LPC Mini-Workshop on
Early CMS Physics
“Min-Bias” and the
“Underlying Event” at the LHC
University of Florida
Rick Field
University of Florida
(for the UE&MB@CMS Group)
D. Acosta, P. Bartalini, R. Field, K. Kotov
University of Perugia
F. Ambroglini, G. Bilei, L. Fano'
CERN
“Minumum Bias” Collisions
Study charged particles
and muons during the
High P Jets
early running of the LHC!
Proton
UE&MB@CMS
A. De Roeck
AntiProton
T
Initial-State Radiation
Outgoing Parton
Hamburg
F.Bechtel, P. Schleper, G. Steinbrueck
PT(hard)
University of Trieste
Proton
AntiProton
D. Treleani et al.
DESY
Drell-Yan Production
Final-State Radiation
Lepton
Outgoing Parton
H. Jung, K. Borras
Summer Student
Proton
E. Izaguirre
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
Anti-Lepton
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 1
Particle Densities
DD = 4 = 12.6
2

31 charged
charged particles
particle
Charged Particles
pT > 0.5 GeV/c || < 1
CDF Run 2 “Min-Bias”
CDF Run 2 “Min-Bias”
Observable
Average
Nchg
Number of Charged Particles
(pT > 0.5 GeV/c, || < 1)
3.17 +/- 0.31
0.252 +/- 0.025
PTsum
(GeV/c)
Scalar pT sum of Charged Particles
(pT > 0.5 GeV/c, || < 1)
2.97 +/- 0.23
0.236 +/- 0.018
Average Density
per unit -
dNchg
chg/dd = 1/4
3/4 = 0.08
0.24
13 GeV/c PTsum
0
-1

+1
Divide by 4
dPTsum/dd = 1/4
3/4 GeV/c = 0.08
0.24 GeV/c
Study the charged particles (pT > 0.5 GeV/c, || < 1) and form the charged
particle density, dNchg/dd, and the charged scalar pT sum density,
dPTsum/dd.
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 2
PYTHIA Tune A
LHC Min-Bias Predictions
Charged Particle Density: dN/dd
Charged Particle Density: dN/dd
1.4
1.4
Pythia 6.206 Set A
CDF Data
14 TeV
Charged density dN/dd
1.0
dN/dd
Pythia 6.206 Set A
CDF Data
UA5 Data
Fit 2
Fit 1
1.2
1.2
1.8 TeV
0.8
0.6
0.4
0.2
0.8
0.6
0.4
0.2
all PT
630 GeV
1.0
=0
0.0
-6
-4
-2
0
Pseudo-Rapidity 
2
4
6
0.0
10
100
1,000
10,000
LHC?
100,000
CM Energy W (GeV)
 Shows the center-of-mass energy dependence of the charged particle density, dNchg/dd, for
“Min-Bias” collisions compared with PYTHIA Tune A with PT(hard) > 0.
 PYTHIA was tuned to fit the “underlying event” in hard-scattering processes at 1.8 TeV and
630 GeV.
 PYTHIA Tune A predicts a 42% rise in dNchg/dd at  = 0 in going from the Tevatron (1.8
TeV) to the LHC (14 TeV). Similar to HERWIG “soft” min-bias, 4 charged particles per unit
 becomes 6.
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 3
PYTHIA Tune A
LHC Min-Bias Predictions
Hard-Scattering in Min-Bias Events
Charged Particle Density
50%
12% of “Min-Bias”
events
have
PT(hard) > 10 GeV/c!
||<1
1.0E+00
Pythia 6.206 Set A
Pythia 6.206 Set A
40%
% of Events
Charged Density dN/dddPT (1/GeV/c)
1.0E-01
1.0E-02
PT(hard) > 5 GeV/c
PT(hard) > 10 GeV/c
30%
20%
1.8 TeV
1.0E-03
10%
14 TeV
1.0E-04
0%
100
1,000
10,000
100,000
CM Energy W (GeV)
630 GeV
LHC?
1.0E-05
 Shows the center-of-mass energy dependence
CDF Data
1.0E-06
0
2
4
6
8
PT(charged) (GeV/c)
1% of “Min-Bias” events
have PT(hard) > 10 GeV/c!
