C2CR07
Rick Field
University of Florida
(for the CDF Collaboration)
Min-Bias at the Tevatron
Outline of Talk
¨ What is Min-Bias? Does it really exist?
¨ “Jets” in Min-Bias Collisions. Clear Jet
CDF Run 2
structure as low as 1 GeV/c!
¨ Extrapolating Tevatron Min-Bias to the
LHC.
“Minumum Bias” Collisions
Proton
AntiProton
¨ Using Pile-Up collisions to Study Min-Bias.
Is Pile-Up Unbiased?
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 1
Proton-AntiProton Collisions
at the Tevatron
Elastic Scattering
Single Diffraction
Double Diffraction
M
M2
M1
σtot = σEL + σSD +σDD +σHC
1.8 TeV: 78mb
= 18mb
+ 9mb
+ (4-7)mb + (47-44)mb
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
AntiProton
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
Final-State
Radiation
Outgoing Parton
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 2
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
σtot = σEL + σSD +σDD +σHC
1.8 TeV: 78mb
= 18mb
+ 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
The “hard core” component
contains both “hard” and
“soft” collisions.
“Hard” Hard Core (hard scattering)
Outgoing Parton
“Soft” Hard Core (no hard scattering)
Proton
AntiProton
Beam-Beam Counters
3.2 < |η| < 5.9
PT(hard)
Proton
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
Final-State
Radiation
Outgoing Parton
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 3
No-Bias vs Min-Bias
Charged Particle Density: dN/dη
5
No Trigger
900 GeV Generated
pyDWT DD NoTtrig
pyDW HC Mbtrig
Charged Particle Density
Charged Particle Density
pyDWT HC NoTrig
4
Charged Particle Density: dN/dη
5
pyDWT SD NoTrig
3
2
1
CDF Min-Bias Trigger
900 GeV Generated
pyDW DD MBtrig
4
pyDW SD MBtrig
3
2
1
Charged Particles (all PT)
Charged Particles (all PT)
0
0
-8
-6
-4
-2
0
2
4
6
8
-8
-6
-4
PseudoRapidity η
4
4
6
8
Charged Particle Density: dN/dη
pyDWT Sum MBtrig
Charged Particle Density
Charged Particle Density
pyDWT HC NoTrig
2
5
No Trigger
900 GeV Weighted
pyDWT Sum NoTrig
0
PseudoRapidity η
Charged Particle Density: dN/dη
5
-2
pyDWT DD NoTtrig
pyDWT SD NoTrig
3
2
1
Charged Particles (all PT)
0
CDF Min-Bias Trigger
900 GeV Weighted
pyDWT HC MBtrig
4
pyDWT DD MBtrig
pyDWT SD MBtrig
3
2
1
Charged Particles (all PT)
0
-8
-6
-4
-2
0
2
4
6
8
-8
-6
PseudoRapidity η
C2CR07-Lake Tahoe
February 28, 2007
-4
-2
0
2
4
6
8
PseudoRapidity η
Rick Field – Florida/CDF
Page 4
No-Bias vs Min-Bias
Charged Particle Density: dN/dη
5
No Trigger
900 GeV Generated
pyDWT DD NoTtrig
pyDW HC Mbtrig
Charged Particle Density
Charged Particle Density
pyDWT HC NoTrig
4
Charged Particle Density: dN/dη
5
pyDWT SD NoTrig
3
2
1
CDF Min-Bias Trigger
900 GeV Generated
pyDW DD MBtrig
4
pyDW SD MBtrig
3
2
1
Charged Particles (all PT)
Charged Particles (all PT)
0
0
-8
-6
-4
-2
0
2
4
6
8
-8
-6
-4
-2
0
2
What you see for “Min-Bias” PseudoRapidity η
depends on your triggger!
Charged Particle Density: dN/dη
Charged Particle Density: dN/dη
4
6
8
PseudoRapidity η
5
pyDWT Sum MBtrig
Charged Particle Density
Charged Particle Density
pyDWT HC NoTrig
4
5
No Trigger
900 GeV Weighted
pyDWT Sum NoTrig
pyDWT DD NoTtrig
pyDWT SD NoTrig
3
2
1
Charged Particles (all PT)
0
CDF Min-Bias Trigger
900 GeV Weighted
pyDWT HC MBtrig
4
pyDWT DD MBtrig
pyDWT SD MBtrig
3
2
1
Charged Particles (all PT)
0
-8
-6
-4
-2
0
2
4
6
8
-8
-6
PseudoRapidity η
C2CR07-Lake Tahoe
February 28, 2007
-4
-2
0
2
4
6
8
PseudoRapidity η
Rick Field – Florida/CDF
Page 5
No-Bias vs Min-Bias
About 2.5 charged particles
per unit η at η = 0.
