“Minimum Bias” at CDF and CMS
“Minumum Bias” Collisions
Proton
CDF Run 2
AntiProton
CMS
Outline of Talk
 Review the CDF Run 2 “minimum bias” tune
(i.e. PYTHIA Tune A).
 Show the “minimum bias” predictions for
PYTHIA Tune A, Tune DW, Tune DWT, and the
ATLAS tune at the LHC.
UE&MB@CMS
High PT Jets
Initial-State Radiation
Outgoing Parton
PT(hard)
Proton
 These tunes are discussed in our CMS note
on the “underlying event”.
AntiProton
Final-State Radiation
Outgoing Parton
CMS NOTE-2006/067
CMS Min-Bias Meeting
June 28, 2006
Rick Field – Florida/CDF/CMS
Page 1
PYTHIA Tune A Min-Bias
Charged Particle Density
Charged Particle Density: dN/dd
1.0
1.0E+00
CDF Published
Pythia 6.206 Set A
0.8
CDF Min-Bias Data
0.6
0.4
0.2
Pythia 6.206 Set A
1.8 TeV all PT
CDF Min-Bias 1.8 TeV
0.0
-4
-3
-2
-1
0
1
2
3
4
Pseudo-Rapidity 
 PYTHIA regulates the perturbative 2-to-2
parton-parton cross sections with cut-off
parameters which allows one to run with
PT(hard) > 0. One can simulate both “hard”
and “soft” collisions in one program.
Charged Density dN/dddPT (1/GeV/c)
dN/dd
1.0E-01
1.8 TeV ||<1
1.0E-02
PT(hard) > 0 GeV/c
1.0E-03
1.0E-04
1.0E-05
CDF Preliminary
1.0E-06
0
2
4
6
8
10
12
14
PT(charged) (GeV/c)
 The relative amount of “hard” versus “soft” depends on the cut-off and can be tuned.
 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)!
CMS Min-Bias Meeting
June 28, 2006
Rick Field – Florida/CDF/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
LHC?
0.0
10
100
1,000
10,000
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.
CMS Min-Bias Meeting
June 28, 2006
Rick Field – Florida/CDF/CMS
Page 3
CDF Run 1 PT(Z)
UE Parameters
ISR Parameters
Parameter
Tune A
Tune AW
MSTP(81)
1
1
MSTP(82)
4
4
PARP(82)
2.0 GeV
2.0 GeV
PARP(83)
0.5
0.5
PARP(84)
0.4
0.4
PARP(85)
0.9
0.9
PARP(86)
0.95
0.95
PARP(89)
1.8 TeV
1.8 TeV
PARP(90)
0.25
0.25
PARP(62)
1.0
1.25
PARP(64)
1.0
0.2
PARP(67)
4.0
4.0
MSTP(91)
1
1
PARP(91)
1.0
2.1
PARP(93)
5.0
15.0
Tune used by the
CDF-EWK group!
Z-Boson Transverse Momentum
0.12
PT Distribution 1/N dN/dPT
PYTHIA 6.2 CTEQ5L
CDF Run 1 Data
PYTHIA Tune A
PYTHIA Tune AW
CDF Run 1
published
0.08
1.8 TeV
Normalized to 1
0.04
0.00
0
2
4
6
8
10
12
14
16
18
20
Z-Boson PT (GeV/c)
 Shows the Run 1 Z-boson pT distribution (<pT(Z)>
≈ 11.5 GeV/c) compared with PYTHIA Tune A
(<pT(Z)> = 9.7 GeV/c), and PYTHIA Tune AW
(<pT(Z)> = 11.7 GeV/c).
Effective Q cut-off, below which space-like showers are not evolved.
Intrensic KT
The Q2 = kT2 in as for space-like showers is scaled by PARP(64)!