10
12
14
of the charged particle density,
dNchg/dddpT, for “Min-Bias” collisions
compared with PYTHIA Tune A with
PT(hard) > 0.
 PYTHIA Tune A predicts that 1% of all “Min-Bias” events at 1.8 TeV are a result of a hard
2-to-2 parton-parton scattering with PT(hard) > 10 GeV/c which increases to 12% at 14 TeV!
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 4
PYTHIA 6.2 Tunes
LHC Min-Bias Predictions
Charged Particle Density: dN/dY
Charged Particle Density: dN/d
12
pyA
pyDW
pyDWT
ATLAS
Generator Level
14 TeV
8
Charged Particle Density
Charged Particle Density
10
6
4
2
pyA
pyDW
pyDWT
ATLAS
Generator Level
14 TeV
10
8
6
4
2
Charged Particles (all pT)
Charged Particles (all pT)
0
0
-10
-8
-6
-4
-2
0
2
4
6
8
10
-10
-8
-6
PseudoRapidity 
-4
-2
0
2
4
6
8
10
Rapidity Y
 Shows the predictions of PYTHIA Tune A, Tune DW, Tune DWT, and the ATLAS tune for the
charged particle density dN/d and dN/dY at 14 TeV (all pT).
 PYTHIA Tune A and Tune DW predict about 6 charged particles per unit  at  = 0, while
the ATLAS tune predicts around 9.
 PYTHIA Tune DWT is identical to Tune DW at 1.96 TeV, but extrapolates to the LHC using
the ATLAS energy dependence.
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 5
PYTHIA 6.2 Tunes
LHC Min-Bias Predictions
Average Number of Charged Particles vs PTmin
Charged PT Distribution
20
100.0
Generator Level
Min-Bias 14 TeV
pyA <PT> = 641 MeV/c
Generator Level
Min-Bias 14 TeV
pyDW <PT> = 665 MeV/c
15
pyA
pyDW
pyDWT
ATLAS
<Nchg>
1/Nev dN/dPT (1/GeV/c)
pyDWT <PT> = 693 MeV/c
ATLAS <PT> = 548 MeV/c
10.0
10
5
Charged Particles (||<1.0, PT>PTmin)
1.0
0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Minimum PT (GeV/c)
Charged Particles (||<1.0)
0.1
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Charged Particle PT (GeV/c)
 Shows the predictions of PYTHIA Tune A, Tune DW, Tune DWT, and the ATLAS tune for the
charged particle pT distribution at 14 TeV (|| < 1) and the average number of charged
particles with pT > pTmin (|| < 1).
 The ATLAS tune has many more “soft” particles than does any of the CDF Tunes. The
ATLAS tune has <pT> = 548 MeV/c while Tune A has <pT> = 641 MeV/c (100 MeV/c more
per particle)!
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 6
CMS Forward detectors:
Hadron Forward Calorimeter HF: 3 ≤|| ≤ 5
Castor Calorimeter: 5.2 ≤|| ≤ 6.5
Beam Scintillation counters BSC
Zero-Degree Calorimeter ZDC
TOTEM detectors:
T1 (CSC) in CMS endcaps, T2 (GEM) behind HF
T1 + T2: 3 ≤ || ≤ 6.8
Roman Pots with Si det. up to 220 m
CMS
Central
Detectors
1000
T1
10
T1
T2
T2
HF
RP
0.1
-12
LPC CMS Workshop
June 8, 2007
CASTOR
1
ZDC
HF
-10
-8
-6
Extended
Tracking
-4
-2
0
+2

Rick Field – Florida/CMS
+4
+6
ZDC
100
CASTOR
pT (GeV)
TOTEM+CMS: pT- coverage
RP
+8 +10
+12
pTmax ~ s exp(-)
Page 7
A CMS “Min-Bias” Trigger
3<|η|<5
Cut on the number
of calorimeter cells:
18 wedges/side
0.175×0.175
>10 cells hit
99% efficient
>10 forward cells
and
>10 backward cells
towers
>15 → 86%
pT > 0.9
Use towers
or GeV/c
fired cells
>20 → 66%Tracking Efficiency
versus pseudorapidity
Tracking Efficiency pT > 0.9 GeV/c
versus transverse momentum
Prescaling by a factor 4×107
an HF trigger with high
efficiency (e.g.: at least 10
cells fired in + and detector) → 1 Hz
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 8
Detector Alignment
Early track studies
will help align the detector!
