Predicting “Min-Bias” and the
“Underlying Event” at the LHC
Early Physics Measurements
Rick Field
University of Florida
Outline of Talk
 “Min-Bias” at 900 GeV, 2.2 TeV, 7 TeV, 10 TeV,

and 14 TeV.
New CDF charged multiplicity
distribution and comparisons with
the QCD Monte-Carlo tunes.
 Relationship between the “underlying

CERN November 6, 2009
Outgoing Parton
PT(hard)
Initial-State Radiation
CDF Run 2
event” in a hard scattering process and
“min-bias” collisions.
The “underlying event” at 900 GeV, 7 TeV,
10 TeV, and 14 teV.
Proton
Proton
Underlying Event
Outgoing Parton
Underlying Event
Final-State
Radiation
 The “underlying event” in Drell-Yan
production at 7 TeV,
 Summary & Conclusions.
UE&MB@CMS Workshop
November 6, 2009
CMS at the LHC
Rick Field – Florida/CDF/CMS
UE&MB@CMS
Page 1
Proton-AntiProton Collisions
at the Tevatron
Elastic Scattering
The CDF “Min-Bias” trigger
picks up most of the “hard
core” cross-section plus a
Double
Diffraction
small
amount of single &
double diffraction.
M2
M1
Single Diffraction
M
stot = sEL + sIN
SD +sDD +sHC
1.8 TeV: 78mb
= 18mb
The “hard core” component
contains both “hard” and
“soft” collisions.
+ 9mb
+ (4-7)mb + (47-44)mb
CDF “Min-Bias” trigger
1 charged particle in forward BBC
AND
1 charged particle in backward BBC
Hard Core
“Inelastic Non-Diffractive Component”
“Hard” Hard Core (hard scattering)
Outgoing Parton
“Soft” Hard Core (no hard scattering)
Proton
AntiProton
PT(hard)
Beam-Beam Counters
3.2 < |h| < 5.9
Proton
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
Final-State
Radiation
Outgoing Parton
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 2
Inelastic Non-Diffractive Cross-Section
Inelastic Non-Diffractive Cross-Section: sHC
Inelastic Non-Diffractive Cross-Section: sHC
Number of Inelastic ND Events
in 1/nb
70
70
60
Cross-Section (mb)
RDF Preliminary
py Tune DW generator level
py Tune DW generator level
50
60,000,000
Number of Events
Cross-Section (mb)
70,000,000
RDF Preliminary
60
40
30
20
10
0
0
2
4
K-Factor = 1.2
My guess!
50,000,000
40,000,000
RDF Preliminary
py Tune DW generator level
50
40
30
20
10
K-Factor = 1.2
Lots of events!
K-Factor = 1.2
0
30,000,000
6
8
10
12
0.1
14
1.0
10.0
100.0
Inelastic Non-Diffractive Events
Center-of-Mass Energy (TeV)
Center-of-Mass Energy (TeV)
20,000,000
0
Linear scale!
2
4
6
8Log scale!
10
12
14
Center-of-Mass Energy (TeV)
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!
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 3
Charged Particle Density: dN/dh
Charged Particle Density: dN/dh
Charged Particle Density: dN/dh
5.0
2.0
Charged Particle Density
Charged Particle Density
generator level
4.0
3.0
PY Tune DW
2.0
PY64 Tune S320
PY64 Tune P329
1.0
PY64 Tune P329
PY Tune A
RDF Preliminary
Min-Bias
1.96 TeV
Charged Particles (all PT)
RDF Preliminary
generator level
1.5
PY Tune DW
PY Tune A
1.0
PY64 Tune S320
0.5
Min-Bias
1.96 TeV
Charged Particles (PT>0.5 GeV/c)
0.0
0.0
-8
-6
-4
-2
0
2
4
6
8
-8
-6
PseudoRapidity h
-4
-2
0
2
4
6
8
PseudoRapidity h
Charged particle (all pT) pseudo-rapidity Charged particle (pT>0.5 GeV/c) pseudodistribution, dNchg/dhdf, at 1.96 TeV for
inelastic non-diffractive collisions from
PYTHIA Tune A, Tune DW, Tune S320, and
Tune P324.
UE&MB@CMS Workshop
November 6, 2009
rapidity distribution, dNchg/dhdf, at 1.96
TeV for inelastic non-diffractive collisions
from PYTHIA Tune A, Tune DW, Tune
S320, and Tune P324.
Rick Field – Florida/CDF/CMS
Page 4
Charged Particle Density: dN/dh
RDF LHC Prediction!
Charged Particle Density: dN/dh
Charged Particle Density: dN/dh
5.0
8.0
Charged Particle Density
Charged Particle Density
PY Tune A
RDF Preliminary
generator level
4.0
3.0
PY Tune DW
2.0
PY64 Tune S320
PY64 Tune P329
1.0
Min-Bias
1.96 TeV
Charged Particles (all PT)
0.0
PY64 Tune P329
RDF Preliminary
generator level
PY Tune DWT
6.0
PY ATLAS
4.0
PY Tune DW
PY Tune A
PY64 Tune S320
2.0
Min-Bias
14 TeV
Charged Particles (all PT)
0.0
-8
-6
-4
-2
0
2
4
6
8
-8
-6
-4
-2
PseudoRapidity h
2
4
6
PseudoRapidity h
“Minumum Bias” Collisions
Proton
0
“Minumum Bias” Collisions
AntiProton
Tevatron
Proton
Proton
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.
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 5
8
Charged Particle Density: dN/dh
RDF LHC Prediction!
