Chris Quigg Symposium

Chris Quigg Symposiun Fermilab December 14, 2009

Rick Field – Florida/CDF/CMS Page 1

Chris Quigg SymposiumChris Quigg SymposiumPredicting MB & UE at the LHC

Rick FieldUniversity of Florida

Proton Proton

PT(hard)

Outgoing Parton

Outgoing Parton

Underlying Event Underlying Event

Initial-State Radiation

Final-State Radiation

CMS at the LHC

CDF Run 2

UE&MB@CMSUE&MB@CMS

Outline of Talk

The inelastic non-diffractive cross section.

The “underlying event” in a hard scattering process.

The QCD Monte-Carlo model tunes.

Relationship between the “underlying event” in a hard scattering process and “min-bias” collisions.

“Min-Bias” and the “underlying event” at the LHC.



J.D.J. StudentsJ.D.J. Students

J.D.JBob

Cahn

Chris Quiggme Gordy

Kane J.D.J

Jimmie & Rick

“Older than Dirt” hat!



Proton-Proton CollisionsProton-Proton Collisions Elastic Scattering Single Diffraction

M

tot = ELSD DD HC

Double Diffraction

M1 M2

Proton Proton

“Soft” Hard Core (no hard scattering)

Proton Proton

PT(hard)

Outgoing Parton

Outgoing Parton




“Hard” Hard Core (hard scattering)

Hard Core The “hard core” component

contains both “hard” and “soft” collisions.

“Inelastic Non-Diffractive Component”

ND



Inelastic Non-Diffractive Cross-SectionInelastic Non-Diffractive Cross-Section

The inelastic non-diffractive cross section versus center-of-mass energy from PYTHIA (×1.2).

Inelastic Non-Diffractive Cross-Section: HC

0

10

20

30

40

50

60

70

0 2 4 6 8 10 12 14

Center-of-Mass Energy (TeV)

Cro

ss-S

ecti

on

(m

b)

RDF Preliminarypy Tune DW generator level

K-Factor = 1.2

Inelastic Non-Diffractive Cross-Section: HC

0

10

20

30

40

50

60

70

0.1 1.0 10.0 100.0


Cro

ss-S

ecti

on

(m

b)


K-Factor = 1.2

tot = ELSD DD ND

Linear scale! Log scale!

HC varies slowly. Only a 13% increase between 7 TeV (≈ 58 mb) and 14 teV (≈ 66 mb). Linear on a log scale!

My guess!



QCD Monte-Carlo Models:QCD Monte-Carlo Models:High Transverse Momentum JetsHigh Transverse Momentum Jets

Start with the perturbative 2-to-2 (or sometimes 2-to-3) parton-parton scattering and add initial and final-state gluon radiation (in the leading log approximation or modified leading log approximation).

Hard Scattering

PT(hard)

Outgoing Parton

Outgoing Parton



Hard Scattering

PT(hard)

Outgoing Parton

Outgoing Parton



Proton Proton


Proton Proton


“Hard Scattering” Component

“Jet”

“Jet”

“Underlying Event”

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.

“Jet”

The “underlying event” is an unavoidable background to most collider observables and having good understand of it leads to

more precise collider measurements!



MPI, Pile-Up, and OverlapMPI, Pile-Up, and Overlap MPI: Additional 2-to-2 parton-parton

scatterings within a single hadron-hadron collision.

Pile-Up

Primary

MPI: Multiple Parton Interactions

Proton Proton

PT(hard)

Outgoing Parton

Outgoing Parton




Pile-Up Proton

Interaction Region z

Proton ProtonProton

Pile-Up: More than one hadron-hadron collision in the beam crossing.

Overlap Overlap: An experimental timing issue where a hadron-hadron collision from the next beam crossing gets included in the hadron-hadron collision from the current beam crossing because the next crossing happened before the event could be read out.



Charged Jet #1Direction

“Transverse” “Transverse”

“Toward”

“Away”

“Toward-Side” Jet

“Away-Side” Jet

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 size in - space, x = 2x120o = 4/3.

