Early LHC Data
Findings & Surprises
Rick Field
University of Florida
Outline of Talk
Outgoing Parton
 How well did we do at predicting the LHC UE data at
900 GeV and 7 TeV? A careful look.
PT(hard)
Initial-State Radiation
Proton
Proton
Underlying Event
Underlying Event
 How well did we do at predicting the LHC MB data
at 900 GeV and 7 TeV? A careful look.
Outgoing Parton
Final-State
Radiation
 PYTHIA 6.4 Tune Z1: New CMS 6.4 tune (pT-ordered
UE&MB@CMS
parton showers and new MPI).
 Strange particle production: A problem for the models?
 New physics in min-bias??: Observation of long-range
same-side correlations at 7 TeV.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 1
QCD Monte-Carlo Models:
High Transverse Momentum Jets
Hard Scattering
Initial-State Radiation
Hard Scattering
PT(hard)
Outgoing Parton
PT(hard)
Initial-State Radiation
Outgoing Parton
Proton
“Hard Scattering” Component
Proton
Final-State Radiation
Outgoing Parton
Underlying Event
Underlying Event
Proton
Final-State Radiation
Proton
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).
 Of course the outgoing colored partons fragment into hadron “jet” and inevitably “underlying event”
observables receive contributions from initial and final-state radiation.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 2
QCD Monte-Carlo Models:
High Transverse Momentum Jets
Hard Scattering
Initial-State Radiation
Hard Scattering
PT(hard)
Outgoing Parton
PT(hard)
Initial-State Radiation
Outgoing Parton
Proton
“Hard Scattering” Component
Proton
Final-State Radiation
Outgoing Parton
Underlying Event
Underlying Event
Proton
Final-State Radiation
Proton
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!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 3
The “Transverse” Region
Charged Jet #1
Direction
“Transverse” region
very sensitive to the
“underlying event”!
Charged Particle  Correlations
PT > 0.5 GeV/c || < cut
CDF Run 1 Analysis cut = 1
“Toward-Side” Jet
Charged Jet #1
Direction


Look at the charged
particle density in the
“transverse” region!
2
Away Region
Transverse
Region
“Toward”
“Toward”
“Transverse”

Leading
ChgJet
“Transverse”
“Transverse”
“Transverse”
Toward Region
Transverse
Region
“Away”
“Away”
Away Region
“Away-Side” Jet
0
-cut

+cut
 Look at charged particle correlations in the azimuthal angle relative to the leading charged
particle jet.
 Define || < 60o as “Toward”, 60o < || < 120o as “Transverse”, and || > 120o as “Away”.
 All three regions have the same area in - space, ×  = 2cut × 120o = 2cut × 2/3.
 Construct densities by dividing by the area in - space.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 4
The “Transverse” Region
Charged Particle  Correlations
PT > 0.5 GeV/c || < cut
Traditional Approach!
Charged Jet #1
Direction
“Transverse” region
very sensitive to the
“underlying event”!
CDF Run 1 Analysis cut = 1
“Toward-Side” Jet
Charged Jet #1
Direction


Look at the charged
particle density in the
“transverse” region!
2
Away Region
Transverse
Region
“Toward”
“Toward”
“Transverse”

Leading
ChgJet
“Transverse”
“Transverse”
“Transverse”
Toward Region
Transverse
Region
“Away”
“Away”
Away Region
“Away-Side” Jet
0
-cut

+cut
 Look at charged particle correlations in the azimuthal angle relative to the leading charged
particle jet.
 Define || < 60o as “Toward”, 60o < || < 120o as “Transverse”, and || > 120o as “Away”.
 All three regions have the same area in - space, ×  = 2cut × 120o = 2cut × 2/3.
 Construct densities by dividing by the area in - space.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 5
“Transverse” Charged Particle Density
PT(chgjet#1) Direction
"Transverse" Charged Particle Density: dN/dd
"Transverse" Charged Density
0.8

RDF Preliminary
Fake Data
pyDW generator level
ChgJet#1
“Toward”
0.6
PTmax
“Transverse”
“Transverse”
0.4
Leading Charged
Particle Jet, chgjet#1.
“Away”
0.2
900 GeV
Charged Particles (||<2.0, PT>0.5 GeV/c)
PTmax Direction
0.0
0
2
4
6
8
10
12
14
16
PTmax or PT(chgjet#1) (GeV/c)
“Toward”
 Fake data (from MC) at 900 GeV on the
“transverse” charged particle density,
dN/dd, as defined by the leading charged
particle (PTmax) and the leading charged
particle jet (chgjet#1) for charged particles
with pT > 0.5 GeV/c and || < 2. The fake
data (from PYTHIA Tune DW) are
generated at the particle level (i.e. generator
level) assuming 0.5 M min-bias events at
900 GeV (361,595 events in the plot).
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010

18
Rick Field – Florida/CDF/CMS
“Transverse”
“Transverse”
Leading Charged
Particle, PTmax.
“Away”
Rick Field
MB&UE@CMS Workshop
CERN, November 6, 2009
Page 6
“Transverse” Charged Particle Density
"Transverse" Charged Particle Density: dN/dd
"Transverse" Charged Particle Density: dN/dd
RDF Preliminary
Fake Data
pyDW generator level
"Transverse" Charged Density
"Transverse" Charged Density
0.8
ChgJet#1
0.6
PTmax
0.4
0.2
900 GeV
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.8
CMS Preliminary
ChgJet#1
data uncorrected
pyDW + SIM
0.6
PTmax
0.4
0.2
900 GeV
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
0.0
0
2
4
6
8
10
12
14
16
18
0
2
6
8
10
12
14
16
18
PTmax or PT(chgjet#1) (GeV/c)
PTmax or PT(chgjet#1) (GeV/c)
 Fake data (from MC) at 900 GeV on the
“transverse” charged particle density,
dN/dd, as defined by the leading charged
particle (PTmax) and the leading charged
particle jet (chgjet#1) for charged particles
with pT > 0.5 GeV/c and || < 2. The fake
data (from PYTHIA Tune DW) are
generated at the particle level (i.e. generator
level) assuming 0.5 M min-bias events at
900 GeV (361,595 events in the plot).
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
4
 CMS preliminary data at 900 GeV on the
“transverse” charged particle density,
dN/dd, as defined by the leading charged
particle (PTmax) and the leading charged
particle jet (chgjet#1) for charged particles
with pT > 0.5 GeV/c and || < 2. The data are
uncorrected and compared with PYTHIA
Tune DW after detector simulation (216,215
events in the plot).
Rick Field – Florida/CDF/CMS
Page 7
“Transverse” Charged PTsum Density
"Transverse" Charged PTsum Density: dPT/dd
"Transverse" Charged PTsum Density: dPT/dd
0.8
0.8
ChgJet#1
Fake Data
pyDW generator level
0.6
PTsum Density (GeV/c)
PTsum Density (GeV/c)
RDF Preliminary
PTmax
0.4
0.2
900 GeV
CMS Preliminary
data uncorrected
pyDW + SIM
0.6
ChgJet#1
PTmax
0.4
0.2
900 GeV
Charged Particles (||<2.0, PT>0.5 GeV/c)
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
0.0
0
2
4
6
8
10
12
14
16
18
0
2
4
6
8
10
12
14
16
18
PTmax or PT(chgjet#1) (GeV/c)
PTmax or PT(chgjet#1) (GeV/c)
 Fake data (from MC) at 900 GeV on the
 CMS preliminary data at 900 GeV on the
“transverse” charged PTsum density,
“transverse” charged PTsum density,
dPT/dd, as defined by the leading charged
dPT/dd, as defined by the leading charged
particle (PTmax) and the leading charged
particle (PTmax) and the leading charged
particle jet (chgjet#1) for charged particles
particle jet (chgjet#1) for charged particles
with pT > 0.5 GeV/c and || < 2. The fake
with pT > 0.5 GeV/c and || < 2. The data are
data (from PYTHIA Tune DW) are generated
uncorrected and compared with PYTHIA
at the particle level (i.e. generator level)
Tune DW after detector simulation (216,215
assuming 0.5 M min-bias events at 900 GeV
events in the plot).
(361,595 events in the plot).
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 8
PYTHIA Tune DW
"Transverse" Charged Particle Density: dN/dd
1.2
PT(chgjet#1) Direction
Charged Particle Density
CMS Preliminary