Charged Particle Density: dN/dh
Charged Particle Density: dN/dh
4.0
PY Tune DWT
PY64 Tune P329
generator level
1.5
PY Tune DW
PY Tune A
1.0
PY64 Tune S320
0.5
Min-Bias
1.96 TeV
Charged Particles (PT>0.5 GeV/c)
PY ATLAS
RDF Preliminary
RDF Preliminary
Charged Particle Density
Charged Particle Density
2.0
3.0
PY64 Tune S320
2.0
PY Tune A
PY Tune DW
1.0
Min-Bias
14 TeV
Charged Particles (PT>0.5 GeV/c)
0.0
PY64 Tune P329
generator level
0.0
-8
-6
-4
-2
0
2
4
6
8
-8
-6
-4
-2
2
4
6
8
PseudoRapidity h
PseudoRapidity h
“Minumum Bias” Collisions
Proton
0
“Minumum Bias” Collisions
AntiProton
Tevatron
Proton
Proton
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.
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 6
Min-Bias “Charged Particle Density
Charged Particle Density: dN/dh
Charged Particle Density (h = 0): dN/dh
3.0
3.0
14 TeV
7 TeV
2.0
1.96 TeV
0.9 TeV
1.0
LHC14
RDF Preliminary
Min-Bias
Charged Density (h = 0)
Charged Particle Density
RDF Preliminary
py Tune DW generator level
0.2 TeV
py Tune DW generator level
LHC7
2.0
Tevatron
900 GeV
RHIC
1.0
Min-Bias
Charged particles pT > 0.5 GeV/c
Charged Particles (PT>0.5 GeV/c)
0.0
0.0
-8
-6
-4
-2
0
2
4
6
0
8
2
PseudoRapidity h
6
8
RHIC
12
14
1.96 TeV → 14 TeV
(dN/dh increase ~1.58 times)
“Minumum Bias” Collisions
“Minumum Bias” Collisions
“Minumum Bias” Collisions
Proton
10
Center-of-Mass Energy (TeV)
0.2 TeV → 1.96 TeV
(dN/dh increase ~1.63 times)
Proton
4
Proton
AntiProton
Tevatron
Proton
Proton
LHC
 Shows the “min-bias” charged particle density, dN/dh, for charged particles (pT > 0.5 GeV/c) for at
0.2 TeV, 0.9 TeV, 1.96 TeV and 14 TeV predicted by PYTHIA Tune DW at the particle level (i.e.
generator level).
Linear scale!
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 7
Min-Bias “Charged Particle Density
Charged Particle Density (h = 0): dN/dh
Charged Particle Density: dN/dh
3.0
3.0
14 TeV
RDF Preliminary
Min-Bias
Charged Density (h = 0)
Charged Particle Density
RDF Preliminary
py Tune DW generator level
7 TeV
2.0
1.96 TeV
0.9 TeV
1.0
0.2 TeV
LHC14
LHC10
LHC7
py Tune DW generator level
2.0
Tevatron
900 GeV
1.0
RHIC
Min-Bias
Charged particles pT > 0.5 GeV/c
Charged Particles (PT>0.5 GeV/c)
0.0
0.0
-8
-6
-4
-2
0
2
4
6
8
0.1
PseudoRapidity h
7 TeV → 14 TeV
(dN/dh ≈ 19% increase)
“Minumum Bias” Collisions
Proton
10.0
100.0
Log scale!
“Minumum Bias” Collisions
Proton
AntiProton
LHC7
1.0
Center-of-Mass Energy (TeV)
Proton
Linear on a log plot!
LHC14
 Shows the “min-bias” charged particle density, dN/dh, for charged particles (pT > 0.5 GeV/c) for at
0.2 TeV, 0.9 TeV, 1.96 TeV and 14 TeV predicted by PYTHIA Tune DW at the particle level (i.e.
generator level).
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 8
Charged Particle Multiplicity
Charged Multiplicity Distribution
Charged Multiplicity Distribution
1.0E+00
1.0E+00
CDF Run 2 Preliminary
CDF Run 2 Preliminary
1.0E-01
1.0E-01
CDF Run 2 <Nchg>=4.5
CDF Run 2 <Nchg>=4.5
1.0E-02
1.0E-02
1.0E-03
1.0E-03
py64 Tune A <Nchg> = 4.1
Probability
Probability
pyAnoMPI <Nchg> = 2.6
1.0E-04
1.0E-05
1.0E-04
1.0E-05
1.0E-06
1.0E-06
HC 1.96 TeV
Min-Bias 1.96 TeV
1.0E-07
1.0E-07
Normalized to 1
Normalized to 1 Charged Particles (|h|<1.0, PT>0.4 GeV/c)
Charged Particles (|h|<1.0, PT>0.4 GeV/c)
1.0E-08
1.0E-08
0
5
10
15
20
25
30
35
40
45
50
55
0
5
20
25
30
35
40
No MPI!
“Minumum Bias” Collisions
Proton
15
45
50
55
Number of Charged Particles
Number of Charged Particles
7 decades!
10
Tune A!
AntiProton
 Data at 1.96 TeV on the charged particle multiplicity (pT > 0.4 GeV/c, |h| < 1) for “min-bias”
collisions at CDF Run 2.
 The data are compared with PYTHIA Tune A and Tune A without multiple parton
interactions (pyAnoMPI).
