recent results on ue and double parton scattering with the ... · introduction underlying event...

Introduction Underlying Event DPI Summary

Recent results on UE and double partonscattering with the ATLAS detector

Ben Wynne

ATLAS CollaborationUniversity of Edinburgh

ISMD 2013

1/19


Introduction

Presenting two ATLAS analyses:• The underlying event in jet production• Measuring DPI in W-boson events with 2 jets

2/19


ATLAS

Different subdetectors relevant for identification of particular objects:• Tracking detectors |η| < 2.5 — charged particles• Calorimeters |η| < 4.8 — charged and neutral particles, jet and electron

identification• Muon tracker |η| < 2.7

3/19


Dataset

Using data collected in 2010:•√

s = 7 TeV• Integrated luminosity 36 pb−1

• Low pileup (increasing over the run to ∼2 interactions perbunch-crossing)

4/19


Underlying Event

5/19


Underlying Event in Jet Production

• Classic definition of eventtopology, oriented by the highestpT jet in the event

• Anti-kT jets with R = 0.4,pT > 20 GeV, |y | < 2.8

• Inclusive selection requires oneor more jets

• Exclusive selection requiresexactly two jets with pT balance

• Most and least active sides of thetransverse region dubbed transmax/min

Δφ−Δφ

toward|Δφ |< 60◦

away|Δφ |> 120◦

transverse60◦ < |Δφ |< 120◦

transverse60◦ < |Δφ |< 120◦

6/19 ATLAS leading jet UE https://cds.cern.ch/record/1497185

https://cds.cern.ch/record/1497185


Leading Jet UE - MC Models

All data distibutions corrected to the particle level, thencompared with the following MC models:• Pythia 6 AUET2B• Pythia 6 DW• Pythia 8 AU2• Herwig + Jimmy AUET2• Herwig++ UE7-2• Alpgen + Herwig + Jimmy AUET1




Leading Jet UE - Charged Particle ΣpT

Inclusive Exclusive

210

> [G

eV]

φdη/d

Tp∑2

<d

0

0.5

1

1.5

2

2.5

3

3.5 Data (2010)PYTHIA6 AUET2B CTEQ6L1PYTHIA6 DWPythia8 AU2 CT10HERWIG/JIMMY AUET2 LO**Herwig++ UE7-2 MRST LO**Alpgen + HERWIG/JIMMY AUET1

| < 2.8)jet

> 20 GeV, |yT

jet 1 (p≥ jetN

| < 2.5chη > 500 MeV, |Tchp

Transverse regionInclusive jet

ATLAS Preliminary = 7 TeVs, -1 = 37 pbintL

[GeV]Tleadp

20 30 40 100 200 300

MC

/Dat

a

0.80.9

11.11.2

210

> [G

eV]

φdη/d

Tp∑2

<d

0

0.5

1

1.5

2

2.5

3 Data (2010)PYTHIA6 AUET2B CTEQ6L1PYTHIA6 DWPythia8 AU2 CT10HERWIG/JIMMY AUET2 LO**Herwig++ UE7-2 MRST LO**Alpgen + HERWIG/JIMMY AUET1

| < 2.8)jet

> 20 GeV, |yT

jet = 2 (pjetN

| > 2.5jet

φ∆/2, |lead > pTsubp

| < 2.5chη > 500 MeV, |Tchp

Transverse regionExclusive dijet


[GeV]Tleadp

20 30 40 100 200 300

MC

/Dat

a

0.80.9

11.11.2

Inclusive selection shows rising activity with lead jet pT, but theexclusive selection gives flat behaviour




Leading Jet UE - Charged Particle Multiplicity

Inclusive Exclusive

210

>φdη/d

chN2

<d

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8


| < 2.8)jet

> 20 GeV, |yT

jet 1 (p≥ jetN

| < 2.5chη > 500 MeV, |Tchp



[GeV]Tleadp

20 30 40 100 200 300

MC

/Dat

a

0.80.9

11.11.2

210

>φdη/d

chN2

<d

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8


| < 2.8)jet

> 20 GeV, |yT

jet = 2 (pjetN

| > 2.5jet


| < 2.5chη > 500 MeV, |Tchp

Transverse regionExclusive dijet


[GeV]Tleadp

20 30 40 100 200 300

MC

/Dat

a

0.80.9

11.11.2

Similar behaviour to ΣpT — note the exclusive profile showsfalling activity with lead jet pT