7 TeV
data uncorrected
pyDW + SIM
0.8
“Toward”
“Transverse”
900 GeV
“Transverse”
0.4
Leading Charged
Particle Jet, chgjet#1.
“Away”
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
0
5
10
15
20
25
30
35
40
45
50
PT(chgjet#1) GeV/c
 CMS preliminary data at 900 GeV and 7 TeV
on the “transverse” charged particle density,
dN/dd, as defined by the leading charged
particle jet (chgjet#1) for charged particles with
pT > 0.5 GeV/c and || < 2. The data are
uncorrected and compared with PYTHIA Tune
DW after detector simulation.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 9
PYTHIA Tune DW
PTmax Direction

Leading Charged
Particle, PTmax.
“Toward”
“Transverse”
“Transverse”
“Away”
"Transverse" Charged Density
"Transverse" Charged Particle Density: dN/dd
1.2
RDF Preliminary
7 TeV
ATLAS corrected data
Tune DW generator level
0.8
900 GeV
0.4
Charged Particles (||<2.5, PT>0.5 GeV/c)
0.0
0
2
4
6
8
10
12
14
16
18
20
PTmax (GeV/c)
 ATLAS preliminary data at 900 GeV and 7 TeV
on the “transverse” charged particle density,
dN/dd, as defined by the leading charged
particle (PTmax) for charged particles with pT >
0.5 GeV/c and || < 2.5. The data are corrected
and compared with PYTHIA Tune DW at the
generator level.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 10
PYTHIA Tune DW
"Transverse" Charged Particle Density: dN/dd
"Transverse" Charged Particle Density: dN/dd
Charged Particle Density
CMS Preliminary
"Transverse" Charged Density
1.2
7 TeV
data uncorrected
pyDW + SIM
0.8
CMS
900 GeV
0.4
Charged Particles (||<2.0, PT>0.5 GeV/c)
1.2
RDF Preliminary
7 TeV
ATLAS corrected data
Tune DW generator level
0.8
ATLAS
900 GeV
0.4
Charged Particles (||<2.5, PT>0.5 GeV/c)
0.0
0.0
0
5
10
15
20
25
30
35
40
45
50
0
2
4
6
8
10
12
14
16
18
20
PTmax (GeV/c)
PT(chgjet#1) GeV/c
 CMS preliminary data at 900 GeV and 7 TeV  ATLAS preliminary data at 900 GeV and 7 TeV
on the “transverse” charged particle density,
on the “transverse” charged particle density,
dN/dd, as defined by the leading charged
dN/dd, as defined by the leading charged
particle jet (chgjet#1) for charged particles with particle (PTmax) for charged particles with pT >
0.5 GeV/c and || < 2.5. The data are corrected
pT > 0.5 GeV/c and || < 2. The data are
uncorrected and compared with PYTHIA Tune and compared with PYTHIA Tune DW at the
generator level.
DW after detector simulation.
PT(chgjet#1) Direction
PTmax Direction


“Toward”
“Transverse”
“Toward”
“Transverse”
“Transverse”
“Away”
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
“Transverse”
“Away”
Rick Field – Florida/CDF/CMS
Page 11
PYTHIA Tune DW
"Transverse" Charged PTsum Density: dPT/dd
1.5
CMS Preliminary
RDF Preliminary
7 TeV
data uncorrected
pyDW + SIM
1.2
PTsum Density (GeV/c)
Charged PTsum Density (GeV/c)
"Transverse" Charged PTsum Density: dPT/dd
1.6
CMS
0.8
900 GeV
0.4
7 TeV
ATLAS corrected data
Tune DW generator level
1.0
ATLAS
900 GeV
0.5
Charged Particles (||<2.5, PT>0.5 GeV/c)
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
0.0
0
5
10
15
20
25
30
35
40
45
50
0
2
 CMS preliminary data at 900 GeV and 7 TeV
on the “transverse” charged PTsum density,
dPT/dd, as defined by the leading charged
particle jet (chgjet#1) for charged particles
with pT > 0.5 GeV/c and || < 2. The data are
uncorrected and compared with PYTHIA
Tune DW after detector simulation.

10
12
14
16
18
“Toward”
“Transverse”
“Transverse”
“Away”
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
8
 ATLAS preliminary data at 900 GeV and 7
TeV on the “transverse” charged PTsum
density, dPT/dd, as defined by the
leading charged particle (PTmax) for
charged particles with pT > 0.5 GeV/c and
|| < 2.5. The data are corrected and
compared with PYTHIA Tune DW at the
generator level. PTmax Direction
“Toward”
“Transverse”
6
PTmax (GeV/c)
PT(chgjet#1) (GeV/c)
PT(chgjet#1) Direction
4
“Transverse”
“Away”
Rick Field – Florida/CDF/CMS
Page 12
20
“Transverse” Charge Density
"Transverse" Charged Particle Density: dN/dd
Rick Field
MB&UE@CMS Workshop
CERN, November 6, 2009
"Transverse" Charged Density
1.2
RDF Preliminary
py Tune DW generator level
7 TeV
0.8
factor of 2!
900 GeV
0.4
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
0
2
4
6
8
10
12
14
16
18
20
PTmax (GeV/c)
PTmax Direction

LHC
900 GeV
“Toward”
“Transverse”
PTmax Direction
900 GeV → 7 TeV
(UE increase ~ factor of 2)
“Transverse”
“Away”
~0.4 → ~0.8

“Toward”
LHC
7 TeV
“Transverse”
“Transverse”
“Away”
 Shows the charged particle density in the “transverse” region for charged particles (pT > 0.5
GeV/c, || < 2) at 900 GeV and 7 TeV as defined by PTmax from PYTHIA Tune DW and at the
particle level (i.e. generator level).
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 13
PYTHIA Tune DW
"Transverse" Charged Particle Density: dN/dd
"Transverse" Charged Particle Density: dN/dd
3.0
3.0
RDF Preliminary
data uncorrected
pyDW + SIM
Ratio: 7 TeV/900 GeV
Ratio: 7 TeV/900 GeV
CMS Preliminary
2.0
CMS
1.0
7 TeV / 900 GeV
ATLAS corrected data
pyDW generator level
2.0
ATLAS
1.0
7 TeV / 900 GeV
Charged Particles (||<2.0, PT>0.5 GeV/c)
Charged Particles (||<2.5, PT>0.5 GeV/c)
0.0
0.0
0
2
4
6
8
10
12
14
16
18
0
1
 Ratio of CMS preliminary data at 900 GeV
and 7 TeV on the “transverse” charged
particle density, dN/dd, as defined by the
leading charged particle jet (chgjet#1) for
charged particles with pT > 0.5 GeV/c and ||
< 2. The data are uncorrected and compared
with PYTHIA Tune DW after detector
simulation. PT(chgjet#1) Direction