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 9
Min-Bias “Associated”
Charged Particle Density
“Associated” densities do
not include PTmax!
Highest pT
charged particle!
Charged Particle Density: dN/dd
PTmax Direction
PTmax Direction
0.5
D
Correlations in 
Charged Particle Density
CDF Preliminary
Associated Density
PTmax not included
data uncorrected
0.4
D
Charge Density
0.3
0.2
0.1
Min-Bias
Correlations
in 
Charged Particles
(||<1.0, PT>0.5 GeV/c)
PTmax
0.0
0
30
60
90
120
150
180
210
240
270
300
330
360
D (degrees)
 Use the maximum pT charged particle in the event, PTmax, to define a direction and look
It is more probable
to find
a particle
at the the “associated”
density, dN
chg/dd,
in “min-bias” collisions (pT > 0.5 GeV/c, || <
accompanying
PTmax
than
it
is
to
1).
find a particle in the central region!
 Shows the data
on the D dependence of the “associated” charged particle density,
dNchg/dd, for charged particles (pT > 0.5 GeV/c, || < 1, not including PTmax) relative
to PTmax (rotated to 180o) for “min-bias” events. Also shown is the average charged
particle density, dNchg/dd, for “min-bias” events.
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 10
Min-Bias “Associated”
Charged Particle Density
Rapid rise in the particle
density in the “transverse”
region as PTmax increases!
Associated Particle Density: dN/dd
PTmaxDirection
Direction
PTmax
D
“Toward”
“Transverse”
“Transverse”
Correlations in 
“Away”
Associated Particle Density
Jet #1
D
PTmax > 2.0 GeV/c
1.0
PTmax > 2.0 GeV/c
PTmax > 1.0 GeV/c
0.8
Charged Particles
(||<1.0, PT>0.5 GeV/c)
CDF Preliminary
data uncorrected
PTmax > 0.5 GeV/c
Transverse
Region
0.6
Transverse
Region
0.4
0.2
Jet #2
PTmax
PTmax not included
Min-Bias
0.0
0
30
60
90
120
150
180
210
240
270
300
330
360
D (degrees)
Ave Min-Bias
0.25 per unit -
PTmax > 0.5 GeV/c
 Shows the data on the D dependence of the “associated” charged particle density,
dNchg/dd, for charged particles (pT > 0.5 GeV/c, || < 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!).
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 11
Min-Bias “Associated”
Charged Particle Density
PY Tune A
PTmax > 2.0 GeV/c
PTmax Direction
Direction
PTmax
D
“Toward”
“Transverse”
“Transverse”
Correlations in 
“Away”
PTmax > 2.0 GeV/c
Associated Particle Density
D
Associated Particle Density: dN/dd
1.0
CDF Preliminary
PY Tune A
0.8
data uncorrected
theory + CDFSIM
PTmax > 0.5 GeV/c
PY Tune A
Transverse
Region
0.6
PY Tune A 1.96 TeV
Transverse
Region
0.4
0.2
PTmax
PTmax not included
(||<1.0, PT>0.5 GeV/c)
0.0
0
30
60
90
120
PTmax > 0.5 GeV/c
150
180
210
240
270
300
330
360
D (degrees)
 Shows the data on the D dependence of the “associated” charged particle density,
dNchg/dd, for charged particles (pT > 0.5 GeV/c, || < 1, not including PTmax) relative
to PTmax (rotated to 180o) for “min-bias” events with PTmax > 0.5 GeV/c and PTmax >
2.0 GeV/c compared with PYTHIA Tune A (after CDFSIM).
 PYTHIA Tune A predicts a larger correlation than is seen in the “min-bias” data (i.e.
Tune A “min-bias” is a bit too “jetty”).
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 12
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!