The exclusive di-jet requirement may veto jets from MPI




Leading Jet UE - Charged and Neutral Particle ΣET

Inclusive Exclusive

210

> [G

eV]

φdη/d

TE

∑2<

d

0

1

2

3

4

5

6


| < 2.8)jet

> 20 GeV, |yT

jet 1 (p≥ jetN

| < 2.5ch,neuη > 500(200) MeV, |ch(neu)pTransverse region

Inclusive jet


[GeV]Tleadp

20 30 40 100 200 300

MC

/Dat

a

0.80.9

11.11.2

210

> [G

eV]

φdη/d

TE

∑2<

d

0

1

2

3

4

5


| < 2.8)jet

> 20 GeV, |yT

jet = 2 (pjetN

| > 2.5jet



Exclusive dijet


[GeV]Tleadp

20 30 40 100 200 300

MC

/Dat

a

0.80.9

11.11.2

Using the ATLAS calorimeters allows the inclusion of neutralparticles

Similar UE behaviour as charged particle ΣpT




Leading Jet UE - Charged and Neutral Particle ΣET

Inclusive Exclusive

210

> [G

eV]

φdη/d

TE

∑2<

d

0

1

2

3

4

5Data (2010)PYTHIA6 AUET2B CTEQ6L1PYTHIA6 DWPythia8 AU2 CT10HERWIG/JIMMY AUET2 LO**Herwig++ UE7-2 MRST LO**Alpgen + HERWIG/JIMMY AUET1

| < 2.8)jet

> 20 GeV, |yT

jet 1 (p≥ jetN


Inclusive jet


[GeV]Tleadp

20 30 40 100 200 300

MC

/Dat

a

0.80.9

11.11.2

210

> [G

eV]

φdη/d

TE

∑2<

d

0

1

2

3

4

5Data (2010)PYTHIA6 AUET2B CTEQ6L1PYTHIA6 DWPythia8 AU2 CT10HERWIG/JIMMY AUET2 LO**Herwig++ UE7-2 MRST LO**Alpgen + HERWIG/JIMMY AUET1

| < 2.8)jet

> 20 GeV, |yT

jet = 2 (pjetN

| > 2.5jet



Exclusive dijet


[GeV]Tleadp

20 30 40 100 200 300

MC

/Dat

a

0.80.9

11.11.2

The calorimeters also give greater acceptance, with |η| < 4.8

Including these regions does not dramatically change the databehaviour, but MC performance is less good




Leading Jet UE - Trans Max/Min

ΣpT Nch

210

> [G

eV]

φdη/d

Tp∑2

<d

-2-10123456

Data (2010) - trans-maxPYTHIA6 AUET2B CTEQ6L1 - trans-maxData (2010) - trans-minPYTHIA6 AUET2B CTEQ6L1 - trans-minData (2010) - trans-diffPYTHIA6 AUET2B CTEQ6L1 - trans-diff

| < 2.8)jet

> 20 GeV, |yT

jet 1 (p≥ jetN

| < 2.5chη > 500 MeV, |TchpInclusive jet


[GeV]Tleadp

20 30 40 100 200 300

MC

/Dat

a

0.80.9

11.11.2

210

>φdη/d

chN2

<d

-0.5

0

0.5

1

1.5

2

2.5

3 Data (2010) - trans-maxPYTHIA6 AUET2B CTEQ6L1 - trans-maxData (2010) - trans-minPYTHIA6 AUET2B CTEQ6L1 - trans-minData (2010) - trans-diffPYTHIA6 AUET2B CTEQ6L1 - trans-diff

| < 2.8)jet

> 20 GeV, |yT

jet 1 (p≥ jetN

| < 2.5chη > 500 MeV, |TchpInclusive jet


[GeV]Tleadp

20 30 40 100 200 300

MC

/Dat

a

0.80.9

11.11.2

Inclusive trans min results similar to exclusive selection,suggesting the pure MPI activity is independent of the hardprocess scale (when collisions are central)




Leading Jet UE - Mean pT vs Multiplicity

Inclusive

0 5 10 15 20 25 30 35 40

> [G

eV]