Charged Jet #1Direction

“Toward”


“Away”

-1 +1

2

0

Leading Jet

Toward Region

Transverse Region

Transverse Region

Away Region

Away Region

Charged Particle Correlations PT > 0.5 GeV/c || < 1

Look at the charged particle density in the “transverse” region!

“Transverse” region very sensitive to the “underlying event”!

CDF Run 1 Analysis

CDF Run 1: Evolution of Charged JetsCDF Run 1: Evolution of Charged Jets“Underlying Event”“Underlying Event”



"Transverse" Charged Particle Density: dN/dd

0.00

0.25

0.50

0.75

1.00

0 5 10 15 20 25 30 35 40 45 50

PT(charged jet#1) (GeV/c)"T

ran

sver

se"

Ch

arg

ed D

ensi

ty

CTEQ3L CTEQ4L CTEQ5L CDF Min-Bias CDF JET20

1.8 TeV ||<1.0 PT>0.5 GeV

Pythia 6.206 (default)MSTP(82)=1

PARP(81) = 1.9 GeV/c

CDF Datadata uncorrectedtheory corrected

Default parameters give very poor description of the “underlying event”!

Note ChangePARP(67) = 4.0 (< 6.138)PARP(67) = 1.0 (> 6.138)

Parameter 6.115 6.125 6.158 6.206

MSTP(81) 1 1 1 1

MSTP(82) 1 1 1 1

PARP(81) 1.4 1.9 1.9 1.9

PARP(82) 1.55 2.1 2.1 1.9

PARP(89) 1,000 1,000 1,000

PARP(90) 0.16 0.16 0.16

PARP(67) 4.0 4.0 1.0 1.0

Plot shows the “Transverse” charged particle density versus PT(chgjet#1) compared to the QCD hard scattering predictions of PYTHIA 6.206 (PT(hard) > 0) using the default parameters for multiple parton interactions and CTEQ3L, CTEQ4L, and CTEQ5L.

PYTHIA default parameters

PYTHIA 6.206 DefaultsPYTHIA 6.206 DefaultsMPI constant

probabilityscattering



Parameter Default

Description

PARP(83) 0.5 Double-Gaussian: Fraction of total hadronic matter within PARP(84)

PARP(84) 0.2 Double-Gaussian: Fraction of the overall hadron radius containing the fraction PARP(83) of the total hadronic matter.

PARP(85) 0.33 Probability that the MPI produces two gluons with color connections to the “nearest neighbors.

PARP(86) 0.66 Probability that the MPI produces two gluons either as described by PARP(85) or as a closed gluon loop. The remaining fraction consists of quark-antiquark pairs.

PARP(89) 1 TeV Determines the reference energy E0.

PARP(82) 1.9 GeV/c

The cut-off PT0 that regulates the 2-to-2 scattering divergence 1/PT4→1/(PT2+PT0

2)2

PARP(90) 0.16 Determines the energy dependence of the cut-off

PT0 as follows PT0(Ecm) = PT0(Ecm/E0) with = PARP(90)

PARP(67) 1.0 A scale factor that determines the maximum parton virtuality for space-like showers. The larger the value of PARP(67) the more initial-state radiation.

Hard Core

Multiple Parton Interaction

Color String

Color String

Multiple Parton Interaction

Color String

Hard-Scattering Cut-Off PT0

1

2

3

4

5

100 1,000 10,000 100,000

CM Energy W (GeV)P

T0

(G

eV

/c)

PYTHIA 6.206

= 0.16 (default)

= 0.25 (Set A))

Take E0 = 1.8 TeV

Reference pointat 1.8 TeV

Determine by comparingwith 630 GeV data!

Affects the amount ofinitial-state radiation!

Tuning PYTHIA:Tuning PYTHIA:Multiple Parton Interaction ParametersMultiple Parton Interaction Parameters

Determines the energy dependence of the MPI!



Old PYTHIA default(more initial-state radiation)New PYTHIA default

(less initial-state radiation)

Parameter Tune B Tune A

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(67) 1.0 4.0

Old PYTHIA default(more initial-state radiation)New PYTHIA default

(less initial-state radiation)

Plot shows the “transverse” charged particle density versus PT(chgjet#1) compared to the QCD hard scattering predictions of two tuned versions of PYTHIA 6.206 (CTEQ5L, Set B (PARP(67)=1) and Set A (PARP(67)=4)).