Charged Particle Density: dN/dη
3
PYTHIA Tune
Tune DW
DW
Charged Particles
Particles
No-Bias 1.96 TeV
(HC+SD+DD+EL)
About 0.9 charged particles (pT >
0.5 GeV/c) per unit η at η = 0.
All
All PT
PT
PT > 0.5 GeV/c
2
Charged Particle Density: dN/dη
1
0
-10
2.0
-8
-6
-4
-2
0
2
4
6
88
10
10
PseudoRapidity η
¨ Charged particle (all pT) pseudo-rapidity
distribution, dNchg/dηdφ, at 1.96 TeV with
no trigger (i.e. no-bias) from PYTHIA
Tune DW.
Charged Particle Density
Charged
Charged Particle
Particle Density
4
PYTHIA Tune DW
Charged Particles (PT > 0.5 GeV/c)
Min-Bias 1.96 TeV
(HC+SD+DD+EL)
1.5
No Trigger
CDF Min-Bias
Trigger
1.0
0.5
0.0
-10
-8
-6
-4
-2
0
2
4
6
8
10
PseudoRapidity η
¨ Charged particle (pT > 0.5 GeV/c) pseudo-
About 1.5 charged particles (pT >
0.5 GeV/c) per unit η at η = 0
with CDF min-bias trigger.
C2CR07-Lake Tahoe
February 28, 2007
rapidity distribution, dNchg/dηdφ, at 1.96
TeV with the CDF Min-Bias trigger from
PYTHIA Tune DW.
Rick Field – Florida/CDF
Page 6
Particle Densities
2π
∆η∆φ = 4π = 12.6
φ
31 charged
charged particles
particle
Charged Particles
pT > 0.5 GeV/c |η| < 1
CDF Run 2 “Min-Bias”
CDF Run 2 “Min-Bias”
Observable
Average
Average Density
per unit η-φ
Nchg
Number of Charged Particles
(pT > 0.5 GeV/c, |η| < 1)
3.17 +/- 0.31
0.252 +/- 0.025
PTsum
(GeV/c)
Scalar pT sum of Charged Particles
(pT > 0.5 GeV/c, |η| < 1)
2.97 +/- 0.23
0.236 +/- 0.018
chg/dηdφ = 1/4π
3/4π = 0.08
0.24
dNchg
13 GeV/c PTsum
0
-1
η
+1
Divide by 4π
dPTsum/dηdφ = 1/4π
3/4π GeV/c = 0.08
0.24 GeV/c
¨ Study the charged particles (pT > 0.5 GeV/c, |η| < 1) and form the charged
particle density, dNchg/dηdφ, and the charged scalar pT sum density,
dPTsum/dηdφ.
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 7
CDF “Min-Bias” Data
Charged Particle Density
Charged Particle Pseudo-Rapidity Distribution: dN/dη
Charged Particle Density: dN/dηdφ
1.0
7
CDF Published
CDF Published
6
0.8
dN/d η d φ
dN/dη
5
4
3
0.6
0.4
2
0.2
CDF Min-Bias 1.8 TeV
CDF Min-Bias 630 GeV
1
CDF Min-Bias 630 GeV
CDF Min-Bias 1.8 TeV
all PT
0
all PT
0.0
-4
-3
-2
-1
0
1
2
3
4
-4
-3
Pseudo-Rapidity η
<dNchg/dη> = 4.2
-2
-1
0
1
2
3
4
Pseudo-Rapidity η
<dNchg/dηdφ> = 0.67
¨ Shows CDF “Min-Bias” data on the number of charged particles per unit pseudo-rapidity
at 630 and 1,800 GeV. There are about 4.2 charged particles per unit η in “Min-Bias”
collisions at 1.8 TeV (|η| < 1, all PT).
¨ Convert to charged particle density, dNchg/dηdφ, by dividing by 2π. There are about 0.67
charged particles per unit η-φ in “Min-Bias” collisions at 1.8 TeV (|η| < 1, all PT).