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 9
Charged Particle Multiplicity
Charged Multiplicity DistributionCharged
0.20
1.0E+00
0.20
CDF Run 2 Preliminary
CDF
1.0E-01
CDF Run 2 <Nchg>=4.5
0.15
py64 Tune A <Nchg> = 4.1
0.15
HC 1.96 TeV
0.05
Normalized to 1
0
2
4
CDF Run 2 Preliminary
CDF Run 2 <Nchg>=4.5
CDF Run 2 <Nchg>=4.5
pyS320 <Nchg> = 4.2
py64 Tune A <Nchg> = 4.1
Charged Particles (|h|<1.0, PT>0.4 GeV/c)
0.10
HC 1.96 TeV
0.05
0.00
Run 2 Preliminary
1.0E-02
pyAnoMPI <Nchg> = 2.6
Probability
0.10
Probability
Probability
Charged Multiplicity Distribution
Multiplicity Distribution
1.0E-03
py64DW <Nchg> = 4.2
1.0E-04
pyS320 <Nchg> = 4.2
pyP329 <Nchg> = 4.4
1.0E-05
1.0E-06
Normalized
to 1 14
12
16
Charged
Particles (|h|<1.0, PT>0.4 GeV/c)
Number of Charged
Particles
1.0E-07
6
8
10
HC 1.96 TeV
Normalized to 1
0.00
0
2
4
6
8 1.0E-08 10
0
12
5
Tune A!Number of Charged Particles
No MPI!
10
Charged Particles (|h|<1.0, PT>0.4 GeV/c)
14
15
20
16
25
30
35
40
45
50
55
Number of Charged Particles
“Minumum Bias” Collisions
Proton
Tune S320!
AntiProton
 Data at 1.96 TeV on the charged particle multiplicity (pT > 0.4 GeV/c, |h| < 1) for “min-bias”
collisions at CDF Run 2.
 The data are compared with PYTHIA Tune A and Tune A without multiple parton
interactions (pyAnoMPI).
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 10
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
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”.
UE&MB@CMS Workshop
November 6, 2009
“Semi-hard” partonparton collision
(pT < ≈2 GeV/c)
Proton
+
+
Proton
Proton
Rick Field – Florida/CDF/CMS
Proton
Proton
+…
Multiple-parton
interactions (MPI)!
Page 11
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
+…
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Multiple-parton
interactions (MPI)!
Page 12
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
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”.
UE&MB@CMS Workshop
November 6, 2009
“Semi-hard” partonparton collision
(pT < ≈2 GeV/c)
Proton
+
+
Proton
Proton
Rick Field – Florida/CDF/CMS
Proton
Proton
+…
Multiple-parton
interactions (MPI)!
Page 13
Min-Bias Correlations
Average PT versus Nchg
Average PT (GeV/c)
1.4
CDF Run 2 Preliminary
pyDW
data corrected
generator level theory
“Minumum Bias” Collisions
1.2
Min-Bias
1.96 TeV
pyA
Proton
1.0
AntiProton
ATLAS
0.8
Charged Particles (|h|<1.0, PT>0.4 GeV/c)
0.6
0
10
20
30
40
50
Number of Charged Particles
 Data at 1.96 TeV on the average pT of charged particles versus the number of charged
particles (pT > 0.4 GeV/c, |h| < 1) for “min-bias” collisions at CDF Run 2. The data are
corrected to the particle level and are compared with PYTHIA Tune A at the particle
level (i.e. generator level).
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 14
Min-Bias: Average PT versus Nchg
 Beam-beam remnants (i.e. soft hard core) produces
Average PT versus Nchg
Average PT (GeV/c)
1.4
CDF Run 2 Preliminary
Min-Bias
1.96 TeV
data corrected
generator level theory
1.2
low multiplicity and small <pT> with <pT>
independent of the multiplicity.
 Hard scattering (with no MPI) produces large
pyA
multiplicity and large <pT>.
pyAnoMPI
1.0
 Hard scattering (with MPI) produces large
0.8
multiplicity and medium <pT>.
ATLAS
Charged Particles (|h|<1.0, PT>0.4 GeV/c)
0.6
0
5
10
15
20
25
30
35
40
This observable is sensitive
to the MPI tuning!
Number of Charged Particles
“Hard” Hard Core (hard scattering)
Outgoing Parton
“Soft” Hard Core (no hard scattering)
PT(hard)
CDF “Min-Bias”
=
Proton
+
AntiProton
Proton
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
Final-State
Radiation
Multiple-Parton Interactions
+
Proton
AntiProton
Underlying Event
Outgoing Parton
UE&MB@CMS Workshop
November 6, 2009
Outgoing Parton
PT(hard)
Initial-State
Radiation
The CDF “min-bias” trigger
picks up most of the “hard
core” component!
Outgoing Parton
Underlying Event
Final-State
Radiation
Rick Field – Florida/CDF/CMS
Page 15
Charged Particle Multiplicity
Charged Multiplicity Distribution
Charged Multiplicity Distribution
1.0E+00
1.0E+00
CDF Run 2 Preliminary
CDF Run 2 Preliminary
1.0E-01
1.0E-01
CDF Run 2 <Nchg>=4.5
1.0E-02
py64 Tune A <Nchg> = 4.1
pyA 900 GeV <Nchg> = 3.3
CDF Run 2 <Nchg>=4.5
1.0E-02
py64 Tune A <Nchg> = 4.1
py64A LHC22 <Nchg> = 4.1
Probability
Probability
pyAnoMPI <Nchg> = 2.6
1.0E-03
1.0E-04
1.0E-05
1.0E-03
The charged multiplicity distribution
does not change between
1.96 and 2.2 TeV
and proton-proton is the same as
Tune A prediction at
proton-antiproton!