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 13
The Evolution of Charged Jets
and the “Underlying Event”
Charged Particle D Correlations
PT > 0.5 GeV/c || < 1
Charged Jet #1
Direction
“Transverse” region
very sensitive to the
“underlying event”!
2
“Toward-Side” Jet
D
“Toward”
2
CDF Run 1 Analysis
UE&MB@CMS
Away
Away Region
Region
Charged Jet #1
Direction
D
Transverse
Transverse
Region
Region
“Toward”
“Transverse”
Look at the charged
particle density in the
“transverse” region!


Leading
Leading
Jet
Jet
“Transverse”
Toward
Toward Region
Region
“Transverse”
“Transverse”
Transverse
Transverse
Region
Region
“Away”
“Away”
Away
Away Region
Region
“Away-Side” Jet
0
0
-1
-2
-1


+1
+1
+2
 Look at charged particle correlations in the azimuthal angle Drelative to the leading charged
particle jet.
 Define |D| < 60o as “Toward”, 60o < |D| < 120o as “Transverse”, and |D| > 120o as “Away”.
 All three regions have the same size in - space, DxD = 2x120o = 4/3.
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 14
The Evolution of Charged Jets
and the “Underlying Event” at the LHC
"Transverse" Charged Particle Density: dN/dd
PY Tune DW
T
PY-ATLAS
T
0.6
0.3
Leading Charged Jet (||<1.0)
Charged Particles (||<1.0, PT>0.9 GeV/c)
HERWIG
0.0
Ratio
PY-ATLAS
PT>0.9,
||<1
MC
MC
MB
MB
JET60
JET60
JET120
JET120
3.0
"Transverse" PTsum Density (GeV/c)
"Transverse" Charged Density
0.9
"Transverse" PTsum Density: dPT/dd
Ratio
PT>0.9,
||<1
P >0.9GeV/P >0.5GeV
MC
MC
Generator Level
MB
MB
14 TeV
JET60
JET60
JET120
JET120
1.2
Generator Level
14 TeV
2.0
PT>0.9GeV/PT>0.5GeV
PY Tune DW
1.0
HERWIG
Leading Charged Jet (||<1.0)
Charged Particles (||<1.0, PT>0.9 GeV/c)
0.0
0
25
50
75
100
125
150
175
200
0
PT(charged jet#1) (GeV/c)
25
50
75
100
125
150
175
200
PT(charged jet#1) (GeV/c)
 Shows average “transverse” charge particle  Shows average “transverse” charge particle
PTsum
Showsdensity
average(||
“transverse”
charge
particle
<
1,
p
>
0.9
GeV)
versus
density
(||
<
1,
p
>
0.9
GeV)
versus
P
(charged
T
T
T
 Shows average “transverse” charge particle
PTsum density
(||
< 1, pT>by
0.9PYTHIA
GeV) versus
jet#1)
prediced
Tune
jet#1)
prediced
PYTHIA
Tune
DW,
density
(|| < 1,by
pT>
0.9 GeV)
versus
PT(charged PPT(charged
jet#1)
theATLAS
generator
level and
at
T(charged
HERWIG,
andatthe
PYTHIA
Tune
HERWIG,
the ATLAS
Tune
at the DW,
jet#1) at theand
generator
levelPYTHIA
and at the
detector
atthe
thedetector
LHC . level .
LHC
level ..
 Shows the ratio, (pT>0.9 GeV/c)/(pT>0.5 GeV/c), for the
“transverse” charge particle and PTsum density (|| < 1)
versus PT(charged jet#1) at the generator level and at
the detector level .
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 15
QCD Monte-Carlo Models:
Lepton-Pair Production
Lepton-Pair Production
Anti-Lepton
Initial-State Radiation
Lepton-Pair Production
Initial-State Radiation
“Jet”
Proton
Anti-Lepton
“Hard Scattering” Component
AntiProton
Lepton
Underlying Event
Underlying Event
Proton
Lepton
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 and final-state radiation.
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 16
The “Central” Region
in Drell-Yan Production
Drell-Yan Production
Look at the charged
particle density and the
PTsum density in the
“central” region!