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 8
CDF “Min-Bias” Data
Energy Dependence
Charged Particle Density: dN/dηdφ
Charged Particle Density: dN/dηdφ
1.4
1.0
CDF Published
Charged density dN/dηdφ
dN/dη dφ
CDF Data
UA5 Data
Fit 2
Fit 1
1.2
0.8
0.6
0.4
0.2
CDF Min-Bias 630 GeV
CDF Min-Bias 1.8 TeV
1.0
0.8
0.6
0.4
0.2
all PT
η=0
0.0
-4
-3
-2
-1
0
1
2
3
Pseudo-Rapidity η
4
0.0
10
100
1,000
10,000
100,000
CM Energy W (GeV)
<dNchg/dηdφ> = 0.51
η = 0 630 GeV
24% increase
<dNchg/dηdφ> = 0.63
η = 0 1.8 TeV
LHC?
¨ Shows the center-of-mass energy dependence of the charged particle density, dNchg/dηdφ,
for “Min-Bias” collisions at η = 0. Also show a log fit (Fit 1) and a (log)2 fit (Fit 2) to the
CDF plus UA5 data.
¨ What should we expect for the LHC?
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 9
PYTHIA Tune A Min-Bias
“Soft” + ”Hard”
PYTHIA Tune A
CDF Run 2 Default
Charged Particle Density: dN/dηdφ
Tuned to fit the
“underlying event”!
Charged Particle Density
1.0
CDF Published
1.0E+00
0.8
CDF Min-Bias Data
1.0E-01
0.6
0.4
0.2
Pythia 6.206 Set A
CDF Min-Bias 1.8 TeV
1.8 TeV all PT
0.0
-4
-3
-2
-1
0
1
2
3
4
Pseudo-Rapidity η
¨ PYTHIA regulates the perturbative 2-to-2
Charged Density dN/dηdφdPT (1/GeV/c)
dN/dη dφ
Pythia 6.206 Set A
1.8 TeV |η|<1
1.0E-02
PT(hard) > 0 GeV/c
1.0E-03
1.0E-04
1.0E-05
parton-parton cross sections with cut-off
CDF Preliminary
parameters which allows one to run with
1.0E-06
0
2
4
6
8
10
12
PT(hard) > 0. One can simulate both “hard”
PT(charged) (GeV/c)
and “soft” collisions in one program.
¨ The relative amount of “hard” versus “soft” depends on the cut-off and can be tuned.
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
14
Page 10
PYTHIA Tune A Min-Bias
“Soft” + ”Hard”
Tuned to fit the
“underlying event”!
PYTHIA Tune A
CDF Run 2 Default
Charged Particle Density: dN/dηdφ
Charged Particle Density
1.0
CDF Published
1.0E+00
0.8
CDF Min-Bias Data
1.0E-01
0.6
0.4
0.2
Pythia 6.206 Set A
CDF Min-Bias 1.8 TeV
1.8 TeV all PT
0.0
-4
-3
-2
-1
0
1
2
3
4
Pseudo-Rapidity η
¨ PYTHIA regulates the perturbative 2-to-2
Charged Density dN/dηdφdPT (1/GeV/c)
dN/dη dφ
Pythia 6.206 Set A
1.8 TeV |η|<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
parton-parton cross sections with cut-off
CDF Preliminary
parameters
which allows one to run with
1.0E-06
Lots of “hard” scattering
0
2
4
6
8
10
12
PT(hard)in>“Min-Bias”!
0. One can simulate both “hard”
PT(charged) (GeV/c)
and “soft” collisions in one program.
¨ The relative amount of “hard” versus “soft” depends on the cut-off and can be tuned.
14
¨ This PYTHIA fit predicts that 12% of all “Min-Bias” events are a result of a hard 2-to-2
parton-parton scattering with PT(hard) > 5 GeV/c (1% with PT(hard) > 10 GeV/c)!
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 11
Min-Bias “Associated”
Charged Particle Density
Highest pT
charged particle!
Charged Particle Density: dN/dηdφ
0.5
PTmax Direction
Correlations in φ
CDF Preliminary
Charged Particle Density
∆φ
“Associated” densities do
not include PTmax!
Associated Density
PTmax not included
data uncorrected
0.4
Charge Density
0.3
0.2
0.1
Charged Particles
(|η|<1.0, PT>0.5 GeV/c)
PTmax
Min-Bias
0.0
0
30
60
90
120
150
180
210
240
270
300
330
360
∆φ (degrees)
¨ Use the maximum pT charged particle in the event, PTmax, to define a direction and
look at the the “associated” density, dNchg/dηdφ, in “min-bias” collisions (pT > 0.5
GeV/c, |η| < 1).