900 GeV!
1.0E-04
1.0E-05
1.0E-06
1.0E-06
HC 1.96 TeV
Min-Bias
1.0E-07
1.0E-07
Normalized to 1
Normalized to 1
Charged Particles (|h|<1.0, PT>0.4 GeV/c)
Charged Particles (|h|<1.0, PT>0.4 GeV/c)
1.0E-08
1.0E-08
0
5
10
15
20
25
30
35
40
45
50
55
0
“Minumum Bias” Collisions
Proton
10
15
20
25
30
35
40
45
50
55
Number of Charged Particles
Number of Charged Particles
No MPI!
5
TuneCollisions
A prediction
“Minumum Bias”
Tune A!
at
2.2 TeV!
AntiProton
Proton
Proton
 Data at 1.96 TeV on the charged particle multiplicity (pT > 0.4 GeV/c, |h| < 1) for “min-bias”
collisions at CDF Run 2. The data are compared with PYTHIA Tune A and Tune A without
multiple parton interactions (pyAnoMPI).
 Prediction from PYTHIA Tune A for proton-proton collisions at 900 GeV and 2.2 TeV.
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 16
LHC Predictions: 900 GeV
Charged Multiplicity Distribution
Charged Multiplicity Distribution
Charged Multiplicity Distribution
Distribution
Momentum
Transverse Momentum
Charged Transverse
Charged
Distribution
0.08
0.16
1.0E+00
RDF Preliminary
30
1.0E+02
py64DW <Nchg> = 14.4 <pT> = 787 MeV/c
RDF
0.06
0.12
1.0E+01
MeV/c
787MeV/c
<pT>==795
14.4<pT>
<Nchg>==14.7
py64DW
pyP329 <Nchg>
20
1.0E+00
HC 900 GeV
1.0E-05
Normalized to 1
1.0E-06
0
10
20
0.02
0.04
HC HC
900900
GeVGeV
Charged Particles (|h|<2.0)
Normalized
to 1 to 1
Normalized
RDF Preliminary
00
HC 900
HC GeV
900 GeV
0
1.0E-03
0.0 0.0 0.2
40
50
0.4
1.0
60
Number of Charged Particles
70
0.6
25
10
4
15
6
20
8
25
10
30
12
35
14
40
16
Number of Charged Particles
Charged Particles (|h|<2.0) Number of Charged Particles
802.0
0.8
1.0
3.0
1.2 4.0 1.4
(GeV/c)
Momentum
Transverse
Transverse
Momentum
(GeV/c)
“Minumum Bias” Collisions
Charged Particles (|h|<2.0, all pT)
0.00
0.00
1.0E-02
Proton
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
pyP329 <Nchg> = 14.7 <pT> = 795 MeV/c
10
30
0.04
pyDW
900
GeV<Nchg>
<Nchg>== 14.2
5.3
pyA
900
GeV
pyDW
14.4
pyS320900
900GeV
GeV<Nchg>
<Nchg> == 5.2
pyS320
900 GeV
GeV<Nchg>
<Nchg>
= 14.2
pyP329 900
= 5.3
pyP329 900 GeV <Nchg> = 14.7
0.08
<Nchg> = 14.2 <pT> = 778 MeV/c
pyS320
All pT
<Nchg> ~ 14
pT > 0.5 geV/c
<Nchg> ~ 5 1.0E-01
1.0E-04
Preliminary
pyS320 <Nchg> = 14.2 <pT> = 778 MeV/c
Probability
Probability
Probability
1.0E-03
d<Nchg>/dpT
d<Nchg>/dpT1/(GeV/c)
1/(GeV/c)
1.0E-01
1.0E-02
RDF
Preliminary
pyA <Nchg>
= 5.0 STdev = 4.5
RDF Preliminary
Charged Particles (|h|<2.0)
1.6
5.0
“Minumum Bias” Collisions
Proton
Proton
Proton
 Charged multiplicity distributions for proton-proton collisions at 900 GeV
(|h| < 2) from PYTHIA Tune A, Tune DW, Tune S320, and Tune P329.
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 17
LHC Predictions: 900 GeV
Charged
Charged
Particle
ChargedParticle
ParticleMultiplicity
Multiplicity
Charged Multiplicity Distribution
Average Number of Charged
Particles
0.40
0.160
0.25
0.16
RDF Preliminary7
pyA <Nchg> = 5.0 STdev = 4.5
0.140
0.20
0.30
0.120
pyDW 900 GeV <Nchg> = 5.3
pyS320 900 GeV <Nchg> = 5.2
0.08
0.04
HC 900 GeV
Normalized to 1
0.00
0
2
4
6
Probability
Probability
pyDW
pyP329 900 GeV <Nchg> = 5.3
6
Average Nchg
Probability
0.12
RDF
Preliminary
RDFPreliminary
Preliminary
RDF
RDF Preliminary
generator
generator
level level
generator
level
1000 events
<Nchg> = 5.1
STdev = 4.6
generator level10
100events
events<Nchg>
<Nchg>= =5.2
4.9STdev
STdev= =3.8
4.9
pyA <Nchg>==5.0
5.0 STdev==4.5
4.5
pyA
pyA <Nchg>
<Nchg> = 5.0 STdev
STdev = 4.5
0.100
0.15
Charged
Particles
(|h|<2.0,
PT>0.5
GeV/c)
Charged
Particles
(|h|<2.0,
PT>0.5
GeV/c)
Charged
Particles
(|h|<2.0,
PT>0.5
GeV/c)
0.20
0.080
If we get 10,000 HC collisions
5
we could measure <Nchg>
4
BUT we also want to measure
Min-Bias 900 GeV
the
activity
in the “underlying event”
3
1
10
100
10000
which
would
take 1000
Number
of Events
1,000
events
100
events
10 events
~2,000,000
HC
24/mb!collisions!
2.4/mb!
LLL===
0.24/mb!