4
5
6
7
8
9
10
11
 Ratio of the ATLAS preliminary data at
900 GeV and 7 TeV on the “transverse”
charged particle density, dN/dd, as
defined by the leading charged particle
(PTmax) for charged particles with pT > 0.5
GeV/c and || < 2.5. The data are corrected
and compared with PYTHIA Tune DW at
the generator level.PTmax Direction
“Toward”
“Toward”
“Transverse”
“Transverse”
“Away”
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
3
PTmax (GeV/c)
PT(chgjet#1) (GeV/c)
“Transverse”
2
“Transverse”
“Away”
Rick Field – Florida/CDF/CMS
Page 14
12
PYTHIA Tune DW
"Transverse" Charged PTsum Density: dPT/dd
"Transverse" Charged PTsum Density: dPT/dd
4.0
3.0
CMS Preliminary
RDF Preliminary
data uncorrected
pyDW + SIM
ATLAS corrected data
pyDW generator level
Ratio: 7 TeV/900 GeV
Ratio: 7 TeV/900 GeV
4.0
2.0
CMS
1.0
3.0
2.0
ATLAS
1.0
7 TeV / 900 GeV
Charged Particles (||<2.0, PT>0.5 GeV/c)
7 TeV / 900 GeV
Charged Particles (||<2.5, PT>0.5 GeV/c)
0.0
0.0
0
2
4
6
8
10
12
14
16
18
0
1
 Ratio of the CMS preliminary data at 900
GeV and 7 TeV on the “transverse” charged
PTsum density, dPT/dd, as defined by the
leading charged particle jet (chgjet#1) for
charged particles with pT > 0.5 GeV/c and ||
< 2. The data are uncorrected and compared
with PYTHIA Tune DW after detector
simulation. PT(chgjet#1) Direction

4
5
6
7
8
9
10
11
12
 Ratio of the ATLAS preliminary data at 900
GeV and 7 TeV on the “transverse” charged
PTsum density, dPT/dd, as defined by the
leading charged particle (PTmax) for charged
particles with pT > 0.5 GeV/c and || < 2.5.
The data are corrected and compared with
PYTHIA Tune DW at the generator level.
“Toward”
PTmax Direction

“Toward”
“Transverse”
“Transverse”
“Away”
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
3
PTmax (GeV/c)
PT(chgjet#1) (GeV/c)
“Transverse”
2
“Transverse”
“Away”
Rick Field – Florida/CDF/CMS
Page 15
“Transverse” Multiplicity Distribution
"Transverse" Charged Particle Multiplicity
Same hard scale at
two different centerof-mass energies!
1.0E+00
PT(chgjet#1) > 3 GeV/c
1.0E-01
CMS Preliminary
data uncorrected
pyDW + SIM
Probability
1.0E-02
CMS
1.0E-03
PT(chgjet#1) Direction
7 TeV
900 GeV

1.0E-04
“Toward”
1.0E-05
Normalized to 1
“Transverse”
“Transverse”
1.0E-06
Charged Particles (||<2.0, PT>0.5 GeV/c)
“Away”
1.0E-07
0
5
10
15
20
25
30
35
40
Number of Charged Particles
 CMS uncorrected data at 900 GeV and 7 TeV on the charged particle multiplicity distribution
in the “transverse” region for charged particles (pT > 0.5 GeV/c, || < 2) as defined by the
leading charged particle jet, chgjet#1, with PT(chgjet#1) > 3 GeV/c compared with PYTHIA
Tune DW at the detector level (i.e. Theory + SIM).
Shows the growth of the
“underlying event” as the center-of-mass energy increases.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 16
“Transverse” Multiplicity Distribution
Same center-of-mass
energy at two different
hard scales!
"Transverse" Charged Particle Multiplicity
1.0E+00
7 TeV
CMS Preliminary
1.0E-01
data uncorrected
pyDW + SIM
Probability
1.0E-02
PT(chgjet#1) > 20 GeV/c
1.0E-03
PT(chgjet#1) Direction

1.0E-04
PT(chgjet#1) > 3 GeV/c
1.0E-05
CMS
Normalized to 1
1.0E-06
“Toward”
“Transverse”
Charged Particles (||<2.0, PT>0.5 GeV/c)
“Transverse”
“Away”
1.0E-07
0
5
10
15
20
25
30
35
40
Number of Charged Particles
 CMS uncorrected data at 7 TeV on the charged particle multiplicity distribution in the
“transverse” region for charged particles (pT > 0.5 GeV/c, || < 2) as defined by the leading
charged particle jet, chgjet#1, with PT(chgjet#1) > 3 GeV/c and PT(chgjet#1) > 20 GeV/c
compared with PYTHIA Tune DW at the detector level (i.e. Theory + SIM).
Shows the growth of the
“underlying event” as the hard scale increases.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 17
PYTHIA Tune DW
How well did we do at predicting the “underlying event” at 900 GeV and 7 TeV?
"Transverse" Charged Particle Density: dN/dd
1.2
CMS Preliminary
CMS Preliminary
ChgJet#1
data uncorrected
pyDW + SIM
0.6
Charged Particle Density
"Transverse" Charged Density
"Transverse" Charged Particle Density: dN/dd
0.8
PTmax
0.4
0.2
900 GeV
Tune DW
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
7 TeV
data uncorrected
pyDW + SIM
0.8
900 GeV
0.4
Tune DW
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
0
2
4
6
8
10
12
14
16
18
0
5
10
15
20
PTmax or PT(chgjet#1) (GeV/c)
25
30
35
40
45
50
PT(chgjet#1) GeV/c
"Transverse" Charged Particle Density: dN/dd
3.0
CMS Preliminary
Ratio: 7 TeV/900 GeV
I am surprised that the
Tunes did not do a better job
of predicting the behavior of
the “underlying event” at
900 GeV and 7 TeV!
Tune DW
data uncorrected
pyDW + SIM
2.0
1.0
7 TeV / 900 GeV
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
0
2
4
6
8
10
12
14
16
18
PT(chgjet#1) (GeV/c)
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 18
PYTHIA Tune DW
How well did we do at predicting the “underlying event” at 900 GeV and 7 TeV?
"Transverse" Charged Particle Density: dN/dd
1.2
CMS Preliminary
CMS Preliminary
ChgJet#1
data uncorrected
pyDW + SIM
0.6
Charged Particle Density
"Transverse" Charged Density
"Transverse" Charged Particle Density: dN/dd
0.8
PTmax
0.4
0.2
900 GeV
Tune DW
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
7 TeV
data uncorrected
pyDW + SIM
0.8
900 GeV
0.4
Tune DW
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
0
2
4
6
8
10
12
14
16
18
0
5
10
15
20
PTmax or PT(chgjet#1) (GeV/c)
25
30
35
40
45
50
PT(chgjet#1) GeV/c
"Transverse" Charged Particle Density: dN/dd
3.0
CMS Preliminary
Ratio: 7 TeV/900 GeV
I am surprised that the
Tunes did as well as they did
at predicting the behavior of
the “underlying event” at
900 GeV and 7 TeV!
Tune DW
data uncorrected
pyDW + SIM
2.0
1.0
7 TeV / 900 GeV
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
0
2
4
6
8
10
12
14
16
18
PT(chgjet#1) (GeV/c)
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 19
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
PT(hard)
Initial-State Radiation
Proton
Proton
Underlying Event
I am surprised that the Tunes did as well as
they did at predicting the behavior of the
“underlying event” at 900 GeV and 7 TeV!
Remember this is “soft” QCD!
Outgoing Parton
“Min-Bias” is a whole different story!
Much more complicated due to
diffraction!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Underlying Event
Rick Field – Florida/CDF/CMS
Final-State
Radiation
PARP(82)
PARP(90)
Color
Diffraction
Connections
Page 20
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.
Outgoing Parton
PT(hard)
Initial-State Radiation
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
diffraction!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Final-State
Radiation
PARP(82)
PARP(90)
Color
Diffraction
Connections
Page 21
Proton-Proton Collisions
Elastic Scattering
Single Diffraction
Double Diffraction
M2
M
M1
stot = sEL +sSD +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
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 22
The Inelastic Non-Diffractive
Cross-Section
“Semi-hard” partonparton collision
(pT < ≈2 GeV/c)
Proton
Proton
+
Proton
+
Proton
Proton
Proton
+
Proton
Proton
+…
Multiple-parton
interactions (MPI)!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 23
The Inelastic Non-Diffractive
Cross-Section
Majority of “minbias” events!
Proton
“Semi-hard” partonparton collision
(pT < ≈2 GeV/c)
Proton
+
Proton
+
Proton
Proton
Proton
+
Proton
Proton
+…
Multiple-parton
interactions (MPI)!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 24
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
+…
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Multiple-parton
interactions (MPI)!
Page 25
The “Underlying Event”
Select inelastic non-diffractive events
that contain a hard scattering
Proton
Hard parton-parton
collisions is hard
(pT > ≈2 GeV/c)
Proton
The “underlying-event” (UE)!
“Semi-hard” partonparton collision
(pT < ≈2 GeV/c)
1/(pT)4→ 1/(pT2+pT02)2
Proton
Given that you have one hard
scattering it is more probable to
have MPI! Hence, the UE has
more activity than “min-bias”.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Proton
+
+
Proton
Proton
Rick Field – Florida/CDF/CMS
Proton
Proton
+…
Multiple-parton
interactions (MPI)!
Page 26
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
1/(pT)4→ 1/(pT2+pT02)2
“Min-Bias” (ND)
Proton
Predict MB (ND)!
Proton
+
Proton
+
Proton
Proton
Proton
+
Proton
Proton
+…
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 27
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
1/(pT)4→ 1/(pT2+pT02)2
“Min-Bias” (add single & double diffraction)
Proton
Predict MB (ND)!
Proton
+
+
Proton
Proton
Proton
Single Diffraction
+…
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Proton
+
Proton
Proton
Double Diffraction
M2
M
Rick Field – Florida/CDF/CMS
M1
Page 28
LHC MB Predictions: 900 GeV
Charged Particle Density: dN/d
Charged Particle Density: dN/d
5
5
RDF Preliminary
Charged Particle Density
Charged Particle Density
RDF Preliminary
4
3
2
ALICE INEL
UA5 INEL
INEL = HC+DD+SD
900 GeV
1
pyDW INEL (2.67)
4
3
2
1
pyS320 INEL (2.70)
Charged Particles (all pT)
UA5
ALICE
NSD = HC+DD
900 GeV
pyDW_10mm (3.04)
pyS320_10mm (3.09)
0
0
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
-3.0
-2.5
-2.0
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
PseudoRapidity 
PseudoRapidity 
“Minumum Bias” Collisions
“Minumum Bias” Collisions
Proton
-1.5
Proton
Proton
Proton
 Compares the 900 GeV ALICE data with PYTHIA Tune DW and Tune S320
Perugia 0. Tune DW uses the old Q2-ordered parton shower and the old MPI
model. Tune S320 uses the new pT-ordered parton shower and the new MPI model.
The numbers in parentheses are the average value of dN/d for the region || <
0.6.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 29
3.0
LHC MB Predictions: 900 GeV
Charged Particle Density: dN/d
Charged Particle Density: dN/d
5
5
RDF Preliminary
Charged Particle Density
Charged Particle Density
RDF Preliminary
4
3
2
ALICE INEL
Off by 11%!
UA5 INEL
INEL = HC+DD+SD
900 GeV
1
5
-1.5
-1.0
-0.5
0.0
4
Charged Particle Density
-2.0
2
UA5
ALICE
1
pyDW_10mm (3.04)
pyS320_10mm (3.09)
pyS320 INEL (2.70)
0
-2.5
3
NSD = HC+DD
Charged Particle Density: dN/d
900 GeV
pyDW INEL (2.67)
Charged Particles (all pT)
-3.0
4
RDF Preliminary
0.5
1.0
1.5
0
2.0
2.5
3.0
-3.0
-2.5
-2.0 times
-1.5 1.11
-1.0
3
0.5
1.0
1.5
2.0
2.5
“Minumum Bias” Collisions
“Minumum Bias” Collisions
2
Proton
1
0.0
PseudoRapidity 
PseudoRapidity 
Proton
-0.5
INEL = HC+DD+SD
900 GeV
Charged Particles (all pT)
Proton
ALICE INEL
UA5 INEL
pyDW times 1.11 (2.97)
pyS320 times 1.11 (3.00)
Proton
0
-3.0 data
-2.5 -2.0
-1.5 PYTHIA
-1.0 -0.5 0.0 Tune
0.5
1.0 DW
1.5 and
2.0
2.5
3.0
 Compares the 900 GeV
with
Tune
S320 Perugia 0.
PseudoRapidity

