MPI@LHC 2010
Review of Tevatron MB and UE Results
Rick Field
University of Florida
Outline of Talk
 Review some CDF Run 2 studies that never got published.
 Discuss the relationship between UE and MB..
Glasgow, Scotland November 2010
“Minimum Bias” Collisions
 Show how well the CDF UE tunes predict the CDF
Proton
MB data.
Proton
 Examine <pT> versus Nchg for MB and UE at
Outgoing Parton
PT(hard)
the Tevatron and the LHC.
Initial-State Radiation
 PYTHIA 6.4 Tune Z1: New CMS 6.4 MB tune
Proton
Proton
Underlying Event
Underlying Event
(pT-ordered parton showers and new MPI).
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Outgoing Parton
Final-State
Radiation
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!
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 2
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.
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 3
CDF RUN 2 Analysis
Charged Particles
pT > 0.5 GeV/c |h| < 1
2
Away Region
Jet #1 Direction
Df
Transverse
Region 1
f
Leading
Jet
AVE “transverse”
(Trans 1 + Trans 2)/2
Area = 4/6
“Toward”
“Trans 1”
“Trans 2”
Toward Region
Transverse
Region 2
“Away”
1 charged particle in the
“transverse 2” region
Away Region
0
-1
h
+1
dNchg/dhdf = 1/(4/6) = 0.48
 Study the charged particles (pT > 0.5 GeV/c, |h| < 1) in the “Transverse 1” and “Transverse
2” and form the charged particle density, dNchg/dhdf, and the charged scalar pT sum
density, dPTsum/dhdf.
 The average “transverse” density is the average of “transverse 1” and “transverse 2”.
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 4
Df Distributions
Charged Particle Density: dN/dhdf
Log Scale!
Jet #1 Direction
10.0
30 < ET(jet#1) < 70 GeV
Df
“Toward”
“Transverse”
“Transverse”
Jet #3
“Away”
Charged Particle Density
CDF Preliminary
“Toward-Side” Jet
data uncorrected
"Transverse"
Region
1.0
Jet#1
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
“Away-Side”
“Away-Side”
Jet Jet
0.1
0
30
60
90
120
Min-Bias
0.25 per unit h-f
150
180
210
Df (degrees)
240
270
300
Leading Jet
330
360
 Shows the Df dependence of the charged particle density, dNchg/dhdf, for charged
particles in the range pT > 0.5 GeV/c and |h| < 1 relative to jet#1 (rotated to 270o) for
“leading jet” events 30 < ET(jet#1) < 70 GeV.
 Also shows charged particle density, dNchg/dhdf, for charged particles in the range pT >
0.5 GeV/c and |h| < 1 for “min-bias” collisions.
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 5
Df Distributions
Refer to this as a
“Leading Jet” event
Jet #1 Direction
Df
Particle Density:
Density: dN/dhdf
dN/dhdf
Charged Particle
“Toward”
“Transverse”
CDF Preliminary
“Transverse”
“Away”
Refer to this as a
“Back-to-Back” event
Jet #1 Direction
Df
“Toward”
“Transverse”
Density
Charged Particle Density
Subset
10.0
10.0
30 << ET(jet#1)
ET(jet#1)<<70
70GeV
GeV
30
Back-to-Back
data uncorrected
Leading Jet
Min-Bias
"Transverse"
"Transverse"
Region
Region
1.0
1.0
Jet#1
Jet#1
Charged Particles
Charged
(|h|<1.0, PT>0.5 GeV/c)
(|h|<1.0,
“Transverse”
0.1
0.1
“Away”
00
30
60
90
120
150
180
180
210
210
240
240
270
270
300
300
330
330 360
360
Df (degrees)
(degrees)
Jet #2 Direction
 Look at the “transverse” region as defined by the leading jet (JetClu R = 0.7, |h| < 2) or
by the leading two jets (JetClu R = 0.7, |h| < 2). “Back-to-Back” events are selected to
have at least two jets with Jet#1 and Jet#2 nearly “back-to-back” (Df12 > 150o) with
almost equal transverse energies (ET(jet#2)/ET(jet#1) > 0.8).
 Shows the Df dependence of the charged particle density, dNchg/dhdf, for charged
particles in the range pT > 0.5 GeV/c and |h| < 1 relative to jet#1 (rotated to 270o) for 30
< ET(jet#1) < 70 GeV for “Leading Jet” and “Back-to-Back” events.
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 6
Min-Bias “Associated”
Charged Particle Density
“Associated” densities do
not include PTmax!
Highest pT
charged particle!
Charged Particle Density: dN/dhdf
PTmax Direction
0.5
PTmax
Direction
Df
Correlations in f
Charged Particle Density
CDF Preliminary
Associated Density
PTmax not included
data uncorrected
0.4
Df
Charge Density
0.3
0.2
0.1
Min-Bias
Correlations
in f
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmax
0.0
0
30
60
90
120
150
180
210
240
270
300
330
360
Df (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/dhdf,
in “min-bias” collisions (pT > 0.5 GeV/c, |h| <
accompanying
PTmax
than
it
is
to
1).
find a particle in the central region!
 Shows the data
on the Df dependence of the “associated” charged particle density,
dNchg/dhdf, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative
to PTmax (rotated to 180o) for “min-bias” events. Also shown is the average charged
particle density, dNchg/dhdf, for “min-bias” events.
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 7
Min-Bias “Associated”
Charged Particle Density
Rapid rise in the particle
density in the “transverse”
region as PTmax increases!
Associated Particle Density: dN/dhdf
PTmaxDirection
Direction
PTmax
Df
“Toward”
“Transverse”
“Transverse”
Correlations in f
“Away”
Associated Particle Density
Jet #1
Df
PTmax > 2.0 GeV/c
1.0
PTmax > 2.0 GeV/c
PTmax > 1.0 GeV/c
0.8
Charged Particles
(|h|<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
Df (degrees)
Ave Min-Bias
0.25 per unit h-f
PTmax > 0.5 GeV/c
 Shows the data on the Df dependence of the “associated” charged particle density,
dNchg/dhdf, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative
to PTmax (rotated to 180o) for “min-bias” events with PTmax > 0.5, 1.0, and 2.0 GeV/c.
 Shows “jet structure” in “min-bias” collisions (i.e. the “birth” of the leading two jets!).
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 8
Min-Bias “Associated”
Charged Particle Density
PY Tune A
PTmax > 2.0 GeV/c
Df
“Toward”
“Transverse”
“Transverse”
Correlations in f
“Away”
Associated Particle Density
PTmax Direction
Direction
PTmax
Df
Associated Particle Density: dN/dhdf
1.0
PTmax > 2.0 GeV/c
PY Tune A
0.8
CDF Preliminary
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
(|h|<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
Df (degrees)
 Shows the data on the Df dependence of the “associated” charged particle density,
dNchg/dhdf, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative
to PTmax (rotated to 180o) for “min-bias” events with PTmax > 0.5 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”).
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 9
Min-Bias “Associated”
Charged PTsum Density
PY Tune A
PTmax Direction
Direction
PTmax
Df
Df
“Toward”
“Transverse”
“Transverse”
Correlations in f
“Away”
Associated PTsum Density (GeV/c)
PTmax > 2.0 GeV/c
Associated PTsum Density: dPT/dhdf
1.0
PTmax > 2.0 GeV/c
PY Tune A
0.8
CDF Preliminary
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
(|h|<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
Df (degrees)
 Shows the data on the Df dependence of the “associated” charged PTsum density,
dPTsum/dhdf, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative
to PTmax (rotated to 180o) for “min-bias” events with PTmax > 0.5 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”).