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
pyA
pyDWT
8
10
12
Number of Charged Particles
14
16
Min-Bias
900 900
GeV
Min-Bias
Min-Bias
900GeV
GeV
0.10
0.060
0.00
0.00
0.000
00 0
22
445
66
88
10
1010
1212
14
1415 16
16
18
18
20
20
20
Charged Particles (|h|<2.0, PT>0.5
GeV/c)
Number
of
Number
ofofCharged
Charged
Particles
Number
ChargedParticles
Particles
“Minumum Bias” Collisions
“Minumum Bias” Collisions
Proton
Normalized
to 1 to 1
Normalized
Normalized to 1
0.10
0.040
0.05
0.020
Proton
Proton
Proton
 Charged multiplicity distributions for proton-proton collisions at 900 GeV
(pT > 0.5 GeV/c, |h| < 2) from PYTHIA Tune A, Tune DW, Tune DWT, Tune
S320, and Tune P329.
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 18
“Transverse” Charged Density
PTmax Direction
f
"Transverse" Charged Particle
Particle Density:
Density: dN/dhdf
dN/dhdf
1.6
“Transverse”
“Transverse”
“Away”
ChgJet#1 Direction
f
“Toward”
“Transverse”
“Transverse”
“Away”
"Transverse" Charged
Charged Density
Density
"Transverse"
“Toward”
RDF
RDF Preliminary
7 TeV
7 TeV
pyTune
TuneS320
DW generator
level
generatorlevel
py
1.2
PTmax
ChgJet#1
PTmax
0.8
ChgJet#1
0.4
0.4
DY(muon-pair)
DY(muon-pair)
< M(pair)
< 110
GeVGeV
< 110
M(pair)
70 <70
PT>0.5 GeV/c)
(|h|<1.0, PT>0.5
Particles (|h|<1.0,
Charged Particles
Charged
GeV/c)
0.0
0.0
Muon-Pair Direction
f
00
55
10
10
15
15
20
20
25
25
30
30
35
35
40
40
45
45
50
50
PT(chgjet#1)
PT(chgjet#1) or
or PTmax
PTmax or
or PT(pair)
PT(pair) (GeV/c)
(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.
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 19
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
f
“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
f
“Toward”
“Transverse”
PTmax Direction
1.96 TeV → 14 TeV
(UE increase ~1.9 times)
LHC
“Transverse”
“Away”
f
“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).
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 20
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
f
“Toward”
LHC7
“Transverse”
100.0
PTmax Direction
7 TeV → 14 TeV
(UE increase ~20%)
f
“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).
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 21
sHC: PTmax > 5 GeV/c
Inelastic HC Cross-Section: PTmax > 5 GeV/c
Inelastic HC Cross-Section: PTmax > 5 GeV/c
Number
of Events Fraction
in 1/nb: PTmax
>>55GeV/c
HC
Cross-Section:
PTmax
GeV/c
1.6
1.5
1,500,000
2.0%
py Tune DW generator level
py Tune
generator
level level
py DW
Tune
DW generator
K-Factor = 1.2
1.0
0.5
0.0
0
2
Numberof
ofEvents
Events
Percent
Cross-Section (mb)
RDF Preliminary
RDF RDF
Preliminary
Preliminary
1.5%
1,000,000
K-Factor = 1.2
Still lots of events!
1.0%
Cross-Section (mb)
RDF Preliminary
py Tune DW generator level
1.2
K-Factor = 1.2
Charged Particles (PTmax > 5 GeV/c |h| < 1)
0.8
0.4
500,000
Charged Particles (PTmax > 5 GeV/c |h| < 1)
0.5%
4
0.0
6
8
10
12
0.1
1.0
10.0
100.0
Charged Particles (PTmax > 5 GeV/c
|h| < 1)
Center-of-Mass
Energy (TeV)
Center-of-Mass Energy (TeV)
0
0.0%
0
Linear scale!
14
0
2
2
4 4
6 6
88
1010
Log scale!
12
12
14
14
Center-of-Mass
Energy
(TeV)
Center-of-Mass
Energy
(TeV)
stot = sEL + sSD +sDD +sHC
In 1,000,000 HC collisions at
900 GeV you get 940 with
PTmax > 5 GeV/c!
 The inelastic non-diffractive PTmax > 5 GeV/c cross section 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!
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 22
“Transverse” Charged Density
Differential Cross-Section: ds/dPT
"Transverse" Charged Particle Density: dN/dhdf
Number of Events in 1 GeV/c
Bin with 1/nb
1.0E+02
10,000,000
RDF Preliminary
7 TeV
0.8
0.4
0.0
0
5
10
py Tune DW generator level
1.0E+00
1,000,000
PTmax
15
1.0E+01
RDF Preliminary
ds/dPT (mb/GeV/c)
1.2
100,000
ChgJet#1
10,000
PTmax
30
35
40
ChgJet#1
1.0E-02
PTmax
K-Factor = 1.2
K-Factor = 1.2
100
25
ChgJet#1
1.0E-01
1.0E-03
1,000
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
20
With 1/nb of “min-bias” data at
7 TeV
we could study7 TeV
the UE out
py Tune DW generator
level
to
PTmax
=
25
GeV/c
or
7 TeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
PT(chgjet#1) = 45 GeV/c !
RDF Preliminary
py Tune DW generator level
Number of Events
"Transverse" Charged Density
1.6
1.0E-04
45
0
50
5
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
PT(chgjet#1) or PTmax (GeV/c)
10
15
20
25
30
35
40
45
PT(chgjet#1) or PTmax (GeV/c)
10
0
5
10
15
20
25
30
35
40
45
50
PT(chgjet#1)
or PTmax
(GeV/c)for charged particles (p > 0.5
 Shows the charged particle density in the
“transverse”
region
T
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.