CMS Min-Bias Meeting
June 28, 2006
Rick Field – Florida/CDF/CMS
Page 4
Jet-Jet Correlations (DØ)
Jet#1-Jet#2 D Distribution
D Jet#1-Jet#2
 MidPoint Cone Algorithm (R = 0.7, fmerge = 0.5)
 L = 150 pb-1 (Phys. Rev. Lett. 94 221801 (2005))
 Data/NLO agreement good. Data/HERWIG
agreement good.
 Data/PYTHIA agreement good provided PARP(67)
= 1.0→4.0 (i.e. like Tune A, best fit 2.5).
CMS Min-Bias Meeting
June 28, 2006
Rick Field – Florida/CDF/CMS
Page 5
PYTHIA Tune DW
PYTHIA 6.2 CTEQ5L
ISR Parameters
Tune DW
Tune AW
MSTP(81)
1
1
MSTP(82)
4
4
PARP(82)
1.9 GeV
2.0 GeV
PARP(83)
0.5
0.5
PARP(84)
0.4
0.4
PARP(85)
1.0
0.9
PARP(86)
1.0
0.95
PARP(89)
1.8 TeV
1.8 TeV
PARP(90)
0.25
0.25
PARP(62)
1.25
1.25
PARP(64)
0.2
0.2
PARP(67)
2.5
4.0
MSTP(91)
1
1
PARP(91)
2.1
2.1
PARP(93)
15.0
15.0
Z-Boson Transverse Momentum
0.12
PT Distribution 1/N dN/dPT
UE Parameters
Parameter
CDF Run 1 Data
PYTHIA Tune DW
HERWIG
CDF Run 1
published
0.08
1.8 TeV
Normalized to 1
0.04
0.00
0
2
4
6
8
10
12
14
16
18
20
Z-Boson PT (GeV/c)
Intrensic KT
 Shows the Run 1 Z-boson pT distribution (<pT(Z)>
≈ 11.5 GeV/c) compared with PYTHIA Tune DW,
and HERWIG.
Tune DW uses DØ’s perfered value of PARP(67)!
Tune DW has a lower value of PARP(67) and slightly more MPI!
CMS Min-Bias Meeting
June 28, 2006
Rick Field – Florida/CDF/CMS
Page 6
PYTHIA 6.2 Tunes
PYTHIA 6.2 CTEQ5L
s(MPI) at 1.96 TeV
s(MPI) at 14 TeV
Parameter
Tune A
Tune DW
Tune DWT
ATLAS
Tune A
309.7 mb
484.0 mb
MSTP(81)
1
1
1
1
Tune DW
351.7 mb
549.2 mb
MSTP(82)
4
4
4
4
Tune DWT
351.7 mb
829.1 mb
PARP(82)
2.0 GeV
1.9 GeV
1.9409 GeV
1.8 GeV
ATLAS
324.5 mb
768.0 mb
PARP(83)
0.5
0.5
0.5
0.5
PARP(84)
0.4
0.4
0.4
0.5
PARP(85)
0.9
1.0
1.0
0.33
PARP(86)
0.95
1.0
1.0
0.66
PARP(89)
1.8 TeV
1.8 TeV
1.96 TeV
1.0 TeV
PARP(90)
0.25
0.25
0.16
0.16
PARP(62)
1.0
1.25
1.25
1.0
PARP(64)
1.0
0.2
0.2
1.0
PARP(67)
4.0
2.5
2.5
1.0
MSTP(91)
1
1
1
1
PARP(91)
1.0
2.1
2.1
1.0
"Transverse" Charged Particle Density: dN/dd
1.0
"Transverse" Charged Density
RDF Preliminary
PY Tune DW
generator level
0.8
PY-ATLAS
0.6
0.4
HERWIG
1.96 TeV
0.2
Leading Jet (||<2.0)
Charged Particles (||<1.0, PT>0.5 GeV/c)
0.0
0
50
100
150
200
250
300
350
400
450
500
PT(particle jet#1) (GeV/c)
PARP(93)
5.0
15.0
15.0
5.0
 Shows the “transverse” charged particle density,
dN/dd, versus PT(jet#1) for “leading jet”
events at 1.96 TeV for Tune DW, ATLAS, and
HERWIG (without MPI).