0.00

0.25

0.50

0.75

1.00

0 5 10 15 20 25 30 35 40 45 50

PT(charged jet#1) (GeV/c)

"Tra

nsv

erse

" C

har

ged

Den

sity

1.8 TeV ||<1.0 PT>0.5 GeV

CDF Preliminarydata uncorrectedtheory corrected

CTEQ5L

PYTHIA 6.206 (Set A)PARP(67)=4

PYTHIA 6.206 (Set B)PARP(67)=1

Run 1 Analysis

Run 1 PYTHIA Tune ARun 1 PYTHIA Tune APYTHIA 6.206 CTEQ5L

CDF Default!



Use the maximum pT charged particle in the event, PTmax, to define a direction and look at the the “associated” density, dNchg/dd, in “min-bias” collisions (pT > 0.5 GeV/c, || < 1).

PTmax Direction

Correlations in

Charged Particle Density: dN/dd

0.0

0.1

0.2

0.3

0.4

0.5

0 30 60 90 120 150 180 210 240 270 300 330 360

(degrees)

Ch

arg

ed

Pa

rtic

le D

en

sit

y

PTmax

Associated DensityPTmax not included

CDF Preliminarydata uncorrected

Charged Particles (||<1.0, PT>0.5 GeV/c)

Charge Density

Min-Bias

“Associated” densities do not include PTmax!

Highest pT charged particle!

PTmax Direction

Correlations in

Shows the data on the dependence of the “associated” charged particle density, dNchg/dd, for charged particles (pT > 0.5 GeV/c, || < 1, not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” events. Also shown is the average charged particle density, dNchg/dd, for “min-bias” events.

It is more probable to find a particle accompanying PTmax than it is to

find a particle in the central region!

CDF Run 1 Min-Bias “Associated”CDF Run 1 Min-Bias “Associated”Charged Particle DensityCharged Particle Density



Associated Particle Density: dN/dd

0.0

0.2

0.4

0.6

0.8

1.0

0 30 60 90 120 150 180 210 240 270 300 330 360

(degrees)

As

so

cia

ted

Pa

rtic

le D

en

sit

y

PTmax > 2.0 GeV/c

PTmax > 1.0 GeV/c

PTmax > 0.5 GeV/c

CDF Preliminarydata uncorrected

PTmaxPTmax not included


Min-Bias

PTmax Direction

Correlations in

Shows the data on the dependence of the “associated” charged particle density, dNchg/dd, for charged particles (pT > 0.5 GeV/c, || < 1, not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” events with PTmax > 0.5, 1.0, and 2.0 GeV/c.

Transverse Region

Transverse Region

Jet #1

Shows “jet structure” in “min-bias” collisions (i.e. the “birth” of the leading two jets!).

Jet #2

Ave Min-Bias0.25 per unit -

PTmax Direction

“Toward”


“Away”

PTmax > 0.5 GeV/c

PTmax > 2.0 GeV/c

CDF Run 1 Min-Bias “Associated”CDF Run 1 Min-Bias “Associated”Charged Particle DensityCharged Particle Density Rapid rise in the particle

density in the “transverse” region as PTmax increases!



Min-Bias “Associated”Min-Bias “Associated”Charged Particle DensityCharged Particle Density

Shows the “associated” charged particle density in the “toward”, “away” and “transverse” regions as a function of PTmax for charged particles (pT > 0.5 GeV/c, || < 1, not including PTmax) for “min-bias” events at 1.96 TeV from PYTHIA Tune A (generator level).

