oregon terascale workshop march 8, 2011 rick field – florida/cdf/cmspage 1 northwest terascale...

Oregon Terascale Workshop March 8, 2011

Rick Field – Florida/CDF/CMS

Northwest Terascale WorkshopNorthwest Terascale WorkshopModeling Min-Bias and the Underlying EventModeling Min-Bias and the Underlying Event

Rick FieldUniversity of Florida

UE&MB@CMSUE&MB@CMS

Part 2 How are “min-bias” collisions related to the

“underlying event”.

CMS

ATLAS

University of Oregon March 7-11, 2011

Min-Bias Collisions at the LHC

PYTHIA 6.4 Tune Z1: CMS tune (pT-ordered parton showers and new MPI). Comparisons with the LHC Min-Bias data.

How well did we do at predicting the behavior of “min-bias” collisions at the LHC (900 GeV and 7 TeV)?

New Physics in Min-Bias?? Observation of long-range same-side correlations at 7 TeV.

Strange particle production: A problem for the models?

Proton Proton

“Minimum Bias” Collisions



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

Underlying Event Underlying Event

Initial-State Radiation

Final-State Radiation

“Hard” Hard Core (hard scattering)

Hard Core The “hard core” component

contains both “hard” and “soft” collisions.

“Inelastic Non-Diffractive Component”

NDtot = ELIN



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

Proton Proton

Proton Proton +

Proton Proton

Proton Proton

+

Proton Proton +

+ …

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

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

Majority of “min-bias” events!

Multiple-parton interactions (MPI)!



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/(pT)4→ 1/(pT2+pT0

2)2



Model of Model of NDND

Proton Proton

Proton Proton +

Proton Proton

Proton Proton

+

Proton Proton +

+ …


Allow leading hard scattering to go to zero pT with same cut-off as the MPI!

Model of the inelastic non-diffractive cross section!


Proton Proton

1/(pT)4→ 1/(pT2+pT0

2)2



UE TunesUE Tunes

Proton Proton

Proton Proton +

Proton Proton

Proton Proton

+

Proton Proton +

+ …

“Underlying Event”

“Min-Bias” (ND)

Fit the “underlying event” in a hard

scattering process.

Predict MB (ND)!

1/(pT)4→ 1/(pT2+pT0

2)2

Allow primary hard-scattering to go to pT = 0 with same cut-off!

Single Diffraction

M

Double Diffraction

M1 M2

“Min-Bias” (add single & double diffraction)

Predict MB (IN)!

All of Rick’s tunes (except X2):A, AW, AWT,DW, DWT,

D6, D6T, CW, X1, and Tune Z1,are UE tunes!



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 (non-diffractive cross-section).

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

Normalized to 1

CDF Run 2 Preliminary

Min-Bias 1.96

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

i

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

CDF Run 2 <Nchg>=4.5

py Tune A <Nchg> = 4.3

pyAnoMPI <Nchg> = 2.6


CDF Run 2 Preliminary

Min-Bias 1.96 Normalized to 1

No MPI! Tune A!



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

Comparison of PYTHIA Tune A with the pT distribution of charged particles for “min-bias” collisions at CDF Run 1 (non-diffractive cross-section).

Charged Particle Density

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 2 4 6 8 10 12 14

PT(charged) (GeV/c)

Ch

arg

ed D

ensi

ty d

N/d

df d

PT

(1/

GeV

/c)

Pythia 6.206 Set A

CDF Min-Bias Data

CDF Preliminary

1.8 TeV ||<1

PT(hard) > 0 GeV/c12% of “Min-Bias” events have PT(hard) > 5 GeV/c!

1% of “Min-Bias” events have PT(hard) > 10 GeV/c!

PYTHIA Tune A 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” at the Tevatron!

Ten decades!

pT = 50 GeV/c!



CDF: Charged pCDF: Charged pTT Distribution Distribution

Published CDF data on the pT distribution of charged particles in Min-Bias collisions (ND) at 1.96 TeV compared with PYTHIA Tune A.

Proton AntiProton


Excess events at large pT!

CDF inconsistent with CMS and UA1!

No excess at large pT!

CDF consistent with CMS and UA1!

50 GeV/c!

Erratum November 18, 2010



MB TunesMB Tunes

Proton Proton +

Proton Proton

Proton Proton

+

Proton Proton +

+ …


“Min-Bias” (ND)

Predict the “underlying event” in a hard

scattering process!

