studying the “underlying event” at cdf

CDF Paper Seminar Fermilab - March 11, 2010

Rick Field – Florida/CDF/CMS

Sorry to be so slow!!

Studying the Studying the “Underlying Event” at CDF“Underlying Event” at CDF

Proton AntiProton

PT(hard)

Outgoing Parton

Outgoing Parton

Underlying Event Underlying Event

Initial-State Radiation

Final-State Radiation

CDF Run 2

Proton AntiProton

Drell-Yan Production

Anti-Lepton

Lepton


“Leading Jet”

The goal is to produce data (corrected to the particle level) that can be used by the theorists to tune and improve the QCD Monte-Carlo models that are used to simulate hadron-hadron collisions.

Rick FieldCraig GroupDeepak Kar

To be submitted to PRD



PYTHIA 6.2 TunesPYTHIA 6.2 TunesParameter Tune AW Tune DW Tune D6

PDF CTEQ5L CTEQ5L CTEQ6L

MSTP(81) 1 1 1

MSTP(82) 4 4 4

PARP(82) 2.0 GeV 1.9 GeV 1.8 GeV

PARP(83) 0.5 0.5 0.5

PARP(84) 0.4 0.4 0.4

PARP(85) 0.9 1.0 1.0

PARP(86) 0.95 1.0 1.0

PARP(89) 1.8 TeV 1.8 TeV 1.8 TeV

PARP(90) 0.25 0.25 0.25

PARP(62) 1.25 1.25 1.25

PARP(64) 0.2 0.2 0.2

PARP(67) 4.0 2.5 2.5

MSTP(91) 1 1 1

PARP(91) 2.1 2.1 2.1

PARP(93) 15.0 15.0 15.0

Intrinsic KT

ISR Parameter

UE Parameters

Uses CTEQ6L

All use LO s with = 192 MeV!

Tune A energy dependence!None of the CDF Tunes included

any “min-bias” data in thedetermination of the parameters!



PYTHIA 6.2 TunesPYTHIA 6.2 TunesParameter Tune DWT Tune D6T ATLAS

PDF CTEQ5L CTEQ6L CTEQ5L

MSTP(81) 1 1 1

MSTP(82) 4 4 4

PARP(82) 1.9409 GeV 1.8387 GeV 1.8 GeV

PARP(83) 0.5 0.5 0.5

PARP(84) 0.4 0.4 0.5

PARP(85) 1.0 1.0 0.33

PARP(86) 1.0 1.0 0.66

PARP(89) 1.96 TeV 1.96 TeV 1.0 TeV

PARP(90) 0.16 0.16 0.16

PARP(62) 1.25 1.25 1.0

PARP(64) 0.2 0.2 1.0

PARP(67) 2.5 2.5 1.0

MSTP(91) 1 1 1

PARP(91) 2.1 2.1 1.0

PARP(93) 15.0 15.0 5.0

Intrinsic KT

ISR Parameter

UE Parameters

All use LO s with = 192 MeV!

ATLAS energy dependence!

Tune A

Tune AW Tune B Tune BW

Tune D

Tune DWTune D6

Tune D6T

These are “old” PYTHIA 6.2 tunes! There are new 6.420 tunes by

Peter Skands (Tune S320, update of S0)Peter Skands (Tune N324, N0CR)

Hendrik Hoeth (Tune P329, “Professor”)

CMS



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 AntiProton


Proton AntiProton


“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!



QCD Monte-Carlo Models:QCD Monte-Carlo Models:Lepton-Pair ProductionLepton-Pair Production

Start with the perturbative Drell-Yan muon pair production and add initial-state gluon radiation (in the leading log approximation or modified leading log approximation).

Proton AntiProton


Proton AntiProton


Lepton-Pair Production

Lepton

Anti-Lepton


Lepton-Pair Production

Lepton

Anti-Lepton


“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-state radiation.

“Jet”

Proton AntiProton

High PT Z-Boson Production

Z-boson

Outgoing Parton

Initial-State Radiation Final-State Radiation


Z-boson

Outgoing Parton



“Hard Scattering” Component



-1 +1

2

0

Leading Jet

Toward Region

Transverse Region

Transverse Region

Away Region

Away Region

Jet #1 Direction

“Transverse” “Transverse”

“Toward”

“Away”

“Toward-Side” Jet

“Away-Side” Jet

““Towards”, “Away”, “Transverse”Towards”, “Away”, “Transverse”

Look at correlations in the azimuthal angle relative to the leading charged particle jet (|| < 1) or the leading calorimeter jet (|| < 2).

