charged
ChargedParticle
ParticleDensity:
Density:dN/dhdf
dN/dhdf
Isajet
Total
"Hard"
data uncorrected
theory corrected
0.75
0.75
"Hard"
0.50
0.50
0.25
0.25
"Remnants"
"Remnants"
Beam-Beam
Remnants
HERWIG
Herwig 6.4 CTEQ5L
PT(hard) > 3 GeV/c
1.8TeV
TeV|h|<1.0
|h|<1.0PT>0.5
PT>0.5GeV
GeV
1.8
0.00
0.00
0
5
10
10
15
15
20
20
25
25
30
30
3535
PT(chargedjet#1)
jet#1) (GeV/c)
(GeV/c)
PT(charged
4040
4545
5050
“Hard”
Component
 Plot shows average “transverse” charge particle density (|h|<1, pT>0.5 GeV) versus PT(charged
jet#1) compared to the QCD hard scattering predictions of HERWIG 5.9 (default parameters with
PT(hard)>3 GeV/c without MPI).
 The predictions of HERWIG are divided into two categories: charged particles that arise from the
break-up of the beam and target (beam-beam remnants); and charged particles that arise from the
outgoing jet plus initial and final-state radiation (hard scattering component).
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 10
Tuning PYTHIA 6.2:
Multiple Parton Interaction Parameters
Parameter
Default
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.
Determines the energy
Probability
that of
thethe
MPI
produces two gluons
dependence
MPI!
with color connections to the “nearest neighbors.
0.33
PARP(86)
0.66
PARP(89)
PARP(82)
PARP(90)
PARP(67)
1 TeV
1.9
GeV/c
0.16
1.0
Multiple Parton Interaction
Color String
Color String
Multiple PartonDetermine
Interactionby comparing
Probability thatAffects
the MPI
theproduces
amount two
of gluons
either as described
by PARP(85)
or as a closed
initial-state
radiation!
gluon loop. The remaining fraction consists of
quark-antiquark pairs.
with 630 GeV data!
Color String
Hard-Scattering Cut-Off PT0
Determines the reference energy E0.
The cut-off PT0 that regulates the 2-to-2
scattering divergence 1/PT4→1/(PT2+PT02)2
Determines the energy dependence of the cut-off
PT0 as follows PT0(Ecm) = PT0(Ecm/E0)e with
e = PARP(90)
A scale factor that determines the maximum
parton virtuality for space-like showers. The
larger the value of PARP(67) the more initialstate radiation.
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
5
PYTHIA 6.206
e = 0.25 (Set A))
4
PT0 (GeV/c)
PARP(85)
Description
Take E0 = 1.8 TeV
3
2
e = 0.16 (default)
1
100
1,000
10,000
100,000
CM Energy W (GeV)
Reference point
at 1.8 TeV
Page 11
PYTHIA 6.206 Defaults
MPI constant
probability
scattering
PYTHIA default parameters
6.115
6.125
6.158
6.206
MSTP(81)
1
1
1
1
MSTP(82)
1
1
1
1
PARP(81)
1.4
1.9
1.9
1.9
PARP(82)
1.55
2.1
2.1
1.9
PARP(89)
1,000
1,000
1,000
PARP(90)
0.16
0.16
0.16
4.0
1.0
1.0
PARP(67)
4.0
1.00
"Transverse" Charged Density
Parameter
"Transverse" Charged Particle Density: dN/dhdf
CDF Data
Pythia 6.206 (default)
MSTP(82)=1
PARP(81) = 1.9 GeV/c
data uncorrected
theory corrected
0.75
0.50
0.25
1.8 TeV |h|<1.0 PT>0.5 GeV
0.00
0
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1) (GeV/c)
CTEQ3L
CTEQ4L
CTEQ5L
CDF Min-Bias
CDF JET20
 Plot shows the “Transverse” charged particle density versus PT(chgjet#1) compared to the
QCD hard scattering predictions of PYTHIA 6.206 (PT(hard) > 0) using the default
parameters for multiple parton interactions and CTEQ3L, CTEQ4L, and CTEQ5L.