Fit MB (ND).

Proton Proton

Most of Peter Skand’s tunes:S320 Perugia 0, S325 Perugia X,

S326 Perugia 6are MB tunes!



MB+UE TunesMB+UE Tunes

Proton Proton

Proton Proton +

Proton Proton

Proton Proton

+

Proton Proton +

+ …


“Min-Bias” (ND)

Fit the “underlying event” in a hard

scattering process!

Fit MB (ND).

Most of Hendrik’s “Professor” tunes: ProQ20, P329

are MB+UE!

The ATLAS AMBT1 Tune is an MB+UE tune, butbecause they include in the fit the ATLAS UE data

with PTmax > 10 GeV/c (big errors) the LHC UE datadoes not have much pull (hence mostly an MB tune!).

Simultaneous fit to both MB & UE



LHC MB Predictions: 900 GeVLHC MB Predictions: 900 GeV

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.

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

e D

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

e D

en

sit

y

UA5

ALICE

pyDW_10mm (3.04)

pyS320_10mm (3.09)

NSD = HC+DD 900 GeV

RDF Preliminary


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

RDF Preliminary

INEL = HC+DD+SD 900 GeV

times 1.11

Charged Particles (all pT)

Off by 11%!



ATLAS INEL dN/dATLAS INEL dN/d

Soft particles!

None of the tunes fit the ATLAS INEL dN/d data with PT > 100 MeV! They all predict too few particles.

The ATLAS Tune AMBT1 was designed to fit the inelastic data for Nchg ≥ 6 with pT > 0.5 GeV/c!

Off by 20-50%!



PYTHIA Tune DWPYTHIA Tune DWCharged Particle Density: dN/d

0

1

2

3

4

5

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

PseudoRapidity

Ch

arg

ed

Par

ticl

e D

ens

ity

900 GeV

pT > 0.15 GeV/c

RDF PreliminaryALICE INEL data

pyDW generator level

pT > 0.5 GeV/c

pT > 1.0 GeV/c

At Least 1 Charged Particle || < 0.8

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.

If one increases the pT the agreement

improves!

Tune DW

Proton Proton


The same thing occurs at 7 TeV! ALICE, ATLAS, and CMS data coming soon.



PYTHIA Tune DWPYTHIA Tune DW

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).


0

1

2

3

4

5

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

PseudoRapidity

Ch

arg

ed

Par

ticl

e D

ens

ity

900 GeV

pT > 0.15 GeV/c



pT > 0.5 GeV/c

pT > 1.0 GeV/c

dashed = ND solid = INEL


Diffraction contributes less at

harder scales!

Tune DW

Proton Proton


Cannot trust PYTHIA 6.2 modeling of diffraction!




0

2

4

6

8

-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

ens

ity

7 TeV

RDF PreliminaryCMS NSD data


dashed = ND solid = NSD

CMS dN/dCMS dN/d

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

Tune DW

All pT

Soft particles!

Proton Proton


Off by 50%!

Okay if the Monte-Carlo does not fitthe data what do we do?

We tune the Monte-Carloto fit the data!

Be careful not to tune away new physics!



CMS dN/dCMS dN/dCharged Particle Density: dN/d

0

2

4

6

8

-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 P

arti

cle

Den

sity

CMS NSD 7 TeV

pyZ1 HC (6.51)

pyZ1 NSD (5.58)

RDF Preliminary

7 TeV


0

2

4

6

8

-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 P

arti

cle

Den

sity

CMS NSD 7 TeV

pyX2 NSD (5.91)

pyZ1 NSD (5.58)CMS NSD all pT

RDF Preliminary

7 TeV

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.

CMSCMS

Tune Z1

Proton Proton


Okay not perfect, but remember we do not know if the DD is correct!



PYTHIA Tune Z1PYTHIA Tune Z1

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.


0

1

2

3

4

5

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

PseudoRapidity

Ch

arg

ed

Par

ticl

e D

ens

ity

900 GeV

pT > 0.15 GeV/c


pyZ1 generator level

pT > 0.5 GeV/c

pT > 1.0 GeV/c


Proton Proton

“Minumum Bias” Collisions

Okay not perfect, but remember we do not know if the SD & DD are correct!



