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Pile-Up in Jets in ATLASBOOST 2013 Sven Menke, MPP Munchen 12-16. Aug 2013, Flagstaff, AZ
on behalf of the ATLAS Collaboration
� Introduction• ATLAS and the LHC
• Pile-Up
• Jets
� Jet Area Method• transverse momentum density ρ
• area based pile-up correction
� Jet Vertex Fraction• track based pile-up suppression
� Jet Shapes� Conclusions
�
ATLAS and the LHC
� LHC: pp collisions at√
s = 7TeV 2010 - 2011 and at√
s = 8TeV sinceMarch 2012
� several upgrade phases (energy and luminosity) are foreseen until 2023:
� end of 2012: ∼ 25 fb−1 pp collisions at 7-8TeV� Phase 0 (until 2019): ∼ 100 fb−1 pp collisions at 13/14TeV� Phase 1 (until 2022): ∼ 300 fb−1 pp collisions at 14TeV� Phase 2 (beyond 2023): ∼ 3000 fb−1 pp collisions at 14TeV
Year2010 2015 2020 2025 2030
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S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 2
The ATLAS Detector
A Torodial LHC ApparatuS: 25m high; 44m long; 7000 t heavy
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 3
The ATLAS Detector � Inner Detector
� Precision Tracking up to |η| < 2.5 in Silicon Detectors (Pixel- andStrip-detectors)
� Immersed in 2TB-field
� 80.4× 106 pixelsensors
� 6.3× 106 siliconstrips
� 351× 103 strawtubes add trackpoints andmeasuretransitionradiation up to|η| < 2.0
� Tracking performance: σpT /pT = 0.038%pT (GeV)⊕ 1.5%
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 4
The ATLAS Detector � Calorimetry
� Calorimeter coverage up to |η| < 4.9
� EM: LAr/Pb Accordion |η| < 1.475/1.375 < |η| < 3.2
� Had Barrel:steel/scintillating tiles|η| . 1.7
� Had Endcap: LAr/Cuparallel plates1.7 . |η| . 3.2
� Forward: LAr/Cu(W)tubular electrodes3.2 . |η| . 4.9
� 3 to 7 samplings
� 188× 103 cells in total
� e/γ: σE/E ' 10%/√
E � jets: σE/E ' 50%/√
E ⊕ 3%
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 5
Pile-Up � important parameters• µ: average number of interactions per
bunch• NPV: number of rec. primary vertices∼ 44%µ + 3 at high µ
• ∆t : bunch distance50 ns in 2012
• signal integration time∼ 500 ns for the LAr
Mean Number of Interactions per Crossing
0 5 10 15 20 25 30 35 40 45
/0.1
]1
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ed L
um
inosity [pb
0
20
40
60
80
100
120
140
160
180 Online LuminosityATLAS
> = 20.7µ, <1Ldt = 21.7 fb∫ = 8 TeV, s
> = 9.1µ, <1Ldt = 5.2 fb∫ = 7 TeV, s
26.7 km ≡ 3560 bunch places each ∆t = 25 ns
Bunch ID
350 400 450 500 550 600 650 700 750 8000
0.2
0.4
0.6
0.8
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Bunch ID
380 400 420 440 460 480 5000
0.2
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Bunch ID
500 1000 1500 2000 2500 3000 35000
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� typical LHC bunch structure in 2012• ∼ 1400 colliding bunch pairs• up to 11 trains ∼ 1000 ns appart• 2-4 sub-trains each ∼ 250 ns• 36 filled bunches
� Pile-up impact depends on bunch crossingNumber (BCID)� up to 10 colliding bunch pairs contribute tosignal
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 6
Pile-Up � Z0 → µµ candidate event with NPV = 25 from 2012
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 7
Jets� jets in ATLAS are made out of “topological clusters”• 3d energy blobs of neighboring calorimeter cells around seed cell
with |E | > 4σ• direct seed neighbors with |E | > 2σ become seeds too• re-clustering of this reduced cell set around local maxima|E| > 2σnoise |E| > 4σnoise 4/2/0 topological clusters
φ cos ×| θ|tan -0.05 0 0.05
φ s
in
×| θ|t
an
-0.05
0
0.05
210
310
410
510
FCal1C
φ cos ×| θ|tan -0.05 0 0.05
φ s
in
×| θ|t
an
-0.05
0
0.05
210
310
410
510
FCal1C
φ cos ×| θ|tan -0.05 0 0.05
φ s
in
×| θ|t
an
-0.05
0
0.05
210
310
410
510
FCal1C
� 2σ cut is removing cells from the signal region� 4σ cut shows seeds for the cluster maker� after clustering all cells in the signal regions are kept� cluster splitter finds hot spots
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 8
Jets � Noise Thresholds� Noise is σelec ⊕ σpile−up
• σelec relevant for no pile-up• σpile−up grows with
õ
� a 20% increase in noise means 20× moreclusters for fixed thresholds!