Charged Particles (pT > 0.5 GeV/c, || < 1)
Lepton
2
Proton
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation

Central Region
Anti-Lepton
Multiple Parton Interactions
Proton
Lepton
AntiProton
Underlying Event
0
-1
Underlying Event
Anti-Lepton

+1
After removing the leptonpair everything else is the
“underlying event”!
 Look at the “central” region after removing the lepton-pair.
 Study the charged particles (pT > 0.5 GeV/c, || < 1) and form the charged particle
density, dNchg/dd, and the charged scalar pT sum density, dPTsum/dd, by dividing
by the area in - space.
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 17
Drell-Yan Production (Run 2 vs LHC)
Drell-Yan Production
Drell-Yan PT(m+m-) Distribution
AntiProton
Proton
1.0E+02
<pT(m+m-)> is much
larger at the LHC!
Lepton-Pair Transverse
Momentum
Lepton
Underlying Event
Underlying Event
Drell-Yan
Initial-State
Shapes of the pT(m+m-)
distribution at the Z-boson mass.
Radiationlevel
generator
1.0E+01
ds/dPT (pb/GeV)
Anti-Lepton
PY Tune DW (solid)
HERWIG (dashed)
1.0E+00
Lepton-Pair Transverse Momentum
Drell-Yan
Average Pair PT
generator level
LHC
60
Drell-Yan PT(m+m-) Distribution
0.10
1.0E-01
1/N dN/dPT (1/GeV)
80
1.0E-02
40
Tevatron Run 2
1.0E-03
Tevatron Run2
0.08
Drell-Yan
LHC
generator level
PY Tune DW (solid)
HERWIG (dashed)
0.06
70 < M(m-pair) < 110 GeV
|(m-pair)| < 6
0.04
70 < M(m-pair) < 110 GeV
|(m-pair)| < 6
0.02 Tevatron Run2
PY Tune DW (solid)
20
HERWIG
(dashed)
1.0E-04
Z
0
0
0
100
200
300
400
500
600
700
Lepton-Pair Invariant Mass (GeV)
LHC
Normalized to 1
1000.00
50
800
900
1000
150
0
5
PT (m+m-) (GeV/c)
200
10
250
15
20
25
30
35
40
PT(m+m-) (GeV/c)
 Average Lepton-Pair transverse momentum  Shape of the Lepton-Pair p distribution at the
T
at the Tevatron and the LHC for PYTHIA
Z-boson mass at the Tevatron and the LHC for
Tune DW and HERWIG (without MPI).
PYTHIA Tune DW and HERWIG (without MPI).
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 18
The “Underlying Event” in
Drell-Yan Production
Drell-Yan Production
The “Underlying Event”
Lepton
Proton
HERWIG (without MPI)
is much less active than
PY Tune AW (with MPI)!
Underlying Event
Charged particle density
versus M(pair)
AntiProton
Underlying Event
“Underlying event” much
more active at the LHC!
Initial-State
Radiation
Anti-Lepton
Charged Particle Density: dN/dd
Charged Particle Density: dN/dd
1.5
1.0
RDF Preliminary
generator level
PY Tune AW
0.8
0.6
0.4
HERWIG
0.2
Drell-Yan
1.96 TeV
Z
Charged Particles (||<1.0, PT>0.5 GeV/c)
(excluding lepton-pair )
Charged Particle Density
Charged Particle Density
RDF Preliminary
generator level
Z
LHC
1.0
PY Tune AW
CDF
0.5
Drell-Yan
Charged Particles (||<1.0, PT>0.5 GeV/c)
(excluding lepton-pair )
HERWIG
0.0
0.0
0
50
100
150
200
250
0
50
100
150
200
250
Lepton-Pair Invariant Mass (GeV)
Lepton-Pair Invariant Mass (GeV)
 Charged particle density versus the lepton-  Charged particle density versus the lepton-pair
invariant mass at 14 TeV for PYTHIA Tune AW
pair invariant mass at 1.96 TeV for PYTHIA
and HERWIG (without MPI).
Tune AW and HERWIG (without MPI).
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 19
Extrapolations to the LHC:
Drell-Yan Production
Drell-Yan Production
Charged particle density
versus M(pair)
Lepton
The “Underlying Event”
Proton
AntiProton
Underlying Event
Tune DW and DWT are
identical at 1.96 TeV, but
have different MPI energy
dependence!