Note Change
PARP(67) = 4.0 (< 6.138)
PARP(67) = 1.0 (> 6.138)
PHZ 6358 University of Florida
November 7, 2011
Default parameters give
very poor description of
the “underlying event”!
Rick Field – Florida/CDF/CMS
Page 12
Run 1 PYTHIA Tune A
PYTHIA 6.206 CTEQ5L
CDF Default Feburary 25, 2000!
"Transverse" Charged Particle Density: dN/dhdf
Parameter
Tune B
Tune A
MSTP(81)
1
1
MSTP(82)
4
4
PARP(82)
1.9 GeV
2.0 GeV
PARP(83)
0.5
0.5
PARP(84)
0.4
0.4
PARP(85)
1.0
0.9
"Transverse" Charged Density
1.00
CDF Preliminary
0.75
1.0
0.95
PARP(89)
1.8 TeV
1.8 TeV
PARP(90)
0.25
0.25
PARP(67)
1.0
4.0
New PYTHIA default
(less initial-state radiation)
PHZ 6358 University of Florida
November 7, 2011
Run 1 Analysis
0.50
0.25
CTEQ5L
PYTHIA 6.206 (Set B)
PARP(67)=1
1.8 TeV |h|<1.0 PT>0.5 GeV
0.00
0
PARP(86)
PYTHIA 6.206 (Set A)
PARP(67)=4
data uncorrected
theory corrected
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1) (GeV/c)
 Plot shows the “transverse” charged particle density
versus PT(chgjet#1) compared to the QCD hard
scattering predictions of two tuned versions of PYTHIA
6.206 (CTEQ5L, Set B (PARP(67)=1) and Set A
(PARP(67)=4)).
Old PYTHIA default
(more initial-state radiation)
Rick Field – Florida/CDF/CMS
Page 13
“Transverse” Charged Densities
Energy Dependence
"Transverse" Charged PTsum Density: dPTsum/dhdf
"Min Transverse" PTsum Density: dPTsum/dhdf
0.60
0.3
Charged PTsum Density (GeV)
Charged PTsum Density (GeV)
e = 0.25
HERWIG 6.4
0.40
e = 0.16
e=0
0.20
HERWIG 6.4
e = 0.25
0.2
Increasing e produces less energy
dependence for the
UE resulting
in
e = 0.16
e=0
less UE activity at the LHC!
CTEQ5L
Pythia 6.206 (Set A)
Pythia 6.206 (Set A)
630 GeV |h|<1.0 PT>0.4 GeV
0.1
CTEQ5L
630 GeV |h|<1.0 PT>0.4 GeV
0.0
0.00
0
5
10
15
20
25
30
35
40
45
50
0
5
10
20
25
30
Lowering PT0 at 630 GeV (i.e.
increasing e) increases UE activity
charged
PTsum density
resulting in
less energy dependence.
40
45
50
Hard-Scattering Cut-Off PT0
5
PYTHIA 6.206
e = 0.25 (Set A))
4
PT0 (GeV/c)
(|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
6.206 (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.
3
2
e = 0.16 (default)
1
100
1,000
Rick Field Fermilab MC Workshop
Reference point
E = 1.8 TeV
October 4, 2002!
PHZ 6358 University of Florida
November 7, 2011
35
PT(charged jet#1) (GeV/c)
PT(charged jet#1) (GeV/c)
 Shows the “transverse”
15
Rick Field – Florida/CDF/CMS
10,000
100,000
CM Energy W (GeV)
0
Page 14
All use LO as
with L = 192 MeV!
PYTHIA 6.2 Tunes
UE Parameters
ISR Parameter
Parameter
Tune AW
Tune DW
Tune D6
PDF
CTEQ5L
CTEQ5L
CTEQ6L
MSTP(81)
1
1
1
MSTP(82)
4
4
4
PARP(82)
2.0 GeV
1.9 GeV
1.8 GeV
PARP(83)
0.5
0.5
0.5
PARP(84)
0.4
0.4
0.4
PARP(85)
0.9
1.0
1.0
PARP(86)
0.95
1.0
1.0
PARP(89)
1.8 TeV
1.8 TeV
1.8 TeV
PARP(90)
0.25
0.25
0.25
PARP(62)
1.25
1.25
1.25
PARP(64)
0.2
0.2
0.2
PARP(67)
4.0
2.5
2.5
MSTP(91)
1
1
1
PARP(91)
2.1
2.1
2.1
PARP(93)
15.0
15.0
15.0
Uses CTEQ6L
Tune A energy dependence!