Tune DW uses the old Q2-ordered parton shower and the old MPI model. Tune
S320 uses the new pT-ordered parton shower and the new MPI model. The
numbers in parentheses are the average value of dN/d for the region || < 0.6.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 30
3.0
ATLAS INEL dN/d
 None of the tunes fit the
ATLAS INEL dN/d
data with PT > 100
MeV! They all predict
too few particles.
Off by 20-50%!
 The ATLAS Tune
AMBT1 was designed to
fit the inelastic data for
Nchg ≥ 6 with pT > 0.5
GeV/c!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Soft particles!
Rick Field – Florida/CDF/CMS
Page 31
PYTHIA Tune DW
If one increases the
hard scale the
agreement improves!
Charged Particle Density: dN/d
5
Charged Particle Density
RDF Preliminary
4
ALICE INEL data
pyDW generator level
At Least 1 Charged Particle || < 0.8
900 GeV
pT > 0.15 GeV/c
Tune DW
3
pT > 0.5 GeV/c
2
pT > 1.0 GeV/c
1
0
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
PseudoRapidity 
 ALICE inelastic data at 900 GeV on the dN/d distribution for charged particles (pT >
PTmin) for events with at least one charged particle with pT > PTmin and || < 0.8 for
PTmin = 0.15 GeV/c, 0.5 GeV/c, and 1.0 GeV/c compared with PYTHIA Tune DW at the
generator level.
The same thing occurs at 7 TeV!
ALICE, ATLAS, and CMS data coming soon.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 32
PYTHIA Tune DW
Diffraction
contributes less at
harder scales!
Charged Particle Density: dN/d
5
Charged Particle Density
RDF Preliminary
4
ALICE INEL data
pyDW generator level
At Least 1 Charged Particle || < 0.8
900 GeV
pT > 0.15 GeV/c
3
Tune DW
pT > 0.5 GeV/c
2
pT > 1.0 GeV/c
1
dashed = ND solid = INEL
0
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
PseudoRapidity 
 ALICE inelastic data at 900 GeV on the dN/d distribution for charged particles (pT >
PTmin) for events with at least one charged particle with pT > PTmin and || < 0.8 for
PTmin = 0.15 GeV/c, 0.5 GeV/c, and 1.0 GeV/c compared with PYTHIA Tune Z1 at the
generator level (dashed = ND, solid = INEL).
Cannot trust PYTHIA 6.2 modeling of diffraction!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 33
CMS dN/d
Charged Particle Density: dN/d
8
CMS
Charged Particle Density
7 TeV
6
4
RDF Preliminary
2
Tune DW
CMS NSD data
pyDW generator level
All pT
dashed = ND solid = NSD
0
-3.0
-2.5
-2.0
-1.5
-1.0
Soft particles!
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
PseudoRapidity 
 Generator level dN/d (all pT). Shows the NSD = HC + DD and the HC = ND
contributions for Tune DW. Also shows the CMS NSD data.
Off by 50%!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 34
CMS dN/d
Charged Particle Density: dN/d
8
CMS
Charged Particle Density
7 TeV
6
4
RDF Preliminary
CMS NSD data
pyDW generator level
Tune DW
Okay if the Monte-Carlo does not fit
dashedthe
= ND solid
= NSD
data
what do we do? All pT
0
We tune the Monte-Carlo
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0
0.5
1.0
1.5
2.0
to fit the
data!
PseudoRapidity 
2
Soft particles!
2.5
3.0
 Generator level dN/d (all pT). Shows the NSD = HC + DD and the HC = ND
contributions for Tune DW. Also shows the CMS NSD data.
Off by 50%!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 35
CMS dN/d
Charged Particle Density: dN/d
8
Charged Particle Density
7 TeV
CMS
6
4
RDF Preliminary
Okay if the Monte-Carlo doesTune
not DW
fit
Soft particles!
2
the data what do we do?
dashed = ND solid = NSD
All pT
We
tune
the
Monte-Carlo
0
-3.0 -2.5 -2.0 -1.5
-1.0 the
-0.5 data!
0.0
0.5
1.0
1.5
2.0
2.5
3.0
to fit
PseudoRapidity 
Be careful not to tune
away new physics!
 Generator level dN/d (all pT). Shows the NSD = HC + DD and the HC = ND
contributions for Tune DW. Also shows the CMS NSD data.
CMS NSD data
pyDW generator level
Off by 50%!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 36
PYTHIA Tune Z1
 All my previous tunes (A, DW, DWT, D6,
D6T, CW, X1, and X2) were PYTHIA 6.4
tunes using the old Q2-ordered parton
showers and the old MPI model (really 6.2
tunes)!
 I believe that it is time to move to PYTHIA
6.4 (pT-ordered parton showers and new
MPI model)!
 Tune Z1: I started with the parameters of
ATLAS Tune AMBT1, but I changed LO* to
CTEQ5L and I varied PARP(82) and PARP(90)
to get a very good fit of the CMS UE data at 900
GeV and 7 TeV.
 The ATLAS Tune AMBT1 was designed to fit
the inelastic data for Nchg ≥ 6 and to fit the
PTmax UE data with PTmax > 10 GeV/c. Tune
AMBT1 is primarily a min-bias tune, while
Tune Z1 is a UE tune!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
PARP(90)
PARP(82)
Color
Connections
Diffraction
Outgoing Parton
PT(hard)
Initial-State Radiation
Proton
Proton
Underlying Event
Outgoing Parton
Underlying Event
Final-State
Radiation
UE&MB@CMS
Page 37
PYTHIA Tune Z1
Tune Z1
(R. Field CMS)
Tune AMBT1
(ATLAS)
CTEQ5L
LO*
PARP(82) – MPI Cut-off
1.932
2.292
PARP(89) – Reference energy, E0
1800.0
1800.0
PARP(90) – MPI Energy Extrapolation
0.275
0.25
PARP(77) – CR Suppression
1.016
1.016
PARP(78) – CR Strength
0.538
0.538
0.1
0.1
PARP(83) – Matter fraction in core
0.356
0.356
PARP(84) – Core of matter overlap
0.651
0.651
PARP(62) – ISR Cut-off
1.025
1.025
PARP(93) – primordial kT-max
10.0
10.0
MSTP(81) – MPI, ISR, FSR, BBR model
21
21
MSTP(82) – Double gaussion matter distribution
4
4
MSTP(91) – Gaussian primordial kT
1
1
MSTP(95) – strategy for color reconnection
6
6
Parameter
Parton Distribution Function
Parameters not
shown are the
PYTHIA 6.4 defaults!
PARP(80) – Probability colored parton from BBR
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 38
PYTHIA Tune Z1
"Transverse" Charged Particle Density: dN/dd
"Transverse" Charged Particle Density: dN/dd
1.2
1.2
CMS Preliminary
D6T
7 TeV
data uncorrected
Theory + SIM
Charged Particle Density
Charged Particle Density
CMS Preliminary
0.8
900 GeV
DW
0.4
CMS
7 TeV
data uncorrected
pyZ1 + SIM
0.8
900 GeV
0.4
CMS
Tune Z1
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
0.0
0
5
10
15
20
25
30
35
40
45
50
0
5