Underlying Event
Initial-State
Radiation
Anti-Lepton
Charged Particle Density: dN/dd
Charged Particle Density: dN/dd
RDF Preliminary
RDFgenerator
Preliminary
level
PY Tune BW
generator level
0.8
0.8
Charged Particle Density: dN/dd
2.5
RDF Preliminary
PY Tune DW
PY Tune DW
PY-ATLAS
0.6
0.6
0.4
0.4
PY Tune A
PY Tune A
0.2
0.2
HERWIG
HERWIG
00
50
50
100
100
1.96 TeV
Drell-Yan
1.96
TeV
Charged
Charged Particles
Particles (||<1.0,
(||<1.0, PT>0.5
PT>0.5 GeV/c)
GeV/c)
(excluding
(excluding lepton-pair
lepton-pair))
Z
0.0
0.0
PY Tune AW
Charged Particle Density
ChargedParticle
Particle
Density
Charged
Density
1.0
1.0
generator level
PY-ATLAS
PY Tune DWT
2.0
1.5
PY Tune DW
1.0
14 TeV
0.5
Z
Charged Particles (||<1.0, PT>0.5 GeV/c)
(excluding lepton-pair )
HERWIG
0.0
150
150
200
200
250
250
300
300
350
350
400
400
450
450
500
500
0
100
Lepton-Pair
Lepton-Pair Invariant
Invariant Mass
Mass (GeV)
(GeV)
200
300
400
500
600
700
800
900
1000
Lepton-Pair Invariant Mass (GeV)
 Average charged particle density versus the  Average charged particle density versus the
lepton-pair invariant mass at 1.96 TeV for
lepton-pair invariant mass at 14 TeV for
PYTHIA Tune A, Tune AW,
DW, Tune
ATLAS
BW,
and
Tune
PYTHIA Tune DW, Tune DWT, ATLAS and
DW and HERWIG
HERWIG
(without MPI
(without
).
MPI).
HERWIG (without MPI).
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 20
Extrapolations to the LHC:
Drell-Yan Production
Drell-Yan Production
The “Underlying Event”
Charged particle charged
PTsum density versus M(pair)
Lepton
Proton
AntiProton
Underlying Event
The ATLAS tune has a much “softer”
distribution of charged particles than
the CDF Run 2 Tunes!
Underlying Event
Initial-State
Radiation
Anti-Lepton
Charged PTsum Density: dPT/dd
Charged PTsum Density: dPT/dd
1.2 RDF Preliminary
generator level
5.0
PY Tune DW
RDF Preliminary
0.9
0.9
Charged PTsum Density: dPT/dd
PY Tune BW
generator level
0.6
0.6
PY Tune A
PY Tune A
PY Tune AW
PY-ATLAS PY Tune DW
1.96 TeV
Drell-Yan
1.96
TeV
0.3
0.3
0.0
0.0
Charged Particles (||<1.0, PT>0.9 GeV/c)
Charged(excluding
Particles (||<1.0,
PT>0.5
lepton-pair
) GeV/c)
(excluding lepton-pair )
HERWIGHERWIG
Z
0
0
50
50
100
100
150
150
200
200
250
250
300
300
350
350
400
400
450
450
500
500
Charged PTsum Density (GeV/c)
Charged
PTsum
Density
(GeV/c)
Charged
PTsum
Density
(GeV/c)
1.2
RDF Preliminary
PY Tune DWT
generator level
PY Tune DW
4.0
PY-ATLAS
3.0
2.0
14 TeV Drell-Yan
1.0
Charged Particles (||<1.0, PT>0.5 GeV/c)
(excluding lepton-pair )
HERWIG
Z
0.0
0
100
Lepton-Pair Invariant Mass (GeV)
Lepton-Pair Invariant Mass (GeV)
200
300
400
500
600
700
800
900
1000
Lepton-Pair Invariant Mass (GeV)
 Average charged PTsum density versus the  Average charged PTsum density versus the
lepton-pair invariant mass at 1.96 TeV for
lepton-pair invariant mass at 14 TeV for
PYTHIA Tune A, Tune
DW, ATLAS,
AW, Tune
and
BW, Tune
PYTHIA Tune DW, Tune DWT, ATLAS, and
DW and HERWIG
HERWIG
(without MPI
(without
).
