C2CR07-Lake Tahoe February 28, 2007 Rick Field – Florida/CDFPage 1 C2CR07 Rick Field University of...

C2CR07-Lake Tahoe February 28, 2007

Rick Field – Florida/CDF

C2CR07C2CR07Rick Field

University of Florida(for the CDF Collaboration)

CDF Run 2

Min-Bias at the Tevatron

Outline of Talk

What is “Min-Bias”? Is it unique?

Extrapolating Tevatron “Min-Bias” to the LHC.

“Jets” in Min-Bias Collisions. Clear Jet structure as low as 1 GeV/c!

Using Pile-Up collisions to Study Min-Bias. Is Pile-Up Unbiased?

Proton AntiProton

“Minumum Bias” Collisions



Proton-AntiProton CollisionsProton-AntiProton Collisionsat the Tevatronat the Tevatron

Elastic Scattering Single Diffraction

M

tot = ELSD DD HC

Double Diffraction

M1 M2

Proton AntiProton

“Soft” Hard Core (no hard scattering)

Proton AntiProton

PT(hard)

Outgoing Parton

Outgoing Parton

Underlying Event Underlying Event

Initial-State Radiation

Final-State Radiation

“Hard” Hard Core (hard scattering)

Hard Core

1.8 TeV: 78mb = 18mb + 9mb + (4-7)mb + (47-44)mb

The CDF “Min-Bias” trigger picks up most of the “hard

core” cross-section plus a small amount of single & double

diffraction.

The “hard core” component contains both “hard” and

“soft” collisions.

Beam-Beam Counters

3.2 < || < 5.9

CDF “Min-Bias” trigger1 charged particle in forward BBC

AND1 charged particle in backward BBC

tot = ELIN



No-Bias vs Min-BiasNo-Bias vs Min-BiasCharged Particle Density: dN/d

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PseudoRapidity

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pyDWT HC NoTrig

pyDWT DD NoTtrig

pyDWT SD NoTrig

No Trigger900 GeV Generated

Charged Particles (all PT)

Charged Particle Density: dN/d

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PseudoRapidity

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pyDW HC Mbtrig

pyDW DD MBtrig

pyDW SD MBtrig

CDF Min-Bias Trigger900 GeV Generated



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pyDWT Sum NoTrig

pyDWT HC NoTrig

pyDWT DD NoTtrig

pyDWT SD NoTrig

No Trigger900 GeV Weighted



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PseudoRapidity

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pyDWT Sum MBtrig

pyDWT HC MBtrig

pyDWT DD MBtrig

pyDWT SD MBtrig

CDF Min-Bias Trigger900 GeV Weighted


What you see for “Min-Bias”depends on your triggger!



No-Bias vs Min-BiasNo-Bias vs Min-BiasCharged Particle Density: dN/d

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PseudoRapidity

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PYTHIA Tune DWCharged Particles

No-Bias 1.96 TeV(HC+SD+DD+EL)

All PT


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PseudoRapidity

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PYTHIA Tune DWCharged Particles

No-Bias 1.96 TeV(HC+SD+DD+EL)

All PT

PT > 0.5 GeV/c


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PYTHIA Tune DWCharged Particles (PT > 0.5 GeV/c) Min-Bias 1.96 TeV

(HC+SD+DD+EL)

CDF Min-Bias Trigger

No Trigger

Charged particle (all pT) pseudo-rapidity distribution, dNchg/dd, at 1.96 TeV with no trigger (i.e. no-bias) from PYTHIA Tune DW.

About 2.5 charged particles per unit at = 0.

About 0.9 charged particles (pT > 0.5 GeV/c) per unit at = 0.

Charged particle (pT > 0.5 GeV/c) pseudo-rapidity distribution, dNchg/dd, at 1.96 TeV with the CDF Min-Bias trigger from PYTHIA Tune DW.

About 1.5 charged particles (pT > 0.5 GeV/c) per unit at = 0 with CDF min-bias trigger.



-1 +1

2

0

1 charged particle

dNchg/dd = 1/4 = 0.08

Study the charged particles (pT > 0.5 GeV/c, || < 1) and form the charged particle density, dNchg/dd, and the charged scalar pT sum density, dPTsum/dd.