10
15
20
25
30
35
40
45
50
PT(chgjet#1) GeV/c
PT(chgjet#1) GeV/c
 CMS preliminary data at 900 GeV and 7 TeV  CMS preliminary data at 900 GeV and 7 TeV
on the “transverse” charged particle density,
on the “transverse” charged particle density,
dN/dd, as defined by the leading charged
dN/dd, as defined by the leading charged
particle jet (chgjet#1) for charged particles
particle jet (chgjet#1) for charged particles
with pT > 0.5 GeV/c and || < 2.0. The data
with pT > 0.5 GeV/c and || < 2.0. The data
are uncorrected and compared with PYTHIA
are uncorrected and compared with PYTHIA
Tune DW and D6T after detector simulation
Tune Z1 after detector simulation (SIM).
(SIM).
Color reconnection suppression.
Color reconnection strength.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Tune Z1 (CTEQ5L)
PARP(82) = 1.932
PARP(90) = 0.275
PARP(77) = 1.016
PARP(78) = 0.538
Rick Field – Florida/CDF/CMS
Tune Z1 is a PYTHIA 6.4 using
pT-ordered parton showers and
the new MPI model!
Page 39
PYTHIA Tune Z1
"Transverse" Charged PTsum Density: dPT/dd
CMS Preliminary
D6T
data uncorrected
Theory + SIM
1.2
Charged PTsum Density (GeV/c)
Charged PTsum Density (GeV/c)
"Transverse" Charged PTsum Density: dPT/dd
1.6
7 TeV
0.8
DW
900 GeV
CMS
0.4
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
0
5
10
15
20
25
30
35
40
45
50
1.6
CMS Preliminary
7 TeV
data uncorrected
pyZ1 + SIM
1.2
0.8
900 GeV
CMS
0.4
Tune Z1
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
0
5
PT(chgjet#1) (GeV/c)
10
15
20
25
30
35
40
45
50
PT(chgjet#1) (GeV/c)
 CMS preliminary data at 900 GeV and 7 TeV  CMS preliminary data at 900 GeV and 7 TeV
on the “transverse” charged PTsum density,
on the “transverse” charged PTsum density,
dPT/dd, as defined by the leading charged
dPT/dd, as defined by the leading charged
particle jet (chgjet#1) for charged particles
particle jet (chgjet#1) for charged particles
with pT > 0.5 GeV/c and || < 2.0. The data
with pT > 0.5 GeV/c and || < 2.0. The data
are uncorrected and compared with PYTHIA
are uncorrected and compared with PYTHIA
Tune DW and D6T after detector simulation
Tune Z1 after detector simulation (SIM).
(SIM).
Color reconnection suppression.
Color reconnection strength.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Tune Z1 (CTEQ5L)
PARP(82) = 1.932
PARP(90) = 0.275
PARP(77) = 1.016
PARP(78) = 0.538
Rick Field – Florida/CDF/CMS
Tune Z1 is a PYTHIA 6.4 using
pT-ordered parton showers and
the new MPI model!
Page 40
PYTHIA Tune Z1
"Transverse" Charged PTsum Density: dPT/dd
1.2
1.5
RDF Preliminary
RDF Preliminary
7 TeV
ATLAS corrected data
Tune Z1 generator level
PTsum Density (GeV/c)
"Transverse" Charged Density
"Transverse" Charged Particle Density: dN/dd
0.8
900 GeV
0.4
ATLAS
Tune Z1
7 TeV
ATLAS corrected data
Tune Z1 generator level
1.0
900 GeV
0.5
ATLAS
Charged Particles (||<2.5, PT>0.5 GeV/c)
Tune Z1
0.0
Charged Particles (||<2.5, PT>0.5 GeV/c)
0.0
0
2
4
6
8
10
12
14
16
18
20
0
2
PTmax (GeV/c)
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
6
8
10
12
14
16
18
PTmax (GeV/c)
 ATLAS preliminary data at 900 GeV and 7
TeV on the “transverse” charged particle
density, dN/dd, as defined by the leading
charged particle (PTmax) for charged
particles with pT > 0.5 GeV/c and || < 2.5.
The data are corrected and compared with
PYTHIA Tune Z1 at the generator level.
Color reconnection suppression.
Color reconnection strength.
4
 ATLAS preliminary data at 900 GeV and 7
TeV on the “transverse” charged PTsum
density, dPT/dd, as defined by the leading
charged particle (PTmax) for charged
particles with pT > 0.5 GeV/c and || < 2.5.
The data are corrected and compared with
PYTHIA Tune Z1 at the generrator level.
Tune Z1 (CTEQ5L)
PARP(82) = 1.932
PARP(90) = 0.275
PARP(77) = 1.016
PARP(78) = 0.538
Rick Field – Florida/CDF/CMS
Tune Z1 is a PYTHIA 6.4 using
pT-ordered parton showers and
the new MPI model!
Page 41
20
PYTHIA Tune Z1
"Transverse" Charged Particle Density: dN/dd
"Transverse" Charged Particle Density: dN/dd
3.0
3.0
CMS Preliminary
DW
D6T
data uncorrected
theory + SIM
Ratio: 7 TeV/900 GeV
Ratio: 7 TeV/900 GeV
CMS Preliminary
2.0
P0
1.0
CW
CMS
7 TeV / 900 GeV
Tune Z1
data uncorrected
pyZ1 + SIM
2.0
1.0
CMS
7 TeV / 900 GeV
Charged Particles (||<2.0, PT>0.5 GeV/c)
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
0.0
0
2
4
6
8
10
12
14
16
18
0
2
PT(chgjet#1) (GeV/c)
6
8
10
12
14
16
18
PT(chgjet#1) (GeV/c)
 Ratio of CMS preliminary data at 900 GeV
and 7 TeV (7 TeV divided by 900 GeV) on the
“transverse” charged particle density as
defined by the leading charged particle jet
(chgjet#1) for charged particles with pT > 0.5
GeV/c and || < 2.0. The data are
uncorrected and compared with PYTHIA
Tune DW, D6T, CW, and P0 after detector
simulation (SIM).
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
4
 Ratio of CMS preliminary data at 900 GeV
and 7 TeV (7 TeV divided by 900 GeV) on the
“transverse” charged particle density as
defined by the leading charged particle jet
(chgjet#1) for charged particles with pT > 0.5
GeV/c and || < 2.0. The data are
uncorrected and compared with PYTHIA
Tune Z1 after detector simulation (SIM).
Rick Field – Florida/CDF/CMS
Page 42
PYTHIA Tune Z1
"Transverse" Charged PTsum Density: dPT/dd
3.0
D6T
CMS Preliminary
CMS Preliminary
DW
data uncorrected
theory + SIM
Ratio: 7 TeV/900 GeV
Ratio: 7 TeV/900 GeV
"Transverse" Charged PTsum Density: dPT/dd
3.0
2.0
P0
CW
1.0
CMS
7 TeV / 900 GeV
data uncorrected
pyZ1 + SIM
Tune Z1
2.0
1.0
CMS
Charged Particles (||<2.0, PT>0.5 GeV/c)
7 TeV / 900 GeV
0.0
Charged Particles (||<2.0, PT>0.5 GeV/c)
0.0
0
2
4
6
8
10
12
14
16
18
0
2
PT(chgjet#1) (GeV/c)
6
8
10
12
14
16
18
PT(chgjet#1) (GeV/c)
 Ratio of CMS preliminary data at 900 GeV
and 7 TeV (7 TeV divided by 900 GeV) on the
“transverse” charged PTsum density as
defined by the leading charged particle jet
(chgjet#1) for charged particles with pT > 0.5
GeV/c and || < 2.0. The data are
uncorrected and compared with PYTHIA
Tune DW, D6T, CW, and P0 after detector