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 23
50
“Transverse” Charged Density
"TransMAX/MIN" Charged Particle Density
"Transverse" Charged Particle Density: dN/dhdf
1.2
1.6
ChgJet#1 Direction
RDF Preliminary
"transMAX"
PYTHIA Tune DW
f
Charged Particle Density
Charged Particle Density
RDF Preliminary
PYTHIA Tune DW
0.8
|h| < 1
0.4
|h| < 2
Charged Particles (PT>0.5 GeV/c)
0.0
1.2
|h| < 1
“Toward”
|h| < 2
0.8
"transMIN"
“Transverse”
“Transverse”
0.4
“Away”
Charged Particles (PT>0.5 GeV/c)
0.0
0
5
10
15
20
25
30
35
40
45
50
0
5
PT(chgjet#1) GeV/c
10
15
20
25
30
35
40
45
50
PT(chgjet#1) GeV/c
 Shows the charged particle density in the “transverse” region for charged particles (pT > 0.5
GeV/c) at 7 TeV for |h| < 1 and |h| < 2 as defined 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 charged particle density in the “transMAX” and “transMIN” region for charged
particles (pT > 0.5 GeV/c) at 7 TeV for |h| < 1 and |h| < 2 as defined 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.
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 24
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!
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 25
Drell-Yan Muon-Pair Cross-Section
Drell-Yan Muon-Pair Cross Section
2,500
Drell-Yan Muon-Pair Events in 10/pb
25,000
RDF Preliminary
RDF Preliminary
py Tune DW generator level
20,000
Number of Events
Cross-Section (pb)
2,000
py Tune DW generator level
70 < M(pair) < 110 GeV
1,500
1,000
500
70 < M(pair) < 110 GeV
15,000
10,000
5,000
K-Factor = 1.3
K-Factor = 1.3
0
0
0
2
4
6
8
10
12
14
0
Center-of-Mass Energy (TeV)
2
4
6
8
10
12
Center-of-Mass Energy (TeV)
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!
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 26
14
Drell-Yan Muon-Pair Cross-Section
Drell-Yan Muon-Pair Cross Section
2,500
Drell-Yan Muon-Pair Events in 10/pb
25,000
RDF Preliminary
RDF Preliminary
py Tune DW generator level
20,000
Number of Events
2,000
Cross-Section (pb)
py Tune DW generator level
70 < M(pair) < 110 GeV
1,500
pT(muon) > 5 GeV/c
|h(muon)| < 2.4
1,000
500
70 < M(pair) < 110 GeV
15,000
pT(muon) > 5 GeV/c
|h(muon)| < 2.4
10,000
5,000
K-Factor = 1.3
K-Factor = 1.3
0
0
0
2
4
6
8
10
12
14
0
2
6
8
10
12
Center-of-Mass Energy (TeV)
Center-of-Mass Energy (TeV)
Linear scale!
4
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!
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 27
14
“Transverse” Charged Density
1.2
0.8
0.0
0
5
10
15
PTmax
1/nb
100,000
DY(muon-pair)
70 < M(pair) < 110 GeV
0.4
py Tune DW generator level
1.0E-02
1,000,000
PTmax
Number of Events
"Transverse" Charged Density
1.6
ds/dPT (mb/GeV/c)
Note at CMS “min-bias” is pre-scaled
by a factor of 5,000 so this really
Differential Cross-Section: ds/dPT
"Transverse"
Charged
Particle
Density:
dN/dhdf of Events in 1 GeV/c Bin
corresponds
to 5/pb
delivered
! Number
1.0E+01
With 10/pb of data at 7 TeV we could
RDF Preliminary
1.0E+00
study the UE in Drell-Yan production
10,000,000
7 TeV
py Tune DW generator level
RDF Preliminary
7 TeV RDF Preliminary
1.0E-01
py Tune DW generator level
out
to
PT(pair)
=
15
GeV/c
!
7 TeV
ChgJet#1
10,000
ChgJet#1
Charged
(|h|<1.0, PT>0.5 GeV/c)
1.0E-03 Particles
PTmax
1.0E-04
1.0E-05
ChgJet#1
1/nb
1.0E-06
1.0E-07
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
1,000
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
DY(CMS muon-pair)
70 < M(pair) < 110 GeV
10/pb
1.0E-08
DY(CMS muon-pair)
70 < M(pair) < 110 GeV
1.0E-09
20
25
100 30
35
40
45
50
0
5
10
PT(chgjet#1) or PTmax or PT(pair) (GeV/c)
15
20
25
30
35
40
45
50
PT(chgjet#1) or PTmax or PT(pair) (GeV/c)
10
0
5
10
15
20
25
30
35
40
45
50
PT(chgjet#1)
or PTmax orregion
PT(pair) for
(GeV/c)
 Shows the charged particle density in
the “transverse”
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 crosssection (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.
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 28
Z-Boson: “Towards” Region
RDF LHC
Prediction!