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 10
Back-to-Back “Associated”
Charged Particle Densities
Maximum pT particle in
the “transverse” region!
PTmaxT
Direction
“Associated” densities do
not include PTmaxT!
Jet #1 Direction
Df
Df
“Toward”
“TransMAX”
PTmaxT
Df
“TransMIN”
PTmaxT
Direction
Jet#1
Region
Jet#2
Region
Jet#1
Region
Jet#2
Region
“Away”
Jet #2 Direction
 Use the leading jet in “back-to-back” events to define the “transverse” region and look at
the maximum pT charged particle in the “transverse” region, PTmaxT.
 Look at the Df dependence of the “associated” charged particle and PTsum densities,
dNchg/dhdf and dPTsum/dhdf for charged particles (pT > 0.5 GeV/c, |h| < 1, not including
PTmaxT) relative to PTmaxT.
 Rotate so that PTmaxT is at the center of the plot (i.e. 180o).
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 11
Back-to-Back “Associated”
Charged Particle Density
“Associated” densities do
not include PTmaxT!
PTmaxT
Direction
Associated Particle Density
Df
Jet #2
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
CDF Preliminary
Jet #3
Jet#2
Region
Associated Particle Density: dN/dhdf
10.0
Jet #1
Jet#1
Region
data uncorrected
Back-to-Back
30 < ET(jet#1) < 70 GeV
PTmaxT not included
1.0
Jet#2
Region
PTmaxT > 2.0 GeV/c
PTmaxT > 1.0 GeV/c
Jet #4??
"Jet#1"
Region
PTmaxT
PTmaxT > 0.5 GeV/c
0.1
0
30
60
90
Log Scale!
120
150
180
210
240
270
300
330
360
Df (degrees)
 Look at the Df dependence of the “associated” charged particle density, dNchg/dhdf for
charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmaxT) relative to PTmaxT
(rotated to 180o) for PTmaxT > 0.5 GeV/c, PTmaxT > 1.0 GeV/c and PTmaxT > 2.0
GeV/c, for “back-to-back” events with 30 < ET(jet#1) < 70 GeV .
 Shows “jet structure” in the “transverse” region (i.e. the “birth” of the 3rd & 4th jet).
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 12
Back-to-Back “Associated”
Charged PTsum Density
“Associated” densities do
not include PTmaxT!
PTmaxT
Direction
Associated PTsum Density (GeV/c)
Jet #3
Df
Jet #2
Jet#2
Region
Associated PTsum Density: dPT/dhdf
10.0
Jet #1
Jet#1
Region
Jet #4??
CDF Preliminary
data uncorrected
Jet#2
Region
1.0
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
Back-to-Back
30 < ET(jet#1) < 70 GeV
PTmaxT not included
PTmaxT > 2.0 GeV/c
PTmaxT
PTmaxT > 1.0 GeV/c
PTmaxT > 0.5 GeV/c
"Jet#1"
Region
0.1
0
30
60
90
Log Scale!
120
150
180
210
240
270
300
330
360
Df (degrees)
 Look at the Df dependence of the “associated” charged particle density, dPTsum/dhdf for
charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmaxT) relative to PTmaxT
(rotated to 180o) for PTmaxT > 0.5 GeV/c, PTmaxT > 1.0 GeV/c and PTmaxT > 2.0
GeV/c, for “back-to-back” events with 30 < ET(jet#1) < 70 GeV .
 Shows “jet structure” in the “transverse” region (i.e. the “birth” of the 3rd & 4th jet).
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 13
Back-to-Back “Associated”
Charged Particle Densities
“Back-to-Back”
charge density
Jet #1 Direction
Df
Charged Particle Density: dN/dhdf
10.0
“Toward”
“Transverse”
“Away”
“Back-to-Back”
“associated” density
Df
Jet #2 Direction
Jet#1
Region
Charged Particle Density
“Transverse”
CDF Preliminary
data uncorrected
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
"Transverse"
Region
1.0
Associated Density
PTmaxT not included
PTmaxT
Back-to-Back
PTmaxT > 0.5 GeV/c
PTmaxT
Direction
30 < ET(jet#1) < 70 GeV
Jet#1
0.1
Jet#2
Region
0
30
60
90
120
150
180
210
240
270
300
330
360
Df (degrees)
 Shows the Df dependence of the “associated” charged particle density, dNchg/dhdf for
charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmaxT) relative to PTmaxT
(rotated to 180o) forItPTmaxT
> 0.5 GeV/c,
PTmaxT
> 1.0 GeV/c and PTmaxT > 2.0
is more probable
to find
a
GeV/c, for “back-to-back”
events with 30PTmaxT
< ET(jet#1) < 70 GeV.
particle accompanying
than it
to charged
find a particle
indensity,
the
 Shows Df dependence
ofisthe
particle
dNchg/dhdf for charged particles
region!
(pT > 0.5 GeV/c, |h| < 1)“transverse”
relative to jet#1
(rotated to 270o) for “back-to-back events” with
30 < ET(jet#1) < 70 GeV.
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 14
Back-to-Back “Associated”
Charged Particle Densities
“Back-to-Back”
charge density
Charged Particle Density: dN/dhdf
Jet #1 Direction
Df
2
CDF Preliminary
346
350
354
358
6
10
14
18
342
22
338
26
334
data uncorrected
“Toward”
30 < ET(jet#1) < 70 GeV
Back-to-Back
30
330
34
326
38
322
42
318
46
314
“Transverse”
“Transverse”
50
310
54
Jet#1
306
58
302
62
298
“Away”
66
294
70
290
“Back-to-Back”
“associated” density
74
286
78
"Transverse"
Region
282
Jet #2 Direction
278
274
82
PTmaxT
270
86
"Transverse"
Region
90
94
266
Df
Jet#1
Region
98
262
102
0.5
258
106
254
110
250
PTmaxT
Direction
114
1.0
246
118
242
122
238
Jet#2
Region
126
234
130
1.5
230
134
226
138
222
142
2.0
218
Polar Plot
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
214
210
154
206
158
202
162
198
194
190
186
Associated Density
PTmaxT not included
146
150
178
174
170
166
182
 Shows the Df dependence of the “associated” charged particle density, dNchg/dhdf, pT > 0.5
GeV/c, |h| < 1 (not including PTmaxT) relative to PTmaxT (rotated to 180o) and the charged
particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1 relative to jet#1 (rotated to 270o) for
“back-to-back events” with 30 < ET(jet#1) < 70 GeV.
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 15
Back-to-Back “Associated”
Charged Particle Densities
“Back-to-Back”
charge density
Charged Particle Density: dN/dhdf
Jet #1 Direction
Df
2
CDF Preliminary
346
350
354
358
6
10
14
18
342
22
338
26
334
data uncorrected
“Toward”
30 < ET(jet#1) < 70 GeV
Back-to-Back
30
330
34
326
38
322
42
318
46
314
“Transverse”
“Transverse”
50
310
54
Jet#1
306
58
302
“Away”
62
298
66
294
70
290
“Back-to-Back”
“associated” density
74
286
Jet #2 Direction
78
"Transverse"
Region
282
278
82
274
PTmaxT
270
86
"Transverse"
Region
90
94
266
Df
Jet#1
Region
98
262
102
0.5
258
106
254
PTmaxT
Direction
110
250
114
1.0
246
118
242
122
238
Jet#2
Region
126
1.5
234
230
130
134
226
138
222
Polar Plot
Associated Density
PTmaxT > 2 GeV/c
(not included)
142
2.0
218
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
214
146
150
210
154
206
158
202
162
198
194
190
186
178
174
170
166
182
 Shows the Df dependence of the “associated” charged particle density, dNchg/dhdf, pT > 0.5
GeV/c, |h| < 1, PTmaxT > 2.0 GeV/c (not including PTmaxT) relative to PTmaxT (rotated to
180o) and the charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1, relative to jet#1
(rotated to 270o) for “back-to-back events” with 30 < ET(jet#1) < 70 GeV.