Intrinsic KT
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 15
All use LO as
with L = 192 MeV!
PYTHIA 6.2 Tunes
UE Parameters
Parameter
Tune DWT
Tune D6T
ATLAS
PDF
CTEQ5L
CTEQ6L
CTEQ5L
MSTP(81)
1
1
1
MSTP(82)
4
4
4
PARP(82)
1.9409 GeV
1.8387 GeV
1.8 GeV
PARP(83)
0.5
0.5
0.5
PARP(84)
Tune
AW
Tune A
ISR Parameter
0.4
Tune
B
1.0
1.0
0.33
PARP(86)
1.0
1.0
0.66
PARP(89)
1.96 TeV
1.96 TeV
1.0 TeV
PARP(90)
0.16
0.16
0.16
PARP(62)
1.25
1.25
1.0
PARP(64)
0.2
0.2
1.0
PARP(67)
2.5
2.5
1.0
MSTP(91)
1
1
1
PARP(93)
Tune 2.1
DW
15.0
2.1
15.0
ATLAS energy dependence!
Tune BW
1.0
Tune D6
5.0
Tune D6T
Intrinsic KT
PHZ 6358 University of Florida
November 7, 2011
0.5
PARP(85)
PARP(91)
Tune D
0.4
Rick Field – Florida/CDF/CMS
Page 16
“Transverse” Charged Density
PTmax Direction
"Transverse" Charged Particle Density: dN/dhdf
Df
1.6
“Transverse”
“Transverse”
“Away”
ChgJet#1 Direction
Df
“Toward”
“Transverse”
“Transverse”
“Away”
"Transverse" Charged Density
“Toward”
RDF Preliminary
7 TeV
py Tune DW generator level
1.2
PTmax
0.8
ChgJet#1
DY(muon-pair)
70 < M(pair) < 110 GeV
0.4
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
Muon-Pair Direction
Df
0
5
10
15
20
25
30
35
40
45
50
PT(chgjet#1) or PTmax or PT(pair) (GeV/c)
“Toward”
“Transverse”
“Transverse”
“Away”
 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.
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 17
Min-Bias “Associated”
Charged Particle Density
"Transverse" Charged Particle Density: dN/dhdf
"Transverse" Charged Particle Density: dN/dhdf
1.2
RDF Preliminary
14 TeV
Min-Bias
"Transverse" Charged Density
"Transverse" Charged Density
1.2
py Tune DW generator level
10 TeV
7 TeV
0.8
1.96 TeV
0.9 TeV
0.4
0.2 TeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
RDF Preliminary
LHC14
py Tune DW generator level
0.8
LHC10
LHC7
Tevatron
900 GeV
0.4
PTmax = 5.25 GeV/c
RHIC
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0.0
0
5
10
15
20
0
25
2
Df
“Toward”
RHIC
“Transverse”
“Transverse”
0.2 TeV → 1.96 TeV
(UE increase ~2.7 times)
Tevatron
“Away”
6
8
10
12
14
Center-of-Mass Energy (TeV)
PTmax (GeV/c)
PTmax Direction
4
PTmax Direction
Df
“Toward”
“Transverse”
PTmax Direction
1.96 TeV → 14 TeV
(UE increase ~1.9 times)
LHC
“Transverse”
“Away”
Df
“Toward”
“Transverse”
“Transverse”
“Away”
 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
Linear scale!
(i.e. generator level).