Charged Particles pT > 0.5 GeV/c || < 1

= 4 = 12.6

1 GeV/c PTsum

dPTsum/dd = 1/4 GeV/c = 0.08 GeV/c

dNchg/dd = 3/4 = 0.24

3 charged particles

dPTsum/dd = 3/4 GeV/c = 0.24 GeV/c

3 GeV/c PTsum

CDF Run 2 “Min-Bias”Observable

AverageAverage Density

per unit -

NchgNumber of Charged Particles

(pT > 0.5 GeV/c, || < 1) 3.17 +/- 0.31 0.252 +/- 0.025

PTsum

(GeV/c)Scalar pT sum of Charged Particles

(pT > 0.5 GeV/c, || < 1) 2.97 +/- 0.23 0.236 +/- 0.018

Divide by 4

CDF Run 2 “Min-Bias”

Particle DensitiesParticle Densities



CDF Run 1 “Min-Bias” DataCDF Run 1 “Min-Bias” DataCharged Particle DensityCharged Particle Density

Shows CDF “Min-Bias” data on the number of charged particles per unit pseudo-rapidity at 630 and 1,800 GeV. There are about 4.2 charged particles per unit in “Min-Bias” collisions at 1.8 TeV (|| < 1, all PT).

Charged Particle Pseudo-Rapidity Distribution: dN/d

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Pseudo-Rapidity

dN

/d

CDF Min-Bias 1.8 TeV

CDF Min-Bias 630 GeV all PT

CDF Published

<dNchg/d> = 4.2

Charged Particle Density: dN/dd

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Pseudo-Rapidity

dN

/d d

CDF Min-Bias 630 GeV

CDF Min-Bias 1.8 TeV all PT

CDF Published

<dNchg/dd> = 0.67

Convert to charged particle density, dNchg/dd by dividing by 2. There are about 0.67 charged particles per unit - in “Min-Bias” collisions at 1.8 TeV (|| < 1, all PT).




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Pseudo-Rapidity

dN

/d d

CDF Min-Bias 630 GeV

CDF Min-Bias 1.8 TeV all PT

CDF Published

Shows the center-of-mass energy dependence of the charged particle density, dNchg/dd for “Min-Bias” collisions at = 0. Also show a log fit (Fit 1) and a (log)2 fit (Fit 2) to the CDF plus UA5 data.


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CM Energy W (GeV)

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N/d

d

CDF DataUA5 DataFit 2Fit 1

= 0

<dNchg/dd> = 0.51 = 0 630 GeV

What should we expect for the LHC?

<dNchg/dd> = 0.63 = 0 1.8 TeV

LHC?24% increase

CDF Run 1 “MinCDF Run 1 “Min--Bias” DataBias” DataEnergy DependenceEnergy Dependence



PYTHIA Tune A Min-BiasPYTHIA Tune A Min-Bias“Soft” + ”Hard”“Soft” + ”Hard”


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Pseudo-Rapidity

dN

/d d

Pythia 6.206 Set A

CDF Min-Bias 1.8 TeV 1.8 TeV all PT

CDF Published

PYTHIA regulates the perturbative 2-to-2 parton-parton cross sections with cut-off parameters which allows one to run with PT(hard) > 0. One can simulate both “hard” and “soft” collisions in one program.

The relative amount of “hard” versus “soft” depends on the cut-off and can be tuned.

Charged Particle Density

1.0E-06

1.0E-05

1.0E-04

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1.0E-01

1.0E+00

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PT(charged) (GeV/c)

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N/d

d d

PT

(1/

GeV

/c)

Pythia 6.206 Set A

CDF Min-Bias Data

CDF Preliminary

1.8 TeV ||<1

PT(hard) > 0 GeV/c

Tuned to fit the “underlying event”!

12% of “Min-Bias” events have PT(hard) > 5 GeV/c!


This PYTHIA fit predicts that 12% of all “Min-Bias” events are a result of a hard 2-to-2 parton-parton scattering with PT(hard) > 5 GeV/c (1% with PT(hard) > 10 GeV/c)!

Lots of “hard” scattering in “Min-Bias”!

PYTHIA Tune ACDF Run 2 Default



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

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


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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!




Associated Particle Density: dN/dd

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PTmax > 2.0 GeV/c

PTmax > 1.0 GeV/c

PTmax > 0.5 GeV/c

CDF Preliminarydata uncorrected

PTmaxPTmax not included

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

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”

“Transverse” “Transverse”

“Away”

PTmax > 0.5 GeV/c

PTmax > 2.0 GeV/c

Rapid rise in the particle density in the “transverse” region as PTmax increases!




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 GeV/c and PTmax > 2.0 GeV/c compared with PYTHIA Tune A (after CDFSIM).

PTmax Direction

Correlations in

Associated Particle Density: dN/dd

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PY Tune A

PTmax > 0.5 GeV/c

PY Tune A

CDF Preliminarydata uncorrectedtheory + CDFSIM

PTmaxPTmax not included (||<1.0, PT>0.5 GeV/c)

PY Tune A 1.96 TeV

PYTHIA Tune A predicts a larger correlation than is seen in the “min-bias” data (i.e. Tune A “min-bias” is a bit too “jetty”).