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 16
Jet Topologies
QCDThree
Four
Jet
QCD
Jet Topology
Topology Charged Particle Density: dN/dhdf
QCD
2-to-4
Scattering
Interactions
Parton
Multiple
2
CDF
Preliminary
Final-State
Jet #1
data uncorrected
Radiation
Outgoing Parton
346
6
10
14
30 < ET(jet#1) < 70 GeV
Outgoing Parton
Outgoing PartonBack-to-Back
18
30
330
34
326
38
322
42
318
46
Jet #1
PT(hard)
50
54
Jet#1
306
58
PT(hard)
302
298
Proton
Proton
358
26
334
310
Jet #3Df
354
22
338
314
Jet#1
Region
350
342
62
66
294
Jet #4
PTmaxT
Direction
70
290
74
286
78
Jet #4
AntiProton
AntiProton
"Transverse"
Jet #3
Region
282
278
Underlying Event
Underlying Event
PTmaxT
270
86
"Transverse"
Region
274
Jet#2
Region
82
90
94
266
98
Underlying Event
262
Jet #2
102
0.5
258
Underlying Event
106
254
110
Jet #2
250
114
1.0
246
118
242
238
126
1.5
234
230
130
134
226
138
222
Final-State
Radiation
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
Associated Density
PTmaxT > 2 GeV/c
(not included)
142
2.0
218
Polar Plot
Initial-State
Radiation
122
214
146
150
210
154
206
158
202
162
198
194
190
186
178
174
170
166
182
Parton
Outgoing
Parton
Outgoing
Parton
 Shows the Df dependence of the
“associated” charged particle Outgoing
density, dN
chg/dhdf, pT > 0.5
GeV/c, |h| < 1, PTmaxT > 2.0 GeV/c (not including PTmaxT) relative to PTmaxT (rotated to
180o) and the charged particle density, dNchg/dhdf, pT > 0.5 GeV/c, |h| < 1, relative to jet#1
(rotated to 270o) for “back-to-back events” with 30 < ET(jet#1) < 70 GeV.
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 17
“Associated” Charge Density
PYTHIA Tune A vs HERWIG
HERWIG (without multiple parton
interactions) too few “associated”
particles in the direction of PTmaxT!
Associated Particle Density: dN/dhdf
Associated Particle Density: dN/dhdf
10.0
10.0
data uncorrected
theory + CDFSIM
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
CDF Preliminary
Back-to-Back
30 < ET(jet#1) < 70 GeV
Associated Particle Density
Associated Particle Density
CDF Preliminary
1.0
PTmaxT > 0.5 GeV/c
PY Tune A
PTmaxT
"Jet#1"
Region
data uncorrected
theory + CDFSIM
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
1.0
PTmaxT
PTmaxT > 0.5 GeV/c
"Jet#1"
Region
HERWIG
0.1
0.1
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
60
90
120
Df (degrees)
And HERWIG (without multiple
parton interactions) too few particles
1.0
Back-to-Back
in Tune
the direction
opposite of PTmaxT!
PYTHIA
A
1.0
CDF Preliminary
CDF Preliminary
240
270
300
330
360
Data - Theory
PTmaxT
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
"Jet#1"
Region
-1.0
Back-to-Back
30 < ET(jet#1) < 70 GeV
0.0
-0.5
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
210
HERWIG
data uncorrected
theory + CDFSIM
0.5
0.0
-0.5
180
Data - Theory: Associated Particle Density dN/dhdf
30 < ET(jet#1) < 70 GeV
data uncorrected
theory + CDFSIM
0.5
150
Df (degrees)
Data - Theory: Associated Particle Density dN/dhdf
Data - Theory
Back-to-Back
30 < ET(jet#1) < 70 GeV
PTmaxT
"Jet#1"
Region
-1.0
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
60
Df (degrees)
MPI@LHC 2010
Glasgow, November 30, 2010
90
120
150
180
210
240
270
300
330
360
Df (degrees)
Rick Field – Florida/CDF/CMS
Page 18
“Associated” PTsum Density
PYTHIA Tune A vs HERWIG
HERWIG (without multiple parton
interactions) does not produce
enough “associated” PTsum in the
direction of PTmaxT!
Associated PTsum Density: dPT/dhdf
PTmaxT > 0.5 GeV/cAssociated PTsum Density: dPT/dhdf
10.0
Associated PTsum Density (GeV/c)
Associated PTsum Density (GeV/c)
10.0
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
1.0
PTmaxT > 0.5 GeV/c
Back-to-Back
30 < ET(jet#1) < 70 GeV
PY Tune A
CDF Preliminary
PTmaxT
data uncorrected
theory + CDFSIM
"Jet#1"
Region
0.1
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
1.0
PTmaxT > 0.5 GeV/c
HERWIG
CDF Preliminary
30
60
90
120
150
180
210
240
270
300
330
360
0
30
60
90
120
Df (degrees)
"Jet#1"
Region
2
CDF Preliminary
And HERWIG (without multiple
parton interactions) does not 2
Charged Particles
produceBack-to-Back
enough PTsum in the
(|h|<1.0, PT>0.5 GeV/c) 30 < ET(jet#1) < 70 GeV
direction
opposite of PTmaxT!1
PTmaxT not included
PYTHIA Tune A
Data - Theory (GeV/c)
data uncorrected
theory + CDFSIM
150
180
210
240
270
300
330
360
Df (degrees)
Data - Theory: Associated PTsum Density dPT/dhdf
Data - Theory: Associated PTsum Density dPT/dhdf
Data - Theory (GeV/c)
PTmaxT
data uncorrected
theory + CDFSIM
0.1
0
1
Back-to-Back
30 < ET(jet#1) < 70 GeV
0
-1
PTmaxT
CDF Preliminary
data uncorrected
theory + CDFSIM
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
Back-to-Back
30 < ET(jet#1) < 70 GeV
PTmaxT not included
0
-1
PTmaxT
HERWIG
"Jet#1"
Region
"Jet#1"
Region
-2
-2
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
60
MPI@LHC 2010
Glasgow, November 30, 2010
90
120
150
180
210
240
270
300
330
360
Df (degrees)
Df (degrees)
Rick Field – Florida/CDF/CMS
Page 19
“Associated” Charge Density
PYTHIA Tune A vs HERWIG
For PTmaxT > 2.0 GeV both
PYTHIA and HERWIG produce
slightly too many “associated”
particles in the direction of PTmaxT!
Associated Particle Density: dN/dhdf
Associated Particle Density: dN/dhdf
10.0
10.0
data uncorrected
theory + CDFSIM
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
CDF Preliminary
Back-to-Back
30 < ET(jet#1) < 70 GeV
Associated Particle Density
Associated Particle Density
CDF Preliminary
1.0
PTmaxT > 2.0 GeV/c
PY Tune A
PTmaxT
"Jet#1"
Region
0.1
data uncorrected
theory + CDFSIM
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
1.0
PTmaxT
PTmaxT > 2.0 GeV/c
HERWIG
"Jet#1"
Region
0.1
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
60
90
120
Df (degrees)
210
240
270
300
330
360
Data - Theory: Associated Particle Density dN/dhdf
data uncorrected
theory + CDFSIM
Data - Theory
HERWIG
0.0
-0.5
Charged Particles
PTmaxT
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT > 2.0 GeV/c (not included)
Back-to-Back
30 < ET(jet#1) < 70 GeV
CDF Preliminary
0.5
0.0
-0.8
180
1.0
theory + CDFSIM
0.8
150
Df (degrees)
But HERWIG (without multiple
parton
interactions)
produces
Data - Theory: Associated
Particle
Density dN/dhdf
too few particles
in the
Back-to-Back
CDF Preliminary
PYTHIA Tune A
direction
opposite
of
PTmaxT!