"Toward" Charged Particle Density:
dN/dhdf
"Toward" Charged Particle Density: dN/dhdf
RDF Preliminary
PY Tune AW
PY Tune DW
generator level
RDF Preliminary
Drell-Yan
1.96 TeV
"Toward" Charged Density
"Toward" Charged Density
PY ATLAS
1.6
0.8
0.6
0.4
PY64 Tune P329
PY64 Tune S320
0.2
70 < M(pair) < 110 GeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
PY Tune DWT
generator level
1.2
0.8
PY Tune DW
PY64 Tune P329
PY64 Tune S320
0.4
70 < M(pair) < 110 GeV
Drell-Yan
14 TeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0.0
0
25
50
75
100
125
150
0
25
50
75
100
Lepton-Pair PT (GeV/c)
Lepton-Pair PT (GeV/c)
Z-BosonDirection
Z-BosonDirection
f
f
“Toward”
“Toward”
“Transverse”
“Transverse”
125
Tevatron
LHC
“Transverse”
“Transverse”
“Away”
“Away”
 Data at 1.96 TeV on the density of charged particles, dN/dhdf, with pT > 0.5 GeV/c and |h| < 1 for “Z-
Boson” events as a function of PT(Z) for the “toward” region from PYTHIA Tune AW, Tune DW, Tune
S320, and Tune P329 at the particle level (i.e. generator level).
 Extrapolations of PYTHIA Tune AW, Tune DW, Tune DWT, Tune S320, and Tune P329, and pyATLAS to
the LHC.
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 29
150
Drell-Yan Charged Multiplicity
Charged
Charged Particle
Particle Multiplicity
Multiplicity
Charged Particle Multiplicity
Average Number of0.07
Charged Particles
0.25
0.040
0.040
35
0.035
RDF Preliminary
Average Nchg
0.020
0.015
0.010
0.005
generator
level
pyDW
<Nchg> =
22.1 STdev = 12.9
pyS320 <Nchg> = 18.5 STdev = 12.1
pyDWT <Nchg> = 25.6 STdev = 14.7
Probability
Probability
30
0.025
pyDWT
7 TeV Drell-Yan
70 < M(pair) < 110 GeV
25
pyDW
It would be nice to have 2/pb
at 7 TeV (acquired)
15
which might mean
10
3/pb
(delivered)!
1
10
100
1000
20
pyS320
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
(excluding lepton-pair )
0.000
RDF Preliminary
Preliminary
Charged Particles (|h|<2.0, PT>0.5 GeV/c) RDFgenerator
RDF
Preliminary
level
generator level
(excluding
lepton-pair
)
generator level
7 TeV Drell-Yan
1000 events <Nchg> = 22.0 STdev = 12.9
100 events <Nchg> = 21.7 STdev = 12.6
70 < M(pair) < 110 GeV
10 events
<Nchg>
= STdev
27.5 STdev
= 13.8
pyDW
<Nchg>
= 22.1
= 12.9
pyDW <Nchg> = 22.1 STdev = 12.9
pyDW
<Nchg>
=
22.1
STdev
=
12.9
0.025
7 TeV Drell-Yan
0.15
0.04
7 TeV<Drell-Yan
70 < M(pair)
110 GeV
7 TeV Drell-Yan
0.020
70 < M(pair)
< 110 GeV
70
<
M(pair)
< 110 GeV
Charged
Particles
(|h|<2.0,
PT>0.5
GeV/c)
0.03
0.10
Charged
Particleslepton-pair
(|h|<2.0, PT>0.5
GeV/c)
0.015
(excluding
)
(excluding lepton-pair )
0.02
0.010
0.05
0.01
0.005
0.035
0.06
0.20
0.030
0.05
generator level
0.030
Probability
RDF Preliminary
0.00
0.00
0.000
0
5
10
15
20
25
30
35
40
45
50
55
60
65
Number of Charged Particles
70
75
80
000 555 10
10
15
20
25
30
35
40
45
50
55 60
60 65
65 70
70 75
75 80
80 85
85 90
90 95
95
10 15
15 20
20 25
25 30
30 35
35 40
40 45
45 50
50 55
90
95
Charged
Particles
(|h|<2.0,
PT>0.5
GeV/c)
Number
Number
of
Charged
Particles
Number
ofCharged
ChargedParticles
Particles
(excluding lepton-pair
) of
Drell-Yan Production Lepton-Pair Production
Lepton
Proton
10000
1,000
100
events
events
Number
of Events
10
events
LLL===210/nb!
2.1/pb!
21/nb!
Proton
Underlying Event
Underlying Event
Anti-Lepton
 Prediction from PYTHIA Tune DW, Tune S320, and Tune P329 for Drell-Yan muon-pair production (70
< M(pair) < 110 GeV) for proton-proton collisions at 7 TeV for the number of charged particles with pT
> 0.5 GeV and |h| < 2 (excluding the lepton-pair).
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
Page 30
Drell-Yan Charged PT & PTsum
Charged Transverse Momentum Distribution
Charged
ChargedPTsum
PTsum Distribution
Distribution
1.0E-01
0.03
1.0E+02
py64DW <Nchg> = 22.1 <PTsum> = 30.4 GeV/c
RDF Preliminary
pyS320 <Nchg> = 18.5 <PTsum> = 25.1 GeV/c
RDF Preliminary
d<Nchg>/dpT (1/GeV/c)
Probability
Probability
generator level
RDF
Preliminary
7 TeV
Drell-Yan
generator level
70 < M(pair) < 110 GeV
1.0E-02
0.02
7 TeV Drell-Yan
70 < M(pair) < 110 GeV
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
(excluding lepton-pair )
1.0E-03
0.01
1.0E-04
0.00
py64DW <Nchg> = 22.1 <PTsum> = 30.4 GeV/c
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
pyS320 <Nchg> = 18.5 <PTsum> = 25.1 GeV/c
(excluding lepton-pair )
0 0
1010
2020
3030
4040
50
50
60
60
generator level
1.0E+01
py64DW <Nchg> = 22.1 <pT> = 1.62 GeV/c
pyS320 <Nchg> = 18.5 <pT> = 1.36 GeV/c
1.0E+00
1.0E-01
7 TeV Drell-Yan
70 < M(pair) < 110 GeV
1.0E-02
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
(excluding lepton-pair )
1.0E-03
70
70
80
90
90
100
100
0
15
20
Lepton
Proton
Underlying Event
Yan muon-pair production (70 < M(pair) < 110 GeV) for
proton-proton collisions at 7 TeV for the charged pT
distribution |h| < 2 (excluding the lepton-pair). The plot
shows the <Nchg> per unit pT versus pT.