CMS Min-Bias Meeting
June 28, 2006
Rick Field – Florida/CDF/CMS
Page 7
PYTHIA 6.2 Tunes
LHC HC 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
“Hard Core” (HC) Min-Bias
-2
0
2
4
6
PseudoRapidity 
8
10
-10
-8
-6
-4
“Hard Core” (HC) Min-Bias
-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 for “hard core” (HC) Min-Bias 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.
CMS Min-Bias Meeting
June 28, 2006
Rick Field – Florida/CDF/CMS
Page 8
PYTHIA 6.2 Tunes
LHC HC 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
“Hard Core” (HC) Min-Bias
Charged Particles (||<1.0)
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Minimum PT (GeV/c)
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 for “hard core” (HC) Min-Bias 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)!
CMS Min-Bias Meeting
June 28, 2006
Rick Field – Florida/CDF/CMS
Page 9
PYTHIA 6.2 Tunes
LHC HC Min-Bias Predictions
Average Number of Charged Particles vs PTmin
Charged Multiplicity Distribution
20
0.100
Generator Level
Min-Bias 14 TeV
pyA <Nchg> = 11.93
pyDW <Nchg> = 11.76
15
pyDWT <Nchg> = 12.95
pyA
pyDW
pyDWT
ATLAS
<Nchg>
Fraction of Events
ATLAS <Nchg> = 18.14
10
0.010
5
Charged Particles (||<1.0, PT>PTmin)
Generator Level
Min-Bias 14 TeV
0
0.0
0.1
0.2
0.3
“Hard Core” (HC) Min-Bias
Charged Particles (||<1.0, All pT)
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Minimum PT (GeV/c)
0.001
0
5
10
15
20
25
30
35
40
45
50
Number of Charged Particles
 Shows the predictions of PYTHIA Tune A, Tune DW, Tune DWT, and the ATLAS tune for
the charged particle multiplicity distribution for “hard core” (HC) Min-Bias 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 <Nchg> = 18.14 (|| < 1) while Tune A has <Nchg> = 11.93 (|| < 1).
CMS Min-Bias Meeting
June 28, 2006
Rick Field – Florida/CDF/CMS
Page 10
PYTHIA Tune DWT
LHC Min-Bias Predictions
Average Number of Charged Particles vs PTmin
Charged Particle Density: dN/d
15
8
pyDWT Generator Level
Min-Bias 14 TeV
HC + SD + DD
HC
6
pyDWT Generator Level
Min-Bias 14 TeV
HC
10
<Nchg>
Charged Particle Density
Charged Particles (all pT)
4
HC + SD + DD
Charged Particles (||<1.0, PT>PTmin)
5
DD
SD
DD
SD
2
0
0
0.0
-10
-8
-6
-4
-2
0
2
4
6
8
0.1
10
PseudoRapidity 
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Minimum PT (GeV/c)
 Shows the predictions of PYTHIA Tune DWT for the charged particle density dN/d (all
pT) and the average number of charged particles with pT > pTmin (|| < 1) for Min-Bias at 14
TeV.
 Shows the contributions from the “hard core” (HC), Single-Diffraction (SD), and doublediffraction (DD) components of Min-Bias collisions. Also shows the sum (HC + SD + DD).
Note the sum is actually (MB = 0.697HC + 0.181SD + 0.122DD)
 For pT > 0.5 GeV/c and || < 1 one is simply adding in zero Nchg for SD and DD.