7 TeV dN/d7 TeV dN/d

Corrected data from CMS and ATLAS at 7 TeV for dN/d (pT > PTmin, direct charged particles including leptons with no corrections for SD or DD) with at least one charged particle with pT > PTmin and || < 0.8 for PTmin = 0.5 GeV/c compared with PYTHIA Tune Z1.


1

2

3

4

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

PseudoRapidity

Ch

arg

ed P

arti

cle

Den

sity

7 TeVMB&UE Preliminary CMS INEL data

pyZ1 generator level pT > 0.5 GeV/c


CMS = solid squares ATLAS = solid circle

Charged Particle Density Ratio: dN/d

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

PseudoRapidity

Ch

arg

ed P

arti

cle

Rat

io

MB&UE PreliminaryCorrected INEL data

7 TeV

pT > 0.5 GeV/c


CMS divided by ATLAS (red)

Ratio of the corrected data from CMS and ATLAS at 7 TeV for dN/d (pT > PTmin) with at least one charged particle with pT > PTmin and || < 0.8 for PTmin = 0.5 GeV/c. CMS divided by ATLAS.

Min-Bias Common Plots



7 TeV dN/d7 TeV dN/d

Corrected data from CMS and ATLAS at 7 TeV for dN/d (pT > PTmin, direct charged particles including leptons with no corrections for SD or DD) with at least one charged particle with pT > PTmin and || < 0.8 for PTmin = 1.0 GeV/c compared with PYTHIA Tune Z1

Ratio of the corrected data from CMS and ATLAS at 7 TeV for dN/d (pT > PTmin) with at least one charged particle with pT > PTmin and || < 0.8 for PTmin = 1.0 GeV/c. CMS divided by ATLAS.


0

1

2

3

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

PseudoRapidity

Ch

arg

ed P

arti

cle

Den

sity

7 TeVMB&UE Preliminary CMS INEL data

pyZ1 generator levelpT > 1.0 GeV/c


CMS = solid squares ATLAS = solid circle


0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

PseudoRapidity

Ch

arg

ed P

arti

cle

Rat

io


7 TeV

pT > 1.0 GeV/c






900 GeV dN/d900 GeV dN/d

Corrected data from CMS, ATLAS, and ALICE at 900 GeV for dN/d (pT > PTmin, direct charged particles including leptons with no corrections for SD or DD) with at least one charged particle with pT > PTmin and || < 0.8 for PTmin = 0.5 GeV/c compared with PYTHIA Tune Z1

Ratio of the corrected data from CMS, ATLAS, and ALICE at 900 GeV for dN/d (pT > PTmin) with at least one charged particle with pT > PTmin and || < 0.8 for PTmin = 0.5 GeV/c. CMS divided by ATLAS and CMS divided by ALICE.


1.0

1.2

1.4

1.6

1.8

2.0

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

PseudoRapidity

Ch

arg

ed P

arti

cle

Den

sity

MB&UE PreliminaryCorrected INEL datapyZ1 generator level

900 GeV

pT > 0.5 GeV/c


CMS = solid squares ALICE = open squares ATLAS = solid circle


0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

PseudoRapidity

Ch

arg

ed P

arti

cle

Rat

io


900 GeV

pT > 0.5 GeV/c


CMS divided by ALICE (blue)





900 GeV dN/d900 GeV dN/d

Corrected data from CMS, ATLAS, and ALICE at 900 GeV for dN/d (pT > PTmin, direct charged particles including leptons with no corrections for SD or DD) with at least one charged particle with pT > PTmin and || < 0.8 for PTmin = 1.0 GeV/c compared with PYTHIA Tune Z1

Ratio of the corrected data from CMS, ATLAS, and ALICE at 900 GeV for dN/d (pT > PTmin) with at least one charged particle with pT > PTmin and || < 0.8 for PTmin = 1.0 GeV/c. CMS divided by ATLAS and CMS divided by ALICE.