30
<
ET(jet#1)
< 70 GeV
data uncorrected
1.6
Data - Theory
Back-to-Back
30 < ET(jet#1) < 70 GeV
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
"Jet#1"
Region
PTmaxT
"Jet#1"
Region
PTmaxT > 2.0 GeV/c (not included)
-1.6
-1.0
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
60
Df (degrees)
MPI@LHC 2010
Glasgow, November 30, 2010
90
120
150
180
210
240
270
300
330
360
Df (degrees)
Rick Field – Florida/CDF/CMS
Page 20
“Associated” PTsum Density
PYTHIA Tune A vs HERWIG
For PTmaxT > 2.0 GeV both
PYTHIA and HERWIG produce
slightly too much “associated” PTsum
in the direction of PTmaxT!
PTmaxT > 2 GeV/c Associated PTsum Density: dPT/dhdf
Associated PTsum Density: dPT/dhdf
10.0
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
Associated PTsum Density (GeV/c)
Associated PTsum Density (GeV/c)
10.0
1.0
PTmaxT > 2.0 GeV/c
Back-to-Back
30 < ET(jet#1) < 70 GeV
PY Tune A
CDF Preliminary
PTmaxT
data uncorrected
theory + CDFSIM
"Jet#1"
Region
0.1
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
1.0
PTmaxT > 2.0 GeV/c
CDF Preliminary
PTmaxT
data uncorrected
theory + CDFSIM
"Jet#1"
Region
0.1
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
60
90
120
Df (degrees)
CDF Preliminary
240
270
300
330
360
Data - Theory
PTmaxT
0
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
"Jet#1"
Region
PTmaxT > 2.0 GeV/c (not included)
Back-to-Back
30 < ET(jet#1) < 70 GeV
HERWIG
data uncorrected
theory + CDFSIM
-1
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
210
Data - Theory: Associated Particle Density dN/dhdf
1
0.0
-1.0
180
2
PYTHIA Tune A
theory + CDFSIM
1.0
150
Df (degrees)
But HERWIG (without multiple
Data - Theory: Associated
Particleinteractions)
Density dN/dhdf
parton
produces
too few particles
in the
Back-to-Back
CDF Preliminary
direction
opposite
of
PTmaxT!
30
<
ET(jet#1)
<
70 GeV
data uncorrected
2.0
Data - Theory
Back-to-Back
30 < ET(jet#1) < 70 GeV
HERWIG
PTmaxT
"Jet#1"
Region
PTmaxT > 2.0 GeV/c (not included)
-2.0
-2
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
60
Df (degrees)
MPI@LHC 2010
Glasgow, November 30, 2010
90
120
150
180
210
240
270
300
330
360
Df (degrees)
Rick Field – Florida/CDF/CMS
Page 21
Jet Multiplicity
Rick Field KITP Collider Workshop 2004
Max pT in the
“transverse” region!
Jet Multiplicity
50%
Jet #1 Direction
Df
“Away”
Jet #2 Direction
HERWIG (without
multiple parton
interactions) does not have equal
amounts of 3 and 4 jet topologies!
Percent of Events
PTmaxT
“TransMIN”
data uncorrected
theory + CDFSIM
PY
HERWIG
Tune A
40%
“Toward”
“TransMAX”
CDF Run 2 Pre-Preliminary
Data
Data
Data
Back-to-Back
30 < ET(jet#1) < 70 GeV
PTmaxT > 2.0 GeV/c
30%
20%
10%
0%
0
1
2
3
Data have about equal amounts
of 3 and 4 jet topologies!
4
5
6
7
8
9
10
Number of Jets
 Shows the data on the number of jets (JetClu, R = 0.7, |h| < 2, ET(jet) > 3 GeV)
for “back-to-back” events with 30 < ET(jet#1) < 70 GeV and PTmaxT > 2.0
GeV/c.

(without
MPI)
after CDFSIM.
Compares
Compares the
the (uncorrected)
(uncorrected) data
data with
with HERWIG
PYTHIA Tune
A after
CDFSIM.
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 22
Rick Field University of Chicago
July 11, 2006
“Leading Jet”
“Back-to-Back”
Jet #1 Direction
Jet #1 Direction
“Toward”
“TransMAX”
“TransMIN”
“Away”
Df
Neither PY Tune A or
“Toward”
HERWIG fits the
ETsum
density in the
“TransMAX”
“TransMIN”
“transferse” region!
HERWIG
does slightly
“Away”
better than Tune A!
"Transverse" ETsum Density (GeV)
Df
"TransMAX" ETsum Density: dET/dhdf
7.0
Jet #2 Direction
CDF Run 2 Preliminary
6.0
"Leading Jet"
1.96 TeV
5.0
4.0
3.0
HW
"Back-to-Back"
2.0
1.0
PY Tune A
MidPoint R = 0.7 |h(jet#1) < 2
Particles (|h|<1.0, all PT)
0.0
 Shows the data on the tower ETsum
0
50
100
150
200
250
300
350
400
450
PT(jet#1) (GeV/c)
"TransMIN" ETsum Density: dET/dhdf
3.0
"Transverse" ETsum Density (GeV)
density, dETsum/dhdf, in the “transMAX”
and “transMIN” region (ET > 100 MeV, |h|
< 1) versus PT(jet#1) for “Leading Jet”
and “Back-to-Back” events.
 Compares the (corrected) data with
PYTHIA Tune A (with MPI) and
HERWIG (without MPI) at the particle
level (all particles, |h| < 1).
data corrected to particle level
CDF Run 2 Preliminary
MidPoint R = 0.7 |h(jet#1) < 2
data corrected to particle level
2.5
Particles (|h|<1.0, all PT)
1.96 TeV
2.0
HW
"Leading Jet"
1.5
1.0
0.5
"Back-to-Back"
PY Tune A
0.0
0
50
100
150
200
250
300
350
400
450
PT(jet#1) (GeV/c)
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 23
Rick Field University of Chicago
July 11, 2006
Possible Scenario??
 PYTHIA Tune A fits the charged particle
"Transverse" pT Distribution: dN/dpT
1.0E+01
"Transverse" PT Distribution
Sharp Rise at
Low PT?
Possible Scenario??
But I cannot get any
of the Monte-Carlo to
do this perfectly!
1.0E+00
Two things changed at the LHC!
NewMultiple
center-of-mass
energies
It is possible that there is a sharp rise in
Parton
(900 GeV & 7 TeV)
the number of particles in the “underlying
Interactions
AND the charged particles
were
event”
at low pT (i.e. pT < 0.5 GeV/c).
measured at smaller pT values!
1.0E-01
1.0E-02
Beam-Beam
Remnants
1.0E-03
PTsum density for pT > 0.5 GeV/c, but it
does not produce enough ETsum for
towers with ET > 0.1 GeV.
 Perhaps there are two components, a vary
1.0E-04
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
pT All Particles (GeV/c)
MPI@LHC 2010
Glasgow, November 30, 2010
4.0
4.5
5.0
“soft” beam-beam remnant component
(Gaussian or exponential) and a “hard”
multiple interaction component.
Rick Field – Florida/CDF/CMS
Page 24
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
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 25
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
+…
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Multiple-parton
interactions (MPI)!
Page 26
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”.