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 18
Min-Bias “Associated”
Charged Particle Density
"Transverse" Charged Particle Density: dN/dhdf
"Transverse" Charged Particle Density: dN/dhdf
1.2
RDF Preliminary
14 TeV
Min-Bias
"Transverse" Charged Density
"Transverse" Charged Density
1.2
py Tune DW generator level
10 TeV
7 TeV
0.8
1.96 TeV
0.9 TeV
0.4
0.2 TeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
RDF Preliminary
py Tune DW generator level
LHC14
LHC10
LHC7
0.8
Tevatron
0.4
900 GeV
RHIC
PTmax = 5.25 GeV/c
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0.0
0
5
10
15
20
25
0.1
Df
“Toward”
LHC7
“Transverse”
100.0
PTmax Direction
7 TeV → 14 TeV
(UE increase ~20%)
Df
“Toward”
LHC14
“Transverse”
“Away”
10.0
Center-of-Mass Energy (TeV)
PTmax (GeV/c)
PTmax Direction
1.0
Linear on a log plot!
“Transverse”
“Transverse”
“Away”
 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
Log scale!
(i.e. generator level).
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 19
Conclusions November 2009
 We are making good progress in understanding and modeling the
“underlying event”. RHIC data at 200 GeV are very important!
Outgoing Parton
PT(hard)
Initial-State Radiation
Proton
 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!
AntiProton
Underlying Event
Underlying Event
Outgoing Parton
Final-State
Radiation
Hard-Scattering Cut-Off PT0
PYTHIA 6.206
e = 0.25 (Set A))
4
PT0 (GeV/c)
 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!
5
3
2
e = 0.16 (default)
1
 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 (old) 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!
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
100
1,000
10,000
100,000
CM Energy W (GeV)
UE&MB@CMS
Page 20
“Transverse” Charged Particle Density
PT(chgjet#1) Direction
"Transverse" Charged Particle Density: dN/dhdf
"Transverse" Charged Density
0.8
Df
RDF Preliminary
Fake Data
pyDW generator level
ChgJet#1
“Toward”
0.6
PTmax
“Transverse”
“Transverse”
0.4
Leading Charged
Particle Jet, chgjet#1.
“Away”
0.2
900 GeV
Prediction!
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
PTmax Direction
0.0
0
2
4
6
8
10
12
14
16
PTmax or PT(chgjet#1) (GeV/c)
“Toward”
 Fake data (from MC) at 900 GeV on the
“transverse” charged particle density,
dN/dhdf, as defined by the leading charged
particle (PTmax) and the leading charged
particle jet (chgjet#1) for charged particles
with pT > 0.5 GeV/c and |h| < 2. The fake
data (from PYTHIA Tune DW) are
generated at the particle level (i.e. generator
level) assuming 0.5 M min-bias events at
900 GeV (361,595 events in the plot).
PHZ 6358 University of Florida
November 7, 2011
Df
18
Rick Field – Florida/CDF/CMS
“Transverse”
“Transverse”
Leading Charged
Particle, PTmax.
“Away”
Rick Field
MB&UE@CMS Workshop
CERN, November 6, 2009
Page 21
“Transverse” Charge Density
"Transverse" Charged Particle Density: dN/dhdf
Rick Field
MB&UE@CMS Workshop
CERN, November 6, 2009
"Transverse" Charged Density
1.2
RDF Preliminary
py Tune DW generator level
7 TeV
0.8
factor of 2!
900 GeV
0.4
Prediction!
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
4
10
0.0
0
2
6
8
12
14
16
18
20
PTmax (GeV/c)
PTmax Direction
Df
LHC
900 GeV
“Toward”
“Transverse”
PTmax Direction
900 GeV → 7 TeV
(UE increase ~ factor of 2)
“Transverse”
“Away”
~0.4 → ~0.8
Df
“Toward”
LHC
7 TeV
“Transverse”
“Transverse”
“Away”
 Shows the charged particle density in the “transverse” region for charged particles (pT > 0.5
GeV/c, |h| < 2) at 900 GeV and 7 TeV as defined by PTmax from PYTHIA Tune DW and at the
particle level (i.e. generator level).
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 22
“Transverse” Charged Particle Density
"Transverse" Charged Particle Density: dN/dhdf
"Transverse" Charged Particle Density: dN/dhdf
RDF Preliminary
Fake Data
pyDW generator level
"Transverse" Charged Density
"Transverse" Charged Density
0.8
ChgJet#1
0.6
PTmax
0.4
0.2
900 GeV
Monte-Carlo!