Define || < 60o as “Toward”, 60o < | < 120o as “Transverse ”, and || > 120o as “Away”. Each of the three regions have area = 2×120o = 4/3.

Jet #1 Direction

“Toward”


“Away”

Correlations relative to the leading jetCharged particles pT > 0.5 GeV/c || < 1Calorimeter towers ET > 0.1 GeV || < 1“Transverse” region is

very sensitive to the “underlying event”!

Look at the charged particle density, the

charged PTsum density and the ETsum density in

all 3 regions!

Z-Boson Direction



Jet #1 Direction

“Toward”


“Away”

“Leading Jet”


Data at 1.96 TeV on the density of charged particles, dN/dd, with pT > 0.5 GeV/c and || < 1 for “leading jet” events as a function of the leading jet pT for the “toward”, “away”, and “transverse” regions. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune A at the particle level (i.e. generator level).

Charged Particle Density: dN/dd

0

1

2

3

4

5

0 50 100 150 200 250 300 350 400

PT(jet#1) (GeV/c)

Ave

rag

e C

har

ged

Den

sity

CDF Run 2 Preliminarydata corrected

pyA generator level

"Leading Jet"MidPoint R=0.7 |(jet#1)|<2

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

"Away"

"Toward"

"Transverse"

Data at 1.96 TeV on the charged particle scalar pT sum density, dPT/dd, with pT > 0.5 GeV/c and || < 1 for “leading jet” events as a function of the leading jet pT for the “toward”, “away”, and “transverse” regions. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune A at the particle level (i.e. generator level).

Factor of ~4.5

Charged PTsum Density: dPT/dd

0.1

1.0

10.0

100.0

0 50 100 150 200 250 300 350 400

PT(jet#1) (GeV/c)

Ch

arg

ed P

Tsu

m D

ensi

ty (

GeV

/c)


pyA generator level

"Leading Jet"MidPoint R=0.7 |(jet#1)|<2


"Toward""Away"

"Transverse"

Factor of ~16

Rick & Craig



Z-Boson Direction

“Toward”


“Away”

“Drell-Yan Producetion”


Data at 1.96 TeV on the density of charged particles, dN/dd, with pT > 0.5 GeV/c and || < 1 for “Z-Boson” events as a function of the leading jet pT for the “toward”, “away”, and “transverse” regions. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune AW at the particle level (i.e. generator level).

Data at 1.96 TeV on the charged particle scalar pT sum density, dPT/dd, with pT > 0.5 GeV/c and || < 1 for “Z-Boson” events as a function of the leading jet pT for the “toward”, “away”, and “transverse” regions. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune AW at the particle level (i.e. generator level).

Deepak Kar’s Thesis

Charged Particle Density: dN/dd

0

1

2

3

0 20 40 60 80 100

PT(Z-Boson) (GeV/c)

Ave

rag

e C

har

ged

Den

sity


pyAW generator level"Away"

"Transverse"

"Toward"

"Drell-Yan Production"70 < M(pair) < 110 GeV

Charged Particles (||<1.0, PT>0.5 GeV/c)excluding the lepton-pair

Factor of ~3

Charged PTsum Density: dPT/dd

0.1

1.0

10.0

0 20 40 60 80 100

PT(Z-Boson) (GeV/c)

Ch

arg

ed

PT

sum

Den

sity

(G

eV/c

)


pyAW generator level


"Away"

"Transverse"

"Toward"


Factor of ~11



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

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


Pro

ba

bil

ity

CDF Run 2 <Nchg>=4.5

Normalized to 1

CDF Run 2 Preliminary

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)


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”

= +


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)




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!



Average PT versus NchgAverage PT versus Nchg

Proton AntiProton


Proton AntiProton


Anti-Lepton

Lepton


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 leveland are compared with PYTHIA Tune A, Tune DW, and the ATLAS tune at the particle level (i.e. generator level).

Particle level predictions for the average pT of charged particles versus the number of charged particles (pT > 0.5 GeV/c, || < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV) at CDF Run 2.