¨ Shows the data on the ∆φ dependence of the “associated” charged particle density,
dNchg/dηdφ, for charged particles (pT > 0.5 GeV/c, |η| < 1, not including PTmax) relative
to PTmax (rotated to 180o) for “min-bias” events. Also shown is the average charged
particle density, dNchg/dηdφ, for “min-bias” events.
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 12
Min-Bias “Associated”
Charged Particle Density
Highest pT
charged particle!
Charged Particle Density: dN/dηdφ
0.5
PTmax Direction
Correlations in φ
CDF Preliminary
Charged Particle Density
∆φ
“Associated” densities do
not include PTmax!
Associated Density
PTmax not included
data uncorrected
0.4
Charge Density
0.3
0.2
0.1
Charged Particles
(|η|<1.0, PT>0.5 GeV/c)
PTmax
Min-Bias
0.0
0
30
60
90
120
150
180
210
240
270
300
330
360
∆φ (degrees)
¨ Use the maximum pT charged particle in the event, PTmax, to define a direction and
is “associated”
more probable
to finddN
a chg
particle
/dηdφ, in “min-bias” collisions (pT > 0.5
look at theItthe
density,
accompanying
PTmax
than
it
is
to
GeV/c, |η| < 1).
find a particle in the central region!
¨ Shows the data
on the ∆φ dependence of the “associated” charged particle density,
dNchg/dηdφ, for charged particles (pT > 0.5 GeV/c, |η| < 1, not including PTmax) relative
to PTmax (rotated to 180o) for “min-bias” events. Also shown is the average charged
particle density, dNchg/dηdφ, for “min-bias” events.
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 13
Min-Bias “Associated”
Charged Particle Density
Associated Particle Density: dN/dηdφ
PTmax Direction
Correlations in φ
Jet #2
Associated Particle Density
Jet #1
∆φ
PTmax > 2.0 GeV/c
1.0
PTmax > 2.0 GeV/c
PTmax > 1.0 GeV/c
PTmax > 0.5 GeV/c
Transverse
Region
0.8
0.6
Charged Particles
(|η|<1.0, PT>0.5 GeV/c)
CDF Preliminary
data uncorrected
Transverse
Region
0.4
0.2
PTmax
PTmax not included
Min-Bias
0.0
0
30
60
90
120
150
180
210
240
270
300
330
360
∆φ (degrees)
PTmax > 0.5 GeV/c
¨ Shows the data on the ∆φ dependence of the “associated” charged particle density,
dNchg/dηdφ, for charged particles (pT > 0.5 GeV/c, |η| < 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!).
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 14
Min-Bias “Associated”
Charged Particle Density
Rapid rise in the particle
density in the “transverse”
region as PTmax increases!
Associated Particle Density: dN/dηdφ
PTmaxDirection
Direction
PTmax
∆φ
“Toward”
“Transverse”
“Transverse”
Correlations in φ
“Away”
Jet #2
Associated Particle Density
Jet #1
∆φ
PTmax > 2.0 GeV/c
1.0
PTmax > 2.0 GeV/c
PTmax > 1.0 GeV/c
PTmax > 0.5 GeV/c
Transverse
Region
0.8
0.6
Charged Particles
(|η|<1.0, PT>0.5 GeV/c)
CDF Preliminary
data uncorrected
Transverse
Region
0.4
0.2
PTmax
PTmax not included
Min-Bias
0.0
0
30
60
90
120
150
180
210
240
270
300
330
360
∆φ (degrees)
Ave Min-Bias
0.25 per unit η-φ
PTmax > 0.5 GeV/c
¨ Shows the data on the ∆φ dependence of the “associated” charged particle density,
dNchg/dηdφ, for charged particles (pT > 0.5 GeV/c, |η| < 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!).
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 15
Min-Bias “Associated”
Charged Particle Density
PY Tune A
PTmax > 2.0 GeV/c
∆φ
“Toward”
“Transverse”
“Transverse”
Correlations in φ
“Away”
Associated Particle Density
PTmax Direction
Direction
PTmax
∆φ
Associated Particle Density: dN/dηdφ
1.0
PTmax > 2.0 GeV/c
PY Tune A
PTmax > 0.5 GeV/c
PY Tune A
Transverse
Region
0.8
0.6
CDF Preliminary
data uncorrected
theory + CDFSIM
PY Tune A 1.96 TeV
Transverse
Region
0.4
0.2
PTmax
PTmax not included
(|η|<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
∆φ (degrees)
¨ Shows the data on the ∆φ dependence of the “associated” charged particle density,
dNchg/dηdφ, for charged particles (pT > 0.5 GeV/c, |η| < 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”).