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
0.8
CMS Preliminary
ChgJet#1
data uncorrected
pyDW + SIM
0.6
PTmax
0.4
0.2
900 GeV
Real Data!
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
0.0
0.0
0
2
4
6
8
10
12
14
16
18
0
2
6
8
10
12
14
16
18
PTmax or PT(chgjet#1) (GeV/c)
PTmax or PT(chgjet#1) (GeV/c)
 Fake data (from MC) at 900 GeV on the
“transverse” charged particle density,
dN/dhdf, as defined by the leading charged
particle (PTmax) and the leading charged
particle jet (chgjet#1) for charged particles
with pT > 0.5 GeV/c and |h| < 2. The fake
data (from PYTHIA Tune DW) are
generated at the particle level (i.e. generator
level) assuming 0.5 M min-bias events at
900 GeV (361,595 events in the plot).
PHZ 6358 University of Florida
November 7, 2011
4
 CMS preliminary data at 900 GeV on the
“transverse” charged particle density,
dN/dhdf, as defined by the leading charged
particle (PTmax) and the leading charged
particle jet (chgjet#1) for charged particles
with pT > 0.5 GeV/c and |h| < 2. The data are
uncorrected and compared with PYTHIA
Tune DW after detector simulation (216,215
events in the plot).
Rick Field – Florida/CDF/CMS
Page 23
“Transverse” Charged PTsum Density
"Transverse" Charged PTsum Density: dPT/dhdf
"Transverse" Charged PTsum Density: dPT/dhdf
0.8
0.8
ChgJet#1
Fake Data
pyDW generator level
0.6
PTsum Density (GeV/c)
PTsum Density (GeV/c)
RDF Preliminary
PTmax
0.4
0.2
900 GeV
Monte-Carlo!
CMS Preliminary
data uncorrected
pyDW + SIM
0.6
ChgJet#1
PTmax
0.4
0.2
900 GeV
Real Data!
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
0.0
0.0
0
2
4
6
8
10
12
14
16
18
0
2
4
6
8
10
12
14
16
18
PTmax or PT(chgjet#1) (GeV/c)
PTmax or PT(chgjet#1) (GeV/c)
 Fake data (from MC) at 900 GeV on the
 CMS preliminary data at 900 GeV on the
“transverse” charged PTsum density,
“transverse” charged PTsum density,
dPT/dhdf, as defined by the leading charged
dPT/dhdf, as defined by the leading charged
particle (PTmax) and the leading charged
particle (PTmax) and the leading charged
particle jet (chgjet#1) for charged particles
particle jet (chgjet#1) for charged particles
with pT > 0.5 GeV/c and |h| < 2. The fake
with pT > 0.5 GeV/c and |h| < 2. The data are
data (from PYTHIA Tune DW) are generated
uncorrected and compared with PYTHIA
at the particle level (i.e. generator level)
Tune DW after detector simulation (216,215
assuming 0.5 M min-bias events at 900 GeV
events in the plot).
(361,595 events in the plot).
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 24
PYTHIA Tune DW
"Transverse" Charged Particle Density: dN/dhdf
"Transverse" Charged Particle Density: dN/dhdf
Charged Particle Density
CMS Preliminary
"Transverse" Charged Density
1.2
7 TeV
data uncorrected
pyDW + SIM
0.8
CMS
900 GeV
0.4
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
1.2
RDF Preliminary
7 TeV
ATLAS corrected data
Tune DW generator level
0.8
ATLAS
900 GeV
0.4
Charged Particles (|h|<2.5, PT>0.5 GeV/c)
0.0
0.0
0
5
10
15
20
25
30
35
40
45
50
0
2
4
6
8
10
12
14
16
18
20
PTmax (GeV/c)
PT(chgjet#1) GeV/c
 CMS preliminary data at 900 GeV and 7 TeV  ATLAS preliminary data at 900 GeV and 7 TeV
on the “transverse” charged particle density,
on the “transverse” charged particle density,
dN/dhdf, as defined by the leading charged
dN/dhdf, as defined by the leading charged
particle jet (chgjet#1) for charged particles with particle (PTmax) for charged particles with pT >
0.5 GeV/c and |h| < 2.5. The data are corrected
pT > 0.5 GeV/c and |h| < 2. The data are
uncorrected and compared with PYTHIA Tune and compared with PYTHIA Tune DW at the
generator level.