MPI@LHC 2010
Glasgow, November 30, 2010
Proton
+
+
Proton
Proton
Rick Field – Florida/CDF/CMS
“Semi-hard” partonparton collision
(pT < ≈2 GeV/c)
Proton
Proton
+…
Multiple-parton
interactions (MPI)!
Page 27
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
+…
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Multiple-parton
interactions (MPI)!
Page 28
UE Tunes
Allow primary hard-scattering to
go to pT = 0 with same cut-off!
“Underlying Event”
Fit the “underlying
event” in a hard
scattering process.
Proton
Proton
All of Rick’s tunes (except X2):
1/(pT)4→ 1/(pT2+pT02)2
A, AW, AWT,DW, DWT,
D6, D6T, CW, X1,
“Min-Bias”
“Min-Bias” (add
(ND)single & double diffraction)
and Tune Z1,
are UE tunes!
Proton
Predict MB (ND)!
Proton
+
+
Proton
Proton
Proton
Single Diffraction
Predict MB (IN)!
MPI@LHC 2010
Glasgow, November 30, 2010
+…
Proton
+
Proton
Proton
Double Diffraction
M2
M
Rick Field – Florida/CDF/CMS
M1
Page 29
MB Tunes
“Underlying Event”
Predict the “underlying
event” in a hard
scattering process!
Proton
Proton
Most of Peter Skand’s tunes:
S320 Perugia
0, S325 Perugia X,
“Min-Bias”
(ND)
S326 Perugia 6
are MB tunes!
Proton
Fit MB (ND).
Proton
+
Proton
+
Proton
Proton
Proton
+
Proton
Proton
+…
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 30
MB+UE Tunes
“Underlying Event”
Fit the “underlying
event” in a hard
scattering process!
Proton
Proton
Most of Hendrik’s “Professor”
tunes: ProQ20, P329
are MB+UE!
Simultaneous fit
to both MB & UE
“Min-Bias” (ND)
Proton
Fit MB (ND).
Proton
+
Proton
+…
MPI@LHC 2010
Glasgow, November 30, 2010
+
Proton
Proton
Proton
+
Proton
Proton
The ATLAS AMBT1 Tune is an MB+UE tune, but
because they include in the fit the ATLAS UE data
with PTmax > 10 GeV/c (big errors) the LHC UE data
does not have much pull (hence mostly an MB tune!).
Rick Field – Florida/CDF/CMS
Page 31
Charged Particle Multiplicity
Charged Multiplicity Distribution
Charged Multiplicity Distribution
1.0E+00
1.0E+00
CDF Run 2 Preliminary
1.0E-01
CDF Run 2 <Nchg>=4.5
CDF Run 2 <Nchg>=4.5
1.0E-02
Probability
Probability
1.0E-02
CDF Run 2 Preliminary
1.0E-01
1.0E-03
1.0E-04
1.0E-05
py Tune A <Nchg> = 4.3
pyAnoMPI <Nchg> = 2.6
1.0E-03
1.0E-04
1.0E-05
1.0E-06
1.0E-06
Min-Bias 1.96
1.0E-07
Min-Bias 1.96
1.0E-07
Charged Particles (|h|<1.0, PT>0.4 GeV/c)
Normalized to 1
Normalized to 1
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
10
Number of Charged Particles
i
20
25
30
35
40
45
50
Number of Charged Particles
“Minimum Bias” Collisions
Proton
15
No MPI!
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 (non-diffractive cross-section).
 The data are compared with PYTHIA Tune A and Tune A without multiple parton
interactions (pyAnoMPI).
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 32
55
PYTHIA Tune A Min-Bias
“Soft” + ”Hard”
Charged Particle Density
1.0E+00
Pythia 6.206 Set A
CDF Min-Bias Data
Charged Density dN/dhdfdPT (1/GeV/c)
1.0E-01
Ten decades!
1.8 TeV |h|<1
1.0E-02
12% of “Min-Bias” events
have PT(hard) > 5 GeV/c!
PT(hard) > 0 GeV/c
1.0E-03
1% of “Min-Bias” events
have PT(hard) > 10 GeV/c!
1.0E-04
1.0E-05
CDF Preliminary
1.0E-06
0
2
4
6
8
PT(charged) (GeV/c)
10
12
14
Lots of “hard” scattering in
“Min-Bias” at the Tevatron!
 Comparison of PYTHIA Tune A with the pT distribution of charged particles for “min-bias”
collisions at CDF Run 1 (non-diffractive cross-section).
pT = 50 GeV/c!
 PYTHIA Tune A predicts that 12% of all “Min-Bias” events are a result of a hard 2-to-2
parton-parton scattering with PT(hard) > 5 GeV/c (1% with PT(hard) > 10 GeV/c)!
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 33
CDF: Charged pT Distribution
Erratum November 18, 2010
Excess
No excess
events
atat
large
large
pTp! T!
“Minimum Bias” Collisions
Proton
AntiProton
50 GeV/c!
 Published CDF data on the pT distribution
of charged particles in Min-Bias collisions
(ND) at 1.96 TeV compared with PYTHIA
Tune A.
MPI@LHC 2010
Glasgow, November 30, 2010
CDF
CDFinconsistent
consistent with
withCMS
CMSand
andUA1!
UA1!
Rick Field – Florida/CDF/CMS
Page 34
Min-Bias Correlations
Average PT versus Nchg
Average PT (GeV/c)
1.4
CDF Run 2 Preliminary
1.2
Min-Bias
1.96 TeV
pyDW
data corrected
generator level theory
pyA
“Minumum
Bias” Collisions
1.0
Proton
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
“Minimum Bias” Collisions
Proton
AntiProton
 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).
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 35
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
MPI@LHC 2010
Glasgow, November 30, 2010
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 36
Transverse: <pT> vs Nchg
“Leading Jet”
Jet #1 Direction
"Transverse" Average PT versus Nchg
Df
2.0
2.0
CDF Run 2 Preliminary
“Toward”
CDF Run 2 Preliminary
Jet #1 Direction
data uncorrected
“Transverse”
“Away”
“Back-to-Back”
Jet #1 Direction
Df
“Toward”
“Transverse”
“Transverse”
“Away”
Average PT (GeV/c)
data uncorrected
“Transverse”
Df
LeadingJet
Jet
Leading
ET(jet#1)< <7070GeV
GeV
3030< <ET(jet#1)
theory + CDFSIM
1.96
TeV
1.5
1.5
Back-to-Back
Back-to-Back
30
30<<ET(jet#1)
ET(jet#1)<<70
70GeV
GeV
“Toward”
1.0
1.0
“Transverse”
“Transverse”
PYTHIA Tune A 1.96 TeV
Min-Bias
Min-Bias
“Away”
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.5
0.5
00
22
44
6
8
10
12
14
16
18
20
22
Number of Charged Particles
Min-Bias
Jet #2 Direction
 Look at the <pT> of particles in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) versus
the number of particles in the “transverse” region: <pT> vs Nchg.
 Shows <pT> versus Nchg in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) for “Leading
Jet” and “Back-to-Back” events with 30 < ET(jet#1) < 70 GeV compared with “min-bias”
collisions.
Rick Field KITP Collider Workshop 2004
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 37
Transverse: <pT> vs Nchg
Not much change in going
from 900 GeV to 7 TeV!
 Average pT versus Nchg (pT > 0.5 geV/c, |h| < 2.5) for the “transverse” region as defined by the
leading charged particle (PTmax > 1 GeV/c) at 7 TeV from ATLAS.