PTmax > 2.0 GeV/c

PTmax > 0.5 GeV/c

PTmax Direction

“Toward”

“Transverse” “Transverse”

“Away”

Transverse Region Transverse

Region

PY Tune A




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Pseudo-Rapidity

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all PT

CDF Data Pythia 6.206 Set A

630 GeV

1.8 TeV

14 TeV

PYTHIA was tuned to fit the “underlying event” in hard-scattering processes at 1.8 TeV and 630 GeV.


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CM Energy W (GeV)

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Pythia 6.206 Set ACDF DataUA5 DataFit 2Fit 1

= 0

Shows the center-of-mass energy dependence of the charged particle density, dNchg/dd for “Min-Bias” collisions compared with PYTHIA Tune A with PT(hard) > 0.

PYTHIA Tune A predicts a 42% rise in dNchg/dd at = 0 in going from the Tevatron (1.8 TeV) to the LHC (14 TeV). Similar to HERWIG “soft” min-bias, 4 charged particles per unit becomes 6.

LHC?

PYTHIA Tune APYTHIA Tune ALHC Min-Bias PredictionsLHC Min-Bias Predictions



Charged Particle Density

1.0E-06

1.0E-05

1.0E-04

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1.0E-02

1.0E-01

1.0E+00

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PT(charged) (GeV/c)

Ch

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N/d

d d

PT

(1/

GeV

/c)

CDF Data

||<1

630 GeV

Pythia 6.206 Set A

1.8 TeV

14 TeV

Hard-Scattering in Min-Bias Events

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10%

20%

30%

40%

50%

100 1,000 10,000 100,000

CM Energy W (GeV)

% o

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PT(hard) > 10 GeV/c

Pythia 6.206 Set A

Shows the center-of-mass energy dependence of the charged particle density, dNchg/dddPT, for “Min-Bias” collisions compared with PYTHIA Tune A with PT(hard) > 0.

PYTHIA Tune A predicts that 1% of all “Min-Bias” events at 1.8 TeV are a result of a hard 2-to-2 parton-parton scattering with PT(hard) > 10 GeV/c which increases to 12% at 14 TeV!



LHC?

PYTHIA Tune APYTHIA Tune ALHC Min-Bias PredictionsLHC Min-Bias Predictions



PYTHIA Tune A and Tune DW predict about 6 charged particles per unit at = 0, while the ATLAS tune predicts around 9.

Shows the predictions of PYTHIA Tune A, Tune DW, Tune DWT, and the ATLAS tune for the charged particle density dN/d and dN/dY at 14 TeV (all pT).

PYTHIA Tune DWT is identical to Tune DW at 1.96 TeV, but extrapolates to the LHC using the ATLAS energy dependence.


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pyA

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Charged Particles (all pT)

Generator Level14 TeV

Charged Particle Density: dN/dY

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PYTHIA 6.2 TunesPYTHIA 6.2 TunesLHC Min-Bias PredictionsLHC Min-Bias Predictions


Rick Field – Florida/CDF Page 16

Using Pile-Up to Study Min-BiasUsing Pile-Up to Study Min-Bias

The primary vertex is the highest PTsum of charged particles pointing towards it.

Proton AntiProton

60 cm

Primary

Normally one only includes those charged particles which point back to the primary vertex.

Pile-Up

However, the primary vertex is presumably the collision that satisfied the trigger and is hence biased.

Perhaps the pile-up is not biases and can serve as a new type of “Min-Bias” collisions.

This assumes that the pile-up is not affected by the trigger (i.e. it is the same for all primary processes).

High PT Jet

Primary

MB

Warning! This analysis is verypreliminary and not “blessed”.You cannot believe it until it is

“blessed”!


Rick Field – Florida/CDF Page 17

Summary and ConclusionsSummary and Conclusions “Min-Bias” is not well defined. What you

see depends on what you trigger on! Every trigger produces some biases.

Proton AntiProton

“Minumum Bias” Collisions

We have learned a lot about “Min-Bias” at the Tevatron, but we do not know what to expect at the LHC.


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This will depend on the Min-Bias Trigger!

Very preliminary results seem to show that pile-up conspires to help give you what you ask for (i.e. satisfy your “trigger” or your event selection)!

If true this means the pile-up is not the same for all processes. It is process (i.e. trigger) dependent! I must double check my analysis

and get it “blessed” before you can trust what I have shown!

C2CR07-Lake Tahoe February 28, 2007 Rick Field – Florida/CDFPage 1 C2CR07 Rick Field University of...

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