DW after detector simulation.
PT(chgjet#1) Direction
PTmax Direction
Df
Df
“Toward”
“Transverse”
“Toward”
“Transverse”
“Transverse”
“Away”
PHZ 6358 University of Florida
November 7, 2011
“Transverse”
“Away”
Rick Field – Florida/CDF/CMS
Page 25
PYTHIA Tune DW
"Transverse" Charged Particle Density: dN/dhdf
"Transverse" Charged Particle Density: dN/dhdf
3.0
1.2
CMS Preliminary
7 TeV
data uncorrected
pyDW + SIM
Ratio: 7 TeV/900 GeV
Charged Particle Density
CMS Preliminary
0.8
Ratio
CMS
900 GeV
0.4
data uncorrected
pyDW + SIM
2.0
CMS
1.0
7 TeV / 900 GeV
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
0.0
0.0
0
5
10
15
20
25
30
35
40
45
50
0
2
4
6
8
10
12
14
16
18
PT(chgjet#1) (GeV/c)
PT(chgjet#1) GeV/c
 CMS preliminary data at 900 GeV and 7 TeV  Ratio of CMS preliminary data at 900 GeV
and 7 TeV on the “transverse” charged
on the “transverse” charged particle density,
particle density, dN/dhdf, as defined by the
dN/dhdf, as defined by the leading charged
particle jet (chgjet#1) for charged particles with leading charged particle jet (chgjet#1) for
charged particles with pT > 0.5 GeV/c and |h|
pT > 0.5 GeV/c and |h| < 2. The data are
< 2. The data are uncorrected and compared
uncorrected and compared with PYTHIA Tune
with PYTHIA Tune DW after detector
DW after detector simulation.
PT(chgjet#1) Direction
simulation. PT(chgjet#1) Direction
Df
Df
“Toward”
“Transverse”
“Toward”
“Transverse”
“Transverse”
“Away”
PHZ 6358 University of Florida
November 7, 2011
“Transverse”
“Away”
Rick Field – Florida/CDF/CMS
Page 26
PYTHIA Tune DW
How well did we do at predicting the “underlying event” at 900 GeV and 7 TeV?
"Transverse" Charged Particle Density: dN/dhdf
1.2
CMS Preliminary
CMS Preliminary
ChgJet#1
data uncorrected
pyDW + SIM
0.6
Charged Particle Density
"Transverse" Charged Density
"Transverse" Charged Particle Density: dN/dhdf
0.8
PTmax
0.4
0.2
900 GeV
Tune DW
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
0.0
7 TeV
data uncorrected
pyDW + SIM
0.8
900 GeV
0.4
Tune DW
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
0.0
0
2
4
6
8
10
12
14
16
18
0
5
10
15
20
PTmax or PT(chgjet#1) (GeV/c)
25
30
35
40
45
50
PT(chgjet#1) GeV/c
"Transverse" Charged Particle Density: dN/dhdf
3.0
CMS Preliminary
Ratio: 7 TeV/900 GeV
I am surprised that the
Tunes did not do a better job
of predicting the behavior of
the “underlying event” at
900 GeV and 7 TeV!
Tune DW
data uncorrected
pyDW + SIM
2.0
1.0
7 TeV / 900 GeV
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
0.0
0
2
4
6
8
10
12
14
16
18
PT(chgjet#1) (GeV/c)
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 27
PYTHIA Tune DW
How well did we do at predicting the “underlying event” at 900 GeV and 7 TeV?