PTmax Direction

“Toward”


“Away”

Associated Charged Particle Density: dN/dd

0.0

0.1

1.0

10.0

0 30 60 90 120 150 180 210 240 270 300 330 360

(degrees)

Ch

arg

ed

Par

ticl

e D

en

sit

y

RDF Preliminarypy Tune A generator level


Min-Bias1.96 TeV

PTmax > 0.5 GeV/cPTmax > 1.0 GeV/c

PTmax > 2.0 GeV/cPTmax > 5.0 GeV/c

PTmax > 10.0 GeV/c


0.0

0.4

0.8

1.2

1.6

0 2 4 6 8 10 12 14 16 18 20

PTmax (GeV/c)

Ch

arg

ed P

arti

cle

Den

sity


Min-Bias1.96 TeV


"Toward"

"Transverse"

"Away"

Shows the dependence of the “associated” charged particle density, dNchg/dd, for charged particles (pT > 0.5 GeV/c, || < 1, not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” events at 1.96 TeV with PTmax > 0.5, 1.0, 2.0, 5.0, and 10.0 GeV/c from PYTHIA Tune A (generator level).


0.0

0.5

1.0

1.5

2.0

2.5

0 5 10 15 20 25

PTmax (GeV/c)

Ch

arg

ed

Par

ticl

e D

en

sit

y


Min-Bias14 TeV

"Toward"

"Transverse"

"Away"



0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 5 10 15 20 25

PTmax (GeV/c)

"Tra

ns

vers

e"

Ch

arg

ed D

ensi

ty


Min-Bias


14 TeV

1.96 TeV

“Toward” Region


PTmax Direction

“Toward”


“Away”

~ factor of 2!



Charged Multiplicity Distribution

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 5 10 15 20 25 30 35 40 45 50 55

Number of Charged Particles

Pro

ba

bil

ity

CDF Run 2 <Nchg>=4.5

py64 Tune A <Nchg> = 4.1

pyAnoMPI <Nchg> = 2.6


CDF Run 2 Preliminary

HC 1.96 TeV

Normalized to 1


1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 5 10 15 20 25 30 35 40 45 50 55


Pro

ba

bil

ity


Normalized to 1


Min-Bias 1.96 TeV


Charged Particle MultiplicityCharged Particle Multiplicity

Data at 1.96 TeV on the charged particle multiplicity (pT > 0.4 GeV/c, || < 1) for “min-bias” collisions at CDF Run 2.

Proton AntiProton

“Minumum Bias” Collisions

The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (pyAnoMPI).

No MPI! Tune A!7 decades!



The “Underlying Event”The “Underlying Event”

Proton Proton

Select inelastic non-diffractive events that contain a hard scattering

Proton Proton

Proton Proton +

Proton Proton

+ + …

“Semi-hard” parton-parton collision(pT < ≈2 GeV/c)

Hard parton-parton collisions is hard(pT > ≈2 GeV/c) The “underlying-event” (UE)!

Multiple-parton interactions (MPI)!

Given that you have one hard scattering it is more probable to have MPI! Hence, the UE has more activity than “min-bias”.



The Inelastic Non-Diffractive The Inelastic Non-Diffractive Cross-SectionCross-Section

Proton Proton

Proton Proton +

Proton Proton

Proton Proton

+

Proton Proton +

+ …


Occasionally one of the parton-parton collisions is hard(pT > ≈2 GeV/c)

Majority of “min-bias” events!




The “Underlying Event”The “Underlying Event”

Proton Proton

Select inelastic non-diffractive events that contain a hard scattering

Proton Proton

Proton Proton +

Proton Proton

+ + …


Hard parton-parton collisions is hard(pT > ≈2 GeV/c) The “underlying-event” (UE)!


Given that you have one hard scattering it is more probable to have MPI! Hence, the UE has more activity than “min-bias”.



Min-Bias CorrelationsMin-Bias Correlations

Data at 1.96 TeV on the average pT of charged particles versus the number of charged particles (pT > 0.4 GeV/c, || < 1) for “min-bias” collisions at CDF Run 2. The data are corrected to the particle level and are compared with PYTHIA Tune A at the particle level (i.e. generator level).