0.2

0.4

0.6

0.8

1.0

1.2

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

PseudoRapidity

Ch

arg

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arti

cle

Den

sity

MB&UE PreliminaryCorrected INEL datapyZ1 generator level

900 GeV

pT > 1.0 GeV/c


CMS = solid squares ALICE = open squares ATLAS = solid circle


0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

PseudoRapidity

Ch

arg

ed P

arti

cle

Den

sity


900 GeV

pT > 1.0 GeV/c


CMS divided by ALICE (blue)





dN/ddN/d||| < 2.4 (2.5)| < 2.4 (2.5)

Corrected data from CMS at 7 TeV for dN/d (pT > PTmin, direct charged particles including leptons with no corrections for SD or DD) with at least one charged particle with pT > PTmin and || < 2.4 for PTmin = 0.5 GeV/c and 1.0 GeV/c compared with PYTHIA Tune Z1. Also shows the ATLAS data || < 2.5 PTmin = 0.5 GeV/c.

Corrected data from CMS at 900 GeV for dN/d (pT > PTmin) with at least one charged particle with pT > PTmin and || < 2.4 for PTmin = 0.5 GeV/c and 1.0 GeV/c compared with PYTHIA Tune Z1. Also shows the ATLAS data || < 2.5 PTmin = 0.5 GeV/c.


0

1

2

3

4

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

PseudoRapidity

Ch

arg

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arti

cle

Den

sity

7 TeV

pT > 0.5 GeV/c

pT > 1.0 GeV/c

At Least 1 Charged Particle || < 2.4 or 2.5MB&UE Preliminary Corrected INEL datapyZ1 generator level

CMS = solid points ATLAS = open squares


0.0

0.5

1.0

1.5

2.0

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

PseudoRapidity

Ch

arg

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arti

cle

Den

sity

900 GeV

pT > 0.5 GeV/c

pT > 1.0 GeV/c

At Least 1 Charged Particle || < 2.4 or 2.5MB&UE Preliminary Corrected INEL datapyZ1 generator level

CMS = solid points ATLAS = open squares


0.98

0.99

1.00

1.01

1.02

1.03

-5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0

PseudoRapidity

Ch

arg

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arti

cle

Rat

io

MB&UE PreliminarypyZ1 generator level

pT > 0.5 GeV/c

At Least 1 Charged Particle || < 2.4 (2.5)

|| < 2.4 divided by || < 2.5

900 GeV

7 TeV

Less than 1% difference for || < 2.4 and || < 2.5!



Other ComparisonsOther Comparisons 7 TeV 7 TeV

Direct charged particles (including leptons) corrected to the particle level with no corrections for SD or DD.



Interesting RatiosInteresting Ratios

Corrected data from CMS at 7 TeV and 900 GeV for dN/d (pT > PTmin, direct charged particles including leptons with no corrections for SD or DD) with at least one charged particle with pT > PTmin and || < 0.8 for PTmin = 1.0 GeV/c compared with PYTHIA Tune Z1. The plot shows PTmin = 1.0 GeV/c divided by PTmin = 0.5 GeV/c at 900 GeV and 7 TeV.

Charged Particle Ratio: dN/d

0.2

0.3

0.4

0.5

0.6

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

PseudoRapidity

Ch

arg

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arti

cle

Rat

io


pT > 1.0 GeV divided by pT > 0.5 GeV/c

CMS Preliminary Corrected INEL datapyZ1 generator level 7 TeV

900 GeV

Charged Particle Ratio: dN/d

1.0

1.5

2.0

2.5

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

PseudoRapidity

Ch

arg

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Rat

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7 TeV divided by 900 GeV

CMS Preliminary Corrected INEL datapyZ1 generator level pT > 1.0 GeV/c

pT > 0.5 GeV/c

Corrected data from CMS at 7 TeV and 900 GeV for dN/d (pT > PTmin, direct charged particles including leptons with no corrections for SD or DD) with at least one charged particle with pT > PTmin and || < 0.8 for PTmin = 1.0 GeV/c compared with PYTHIA Tune Z1. The plot shows 7 TeV divided by 900 GeV for PTmin = 0.5 GeV/c and 1.0 GeV/c.

Measure of the pT dependence! Measure of the energy dependence!



NSD Multiplicity DistributionNSD Multiplicity Distribution

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.


1.0E-04

1.0E-03

1.0E-02

1.0E-01

0 20 40 60 80 100


Pro

ba

bil

ity

Charged Particles (all PT, ||<2.0)

RDF Preliminarydata CMS NSD


7 TeV

900 GeV

CMS

Tune Z1

Difficult to produce enough events with large multiplicity!

Proton Proton

“Minumum Bias” Collisions

Okay not perfect!But not that bad!



