Predicting “Min-Bias” and the “Underlying Event” at the LHC

CMS-QCD Group Meeting November 10, 2009

Rick Field – Florida/CDF/CMS

Predicting “Min-Bias” and the Predicting “Min-Bias” and the “Underlying Event” at the LHC“Underlying Event” at the LHC

Rick FieldUniversity of Florida

Outline of Talk

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 Relationship between the “underlying

event” in a hard scattering process and “min-bias” collisions.

The “underlying event” at 900 GeV and 7 TeV.

Summary.UE&MB@CMSUE&MB@CMS

Important 900 GeV Measurements

New CDF charged multiplicity distribution and comparisons with the QCD Monte-Carlo tunes.

CERN November 10, 2009

The inelastic non-diffractive cross section.

“Min-Bias at 900 GeV and 2.2 TeV.



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: sHC

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Center-of-Mass Energy (TeV)

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RDF Preliminarypy Tune DW generator level

K-Factor = 1.2

Inelastic Non-Diffractive Cross-Section: sHC

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Cro

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K-Factor = 1.2

stot = sELsSD sDD sHC

Linear scale! Log scale!

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

My guess!



Charged Multiplicity Distribution

1.0E-08

1.0E-07

1.0E-06

1.0E-05

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1.0E-01

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Number of Charged Particles

Pro

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CDF Run 2 <Nchg>=4.5

py64 Tune A <Nchg> = 4.1

pyAnoMPI <Nchg> = 2.6

Charged Particles (|h|<1.0, PT>0.4 GeV/c)

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

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Pro

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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, |h| < 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!




Data at 1.96 TeV on the charged particle multiplicity (pT > 0.4 GeV/c, |h| < 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).

No MPI!Tune A!


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HC 1.96 TeV

Normalized to 1


1.0E-08

1.0E-07

1.0E-06

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1.0E-03

1.0E-02

1.0E-01

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pyS320 <Nchg> = 4.2



HC 1.96 TeV

Normalized to 1

Tune S320!


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py64DW <Nchg> = 4.2

pyS320 <Nchg> = 4.2

pyP329 <Nchg> = 4.4



HC 1.96 TeV

Normalized to 1



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”.




1.0E-08

1.0E-07

1.0E-06

1.0E-05

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pyA 900 GeV <Nchg> = 3.3

py64A LHC22 <Nchg> = 4.1



Min-Bias

Normalized to 1


Data at 1.96 TeV on the charged particle multiplicity (pT > 0.4 GeV/c, |h| < 1) for “min-bias” collisions at CDF Run 2. The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (pyAnoMPI).

Proton AntiProton


Proton Proton


Prediction from PYTHIA Tune A for proton-proton collisions at 900 GeV and 2.2 TeV.

Tune A prediction at 900 GeV!


1.0E-08

1.0E-07

1.0E-06

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HC 1.96 TeV

Normalized to 1

No MPI! Tune A! Tune A prediction at 2.2 TeV!

The charged multiplicity distributiondoes not change between

1.96 and 2.2 TeVand proton-proton is the same as

proton-antiproton!



LHC Predictions: 900 GeVLHC Predictions: 900 GeV

Proton Proton


Charged multiplicity distributions for proton-proton collisions at 900 GeV (|h| < 2) from PYTHIA Tune A, Tune DW, Tune S320, and Tune P329.

Proton Proton



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RDF Preliminary

HC 900 GeV

Normalized to 1

Charged Particles (|h|<2.0)

pT > 0.5 geV/c

<Nchg> ~ 5

All pT

<Nchg> ~ 14


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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 (|h|<2.0, all pT)

RDF Preliminary


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pyA <Nchg> = 5.0 STdev = 4.5


pyS320 900 GeV <Nchg> = 5.2

pyP329 900 GeV <Nchg> = 5.3

RDF Preliminary

HC 900 GeV

Normalized to 1


Charged Transverse Momentum Distribution

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.0E+01

1.0E+02

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Transverse Momentum (GeV/c)

d<

Nc

hg

>/d

pT

1/(

GeV

/c)

py64DW <Nchg> = 14.4 <pT> = 787 MeV/c

pyS320 <Nchg> = 14.2 <pT> = 778 MeV/c

pyP329 <Nchg> = 14.7 <pT> = 795 MeV/c

RDF Preliminary

HC 900 GeV Charged Particles (|h|<2.0)

Charged Transverse Momentum Distribution

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Transverse Momentum (GeV/c)

d<

Nc

hg

>/d

pT

1/(

GeV

/c)

py64DW <Nchg> = 14.4 <pT> = 787 MeV/c

pyS320 <Nchg> = 14.2 <pT> = 778 MeV/c

pyP329 <Nchg> = 14.7 <pT> = 795 MeV/c

RDF Preliminary

HC 900 GeV




““Transverse” Charged DensityTransverse” Charged Density

PTmax Direction

“Toward”

“Transverse” “Transverse”

“Away”

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

"Transverse" Charged Particle Density: dN/dhd

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PTmax (GeV/c)

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

RDF Preliminarygenerator level

pyS320

pyDW

PTmax Direction

“Toward”


“Away”

PTmax > 5 GeV/c!