Proton AntiProton


Average PT versus Nchg

0.6

0.8

1.0

1.2

1.4

0 10 20 30 40 50


Ave

rag

e P

T (

GeV

/c)

CDF Run 2 Preliminarydata corrected

generator level theory


Min-Bias1.96 TeV

ATLAS

pyA

pyDW



Min-Bias: Average PT versus NchgMin-Bias: Average PT versus Nchg

Proton AntiProton

“Soft” Hard Core (no hard scattering)

Proton AntiProton

PT(hard)

Outgoing Parton

Outgoing Parton




“Hard” Hard Core (hard scattering)

CDF “Min-Bias”

= +

Average PT versus Nchg

0.6

0.8

1.0

1.2

1.4

0 5 10 15 20 25 30 35 40


Ave

rag

e P

T (

GeV

/c)

CDF Run 2 Preliminarydata corrected

generator level theory


Min-Bias1.96 TeV

pyAnoMPI

ATLAS

pyA

Proton AntiProton

Multiple-Parton Interactions

PT(hard)

Outgoing Parton

Outgoing Parton




+

Beam-beam remnants (i.e. soft hard core) produces low multiplicity and small <pT> with <pT> independent of the multiplicity.

Hard scattering (with no MPI) produces large multiplicity and large <pT>.

Hard scattering (with MPI) produces large multiplicity and medium <pT>.

The CDF “min-bias” trigger picks up most of the “hard

core” component!

This observable is sensitive to the MPI tuning!



Charged Particle MultiplicityCharged Particle Multiplicity

Data at 1.96 TeV on the charged particle multiplicity (pT > 0.4 GeV/c, || < 1) for “min-bias” collisions at CDF Run 2.

Proton AntiProton


The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (pyAnoMPI).


1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 5 10 15 20 25 30 35 40 45 50 55


Pro

bab

ility


py Tune A <Nchg> = 4.3

pyAnoMPI <Nchg> = 2.6



Min-Bias 1.96 Normalized to 1

No MPI!

Tune A!


1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 5 10 15 20 25 30 35 40 45 50 55


Pro

ba

bil

ity


py Tune A <Nchg> = 4.3

pyA 900 GeV <Nchg> = 3.3



Min-BiasNormalized to 1

Proton Proton


Prediction from PYTHIA Tune A for proton-proton collisions at 900 GeV.

Tune A prediction at 900 GeV!



Peter’s Pythia Tunes WEBsitePeter’s Pythia Tunes WEBsite

http://home.fnal.gov/~skands/leshouches-plots/




Shows the “associated” charged particle density in the “transverse” regions as a function of PTmax for charged particles (pT > 0.5 GeV/c, || < 1, not including PTmax) for “min-bias” events at 0.2 TeV and 14 TeV from PYTHIA Tune DW and Tune DWT at the particle level (i.e. generator level). The STAR data from RHIC favors Tune DW!

PTmax Direction

“Toward”


“Away”


0.0

0.1

0.2

0.3

0 2 4 6 8 10 12 14 16 18 20

PTmax (GeV/c)

"Tra

ns

ve

rse

" C

ha

rge

d D

en

sit

y

Min-Bias0.2 TeV

RDF Preliminarygenerator level


PY Tune DWT

PY Tune DW


0.0

0.4

0.8

1.2

1.6

0 2 4 6 8 10 12 14 16 18 20

PTmax (GeV/c)

"Tra

ns

ve

rse

" C

ha

rge

d D

en

sit

y RDF Preliminarygenerator level

Min-Bias14 TeV Charged Particles (||<1.0, PT>0.5 GeV/c)

PY Tune DW

PY Tune DWT

PTmax Direction

“Toward”


“Away”

RHIC LHC

0.2 TeV → 14 TeV (~factor of 70 increase)

~1.35

~1.35

35% more at RHIC means 26% less at the LHC!




Shows the “associated” charged particle density in the “transverse” region as a function of PTmax for charged particles (pT > 0.5 GeV/c, || < 1, not including PTmax) for “min-bias” events at 0.2 TeV, 1.96 TeV and 14 TeV predicted by PYTHIA Tune DW at the particle level (i.e. generator level).