"Transverse" Charged Particle Density: dN/dhdf
1.2
CMS Preliminary
CMS Preliminary
ChgJet#1
data uncorrected
pyDW + SIM
0.6
Charged Particle Density
"Transverse" Charged Density
"Transverse" Charged Particle Density: dN/dhdf
0.8
PTmax
0.4
0.2
900 GeV
Tune DW
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
0.0
7 TeV
data uncorrected
pyDW + SIM
0.8
900 GeV
0.4
Tune DW
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
0.0
0
2
4
6
8
10
12
14
16
18
0
5
10
15
20
PTmax or PT(chgjet#1) (GeV/c)
25
30
35
40
45
50
PT(chgjet#1) GeV/c
"Transverse" Charged Particle Density: dN/dhdf
3.0
CMS Preliminary
Ratio: 7 TeV/900 GeV
I am surprised that the
Tunes did as well as they did
at predicting the behavior of
the “underlying event” at
900 GeV and 7 TeV!
Tune DW
data uncorrected
pyDW + SIM
2.0
1.0
7 TeV / 900 GeV
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
0.0
0
2
4
6
8
10
12
14
16
18
PT(chgjet#1) (GeV/c)
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 28
How Universal are the Tunes?
 Do we need a separate tune for each center-of-mass energy?
Outgoing Parton
PT(hard)
900 GeV, 1.96 TeV, 7 TeV, etc.
Initial-State Radiation
Proton
PYTHIA Tune DW did a nice (although not perfect)
job predicting the LHC Jet Production and Drell-Yan
UE data. I am still hoping for a single tune that will
describe all energies!
Proton
Underlying Event
Underlying Event
Outgoing Parton
Final-State
Radiation
Outgoing Parton
PT(hard)
Initial-State Radiation
Proton
 Do we need a separate tune for each hard QCD
Proton
Underlying Event
Underlying Event
subprocess? Jet Production, Drell-Yan Production, etc.
Outgoing Parton
The same tune can describe both Jet Production and Drell-Yan!
 Do we need separate tunes for “Min-Bias” (MB) and the
Proton
Final-State
Radiation
Color
“Minimum Bias” Collisions
Proton
Connections
“underlying event” (UE) in a hard scattering process?
PHTHIA Tune Z1 does fairly well at both the UE and MB,
but you cannot expect such a naïve approach to be perfect!
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Diffraction
Page 29
QCD Monte-Carlo Models:
Lepton-Pair Production
Lepton-Pair
Production
High
PT Z-Boson
Production
Anti-Lepton
Outgoing Parton
Initial-State
Initial-State Radiation
Radiation
High P
T Z-Boson Production
Lepton-Pair
Production
Initial-State
Initial-StateRadiation
Radiation
“Jet”
Proton
Proton
Final-State Radiation
Outgoing
Parton
Anti-Lepton
Final-State Radiation
“Hard Scattering” Component
AntiProton
AntiProton
Underlying Event
Lepton
Z-boson
Underlying Event
Proton
Lepton
Z-boson
AntiProton
Underlying Event
Underlying Event
“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.
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 30
Charged Particle Density
1.96 TeV
data corrected
pyDW generator level
Charged Particle Density
Average Charged Density
3
Drell-Yan Production
70 < M(pair) < 110 GeV
2
1
Average Charged Density
Large increase in the UE
in going from 1.96 TeV
Charged Particle Density: dN/dhdf
Charged Particle Density: dN/dhdf
"Toward" Charged Particle Density: dN/dhdf
to 7 TeV as predicted by
3
Tune DW! 1.2 RDF Preliminary
CDF RunPYTHIA
2
CMS Preliminary
data corrected
"Away"
pyDW generator level
0.8
Drell-Yan
Production
Charged Particles
(|h|<1.0, PT>0.5
GeV/c)
excluding the lepton-pair
0
10
20
30
40
50
60
0
70
PT(lepton-pair) GeV/c
80
20
90
Initial-State Radiation