"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


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




PTmax Direction

“Toward”


“Away”


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pyS320 <Nchg> = 3.4 <NchgDen> = 0.41





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pyS320 900 GeV <Nchg> = 5.2

pyP329 900 GeV <Nchg> = 5.3

RDF Preliminary

HC 900 GeV

Normalized to 1


Proton Proton


NchgDen = 0.21The “underlying event” is twice as active as an average HC collision!

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

Shows the charged particle multiplicity distribution in HC collisions (pT > 0.5 GeV/c, |h| < 2) at 900 GeV PYTHIA Tune A, Tune DW, Tune S320, and Tune P329 at the particle level (i.e. generator level).



ssHCHC: PTmax > 5 GeV/c: PTmax > 5 GeV/c

The inelastic non-diffractive PTmax > 5 GeV/c cross section (|h| < 1) versus center-of-mass energy from PYTHIA (×1.2).


Linear scale! Log scale!

Inelastic HC Cross-Section: PTmax > 5 GeV/c

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1.0

1.5

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Cro

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Charged Particles (PTmax > 5 GeV/c |h| < 1)

Inelastic HC Cross-Section: PTmax > 5 GeV/c

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sHC(PTmax > 5 GeV/c) varies more rapidly. Factor of 2.3 increase between 7 TeV (≈ 0.56 mb) and 14 teV (≈ 1.3 mb). Linear on a linear scale!

HC Cross-Section: Fraction PTmax > 5 GeV/c

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Number of Events in 1/nb: PTmax > 5 GeV/c

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Nu

mb

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tsRDF Preliminary

py Tune DW generator level


K-Factor = 1.2

Still lots of events!

In 1,000,000 HC collisions at 900 GeV you get 940 with

PTmax > 5 GeV/c!



PTmax Cross-Section 900 GeVPTmax Cross-Section 900 GeV

The inelastic non-diffractive PTmax > 5 GeV/c cross section (|h| < 2) at 900 GeV from PYTHIA Tune DW and Tune S320.


Differential Cross-Section: ds/dPTmax

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1.0E-04

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1.0E-02

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PTmax (GeV/c)

ds /

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K-Factor = 1.2


pyDW

pyS320

HC 900 GeV

Number of Events with PTmax > PT0

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100

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PT0 (GeV/c)

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pyDW 1,885 Events with PTmax > 5 GeV/c

pyS320 3,160 Events with PTmax > 5 GeV/c

1,000,000 HC Collisions

HC 900 GeV



Number of events with PTmax > PT0 (|h| < 2) for 1,000,000 HC collisions at 900 GeV from PYTHIA Tune DW and Tune S320.

In 1,000,000 HC collisions at 900 GeV you get ~3,000 with

PTmax > 5 GeV/c!

Need about 10,000 HC events with PTmax > 5 GeV/c to do a nice analysis!

If we get 3,400,000 HC collisionsat 900 GeV we could do both

“min-bias” AND the “underlying event”and compare them!

Very important to do BOTH“soft” and “hard” physics!



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

Shows the “associated” charged particle density in the “transverse” region as a function of PTmax for charged particles (pT > 0.5 GeV/c, |h| < 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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1.2

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PTmax (GeV/c)

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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



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

Shows the “associated” charged particle density in the “transverse” region as a function of PTmax for charged particles (pT > 0.5 GeV/c, |h| < 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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PTmax (GeV/c)

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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

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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PTmax (GeV/c)

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pyS320

pyDW


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PTmax (GeV/c)

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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, |h| < 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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pyS320 900 GeV <Nchg> = 14.2

pyP329 900 GeV <Nchg> = 14.7

HC 900 GeV

Normalized to 1 Charged Particles (|h|<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/dh).

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”


0.0

0.2

0.4

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0 2 4 6 8 10 12 14 16 18 20

PTmax (GeV/c)

"Tra

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pyS320

pyDW


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pyS320 900 GeV <Nchg> = 5.2

pyP329 900 GeV <Nchg> = 5.3

RDF Preliminary

HC 900 GeV

Normalized to 1



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pyS320 <Nchg> = 3.4 <NchgDen> = 0.41





0.0

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"Tra

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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!

Predicting “Min-Bias” and the “Underlying Event” at the LHC

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Transcript of Predicting “Min-Bias” and the “Underlying Event” at the LHC