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 38
“Transverse 1” Region vs
“Transverse 2” Region
Jet #1 Direction
Df
Jet #1 Direction
“Toward”
“Trans 1”
“Trans 2”
“Away”
“Back-to-Back”
Jet #1 Direction
Df
“Toward”
“Trans 1”
"Transverse 1" vs "Transverse 2"
3.5
1.8
“Trans 2”
"Transverse
"Transverse
2" <PT>
2" Nchg
(GeV/c)
“Leading Jet”
CDF
CDFRun
Run22Preliminary
Preliminary 3030< <ET(jet#1)
ET(jet#1)< <7070GeV
GeV
Df
3.0
1.6
data
datauncorrected
uncorrected
2.5
1.4
Leading Jet
Leading Jet
1.96 TeV
“Toward”
2.0
1.2
“Trans1.51”
“Trans 2”
1.96 TeV
1.0
1.0
Back-to-Back
Back-to-Back
Charged
ChargedParticles
Particles(|h|<1.0,
(|h|<1.0,PT>0.5
PT>0.5GeV/c)
GeV/c)
“Away”
0.5
0.8
0
2
4
6
8
10
12
14
"Transverse 1" Nchg
“Away”
Jet #2 Direction
 Use the leading jet to define two “transverse” regions and look at the correlations
between “transverse 1” and “transverse 2”.
Shows
Shows the
the average
average number
pT of charged
particles
in thein“transverse
2” region
versusversus
the number
of charged
particles
the “transverse
2” region
the
of charged
particlesparticles
in the “transverse
1” region1”for
pT > for
0.5 p
GeV/c
and |h| < 1 for
number
of charged
in the “transverse
region
T > 0.5 GeV/c and |h| < 1
“Leading
Jet”Jet”
andand
“Back-to-Back”
events.
for
“Leading
“Back-to-Back”
events.
Rick Field KITP Collider Workshop 2004
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 39
“Transverse 1” Region vs
“Transverse 2” Region
"Transverse 1" vs "Transverse 2"
"Transverse 1" vs "Transverse 2"
3.5
3.0
"Transverse 2" Nchg
data uncorrected
theory + CDFSIM
Leading Jet
30 < ET(jet#1) < 70 GeV
CDF Run 2 Preliminary
"Transverse 2" Nchg
CDF Run 2 Preliminary
3.0
PY Tune A
2.5
1.96 TeV
2.0
HW
1.5
data uncorrected
theory + CDFSIM
2.5
PY Tune A
2.0
1.5
HW
1.0
1.0
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.5
0.5
0
2
4
6
8
10
12
14
0
2
4
"Transverse 1" Nchg
6
8
10
12
"Transverse 1" Nchg
"Transverse 1" vs "Transverse 2"
"Transverse 1" vs "Transverse 2"
1.8
1.50
CDF Run 2 Preliminary
data uncorrected
theory + CDFSIM
1.6
PY Tune A
1.96 TeV
1.4
Leading Jet
30 < ET(jet#1) < 70 GeV
"Transverse 2" <PT> (GeV/c)
"Transverse 2" <PT> (GeV/c)
Back-to-Back
30 < ET(jet#1) < 70 GeV
1.2
HW
1.0
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
CDF Run 2 Preliminary
data uncorrected
theory + CDFSIM
1.25
Back-to-Back
30 < ET(jet#1) < 70 GeV
1.00
PY Tune A
0.75
HW
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.8
0.50
0
2
4
6
8
10
12
14
0
"Transverse 1" Nchg
2
4
6
8
10
12
"Transverse 1" Nchg
Rick Field KITP Collider Workshop 2004
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 40
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.
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 41
Average PT versus Nchg
Average PT
PT versus
versus Nchg
Nchg
Average
Average PT versus Nchg
2.5
2.5
CDF Run 2 Preliminary
data corrected
generator level theory
1.2
CDFRun
Run22Preliminary
Preliminary
CDF
Min-Bias
1.96 TeV
Average
Average PT
PT (GeV/c)
(GeV/c)
Average PT (GeV/c)
1.4
pyA
pyAnoMPI
1.0
0.8
ATLAS
data corrected
generator
level theory
generator level theory
2.0
2.0
HW
HW
pyAW
pyAW
"Drell-YanProduction"
Production"
"Drell-Yan
70<<M(pair)
M(pair)<<110
110GeV
GeV
70
1.5
1.5
JIM
JIM
1.0
1.0
ATLAS
ATLAS
Charged Particles (|h|<1.0, PT>0.4 GeV/c)
0.6
ChargedParticles
Particles(|h|<1.0,
(|h|<1.0,PT>0.5
PT>0.5GeV/c)
GeV/c)
Charged
excludingthe
thelepton-pair
lepton-pair
excluding
0.5
0.5
0
5
10
15
20
25
30
35
40
00
55
10
10
Number of Charged Particles
15
15
20
20
25
25
30
30
Numberof
ofCharged
ChargedParticles
Particles
Number
Drell-Yan Production
Lepton
“Minumum Bias” Collisions
Proton
AntiProton
Proton
AntiProton
Underlying Event
Underlying Event
Anti-Lepton
 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 leveland are compared with PYTHIA
Tune A, Tune DW, and the ATLAS tune at the particle level (i.e. generator level).
 Particle level predictions for the average pT of charged particles versus the number of charged particles (pT > 0.5
GeV/c, |h| < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV) at CDF Run 2.
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 42
35
35
Average PT versus Nchg
 Z-boson production (with low pT(Z) and no MPI)
No MPI!
Average PT versus Nchg
produces low multiplicity and small <pT>.
2.5
Average PT (GeV/c)
CDF Run 2 Preliminary
data corrected
generator level theory
2.0
HW
 High pT Z-boson production produces large
pyAW
multiplicity and high <pT>.
"Drell-Yan Production"
70 < M(pair) < 110 GeV
 Z-boson production (with MPI) produces large
1.5
multiplicity and medium <pT>.
JIM
1.0
ATLAS
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
excluding the lepton-pair
0.5
0
5
10
15
20
25
30
35
Number of Charged Particles
Drell-Yan Production (no MPI)
High PT Z-Boson Production
Lepton
Initial-State Radiation
Outgoing Parton
Final-State Radiation
Drell-Yan
=
Proton
AntiProton
Underlying Event
Underlying Event
Anti-Lepton
+
+
Drell-Yan Production (with MPI)
Proton
Proton
Lepton
AntiProton
Z-boson
AntiProton
Underlying Event
Underlying Event
Anti-Lepton
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 43
Average PT(Z) versus Nchg
No MPI!
Average PT versus Nchg
PT(Z-Boson)
PT(Z-Boson) versus
versus Nchg
Nchg
80
80
2.5
data corrected
generator level theory
2.0
CDF
CDF Run
Run 22 Preliminary
Preliminary
HW
Average PT(Z) (GeV/c)
Average PT (GeV/c)
CDF Run 2 Preliminary
pyAW
"Drell-Yan Production"
70 < M(pair) < 110 GeV
1.5
JIM
1.0
ATLAS
generator
level theory
data corrected
generator level theory
60
60
pyAW
pyAW
HW
HW
"Drell-Yan
"Drell-Yan Production"
Production"
70
70 << M(pair)
M(pair) << 110
110 GeV
GeV
40
40
JIM
JIM
20
20
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
excluding the lepton-pair
ATLAS
ATLAS
Charged
Charged Particles
Particles (|h|<1.0,
(|h|<1.0, PT>0.5
PT>0.5 GeV/c)
GeV/c)
excluding
excluding the
the lepton-pair
lepton-pair
00
0.5
0
5
10
15
20
25
30
35
00
55
Outgoing Parton
Lepton
Initial-State Radiation
Proton
Proton
AntiProton
Underlying Event
Underlying Event
15
15
20
20
25
25
30
30
35
35
40
40
Number
Number of
of Charged
Charged Particles
Particles
Number of Charged Particles
High PDrell-Yan
Production
T Z-BosonProduction
10
10
 Predictions for the average PT(Z-Boson) versus
the number of charged particles (pT > 0.5
GeV/c, |h| < 1, excluding the lepton-pair) for for
Drell-Yan production (70 < M(pair) < 110 GeV)
at CDF Run 2.