MB & UEMB & UE

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.


1.0E-04

1.0E-03

1.0E-02

1.0E-01

0 20 40 60 80 100


Pro

ba

bil

ity

Charged Particles (all PT, ||<2.0)

RDF Preliminarydata CMS NSD


7 TeV

900 GeV

"Transverse" Charged Particle Multiplicity

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


Pro

bab

ilit

y

CMS Preliminarydata uncorrected

pyZ1 + SIM

Normalized to 1


PT(chgjet#1) > 3 GeV/c

900 GeV 7 TeV

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).

CMS CMSTune Z1

Tune Z1

“Min-Bias”


Difficult to produce enough events with large multiplicity!

Difficult to produce enough events with large “transverse” multiplicity at low

hard scale!



MB & UEMB & UE

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.

CMS

Tune Z1

Charged Particle Multiplicity

1.0E-05

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bab

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CMS PreliminaryTune Z1

Normalized to 1

Charged Particles (||<2.0)

7 TeV

Underlying Event"Transverse" Region

pT > 0.5 GeV/cPT(chgjet#1) > 20 GeV/c

Min-BiasNSD All pT

Amazing what we are asking the Monte-Carlo models to fit!

Charged Particle Multiplicity

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CMS PreliminaryTune Z1

Normalized to 1

Charged Particles (||<2.0)

7 TeV

Underlying Event"Transverse" Region

pT > 0.5 GeV/cPT(chgjet#1) > 20 GeV/c

Min-BiasNSD All pT



New Physics in “Min-Bias”?New Physics in “Min-Bias”?

Proton Proton +

Proton Proton

Proton Proton

+

Proton Proton +

+ …



The Inelastic Cross Section

CMS Two-Particle Correlations at 7 TeV.



Two Particle Angular CorrelationsTwo Particle Angular Correlations

Correlation, R, is ~(S-B)/B.

Proton Proton


Signal, S, is two particles in the same event.

Background, B, is two particles in two different events.



Two Particle Angular CorrelationsTwo Particle Angular Correlations

Bose-EinsteinCMS “min-bias” 7 TeV

y-axis

x-axis

Jet#1 Jet#2

Two Particles in Same Jet

y-axis

x-axis

Jet#1 Jet#2

Two Particles in Two Jets



High Multiplicity at 7 TeVHigh Multiplicity at 7 TeV

Proton Proton


Select Events with High Multiplicity



Two Particle Angular CorrelationsTwo Particle Angular CorrelationsAverage “Min-Bias” High Multiplicity “Min-Bias”

y-axis

x-axis

Jet#1 Jet#2

Two Particles in Same Jet

Lots of jets at high multiplicity!



Two Particle Angular CorrelationsTwo Particle Angular CorrelationsAverage “Min-Bias” High Multiplicity “Min-Bias”

y-axis

x-axis

Jet#1 Jet#2

Two Particles in Two Jets



Long-Range Same-Side Long-Range Same-Side CorrelationsCorrelations

Not there in PYTHIA8!

High Multiplicity “Min-Bias”High Multiplicity “Min-Bias”

Also not there in PYTHIA 6 and HERWIG++!



Correlation in Heavy Ion Correlation in Heavy Ion CollisionsCollisions

Long range correlations expected in “collective flow” in heavy ion collisions.



Correlation in Heavy Ion Correlation in Heavy Ion CollisionsCollisions

Long-range “Ridge”-like structure in at f ≈ 0!



Proton-Proton vs Au-AuProton-Proton vs Au-Au

I am not ready to jump on the quark-gluon plasma bandwagon quite yet!

Proton-Proton Collisions 7 TeV Gold-Gold Collisions 200 GeV

QGP



Jet-Jet CorrelationsJet-Jet CorrelationsAre the “leading-log” or “modified leading-log” QCD Monte-Carlo Models missing

an important QCD correlation?

Proton Proton

y-axis

z-axis

x-axis

Leading Jet

Initial or Final-State Radiation

The leading jet and the incident protons form a plane (yz-plane in the figure). This is the plane of the hard scattering.

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 f ≈ 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?



Jet-Jet CorrelationsJet-Jet Correlations

Proton Proton

y-axis

z-axis

x-axis

Leading Jet

Initial or Final-State Radiation

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?

??