“Transverse”
“Transverse”
“Away”
"Toward"
Charged Particles (PT>0.5 GeV/c)
0 60
PT(lepton-pair) GeV/c
Outgoing Parton
T
"Transverse"
1
100
40
High P Z-Boson Production
CDF:DfProton-Antiproton
Collisions at 1.96 GeV
Lepton Cuts: pT > 20 GeV |h| < 1.0
“Toward”
Proton
Mass Cut:
70 < M(lepton-pair) < 110
GeV
AntiProton
Charged Particles: pT > 0.5 GeV/c |h| < 1.0
Z-Boson Direction
"Away"
Drell-Yan Production
60 < M(pair) < 120 GeV
2
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
excluding the lepton-pair
0
0.0
0
CMS
CDF 1.96 TeV
0.4
"Transverse"
"Toward"
7 TeV
data corrected
CMS pyDW
7 TeV
generator level
2080
40
100
60
80
100
PT(lepton-pair) GeV/c
High P Z-Boson Production
CMS: Proton-Proton
Collisions at 7 GeV
Df
Lepton Cuts: pT > 20 GeV |h| < 2.4
“Toward”
Mass Cut:Proton
60 < M(lepton-pair) < 120 Proton
GeV
Charged Particles: pT > 0.5 GeV/c |h| < 2.0
Z-Boson Direction
Outgoing Parton
T
Initial-State Radiation
“Transverse”
“Transverse”
“Away”
Z-boson
Z-boson
 CDF data at 1.96 TeV on the density of charged particles, dN/dhdf, with pT > 0.5 GeV/c and |h| < 1 for Drell-
Yan production as a function of PT(Z) for the “toward”, “away”, and “transverse” regions compared with
PYTHIA Tune DW.
 CMS data at 7 TeV on the density of charged particles, dN/dhdf, with pT > 0.5 GeV/c and |h| < 2 for DrellYan production as a function of PT(Z) for the “toward”, “away”, and “transverse” regions compared with
PYTHIA Tune DW.
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 31
PYTHIA Tune DW
Charged Particle Density: dN/dhdf
"Toward" Charged Particle Density: dN/dhdf
3
1.2
CMS
7 TeV
data corrected
pyDW generator level
"Away"
Drell-Yan Production
60 < M(pair) < 120 GeV
2
Charged Particle Density
Average Charged Density
CMS Preliminary
data corrected
pyDW generator level
CMS 7 TeV
0.8
CDF 1.96 TeV
Overall PYTHIA0.4Tune DW
"Toward"
is in amazingly good agreement
with the
Charged Particles (PT>0.5 GeV/c)
Drell-Yan Production
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
excluding
the
lepton-pair
Tevatron Jet production 0.0
and Drell-Yan data
20
40
60 did a very
80
100 job in
0 predicting
20
60
80
and
good
the40
PT(lepton-pair) GeV/c
PT(lepton-pair) GeV/c
LHC Jet production and Drell-Yan data!
"Transverse" Charged Particle Density: dN/dhdf
"Transverse" Charged Particle Density: dN/dhdf
(although not perfect)
"Transverse"
1
0
0
100
1.5
1.5
RDF Preliminary
data corrected
pyDW generator level
Charged Particle Density
RDF Preliminary
Charged Particle Density
RDF Preliminary
CMS 7 TeV
1.0
CDF 1.96 TeV
0.5
CMS 900 GeV
CMS 7 TeV
data corrected
pyDW generator level
1.0
CDF 1.96 TeV
0.5
CMS 900 GeV
Charged Particles (PT>0.5 GeV/c)
Charged Particles (PT>0.5 GeV/c)
0.0
0.0
0
20
40
60
80
100
0
100
150
200
250
PT(chgjet#1 or jet#1) GeV/c
PT(chgjet#1 or jet#1) GeV/c
PHZ 6358 University of Florida
November 7, 2011
50
Rick Field – Florida/CDF/CMS
Page 32
300
Optional Homework
 Run PYTHIA Z-Boson Production at 7 TeV:
MSEL=11, CKIN(1)=70.0, CKIN(2)=110.0
High PT Z-Boson Production
Outgoing Parton
Initial-State Radiation
Proton
Proton
Z-boson
 Run with two values of the MPI cut-off pT0 = PARP(82): 1.5 GeV/c and 3.0 GeV/c.
 Look at the overall number of outgoing stable particles and study how this
depends on the MPI cut-off pT0.
PHZ 6358 University of Florida
November 7, 2011
Rick Field – Florida/CDF/CMS
Page 33