Anti-Lepton
Z-boson
 Data on the average pT of charged particles versus the number of charged particles (pT > 0.5 GeV/c, |h| < 1,
excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV) at CDF Run 2. The data are
corrected to the particle level and are compared with various Monte-Carlo tunes at the particle level (i.e.
generator level).
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 44
Average PT versus Nchg
PT(Z) < 10 GeV/c
Average
Charged
PT
versus
Nchg
Average
Average Charged
Charged PT
PT versus
versus Nchg
Nchg
CDF
Run
Preliminary
CDF
CDF Run
Run 22
2 Preliminary
Preliminary
data corrected
generator
level
generator
level theory
theory
generator level theory
1.2
1.2
1.2
pyAW
pyAW
pyAW
1.0
1.0
1.0
HW
HW
HW
0.8
0.8
0.8
"Drell-Yan
Production"
"Drell-Yan
"Drell-Yan Production"
Production"
70
M(pair)
110
GeV
70
70 <<
< M(pair)
M(pair) <<
< 110
110 GeV
GeV
PT(Z)
10
GeV/c
PT(Z)
PT(Z) <<
< 10
10 GeV/c
GeV/c
CDF Run 2 Preliminary
JIM
JIM
Average PT (GeV/c)
Average
PT
(GeV/c)
AveragePT
PT(GeV/c)
(GeV/c)
Average
1.4
1.4
1.4
Average PT versus Nchg
1.4
ATLAS
ATLAS
Drell-Yan PT > 0.5 GeV PT(Z) < 10 GeV/c
data corrected
generator level theory
1.2
pyAW
No MPI!
1.0
Min-Bias PT > 0.4 GeV/c
0.8
Charged
Particles
(|h|<1.0,
PT>0.5
GeV/c)
Charged
Charged Particles
Particles (|h|<1.0,
(|h|<1.0, PT>0.5
PT>0.5 GeV/c)
GeV/c)
excluding
the
lepton-pair
excluding
excluding the
the lepton-pair
lepton-pair
Charged Particles (|h|<1.0)
pyA
0.6
0.6
0.6
0.6
00
0
55
5
10
10
10
15
15
15
20
20
20
25
25
25
30
30
30
35
35
35
0
Number
of
Charged
Particles
Number
Number of
of Charged
Charged Particles
Particles
Drell-Yan Production
Proton
20
30
40
Number of Charged Particles
Lepton
AntiProton
Underlying Event
10
Underlying Event
Remarkably similar behavior!
Perhaps indicating that MPIProton
playing an important role in
both processes.
“Minumum Bias” Collisions
AntiProton
Anti-Lepton
 Predictions
for thepTaverage
pT ofparticles
chargedversus
particles
theofnumber
charged(p
particles
(pT > 0.5
Data the average
of charged
theversus
number
chargedofparticles
|h|GeV/c,
< 1, |h|
T > 0.5 GeV/c,
<
1, excluding
the lepton-pair)
forDrell-Yan
for Drell-Yan
production
< M(pair)
110 GeV,
PT(pair)
10 GeV/c)
at
excluding
the lepton-pair)
for for
production
(70 <(70
M(pair)
< 110< GeV,
PT(pair)
< 10<GeV/c)
at CDF
CDF
Run
Run 2.
The2.data are corrected to the particle level and are compared with various Monte-Carlo tunes at the
particle level (i.e. generator level).
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 45
ATLAS: <pT> versus Nchg
“Minimum Bias” Collisions
Proton
Proton
 Shows the 900 GeV and 7 TeV ATLAS MB corrected data on <pT> versus Nchg
(pT > 100 MeV/c, |h| < 2.5).
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 46
NSD: <pT> versus Nchg
Average PT versus Nchg
0.7
CMS 900 GeV |eta| < 2.4
pyZ1 NSD LHC09
pyZ1 LHC09 <pT>=0.489
0.5
CMS
0.4
CMS Preliminary
CMS 900 GeV <pT>=0.460
data corrected
generator level theory
900 GeV
Average PT (GeV/c)
Average PT (GeV/c)
CMS Preliminary
0.6
Average PT versus Nchg
0.7
data corrected
generator level theory
0.6
0.5
CMS
0.4
CMS 7 TeV |eta| < 2.4
CMS 7 TeV <pT>=0.545
pyZ1 NSD LHC7
pyZ1 NSD LHC7 <pT>=0.577
7 TeV
Charged Particles (|h|<2.4, All pT)
Charged Particles (|h|<2.4, All pT)
0.3
0.3
0
10
20
30
40
50
60
70
80
90 100 110 120 130 140 150
Number of Charged Particles
Overall average pT
0
10
20
30
40
50
60
70
80
90 100 110 120 130 140 150
Number of Charged Particles
Overall average pT
Shows the 900 GeV and 7 TeV CMS NSD corrected data on <pT> versus
Nchg (all pT, |h| < 2.4) compared with Tune Z1.
“Minimum Bias” Collisions
Proton
MPI@LHC 2010
Glasgow, November 30, 2010
Okay not perfect!
But not that bad!
Rick Field – Florida/CDF/CMS
Proton
Page 47
NSD: <pT> versus Nchg
Charged Multiplicity Distribution
1.0E-01
“Minimum Bias” Collisions
RDF Preliminary
data CMS NSD
pyZ1 generator level
Proton
Probability
1.0E-02
Proton
7 TeV
900 GeV
1.0E-03
Charged Particles
(all PT, |h|<2.0)
1.0E-04
0
20
40
60
80
100
Number of Charged Particles
Average PT versus Nchg
Average PT versus Nchg
0.7
CMS Preliminary
CMS 900 GeV <pT>=0.460
data corrected
generator level theory
pyZ1 NSD LHC09
pyZ1 LHC09 <pT>=0.489
<pT> increases by 20%
0.5
0.4
900 GeV
Average PT (GeV/c)
Average PT (GeV/c)
CMS Preliminary
0.6
0.7
CMS 900 GeV |eta| < 2.4
data corrected
generator level theory
0.6
0.5
0.4
CMS 7 TeV |eta| < 2.4
CMS 7 TeV <pT>=0.545
pyZ1 NSD LHC7
pyZ1 NSD LHC7 <pT>=0.577
7 TeV
Charged Particles (|h|<2.4, All pT)
Charged Particles (|h|<2.4, All pT)
0.3
0.3
0
10
20
30
40
50
60
70
80
0
90 100 110 120 130 140 150
10
20
30
40
50
60
70
80
90 100 110 120 130 140 150
Number of Charged Particles
Number of Charged Particles
Note that for a given multiplicity <pT> increase only very slightly with in
going from 900 GeV to 7 TeV (2%-4%). However, the average pT increases
by ~20% due mainly from the broadening of the multiplicity distribution!