simulation (SIM).
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
4
 Ratio of CMS preliminary data at 900 GeV
and 7 TeV (7 TeV divided by 900 GeV) on the
“transverse” charged PTsum density as
defined by the leading charged particle jet
(chgjet#1) for charged particles with pT > 0.5
GeV/c and || < 2.0. The data are
uncorrected and compared with PYTHIA
Tune Z1 after detector simulation (SIM).
Rick Field – Florida/CDF/CMS
Page 43
PYTHIA Tune Z1
"Transverse" Charged Particle Density: dN/dd
"Transverse" Charged PTsum Density: dPT/dd
4.0
3.0
RDF Preliminary
RDF Preliminary
ATLAS corrected data
Tune Z1 generator level
ATLAS corrected data
Tune Z1 generator level
Ratio: 7 TeV/900 GeV
Ratio: 7 TeV/900 GeV
4.0
Tune Z1
2.0
ATLAS
1.0
7 TeV / 900 GeV
3.0
Tune Z1
2.0
1.0
ATLAS
7 TeV / 900 GeV
Charged Particles (||<2.5, PT>0.5 GeV/c)
0.0
Charged Particles (||<2.5, PT>0.5 GeV/c)
0.0
0
1
2
3
4
5
6
7
8
9
10
11
12
0
1
PTmax (GeV/c)
3
4
5
6
7
8
9
10
11
12
PTmax (GeV/c)
 Ratio of the ATLAS preliminary data on the
charged particle density in the “transverse”
region for charged particles (pT > 0.5 GeV/c,
|| < 2.5) at 900 GeV and 7 TeV as defined by
PTmax compared with PYTHIA Tune Z1 at
the generator level.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
2
 Ratio of the ATLAS preliminary data on the
charged PTsum density in the “transverse”
region for charged particles (pT > 0.5 GeV/c,
|| < 2.5) at 900 GeV and 7 TeV as defined by
PTmax compared with PYTHIA Tune Z1 at
the generator level.
Rick Field – Florida/CDF/CMS
Page 44
“Transverse” Multiplicity Distribution
"Transverse" Charged Particle Multiplicity
"Transverse" Charged Particle Multiplicity
1.0E+00
1.0E+00
PT(chgjet#1) > 3 GeV/c
data uncorrected
Theory + SIM
1.0E-01
1.0E-01
Probability
1.0E-03
7 TeV
900 GeV
1.0E-04
D6T
1.0E-05
CMS Preliminary
data uncorrected
pyZ1 + SIM
CMS
1.0E-02
CMS
1.0E-02
Probability
PT(chgjet#1) > 3 GeV/c
CMS Preliminary
Tune Z1
1.0E-03
7 TeV
900 GeV
1.0E-04
1.0E-05
DW
Normalized to 1
Normalized to 1
1.0E-06
1.0E-06
Charged Particles (||<2.0, PT>0.5 GeV/c)
Charged Particles (||<2.0, PT>0.5 GeV/c)
1.0E-07
1.0E-07
0
5
10
15
20
25
30
35
40
Number of Charged Particles
0
5
10
15
20
25
30
35
40
Number of Charged Particles
 CMS uncorrected data at 900 GeV and 7 TeV on  CMS uncorrected data at 900 GeV and 7
TeV on the charged particle multiplicity
the charged particle multiplicity distribution in
the “transverse” region for charged particles (pT > distribution in the “transverse” region
for charged particles (pT > 0.5 GeV/c, ||
0.5 GeV/c, || < 2) as defined by the leading
< 2) as defined by the leading charged
charged particle jet with PT(chgjet#1) > 3 GeV/c
compared with PYTHIA Tune DW and Tune D6T particle jet with PT(chgjet#1) > 3 GeV/c
compared with PYTHIA Tune Z1 at the
at the detector level (i.e. Theory + SIM).
detector level (i.e. Theory + SIM).
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 45
“Transverse” PTsum Distribution
"Transverse" Charged PTsum Distribution
"Transverse" Charged PTsum Distribution
1.0E+00
1.0E+00
CMS Preliminary
1.0E-01
1.0E-01
1.0E-02
CMS
1.0E-02
7 TeV
1.0E-03
900 GeV
CMS Preliminary
PT(chgjet#1) > 3 GeV/c
data uncorrected
Theory + SIM
Probability
Probability
PT(chgjet#1) > 3 GeV/c
D6T
1.0E-04
data uncorrected
pyZ1+ SIM
CMS
Tune Z1
7 TeV
1.0E-03
900 GeV
1.0E-04
DW
1.0E-05
1.0E-05
Normalized to 1
Normalized to 1
Charged Particles (||<2.0, PT>0.5 GeV/c)
Charged Particles (||<2.0, PT>0.5 GeV/c)
1.0E-06
1.0E-06
0
5
10
15
20
25
30
35
40
45
50
0
PTsum (GeV/c)
5
10
15
20
25
30
35
40
45
50
PTsum (GeV/c)
 CMS uncorrected data at 900 GeV and 7 TeV  CMS uncorrected data at 900 GeV and 7 TeV
on the charged scalar PTsum distribution in
on the charged scalar PTsum distribution in
the “transverse” region for charged particles
the “transverse” region for charged particles
(pT > 0.5 GeV/c, || < 2) as defined by the
(pT > 0.5 GeV/c, || < 2) as defined by the
leading charged particle jet with
leading charged particle jet with
PT(chgjet#1) > 3 GeV/c compared with
PT(chgjet#1) > 3 GeV/c compared with
PYTHIA Tune DW, and Tune D6T at the
PYTHIA Tune Z1, at the detector level (i.e.
detector level (i.e. Theory + SIM).
Theory + SIM).
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 46
“Transverse” Multiplicity Distribution
"Transverse" Charged Particle Multiplicity
"Transverse" Charged Particle Multiplicity
1.0E+00
1.0E+00
7 TeV
7 TeV
CMS Preliminary
data uncorrected
Theory + SIM
1.0E-01
1.0E-01
CMS
1.0E-02
CMS
1.0E-02
data uncorrected
pyZ1 + SIM
Tune Z1
PT(chgjet#1) > 20 GeV/c
Probability
Probability
PT(chgjet#1) > 20 GeV/c
D6T
1.0E-03
CMS Preliminary
1.0E-04
PT(chgjet#1) > 3 GeV/c
1.0E-03
1.0E-04
PT(chgjet#1) > 3 GeV/c
1.0E-05
1.0E-05
DW
Normalized to 1
Normalized to 1
1.0E-06
1.0E-06
Charged Particles (||<2.0, PT>0.5 GeV/c)
Charged Particles (||<2.0, PT>0.5 GeV/c)
1.0E-07
1.0E-07
0
5
10
15
20
25
30
35
40
0
Number of Charged Particles
5
10
15
20
25
30
35
40
Number of Charged Particles
 CMS uncorrected data at 7 TeV on the
 CMS uncorrected data at 7 TeV on the
charged particle multiplicity distribution in
charged particle multiplicity distribution in
the “transverse” region for charged particles the “transverse” region for charged particles
(pT > 0.5 GeV/c, || < 2) as defined by the
(pT > 0.5 GeV/c, || < 2) as defined by the
leading charged particle jet with PT(chgjet#1) leading charged particle jet with PT(chgjet#1)
> 3 GeV/c and PT(chgjet#1) > 20 GeV/c
> 3 GeV/c and PT(chgjet#1) > 20 GeV/c
compared with PYTHIA Tune DW and Tune compared with PYTHIA Tune Z1 at the
D6T at the detector level (i.e. Theory + SIM). detector level (i.e. Theory + SIM).
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 47
“Transverse” Multiplicity Distribution
"Transverse" Charged Particle Multiplicity
1.0E+00
7 TeV
PT(chgjet#1) Direction
CMS Preliminary
Difficult to produce
enough events with
large “transverse”
multiplicity at low
hard scale!
data uncorrected
pyZ1 + SIM
1.0E-01