MPI).
HERWIG (without MPI).
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 21
Extrapolations to the LHC:
Drell-Yan Production
Drell-Yan Production
The “Underlying Event”
The ATLAS tune has a much “softer”
distribution of chargedAntiProton
particles than
Underlying Event
the CDF Run 2 Tunes!
Initial-State
Proton
Charged Particles
(||<1.0, pT > 0.5 GeV/c)
Charged particle density
versus M(pair)
Lepton
Underlying Event
Radiation
Charged Particles
(||<1.0, pT > 0.9 GeV/c)
Anti-Lepton
Charged Particle Density: dN/dd
Charged Particle Density: dN/dd
Drell-Yan
PY Tune DWT
Generator Level
14 TeV
Charged Particle
4.0 Density: dN/dd
PY-ATLAS
generator level
2.0
1.5
1.0
0.5
Z
HERWIG
100
200
0.0
0
Charged Particle Density
Charged Particle Density
RDF Preliminary
300
1.2
PY-ATLAS
PY Tune DWT
3.0
PY Tune DW
PY Tune DW
2.0
14 TeV
1.0
Charged Particles (||<1.0, PT>0.5 GeV/c)
(excluding lepton-pair )
Charged Particle Density
2.5
0.8
Charged Particles (pT > min, ||<1.0)
(excluding lepton-pair
PY Tune DW )
0.4
PY-ATLAS
70 < M(m+m-) < 110 GeV
Z
Generator Level
14 TeV
HERWIG
Charged Particles (||<1.0, PT>0.9 GeV/c)
(excluding lepton-pair )
0.0
400
500
600
HERWIG
700
800
900
1000
0
100
200
300
400
500
600
700
800
900
1000
Lepton-Pair Invariant Mass (GeV)
Lepton-Pair Invariant Mass (GeV)
0.0
particle
0.0
0.2
0.4(pT >0.60.5 0.8  Average
1.0
1.2charged
1.4
1.6
1.8density (pT > 0.9 GeV/c)
 Average charged particle
density
the lepton-pair invariant mass at 14 TeV
GeV/c) versus the lepton-pair invariantMinimum
mass pversus
T (GeV/c)
at 14 TeV for PYTHIA Tune DW, Tune DWT, for PYTHIA Tune DW, Tune DWT, ATLAS and
HERWIG (without MPI).
ATLAS and HERWIG (without MPI).
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 22
UE&MB@CMS
“Minimum-Bias” Collisions
Gian Mario
 Min-Bias
Me Studies: Charged particle distributions and
(Jimmy)
Livio
Proton
Proton
High PT Jet Production
Outgoing Parton
Filippo
PT(hard)
Initial-State
Radiation
Proton
correlations. Construct “charged particle jets” and look
at “mini-jet” structure and the onset of the “underlying
event”. (requires only charged tracks)
Proton
Underlying Event
Outgoing Parton
Underlying Event
Final-State
Radiation
Drell-Yan Production
Lepton
 “Underlying Event” Studies: The “transverse region” in
“leading chgjet” and “back-to-back” chgjet production and
in the “central region” in Drell-Yan production. (requires
charged tracks and muons for Drell-Yan)
Paolo
Proton
Proton
Underlying Event
Underlying Event
Initial-State
Radiation
Anti-Lepton
Drell-Yan Production
Lepton-Pair
PT(pair)
Proton
Proton
Underlying Event
 Drell-Yan Studies: Transverse momentum distribution of
the lepton-pair versus the mass of the lepton-pair,
2
March 2006
<pPerugia,
T(pair)>, <pT (pair)>, ds/dpT(pair) (only requires
muons). Event structure for large lepton-pair pT (i.e. mm
+chgjets, requires muons and charged tracks).
Underlying Event
Initial-State
Radiation
Final-State
Radiation
Outgoing Parton
LPC CMS Workshop
June 8, 2007
Rick Field – Florida/CMS
Page 23