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 48
Energy Dependence
Ratio: Average PT versus Nchg
Ratio: Average PT versus Nchg
1.3
CMS Preliminary
CMS Preliminary
Charged Particles (|h|<2.4, All pT)
data corrected
generator level theory
Ratio: 7 TeV / 900 GeV
Ratio: 7 TeV / 900 GeV
1.3
1.2
1.1
CMS Ratio |eta| < 2.4
1.0
CMS Ratio = 1.185
7 TeV / 900 GeV
5
10
15
20
Tune PQ20
1.1
1.0
7 TeV / 900 GeV
pyX1844 Ratio = 1.194
25
30
35
40
45
50
55
60
Tune P0
Tune P329
1.2
pyX1844_10mm NSD Ratio
0.9
0
data corrected
generator level theory
Charged Particles (|h|<2.4, All pT)
0.9
65
0
5
10
Overall average pTNumber of Charged Particles
15
20
25
30
35
40
45
50
55
60
65
Number of Charged Particles
 Shows the energy dependence of the CMS NSD corrected data on <pT> versus Nchg
(all pT, |h| < 2.4) compared with Tune X2. Also shows the energy dependence of the
overall <pT> compared with Tune X2.
 Shows the energy dependence of the CMS NSD corrected data on <pT> versus Nchg
(all pT, |h| < 2.4) compared with Tune P0, Tune PQ20, and Tune P329. It will be
interesting to see if any tune can get this right!
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 49
Energy Dependence
Ratio: Average PT versus Nchg
Ratio: 7 TeV / 900 GeV
1.3
Amazing!
CMS Preliminary
Charged Particles (|h|<2.4, All pT)
data corrected
generator level theory
1.2
1.1
CMS Ratio |eta| < 2.4
1.0
CMS Ratio = 1.185
7 TeV / 900 GeV
pyZ1 NSD Ratio
0.9
pyZ1 Ratio = 1.149
0
5
10
15
20
25
30
35
40
45
50
55
60
65
Number of Charged Particles
ATLAS AMBT1 probably
does well here also!
<pT> versus Nchg
 Shows the energy dependence of the CMS NSD corrected data on
(all pT, |h| < 2.4) compared with Tune Z1. Also shows the energy dependence of the
overall <pT> compared with Tune Z1.
“Minimum Bias” Collisions
Proton
MPI@LHC 2010
Glasgow, November 30, 2010
First Tune (except PhoJet)Proton
to come close here!
Rick Field – Florida/CDF/CMS
Page 50
NSD Multiplicity Distribution
Charged Multiplicity Distribution
1.0E-01
RDF Preliminary
data CMS NSD
pyZ1 generator level
Difficult to produce
enough events with
large multiplicity!
CMS
Probability
1.0E-02
7 TeV
900 GeV
1.0E-03
Charged Particles
(all PT, |h|<2.0)
Tune Z1
1.0E-04
0
20
40
60
80
100
Number of Charged Particles
 Generator level charged multiplicity distribution (all pT, |h| < 2) at 900 GeV and 7
TeV. Shows the NSD = HC + DD prediction for Tune Z1. Also shows the CMS
NSD data.
“Minumum Bias” Collisions
Proton
MPI@LHC 2010
Glasgow, November 30, 2010
Okay not perfect!
But not that bad!
Rick Field – Florida/CDF/CMS
Proton
Page 51
MB & UE
"Transverse" Charged Particle Multiplicity
Charged Multiplicity Distribution
1.0E+00
1.0E-01
“Min-Bias”
RDF Preliminary
PT(chgjet#1) > 3 GeV/c
data CMS NSD
pyZ1 generator level
CMS
1.0E-02
Probability
Probability
data uncorrected
pyZ1 + SIM
1.0E-01
CMS
1.0E-02
CMS Preliminary
7 TeV
Tune Z1
1.0E-03
7 TeV
900 GeV
1.0E-04
900 GeV
1.0E-03
“Underlying Event”
1.0E-05
Normalized to 1
Charged Particles
(all PT, |h|<2.0)
1.0E-04
0
20
1.0E-06
Difficult to produce
40
60
80
enough
events
with
Number of Charged Particles
large multiplicity!
1.0E-07
0
100
 Generator level charged multiplicity
distribution (all pT, |h| < 2) at 900 GeV
and 7 TeV. Shows the NSD = HC + DD
prediction for Tune Z1. Also shows the
CMS NSD data.
MPI@LHC 2010
Glasgow, November 30, 2010
Charged Particles (|h|<2.0, PT>0.5 GeV/c)
Tune Z1
5
10
15
20
25
30
35
40
Number of Charged Particles
 CMS uncorrected
Difficult
datatoatproduce
900 GeV and 7
TeV on the charged
enoughparticle
events with
multiplicity
distribution inlarge
the “transverse”
“transverse” region
for charged particles
multiplicity
(pT >at0.5
low
GeV/c, |h|
< 2) as defined byhard
the leading
scale! charged
particle jet with PT(chgjet#1) > 3 GeV/c
compared with PYTHIA Tune Z1 at the
detector level (i.e. Theory + SIM).
Rick Field – Florida/CDF/CMS
Page 52
MB & UE
ChargedParticle
ParticleMultiplicity
Multiplicity
Charged
1.0E+00
1.0E+00
CMS
TeV
77 TeV
CMS Preliminary
Preliminary
CMS
Tune Z1
Z1
Tune
Min-Bias
NSD All pT
1.0E-01
1.0E-01
Probability
Probability
Min-Bias
NSD All pT
1.0E-02
1.0E-02
Underlying Event
"Transverse" Region
pT > 0.5 GeV/c
PT(chgjet#1) > 20 GeV/c
1.0E-03
1.0E-03
1.0E-04
1.0E-04
Normalizedto
to11
Normalized
Underlying Event
"Transverse" Region
pT > 0.5 GeV/c
PT(chgjet#1) > 20 GeV/c
Tune Z1
Charged Particles (|h|<2.0)
Charged Particles (|h|<2.0)
1.0E-05
1.0E-05
00
5
2010
1540
20
60
25
30 80 35
100
40
Number of
of Charged
Charged Particles
Particles
Number
 CMS uncorrected data at 7 TeV on the charged particle multiplicity distribution in the
“transverse” region for charged particles (pT > 0.5 GeV/c, |h| < 2) as defined by the leading
charged particle jet with PT(chgjet#1) > 20 GeV/c compared with PYTHIA Tune Z1 at the
detector level (i.e. Theory + SIM). Also shows the CMS corrected NSD multiplicity
distribution (all pT, |h| < 2) compared with Tune Z1 at the generator.
Amazing what we are asking the Monte-Carlo models to fit!
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 53
UE Summary
 The “underlying event” at 7 TeV and
900 GeV is almost what we expected!
With a little tuning we should be able
to describe the data very well (see
Tune Z1 later in this talk).
Outgoing Parton
ATLAS has pushed the
PT(hard)
UE measurements
down
Initial-State Radiation
to pT > 100 MeV!
Proton
Proton
Underlying Event
Underlying Event
Warning! All the UE studies look
Parton
at charged particles with pT > 0.5Outgoing
GeV/c.
I am surprised thatWe
thedoTunes
did as well as
not know if the models correctly
they did at predictingdescribe
the behavior
the pT values!
the UE atof
lower
“underlying event” at 900 GeV and 7 TeV!
Remember this is “soft” QCD!
“Min-Bias” is a whole different story!
Much more complicated due to very
soft particles and diffraction!
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Final-State
Radiation
PARP(82)
PARP(90)
Color
Diffraction
Connections
Page 54
Min-Bias Summary
We are a long way from having a Monte-Carlo model that will fit all the
features of the LHC min-bias data! There are more soft particles that
expected!
We need a better understanding and modeling of diffraction!
It is difficult for the Monte-Carlo models to produce a soft event (i.e. no
large hard scale) with a large multiplicity. There seems to be more “minbias” high multiplicity soft events at 7 TeV than predicted by the models!
The models do not produce enough strange particles! I have no idea what is
going on here! The Monte-Carlo models are constrained by LEP data.
Color
Diffraction
Connections
MPI@LHC 2010
Glasgow, November 30, 2010
Rick Field – Florida/CDF/CMS
Page 55