Tune Z1
1.0E-02
“Toward”
“Transverse”
“Transverse”
“Away”
Probability
PT(chgjet#1) > 20 GeV/c
1.0E-03
CMS
1.0E-04
PT(chgjet#1) > 3 GeV/c
1.0E-05
Normalized to 1
1.0E-06
Charged Particles (||<2.0, PT>0.5 GeV/c)
1.0E-07
0
5
10
15
20
25
30
35
40
Number of Charged Particles
 CMS uncorrected data at 7 TeV on the charged particle multiplicity distribution in the
“transverse” region for charged particles (pT > 0.5 GeV/c, || < 2) as defined by the leading
charged particle jet, chgjet#1, with PT(chgjet#1) > 3 GeV/c and PT(chgjet#1) > 20 GeV/c
compared with PYTHIA Tune Z1 at the detector level (i.e. Theory + SIM).
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 48
“Transverse” PTsum Distribution
"Transverse" Charged PTsum Distribution
"Transverse" Charged PTsum Distribution
1.0E+00
1.0E+00
7 TeV
data uncorrected
Theory + SIM
1.0E-01
1.0E-01
CMS
1.0E-02
CMS Preliminary
1.0E-03
PT(chgjet#1) > 3 GeV/c
1.0E-04
data uncorrected
pyZ1 + SIM
CMS
1.0E-02
PT(chgjet#1) > 20 GeV/c
Probability
Probability
7 TeV
CMS Preliminary
Tune Z1
PT(chgjet#1) > 20 GeV/c
1.0E-03
PT(chgjet#1) > 3 GeV/c
1.0E-04
D6T
Normalized to 1
1.0E-05
Normalized to 1
1.0E-05
DW
Charged Particles (||<2.0, PT>0.5 GeV/c)
Charged Particles (||<2.0, PT>0.5 GeV/c)
1.0E-06
1.0E-06
0
5
10
15
20
25
30
35
40
45
50
0
PTsum (GeV/c)
5
10
15
20
25
30
35
40
45
50
PTsum (GeV/c)
 CMS uncorrected data at 7 TeV on the charged  CMS uncorrected data at 7 TeV on the charged
PTsum distribution in the “transverse” region for
PTsum distribution in the “transverse” region
charged particles (pT > 0.5 GeV/c, || < 2) as
for charged particles (pT > 0.5 GeV/c, || < 2)
defined by the leading charged particle jet with
as defined by the leading charged particle jet
PT(chgjet#1) > 3 GeV/c and PT(chgjet#1) > 20
with PT(chgjet#1) > 3 GeV/c and PT(chgjet#1)
GeV/c compared with PYTHIA Tune Z1 at the
> 20 GeV/c compared with PYTHIA Tune DW
detector level (i.e. Theory + SIM).
and Tune D6T at the detector level (i.e. Theory
+ SIM).
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 49
“Transverse” PTsum Distribution
"Transverse" Charged PTsum Distribution
1.0E+00
7 TeV
PT(chgjet#1) Direction
CMS Preliminary