PTmax Direction

“Toward”


“Away”

PTmax Direction

“Toward”


“Away”

RHIC Tevatron

0.2 TeV → 1.96 TeV (UE increase ~2.7 times)


0.0

0.4

0.8

1.2

0 5 10 15 20 25

PTmax (GeV/c)

"Tra

ns

ve

rse

" C

ha

rge

d D

en

sit

y



Min-Bias 14 TeV

1.96 TeV

0.2 TeV

PTmax Direction

“Toward”


“Away”

LHC

1.96 TeV → 14 TeV (UE increase ~1.9 times)

~2.7

~1.9



The “Underlying Event” at STARThe “Underlying Event” at STAR

At STAR they have measured the “underlying event at W = 200 GeV (|| < 1, pT > 0.2 GeV) and compared their uncorrected data with PYTHIA Tune A + STAR-SIM.



LHC Predictions: 900 GeVLHC Predictions: 900 GeV

Proton Proton


Compares the 900 GeV data with my favorite PYTHIA Tunes (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.

Proton Proton


Charged Particle Density: dN/d

0

1

2

3

4

5

-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

PseudoRapidity

Ch

arg

ed

Par

ticl

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en

sit

y

ALICE INEL

UA5 INEL

pyDW INEL (2.67)

pyS320 INEL (2.70)

RDF Preliminary

INEL = HC+DD+SD 900 GeV

Charged Particles (all pT)


0

1

2

3

4

5

-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

PseudoRapidity

Ch

arg

ed

Par

ticl

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en

sit

y

UA5

ALICE

pyDW_10mm (3.04)

pyS320_10mm (3.09)

NSD = HC+DD 900 GeV

RDF Preliminary

(SD + DD)/INEL = 28±8%DD/NSD = 12±4%



LHC Predictions: 900 GeVLHC Predictions: 900 GeV

Proton Proton


Shows the individual HC, DD, and SD predictions of PYTHIA Tune DW and Tune S320 Perugia 0. The numbers in parentheses are the average value of dN/d for the region || < 0.6. I do not trust PYTHIA to model correctly the DD and SD contributions! I would like to know how well these tunes model the HC component. We need to look at observables where only HC contributes!

Proton Proton



0

1

2

3

4

5

-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

PseudoRapidity

Ch

arg

ed

Par

ticl

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en

sit

y

ALICE INELUA5 INELpyDW times 1.11 (2.97)pyS320 times 1.11 (3.00)

RDF Preliminary


times 1.11



0

1

2

3

4

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6

PseudoRapidity

Ch

arg

ed

Par

ticl

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en

sit

y

pyDW HC (3.30)

pyS320 HC (3.36)

pyDW SD (0.61)

pyS320 SD (0.53)

pyDW DD (0.59)

pyS320 DD (0.53)

900 GeV

RDF Preliminary Only HC

Only DD


Only SD


0

1

2

3

4

5

-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

PseudoRapidity

Ch

arg

ed

Par

ticl

e D

en

sit

y

ALICE INEL

UA5 INEL

pyDW INEL NPT1>0 (4.24)

pyS320 INEL NPT1>0 (4.48)

pyDW INEL (2.67)

pyS320 INEL (2.70)

RDF Preliminary



Off by 11%!

(SD + DD)/INEL = 28±8%

Require at least one charged particle to have pT > 1 GeV/c. This is > 99% HC only!




Shows the “associated” charged particle density in the “transverse” region as a function of PTmax for charged particles (pT > 0.5 GeV/c, || < 1, not including PTmax) for “min-bias” events at 0.2 TeV, 0.9 TeV, 1.96 TeV, 7 TeV, 10 TeV, 14 TeV predicted by PYTHIA Tune DW at the particle level (i.e. generator level).

PTmax Direction

“Toward”


“Away”

PTmax Direction

“Toward”


“Away”

RHIC Tevatron

0.2 TeV → 1.96 TeV (UE increase ~2.7 times)

PTmax Direction

“Toward”


“Away”

LHC

1.96 TeV → 14 TeV (UE increase ~1.9 times)

Linear scale!