CMS Min-Bias Meeting
June 28, 2006
Rick Field – Florida/CDF/CMS
Page 11
PYTHIA Tune DWT
LHC Min-Bias Predictions
Average Number of charged particles
with pT > pTmin and || < 1
Components
Cross-Section (14 TeV)
% Total
HC
55.22 mb
69.7%
SD
14.30 mb
18.1%
PTmin
HC
(pyDWT)
SD
DD
Total
DD
9.69 mb
12.2%
0.0
12.95
1.57
1.60
9.50
Total
79.21 mb
100%
0.1
12.45
1.48
1.50
9.13
0.2
10.90
1.17
1.19
7.94
0.3
9.09
0.82
0.83
6.58
0.4
7.48
0.54
0.54
5.37
0.5
6.16
0.33
0.33
4.38
0.6
5.09
0.19
0.19
3.60
0.7
4.24
0.10
0.10
2.98
0.8
3.56
0.05
0.05
2.49
0.9
3.01
0.03
0.03
2.10
1.0
2.57
0.01
0.01
1.79
 Shows the cross-sections (in mb) the “hard
core” (HC), Single-Diffraction (SD), and
double-diffraction (DD) components of MinBias collisions from PYTHIA.
 Shows the predictions of PYTHIA Tune
DWT for the average umber of charged
particles with pT > pTmin (|| < 1) for
Min-Bias at 14 TeV.
CMS Min-Bias Meeting
June 28, 2006
Rick Field – Florida/CDF/CMS
Page 12
Conclusions
Outgoing Parton
“Minumum Bias” Collisions
Tevatron
LHC
PT(hard)
Initial-State Radiation
Proton
AntiProton
Proton
AntiProton
Underlying Event
 We cannot use the new underlying event model in
PYTHIA 6.3. It has not been studied (and tuned)
well enough yet!
Outgoing Parton
Underlying Event
Final-State
Radiation
 The ATLAS tune is “goofy”! It produces too many “soft” particles. The charged
particle <pT> is too low and does not agree with the CDF Run 2 data. The ATLAS tune
agrees with <Nchg> but not with <PTsum> at the Tevatron.
 PYTHIA Tune DW is very similar to Tune A except that it fits the CDF PT(Z) distribution
and it uses the DØ prefered value of PARP(67) = 2.5 (determined from the dijet D
distribution).
 PYTHIA Tune DWT is identical to Tune DW at 1.96 TeV but uses the ATLAS energy
extrapolation to the LHC (i.e. PARP(90) = 0.16).
CMS Min-Bias Meeting
June 28, 2006
Rick Field – Florida/CDF/CMS
Page 13
Conclusions
Outgoing Parton
“Minumum Bias” Collisions
Tevatron
LHC
PT(hard)
Initial-State Radiation
Proton
AntiProton
Proton
AntiProton
Underlying Event
I think more
needs
 We cannot use the new underlying
eventwork
model
in to be done
Outgoing Parton


Underlying Event
Final-State
Radiation
comparing
various tunes.
PYTHIA 6.3. It has not beeninstudied
(andthe
tuned)
The ATLAS tune cannot be right
well enough yet!
because it does not fit the Tevatron
Right now
like Tune
The ATLAS tune is “goofy”!data.
It produces
too Imany
“soft”DW.
particles. The charged
Probably
no tune
fitthe
theCDF
CMSRun
data.
particle <pT> is too low and
does not
agreewill
with
2 data. The ATLAS tune
That
is
why
we
want
to
measure
MB&UE
agrees with <Nchg> but not with <PTsum> at the Tevatron.
at CMS and retune the Monte-Carlo
models!
PYTHIA Tune DW is very similar to Tune
A except that it fits the CDF P (Z) distribution
T
and it uses the DØ prefered value of PARP(67) = 2.5 (determined from the dijet D
distribution).
 PYTHIA Tune DWT is identical to Tune DW at 1.96 TeV but uses the ATLAS energy
extrapolation to the LHC (i.e. PARP(90) = 0.16).
CMS Min-Bias Meeting
June 28, 2006
Rick Field – Florida/CDF/CMS
Page 14