0.5

1.0

1.5

2.0

2.5

0 5 10 15 20 25 30 35


Ave

rag

e P

T (

GeV

/c)

CDF Run 2 Preliminarygenerator level theory



HW

JIM

pyAW

ATLAS


0.5

1.0

1.5

2.0

2.5

0 5 10 15 20 25 30 35


Ave

rag

e P

T (

GeV

/c)





HW

JIM

pyAW

ATLAS


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)




Min-Bias1.96 TeV

pyAnoMPI

ATLAS

pyA




Proton AntiProton

Drell-Yan Production (no MPI)

Anti-Lepton

Lepton



0.5

1.0

1.5

2.0

2.5

0 5 10 15 20 25 30 35


Ave

rag

e P

T (

GeV

/c)





HW

JIM

pyAW

ATLAS

Proton AntiProton

Drell-Yan Production (with MPI)

Anti-Lepton

Lepton


Drell-Yan

Proton AntiProton


Z-boson

Outgoing Parton

Initial-State Radiation Final-State Radiation

= +

Z-boson production (with low pT(Z) and no MPI) produces low multiplicity and small <pT>.

+

High pT Z-boson production produces large multiplicity and high <pT>.

Z-boson production (with MPI) produces large multiplicity and medium <pT>.

No MPI!



Average PT(Z) versus NchgAverage PT(Z) versus Nchg

Proton AntiProton


Anti-Lepton

Lepton


Data on the average pT of charged particles versus the number of charged particles (pT > 0.5 GeV/c, || < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV) at CDF Run 2. The data are corrected to the particle level and are compared with various Monte-Carlo tunes at the particle level ( i.e. generator level).


0.5

1.0

1.5

2.0

2.5

0 5 10 15 20 25 30 35


Ave

rag

e P

T (

GeV

/c)





HW

JIM

pyAW

ATLAS

PT(Z-Boson) versus Nchg

0

20

40

60

80

0 5 10 15 20 25 30 35 40


Ave

rag

e P

T(Z

) (G

eV

/c)




pyAW

HW

JIM

ATLAS

No MPI!

Predictions for the average PT(Z-Boson) versus the number of charged particles (pT > 0.5 GeV/c, || < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV) at CDF Run 2.

PT(Z-Boson) versus Nchg

0

20

40

60

80

0 5 10 15 20 25 30 35 40


Ave

rag

e P

T(Z

) (G

eV/c

)





pyAW

HW

JIM

ATLAS

Proton AntiProton


Z-boson

Outgoing Parton





Proton AntiProton


Anti-Lepton

Lepton


Predictions for the average pT of charged particles versus the number of charged particles (pT > 0.5 GeV/c, || < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV, PT(pair) < 10 GeV/c) at CDF Run 2.

Average Charged PT versus Nchg

0.6

0.8

1.0

1.2

1.4

0 5 10 15 20 25 30 35


Ave

rag

e P

T (

GeV

/c)



PT(Z) < 10 GeV/c


HW

pyAW


0.6

0.8

1.0

1.2

1.4

0 5 10 15 20 25 30 35


Ave

rag

e P

T (

GeV

/c)



PT(Z) < 10 GeV/c


HW

JIM

ATLAS

pyAW


0.6

0.8

1.0

1.2

1.4

0 5 10 15 20 25 30 35


Ave

rag

e P

T (

GeV

/c)




PT(Z) < 10 GeV/c


HW

JIM

ATLAS

pyAW

Data the average pT of charged particles versus the number of charged particles (pT > 0.5 GeV/c, || < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV, PT(pair) < 10 GeV/c) at CDF Run 2. The data are corrected to the particle level and are compared with various Monte-Carlo tunes at the particle level (i.e. generator level).

PT(Z) < 10 GeV/c

No MPI!


0.6

0.8

1.0

1.2

1.4

0 10 20 30 40


Ave

rag

e P

T (

Ge

V/c

)



Charged Particles (||<1.0)pyA

Min-Bias PT > 0.4 GeV/c

Drell-Yan PT > 0.5 GeV PT(Z) < 10 GeV/c

pyAW

Proton AntiProton

“Minumum Bias” Collisions Remarkably similar behavior! Perhaps indicating that MPI playing an important role in

both processes.

It is my fault for being so slow!It is important that we publish

this paper now!

studying the “underlying event” at cdf

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