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 16
PYTHIA Tune A
LHC Min-Bias Predictions
Charged Particle Density: dN/dηdφ
Charged Particle Density: dN/dηdφ
1.4
1.4
Pythia 6.206 Set A
CDF Data
14 TeV
Charged density dN/dηdφ
1.0
dN/d η dφ
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
0.0
-6
-4
-2
0
Pseudo-Rapidity η
2
0.8
0.6
0.4
0.2
all PT
630 GeV
1.0
4
6
η=0
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/dηdφ,
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/dηdφ at η = 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 η becomes 6.
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 17
PYTHIA Tune A
LHC Min-Bias Predictions
Hard-Scattering in Min-Bias Events
Charged Particle Density
12% of “Min-Bias”
50% events
have PT(hard) > 10 GeV/c!
1.0E+00
|η|<1
Pythia 6.206 Set A
% of Events
1.0E-01
Charged Density dN/dηdφdPT (1/GeV/c)
Pythia 6.206 Set A
40%
1.0E-02
1.8 TeV
PT(hard) > 5 GeV/c
PT(hard) > 10 GeV/c
30%
20%
1.0E-03
10%
14 TeV
1.0E-04
0%
100
1,000
10,000
100,000
CM Energy W (GeV)
630 GeV
1.0E-05
¨ Shows the center-of-mass energy
CDF Data
1.0E-06
0
2
LHC?
4
6
8
PT(charged) (GeV/c)
1% of “Min-Bias” events
have PT(hard) > 10 GeV/c!
10
12
14
dependence of the charged particle density,
dNchg/dηdφdPT, 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!
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 18
PYTHIA 6.2 Tunes
LHC Min-Bias Predictions
Charged Particle Density: dN/dY
Charged Particle Density: dN/dη
12
pyA
Generator Level
14 TeV
8
pyDW
pyDWT
Charged Particle Density
Charged Particle Density
10
ATLAS
6
4
2
pyA
Generator Level
14 TeV
10
pyDW
pyDWT
ATLAS
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
-4
PseudoRapidity η
-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/dη and dN/dY at 14 TeV (all pT).
¨ PYTHIA Tune A and Tune DW predict about 6 charged particles per unit η at η = 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.
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 19
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 (|η|<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 (|η|<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 (|η| < 1) and the average number of charged
particles with pT > pTmin (|η| < 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)!
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 20
Using Pile-Up to Study Min-Bias
Proton
Primary
Pile-Up
AntiProton
60 cm
MB
¨ The primary vertex is the highest PTsum of charged particles pointing towards it.
¨ Normally one only includes those charged particles which point back to the primary
vertex.
¨ However, the primary vertex is presumably the collision that satisfied the trigger
and is hence biased.
¨ Perhaps the pile-up is not biases and can serve as a new type of “Min-Bias”
collisions.
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 21
Using Pile-Up to Study Min-Bias
Proton
Primary
Pile-Up
AntiProton
60 cm
High PT Jet
¨ The primary vertex is the highest PTsum of charged particles pointing towards it.
¨ Normally one only includes those charged particles which point back to the primary
vertex.
¨ However, the primary vertex is presumably the collision that satisfied the trigger
and is hence biased.
¨ Perhaps the pile-up is not biases and can serve as a new type of “Min-Bias”
collisions.
¨ This assumes that the pile-up is not affected by the trigger (i.e. it is the same for all
primary processes).
C2CR07-Lake Tahoe
February 28, 2007
Rick Field – Florida/CDF
Page 22
Summary and Conclusions
“Minumum Bias” Collisions
¨ “Min-Bias” is not well defined. What you
see depends on what you trigger on! Every
trigger produces some biases.
Proton
¨ Very preliminary results seem to show that
pile-up conspires to help give you what you
ask for (i.e. satisfy your “trigger” or your
event selection)!
If true this means the pile-up is not the
same for all processes. It is process (i.e.
trigger) dependent!
C2CR07-Lake Tahoe
February 28, 2007
Charged Particle Density: dN/dη
10
Charged Particle Density
¨ We have learned a lot about “Min-Bias” at the
Tevatron, but we do not know what to expect at
the LHC. This will depend on the Min-Bias Trigger!
AntiProton
pyA
pyDW
pyDWT
ATLAS
Generator Level
14 TeV
8
6
4
2
Charged Particles (all pT)
0
-10
-8
-6
-4
-2
0
2
4
6
8
10
PseudoRapidity η
I must double check my analysis
and get it “blessed” before you can
trust what I have shown!
Rick Field – Florida/CDF
Page 33