High Multiplicity at 7 TeVHigh Multiplicity at 7 TeV

Proton Proton


Select Events with High Multiplicity

We need to study the structure of the high multiplicity min-bias events! Does high multiplicity imply high PT

jets? Are there a class of “soft” high multiplicity events? If so what is the source of these events?



Strange Particle ProductionStrange Particle Production

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.

ALICE preliminarystat. error only

PhojetPythia ATLAS-CSCPythia D6TPythia Perugia-0

Factor of 2!

Jan Fiete Grosse-OetringhausLPCC MB&UE Meeting

September 2010



Charged Particle dN/dCharged Particle dN/d 7 TeV 7 TeVCharged Particle Density: dN/d

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Charged particle (direct, including leptons) pseudorapidity distribution, dN/d (ND), at 7 TeV for all pT, pT > 0.5 GeV/c, pT > 1.0 GeV/c, pT > 2.0 GeV/c, and pT > 3.0 GeV/c from Tune Z1.


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Charged particle (direct, including leptons) pseudorapidity distribution, dN/d, at 7 TeV for all pT from Tune Z1. Shows the individual contributions from ND, SD, DD, and INEL = ND + SD + DD.



Charged Particle dN/dCharged Particle dN/d 7 TeV 7 TeVCharged Particle Ratio: Flavor/All Charged

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PYTHIA Tune Z1 7 TeV INEL

Charged particle ratios versus at 7 TeV (ND all pT). Shows (+ +-)/(all charged), (K+ + K-)/(all charged), proton/(all charged), antiproton/(all charged), and sum/(all charged), where sum = + + - + K+ + K- + p + pbar.

Charged particle ratios versus at 7 TeV (INEL = ND + SD +DD all pT). Shows (+ +-)/(all charged), (K+ + K-)/(all charged), proton/(all charged), antiproton/(all charged), and sum/(all charged), where sum = + + - + K+ + K- + p + pbar.



Charged Particle dN/dCharged Particle dN/d 7 TeV 7 TeVCharged Particle Ratio: Flavor/All Charged

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Charged particle ratios versus at 7 TeV (ND pT > 0.5 GeV/c). Shows (+ +-)/(all charged), (K+ + K-)/(all charged), proton/(all charged), antiproton/(all charged), and sum/(all charged), where sum = + + - + K+ + K- + p + pbar.


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Charged particle ratios versus at 7 TeV (ND pT > 1.0 GeV/c). Shows (+ +-)/(all charged), (K+ + K-)/(all charged), proton/(all charged), antiproton/(all charged), and sum/(all charged), where sum = + + - + K+ + K- + p + pbar.


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Charged Particle RatiosCharged Particle Ratios

Charged particle ratios versus pT at 7 TeV (ND || < 2). Shows (+ +-)/(all charged), (K+ + K-)/(all charged), (p + pbar)/(all charged), and sum/(all charged), where sum = + + - + K+ + K- + p + pbar.


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PYTHIA Tune Z1 7 TeV ND || < 0.8

Charged particle ratios versus pT at 7 TeV (ND || < 0.8). Shows (+ +-)/(all charged), (K+ + K-)/(all charged), (p + pbar)/(all charged), and sum/(all charged), where sum = + + - + K+ + K- + p + pbar.

Charged particle ratios versus pT at 7 TeV (INEL || < 0.8). Shows (+ +-)/(all charged), (K+ + K-)/(all charged), (p + pbar)/(all charged), and sum/(all charged), where sum = + + - + K+ + K- + p + pbar.


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Strange Particle Ratio: (K+ + K-)/(+ + -)

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PYTHIA Tune Z1 7 TeV || < 0.8

ND = open squares INEL = black dots



Charged Particle RatiosCharged Particle Ratios

Charged particle (direct, including leptons) pseudorapidity distribution, dN/d (ND all pT), at 7 TeV and 900 GeV from Tune Z1.


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PYTHIA Tune Z1 900 GeV ND

Charged particle ratios versus at 900 GeV (ND all pT). Shows (+ +-)/(all charged), (K+ + K-)/(all charged), proton/(all charged), antiproton/(all charged), and sum/(all charged), where sum = + + - + K+ + K- + p + pbar.


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A lot more strange mesons at large pT than predicted by the Monte-Carlo Models and a different shape of the curve!


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Plateau!