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Min-Bias 14 TeV

1.96 TeV

0.2 TeV

7 TeV

0.9 TeV

10 TeV


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PTmax = 5.25 GeV/c

RHIC

Tevatron900 GeV

LHC7

LHC14

LHC10




Shows the “associated” charged particle density in the “transverse” region as a function of PTmax for charged particles (pT > 0.5 GeV/c, || < 1, not including PTmax) for “min-bias” events at 0.2 TeV, 0.9 TeV, 1.96 TeV, 7 TeV, 10 TeV, 14 TeV predicted by PYTHIA Tune DW at the particle level (i.e. generator level).

Log scale!


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Min-Bias 14 TeV

1.96 TeV

0.2 TeV

7 TeV

0.9 TeV

10 TeV


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Tevatron

900 GeV

LHC7

LHC14LHC10

PTmax Direction

“Toward”


“Away”

PTmax Direction

“Toward”


“Away”

LHC7 LHC14

7 TeV → 14 TeV (UE increase ~20%)

Linear on a log plot!



““Transverse” Charge DensityTransverse” Charge Density

PTmax Direction

“Toward”


“Away”

PTmax Direction

“Toward”


“Away”

LHC 900 GeV

LHC7 TeV

900 GeV → 7 TeV (UE increase ~ factor of 2.1)


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Charged Particles (||<2.0, PT>0.5 GeV/c) HC 900 GeV


pyS320

pyDW


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900 GeV

7 TeV

Shows the charged particle density in the “transverse” region for charged particles (pT > 0.5 GeV/c, || < 2) at 900 GeV as defined by PTmax from PYTHIA Tune DW and Tune S320 at the particle level (i.e. generator level).

factor of 2!




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pyA 900 GeV <Nchg> = 14.2

pyDW 900 GeV <Nchg> = 14.4

pyS320 900 GeV <Nchg> = 14.2

pyP329 900 GeV <Nchg> = 14.7

HC 900 GeV

Normalized to 1 Charged Particles (||<2.0, all pT)

RDF Preliminary

Important 900 GeV Measurements

Proton Proton


Proton Proton

PT(hard)

Outgoing Parton

Outgoing Parton




PTmax Direction

“Toward”


“Away”

The amount of activity in “min-bias” collisions (multiplicity distribution, pT distribution, PTsum distribution, dNchg/d).

The amount of activity in the “underlying event” in hard scattering events (“transverse” Nchg distribution, “transverse” pT distribution, “transverse” PTsum distribution for events with PTmax > 5 GeV/c).

We should map out the energy dependence of the “underlying event” in a hard scattering process from 900 GeV to 14 TeV!

Proton Proton

PT(hard)

Outgoing Parton

Outgoing Parton




PTmax Direction

“Toward”


“Away”


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Charged Particles (||<2.0, PT>0.5 GeV/c) HC 900 GeV


pyS320

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pyA <Nchg> = 5.0 STdev = 4.5

pyDW 900 GeV <Nchg> = 5.3

pyS320 900 GeV <Nchg> = 5.2

pyP329 900 GeV <Nchg> = 5.3

RDF Preliminary

HC 900 GeV

Normalized to 1


"Transverse" Charged Particle Multiplicity

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py64DW <Nchg> = 3.5 <NchgDen> = 0.42

pyS320 <Nchg> = 3.4 <NchgDen> = 0.41


HC 900 GeV PTmax > 5 GeV/c



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py Tune DW generator level


PTmax = 5.25 GeV/c

For every 1,000 events here

We get 3 events here!

It is very important to measureBOTH “min-bias” and the and the

“underlying event” at 900 GeV!To do this we need to collect

about 5,000,000 CMS min-bias triggers!



The “Underlying Event” at 900 GeV The “Underlying Event” at 900 GeV

Show how well we could measure the “transverse” charged particle density versus PTmax with 10 M, 1 M, and 0.5 M “min-bias” (MB) events collected by CMS. Assumes that for all the events that the tracker is working well! The goal is to see how well the data (red squares) agree with the QCD MC prediction (black curve).


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RDF PreliminarypyDW generator level

900 GeV10 Million MB Collisions


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900 GeV1 Million MB Collisions


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900 GeV0.5 Million MB Collisions

Unfortunately, looks like this is all we will get!

Documents

Chris Quigg Symposium