Anti-Lepton
 Prediction from PYTHIA Tune DW, Tune S320 for Drell-Yan muon-pair production (70 < M(pair) < 110
GeV) for proton-proton collisions at 7 TeV for the PTsum distributions with pT > 0.5 GeV and |h| < 2
(excluding the lepton-pair). The plot shows the probability of having a given PTsum in the event.
UE&MB@CMS Workshop
November 6, 2009
25
 Prediction from PYTHIA Tune DW, Tune S320 for Drell-
Drell-Yan Production Lepton-Pair Production
Underlying Event
10
Charged Particle pT (GeV/c)
ChargedParticle
ParticlePTsum
PTsum (GeV/c)
(GeV/c)
Charged
Proton
5
Rick Field – Florida/CDF/CMS
Page 31
Early LHC Measurements
“Minumum Bias” Collisions
 The amount of activity in “min-bias” collisions (multiplicity distribution,
pT distribution, PTsum distribution, dNchg/dh).
d<Nchg>/dpT 1/(GeV/c)
Proton
RDF Preliminary
RDF Preliminary
py64DW <Nchg> = 14.4 <pT> = 787 MeV/c
20
1.0E-02
10
pyS320 <Nchg>
All pT = 14.2 <pT> = 778 MeV/c
~ 14
pyP329 <Nchg>
<Nchg>
= 14.7 <pT> = 795 MeV/c
1.0E-03
pT > 0.5 geV/c
<Nchg> ~ 5
HC 900 GeV
900 GeV
0
Normalized to 1
1.0E-06
0.2
0.0
0.4
0
f
Initial-State Radiation
0.8
30
1.0
40
50
1.2
60
1.4
70
1.6
80
"Transverse" Charged Particle Density: dN/dhdf
Underlying Event
Final-State
Radiation
“Transverse”
“Away”
 The amount of activity in the “underlying event” in hard scattering
events (“transverse” Nchg distribution, “transverse” pT distribution,
“transverse” PTsum distribution for events with PTmax > 5 GeV/c).
"Transverse" Charged Density
1.6
“Transverse”
Outgoing Parton
20
Transverse
Momentum (GeV/c)
Number of Charged Particles
“Toward”
Proton
Underlying Event
0.6
10
PT(hard)
Proton
Charged Particles (|h|<2.0)
1.0E-04
HC
1.0E-05
PTmax Direction
Outgoing Parton
Charged Particles (|h|<2.0)
1.0E-01
Probability
Proton
Multiplicity
Distribution
ChargedCharged
Transverse
Momentum
Distribution
1.0E+00
30
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
0
5
10
15
20
25
30
35
40
45
50
PT(chgjet#1) or PTmax or PT(pair) (GeV/c)
Drell-Yan Production
Lepton
Charged
Particle
Multiplicity
Charged
Transverse
Momentum
Distribution
0.040
1.0E+02
Proton
RDF
RDFPreliminary
Preliminary
Proton
0.035
1.0E+01
0.030
Underlying Event
Probability
d<Nchg>/dpT (1/GeV/c)
Underlying Event
generator
generatorlevel
level
pyDW <Nchg> = 22.1 STdev = 12.9
py64DW <Nchg> = 22.1 <pT> = 1.62 GeV/c
pyS320 <Nchg> = 18.5 STdev = 12.1
pyS320
<Nchg>
= 18.5
<pT>STdev
= 1.36=GeV/c
pyDWT
<Nchg>
= 25.6
14.7
0.025
1.0E+00
Anti-Lepton
 The amount of activity in the “underlying event” in Drell-Yan
events (Nchg distribution, pT distribution, PTsum distribution,
excluding the lepton-pair),
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
0.020
1.0E-01
0.015
7 TeV Drell-Yan
70 <7M(pair)
< 110 GeV
TeV Drell-Yan
70 < M(pair) < 110 GeV
0.010
1.0E-02
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
(excluding lepton-pair )
(excluding lepton-pair )
1.0E-03
0.005
0.000
0
0
5
10
15
5
20
25
30
10
35 40
45
15
50 55
60
20
65 70
75
Charged
Particle Particles
pT (GeV/c)
Number
of Charged
Page 32
25
80
Summary & Conclusions
 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!
is veryTune”!
important to
Py64 S320 = LHCIt
“Reference
Proton
Underlying Event
Underlying Event
Outgoing Parton
measure
BOTH= 0.16
“min-bias”
 It is clear now that the default
value PARP(90)
is
not correct and the valueand
shouldthe
be closer
to the Tune A event”
“underlying
value of 0.25.
atare900
GeV!
 The new and old PYTHIA tunes
beginning
to I hope
converge and I believe we arewe
finally
position toevents.
make
getin aenough
some legitimate predictions at the LHC!
Final-State
Radiation
Hard-Scattering Cut-Off PT0
5
PYTHIA 6.206
 = 0.25 (Set A))
PT0 (GeV/c)
4
3
2
 = 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!
UE&MB@CMS Workshop
November 6, 2009
Rick Field – Florida/CDF/CMS
100
1,000
10,000
100,000
CM Energy W (GeV)
UE&MB@CMS
Page 33