T<

mea

n p

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8 Data (2010)PYTHIA6 AUET2B CTEQ6L1PYTHIA6 DWPythia8 AU2 CT10HERWIG/JIMMY AUET2 LO**Herwig++ UE7-2 MRST LO**Alpgen + HERWIG/JIMMY AUET1

| < 2.8)jet

> 20 GeV, |yT

jet 1 (p≥ jetN

| < 2.5chη > 500 MeV, |Tchp



chN0 5 10 15 20 25 30 35 40

MC

/Dat

a

0.80.9

11.11.2

The behaviour of this distribution has been well established inpast experiments, but note that even recent MC tunes can stillget it wrong




Double Parton Interactions

14/19


DPI in W→ lν + 2 jets

W+

ν

ℓ̄

qg

q

g

νq

ℓ̄

W+

⊗

q̄

vs

Compare the rate of production of W + 2 associated jets (left)with rate of double parton interactions producing a W-boson inone case and a dijet in the other (right)

15/19 ATLAS double parton interactions in W→ lν NewJ.Phys.15(2013)033038

New J. Phys. 15 (2013) 033038


Observables

In DPI events the dijet system should conserve momentumindependently of the W-boson decay, so examine the totaltransverse momentum of the two jets:

∆jets = |~p1T + ~p2

T|

To remove dependence on the jet energy scale, this observableis normalised:

∆njets =

|~p1T + ~p2

T||~p1

T|+ |~p2T|

∆njets is the observable used for fitting, but ∆jets distributions are

retained for cross-checks


New J. Phys. 15 (2013) 033038


Templates

njetsΔ

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Events/0.03

0

0.02

0.04

0.06

0.08

0.1

0.12=7 TeVsdata - physics BG,νWl

Fit distributionA+H+J template Atemplate B

ATLAS

-1Ldt=36 pb∫

[GeV]jetsΔ0 20 40 60 80 100 120 140

Events/3GeV

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07=7 TeVsdata - physics BG,νWl

Fit distributionA+H+J template Atemplate B

ATLAS

-1Ldt=36 pb∫

Fit the distributions of these two observables using two templates:• Template A: W + 2 jets, using Alpgen + Herwig + Jimmy• Template B: Data sample of di-jet events

Extract the fraction of DPI events: f (D)DP = 0.08± 0.01(stat.)± 0.02(sys.)


New J. Phys. 15 (2013) 033038


Effective cross-section

[GeV]s

210 310 410

[mb]

eff

σ

02468

10121416182022

AFS (4 jets - no errors given)UA2 (4 jets - lower limit)CDF (4 jets)

+ 3 jets)γCDF (+ 3 jets)γD0 (

ATLAS (W + 2 jets)

ATLAS

The extracted value for the effective DPI cross-section is

σeff(7 TeV) = 15± 3(stat.)+5−3(sys.) mb

This is comparable to values measured at other centre-of-massenergies at other experiments


New J. Phys. 15 (2013) 033038


Summary

Analysis of low-pileup 2010 data still yielding interesting results:

• The underlying event in leading jet events has beenmeasured

• Exclusive di-jet selection showing flat/falling UE activity• High |η| acceptance (potential for MC improvement)• Results up to 800 GeV leading jet pT

• The effective cross-section for DPI has been measured inevents containing both a W-boson decay and 2 jets

• σeff(7 TeV) = 15± 3(stat.)+5−3(sys.) mb

• Comparable to previous results at lower√

s

19/19

Appendix

For Further Reading I

The underlying event in jet events at 7 TeV with the ATLASexperimenthttps://cds.cern.ch/record/1497185

Measurement of hard double-parton interactions in W(→ lν) + 2 jet events at

√s = 7 TeV with the ATLAS

detectorNew J. Phys. 15 (2013) 033038https://cds.cern.ch/record/1510534

20/19



Appendix

Backup

21/19

Appendix

W + 2 jets unfolded

njetsΔ

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Eve

nts

/0.0

3

0

0.02

0.04

0.06

0.08

0.1

0.12=7 TeVsunfolded data,νWl

Fit distributionA+H+J particle-level template APYTHIA particle-level template B

ATLAS

-1Ldt=36 pb∫

[GeV]jetsΔ0 20 40 60 80 100 120 140

Eve

nts

/3G

eV

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07=7 TeVsunfolded data,νWl

Fit distributionA+H+J particle-level template APYTHIA particle-level template B

ATLAS

-1Ldt=36 pb∫

Unfolded data and MC templates at particle level

22/19

recent results on ue and double parton scattering with the ... · introduction underlying event...

Documents