PYTHIA Fragmentation PYTHIA Fragmentation ParametersParameters

PARJ(1) : (D = 0.10) is P(qq)/P(q), the suppression of diquark-antidiquark pair production in the colour field, compared with quark–antiquark production.

PARJ(2) : (D = 0.30) is P(s)/P(u), the suppression of s quark pair production in the field compared with u or d pair production.

PARJ(3) : (D = 0.4) is (P(us)/P(ud))/(P(s)/P(d)), the extra suppression of strange diquark production compared with the normal suppression of strange quarks.

PARJ(4) : (D = 0.05) is (1/3)P(ud1)/P(ud0), the suppression of spin 1 diquarks compared with spin 0 ones (excluding the factor 3 coming from spin counting).

Look at the affect of changing PARJ(2)

from 0.3 to 0.5!



Charged Particle RatiosCharged Particle RatiosCharged Particle Density: dN/d

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s/u = 0.3 (default)

s/u = 0.5


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PYTHIA Tune Z1 7 TeV ND s/u = 0.5

Charged particle (direct, including leptons) pseudorapidity distribution, dN/d (ND all pT), at 7 TeV for PARJ(2) = s/u = 0.3 (default) and PARJ(2) = s/u = 0.5 from Tune Z1.

Charged particle ratios versus at 7 TeV (ND all pT) with PARJ(2) = s/u = 0.3 (default) and PARJ(2) = s/u = 0.5 from Tune Z1. Shows (+ +-)/(all charged), (K+ + K-)/(all charged), proton/(all charged), antiproton/(all charged), and sum/(all charged), where sum = + + - + K+ + K- + p + pbar.


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Charged particle ratios versus pT at 7 TeV (ND || < 0.8) with PARJ(2) = s/u = 0.3 (default) and PARJ(2) = s/u = 0.5 from Tune Z1. Shows (+ +-)/(all charged), (K+ + K-)/(all charged), (p + pbar)/(all charged), and sum/(all charged), where sum = + + - + K+ + K- + p + pbar.


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A lot more strange mesons at large pT than predicted by the Monte-Carlo Models and a different shape of the curve!

Not good!

Plateau!



Protons & AntiprotonsProtons & Antiprotons

ALICE preliminarystat. error only

PhojetPythia ATLAS-CSCPythia D6TPythia Perugia-0

Jan Fiete Grosse-OetringhausLPCC MB&UE Meeting

September 2010

Tune Z1 (ND) does not get this right either and this curve does not depend on PARJ(2)!

Proton+AntiP Ratio: (p+pbar)/(+ + -)

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““Transverse” Particle RatiosTransverse” Particle RatiosLeading Particle Ratio: Flavor/All Charged

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PTmax Direction

f

“Toward”

“Transverse” “Transverse”

“Away”

Leading charged particle ratios versus pT at 7 TeV (|| < 2.0). Shows (+ +-)/(all charged), (K+ + K-)/(all charged), (p + pbar)/(all charged), and sum/(all charged), where sum = + + - + K+ + K- + p + pbar.

"Transverse" Ratio: Flavor/All Charged

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Charged particle ratios in the “transverse” region (pT > 0.5 GeV/c, || < 2.0) versus the leading charged particle, PTmax, at 7 TeV. Shows (+ +-)/(all charged), (K+ + K-)/(all charged), (p + pbar)/(all charged), and sum/(all charged), where sum = + + - + K+ + K- + p + pbar.



SummarySummary

We need a better understanding and modeling of diffraction!

So far no luck at fitting the min-bias charged kaon to charged pion ratio. Increasing s/u produces more strange particles, but the shape of the curve versus pT is different! But I am just getting started at this!

PARJ(2)

protons

antiprotonss

Kaons

Diffraction

Also not getting the protons + antiprotons right. Changing PARJ(2) does nothing here! Must check out some of the other parameters

The Monte-Carlo models are constrained by LEP data. Must make sure that I do not destroy the agreement with the LEP data!



Min-Bias SummaryMin-Bias Summary

We need a better understanding and modeling of diffraction!

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!

PARP(90)Color

Connections

PARP(82)

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 “min-bias” 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! Also not getting the protons + antiprotons right! The Monte-Carlo models are constrained by LEP data.

oregon terascale workshop march 8, 2011 rick field – florida/cdf/cmspage 1 northwest terascale...

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