Tune Z1
“Transverse”
“Transverse”
Probability
1.0E-02
“Toward”
Difficult to produce
enough events with
large “transverse”
PTsum at low hard
scale!
data uncorrected
pyZ1 + SIM
1.0E-01
PT(chgjet#1) > 20 GeV/c
1.0E-03
PT(chgjet#1) > 3 GeV/c
CMS
1.0E-04
“Away”
Normalized to 1
1.0E-05
Charged Particles (||<2.0, PT>0.5 GeV/c)
1.0E-06
0
5
10
15
20
25
30
35
40
45
50
PTsum (GeV/c)
 CMS uncorrected data at 7 TeV on the charged PTsum distribution in the “transverse” region
for charged particles (pT > 0.5 GeV/c, || < 2) as defined by the leading charged particle jet,
chgjet#1, with PT(chgjet#1) > 3 GeV/c and PT(chgjet#1) > 20 GeV/c compared with PYTHIA
Tune Z1 at the detector level (i.e. Theory + SIM).
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 50
CMS dN/d
Charged Particle Density: dN/d
Charged Particle Density: dN/d
8
RDF Preliminary
RDF Preliminary
Charged Particle Density
Charged Particle Density
8
6
Tune Z1
4
CMS
2
CMS NSD 7 TeV
7 TeV
pyZ1 HC (6.51)
pyZ1 NSD (5.58)
0
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
6
4
CMS
2
CMS NSD 7 TeV
7 TeV
pyX2 NSD (5.91)
pyZ1 NSD (5.58)
CMS NSD all pT
0
-3.0
-2.5
-2.0
PseudoRapidity 
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
PseudoRapidity 
 Generator level dN/d (all pT). Shows
the NSD = HC + DD and the HC = ND
contributions for Tune Z1. Also shows
the CMS NSD data.
 Generator level dN/d (all pT). Shows
the NSD = HC + DD prediction for
Tune Z1 and Tune X2. Also shows the
CMS NSD data.
Okay not perfect, but remember
we do not know if the DD is correct!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
3.0
Rick Field – Florida/CDF/CMS
Page 51
PYTHIA Tune Z1
If one increases the
hard scale the
agreement improves!
Charged Particle Density: dN/d
5
Charged Particle Density
RDF Preliminary
4
ALICE INEL data
pyZ1 generator level
At Least 1 Charged Particle || < 0.8
900 GeV
pT > 0.15 GeV/c
3
pT > 0.5 GeV/c
2
pT > 1.0 GeV/c
1
0
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
PseudoRapidity 
 ALICE inelastic data at 900 GeV on the dN/d distribution for charged particles (pT >
PTmin) for events with at least one charged particle with pT > PTmin and || < 0.8 for
PTmin = 0.15 GeV/c, 0.5 GeV/c, and 1.0 GeV/c compared with PYTHIA Tune Z1 at the
generator level.
Okay not perfect, but remember
we do not know if the SD & DD are correct!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 52
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, ||<2.0)
Tune Z1
1.0E-04
0
20
40
60
80
100
Number of Charged Particles
 Generator level charged multiplicity distribution (all pT, || < 2) at 900 GeV and 7
TeV. Shows the NSD = HC + DD prediction for Tune Z1. Also shows the CMS
NSD data.
Okay not perfect!
But not that bad!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 53
MB & UE
"Transverse" Charged Particle Multiplicity
Charged Multiplicity Distribution
1.0E+00
1.0E-01
RDF Preliminary
“Min-Bias”
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
1.0E-06
Charged Particles
(all PT, ||<2.0)
Charged Particles (||<2.0, PT>0.5 GeV/c)
Tune Z1
1.0E-07
1.0E-04
0
20
40
60
80
0
100
10
15
20
25
30
35
40
Number of Charged Particles
Number of Charged Particles
 Generator level charged multiplicity
distribution (all pT, || < 2) at 900 GeV
and 7 TeV. Shows the NSD = HC + DD
prediction for Tune Z1. Also shows the
CMS NSD data.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
5
 CMS uncorrected data at 900 GeV and 7
TeV on the charged particle multiplicity
distribution in the “transverse” region
for charged particles (pT > 0.5 GeV/c, ||
< 2) as defined by the leading 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 54
MB & UE
Charged Particle Multiplicity
1.0E+00
CMS
7 TeV
Tune Z1
Min-Bias
NSD All pT
1.0E-01
Probability
CMS Preliminary
1.0E-02
1.0E-03
Underlying Event
"Transverse" Region
pT > 0.5 GeV/c
PT(chgjet#1) > 20 GeV/c
1.0E-04
Normalized to 1
Tune Z1
Charged Particles (||<2.0)
1.0E-05
0
5
10
15
20
25
30
35
40
Number of Charged Particles
 CMS uncorrected data at 7 TeV on the charged particle multiplicity distribution in the
“transverse” region for charged particles (pT > 0.5 GeV/c, || < 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, || < 2) compared with Tune Z1 at the generator.
Amazing what we are asking the Monte-Carlo models to fit!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 55
MB & UE
Charged Particle Multiplicity
1.0E+00
CMS
7 TeV
CMS Preliminary
Tune Z1
Tune Z1
1.0E-01
Probability
Min-Bias
NSD All pT
1.0E-02
1.0E-03
1.0E-04
Underlying Event
"Transverse" Region
pT > 0.5 GeV/c
PT(chgjet#1) > 20 GeV/c
Normalized to 1
Charged Particles (||<2.0)
1.0E-05
0
20
40
60
80
100
Number of Charged Particles
 CMS uncorrected data at 7 TeV on the charged particle multiplicity distribution in the
“transverse” region for charged particles (pT > 0.5 GeV/c, || < 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, || < 2) compared with Tune Z1 at the generator.
Amazing what we are asking the Monte-Carlo models to fit!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 56
Strange Particle Production
Factor of 2!
ALICE preliminary
stat. error only
Phojet
Pythia ATLAS-CSC
Pythia D6T
Pythia Perugia-0
 A lot more strange mesons at large pT than predicted by the Monte-Carlo
Models!
 K/ ratio fairly independent of the center-of-mass energy.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 57
Two Particle Angular Correlations
 Signal, S, is two particles in the same event. Background, B, is two particles in two different
events.
 Correlation, R, is ~(S-B)/B.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 58
Two Particle Angular Correlations
CMS “min-bias” 7 TeV
Bose-Einstein
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 59
Two Particle Angular Correlations
CMS “min-bias” 7 TeV
x-axis
Two Particles in Same Jet
y-axis
Jet#2
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Jet#1
Page 60
Two Particle Angular Correlations
CMS “min-bias” 7 TeV
x-axis
Two Particles in Two Jets
y-axis
Jet#2
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Jet#1
Page 61
CMS High Multiplicity Trigger
Statistics for high
multiplicity enhanced
by ~1,000!
 A dedicated high multiplicity trigger was implemented in the two levels of the CMS trigger
system. Level 1 (L1): Sum of the total ET (ECAL, HCAL, and HF) > 60 GeV.
 High-level trigger (HLT): number of online tracks built from the three layers of pixel detectors
>70 (85).
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 62
Two Particle Angular Correlations
High Multiplicity “Min-Bias”
Average “Min-Bias”
x-axis
Two Particles in Same Jet
y-axis
Jet#2
Jet#1
Lots of jets at high multiplicity!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 63
Two Particle Angular Correlations
High Multiplicity “Min-Bias”
Average “Min-Bias”
x-axis
Two Particles in Two Jets
y-axis
Jet#2
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Jet#1
Rick Field – Florida/CDF/CMS
Page 64
Two Particle Angular Correlations
Average “Min-Bias”
High Multiplicity “Min-Bias”
Long range (in ) same side correlations! What is this?
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 65
Correlation in Heavy Ion
Collisions
Long range correlations expected in “collective flow” in heavy ion collisions.
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 66
Correlation in Heavy Ion
Collisions
Long-range “Ridge”-like structure in  at  ≈ 0!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 67
Long-Range Same-Side
Correlations
High Multiplicity “Min-Bias”
Not there in PYTHIA8!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
High Multiplicity “Min-Bias”
Also not there in PYTHIA 6 and HERWIG++!
Rick Field – Florida/CDF/CMS
Page 68
Proton-Proton vs Au-Au
Proton-Proton Collisions 7 TeV
Gold-Gold Collisions 200 GeV
QGP
I am not ready to jump on the
quark-gluon plasma bandwagon
quite yet!
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 69
Jet-Jet Correlations
 Are the “leading-log” or “modified leading-log” QCD Monte-Carlo Models missing
x-axis
an important QCD correlation?
 The leading jet and the incident protons
form a plane (yz-plane in the figure). This
is the plane of the hard scattering.
Proton
Proton
z-axis
Initial or FinalState Radiation
Leading Jet
y-axis
 Initial & final-state radiation prefers to lie in this plane. This is a higher order
effect that you can see in the 2→3 or 2→4 matrix elements, but it is not there if
you do 2→2 matrix elements and then add radiation using a naïve leading log
approximation (i.e. independent emission).
 I do not know to what extent this higher order jet-jet correlation is incorporated in
the QCD Monte-Carlo models.
 I would think that this jet-jet correlation would produce a long range (in )
correlation with  ≈ 0 from two particles with one in the leading jet and one in the
radiated jet. Why don’t we see this in the Monte-Carlo models?
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 70
Jet-Jet Correlations
x-axis
Proton
Proton
z-axis
Initial or FinalState Radiation
Leading Jet
y-axis
 Initial & Final-State Radiation: There
should be more particles “in-the-plane” of
the hard scattering (yz-plane in the figure)
than “out-of –the-plane”.
??
 I do not understand why this does not
result in a long-range same-side
correlation?
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 71
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
Southeastern APS Meeting
Baton Rouge, LA October 23, 2010
Rick Field – Florida/CDF/CMS
Page 72