� thresholds and filter weights are adjusted toexpected maximum 〈µ〉• modified weights slightly increase σelec and decreaseσpile−up from
õ scaling
� average cell-level bias• f(BCID) . O(0.3σpile−up) corrected in 2012 t (s)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
610×
Pile
Up S
ignal fo
r one b
unch tra
in
0.04
0.02
0
0.02
0.04 = 25nsBC t∆
= 50nsBC t∆
t [s]
0.2 0.3 0.4 0.5 0.6 0.7 0.8
610×
LA
r S
ignal [a
.u.]
0.2
0
0.2
0.4
0.6
0.8
1
LAr Ioniziation Current
LAr Readout Signal
bunch train
2010 µ = 0 2012 µ = 30 2022 µ = 200?
|η|
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Tota
l N
ois
e [
MeV
]
10
210
310
410FCal1
FCal2
FCal3
HEC1
HEC2
HEC3
HEC4
PS
EM1
EM2
EM3
Tile1
Tile2
Tile3
Gap
ATLAS
Simulation
= 0µ = 7 TeV, s
|η|
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Tota
l N
ois
e [
MeV
]
10
210
310
410
FCal1
FCal2
FCal3
HEC1
HEC2
HEC3
HEC4
PS
EM1
EM2
EM3
Tile1
Tile2
Tile3
Gap
ATLAS
Simulation
Preliminary
50 ns bunch spacing
= 30µ = 8 TeV, s
|η|
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Tota
l N
ois
e [
MeV
]10
210
310
410
FCal1
FCal2
FCal3
HEC1
HEC2
HEC3
HEC4
PS
EM1
EM2
EM3
Tile1
Tile2
Tile3
Gap
ATLAS Preliminary
Simulation
50 ns bunch spacing
= 200µ = 14 TeV, s
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 9
Jet Area Method ATLAS-CONF-2013-083
� jet area Ajet (arXiv:0802.1188) measures jetsusceptibility to soft particles
2RπJet area/
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
Nor
mal
ised
ent
ries
0
0.1
0.2
0.3
0.4
0.5 R = 0.4tanti-k
R = 0.6tanti-k
Cam/Aach R = 1.2
< 80 GeVjet
T p≤40
LCW Topo-clusterPythia Dijet 2012
ATLAS Simulation Preliminary
[GeV]ρ0 5 10 15 20 25 30
Nor
mal
ised
ent
ries
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
= 6PVN = 10PVN
= 14PVN = 18PVN
ATLAS Simulation Preliminary
< 21⟩µ⟨ ≤20
= 8 TeVsPythia Dijet LCW TopoClusters
η-5 -4 -3 -2 -1 0 1 2 3 4 5
[GeV
]⟩ρ⟨
0
5
10
15
20
25
30 = 1⟩µ⟨ = 8⟩µ⟨ = 16⟩µ⟨ = 26⟩µ⟨
| < 4.9, R = 0.4η|ATLAS Simulation Preliminary
= 8 TeVsPythia Dijet 2012, LCW Topo-clusters
• by adding many soft particles(ghosts) during the jet forming
• Ajet = N jetg /νg
N jetg number of ghosts in jet
νg number density of ghosts in y − φ
� momentum density: ρjet = pjet⊥ /Ajet
� ρ = median{ρjet,i} measures event pile-upactivity (arXiv:0707.1378)• median suppresses bias from hard scatter• event-by-event follows pile-up fluctuations• kT jets with R = 0.4 for |ηjet| < 2.0
� less pile-up jets in forward region
� any jet in the event can then be corrected:pjet,corr⊥ = pjet
⊥ − Ajet × ρ• jet algorithm/size can differ from the one used for ρ
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 10
Jet Area Method � Performance
� dependency of pjet⊥ on in-time pile-up (NPV)
• before and after jet area pile-up correction• in simulated di-jet events for 160 < p⊥ < 320GeV jets vs. |η|• for AntiKt jets with R = 0.4, R = 0.6 and R = 1.0
|η|0 0.5 1 1.5 2 2.5 3 3.5
[GeV
]P
VN∂
Tp∂
-1
0
1
2
3
4
5 < 320 GeVtrueT
p≤160
< 24PV7 < N LCW R = 0.4tAnti-k
= 8 TeVsPythia Dijet, = 21⟩µ⟨
ATLAS Simulation Preliminary
Uncorrected
Corrected
|η|0 0.5 1 1.5 2 2.5 3 3.5
[GeV
]P
VN∂
Tp∂
-1
0
1
2
3
4
5 < 320 GeVtrueT
p≤160
< 24PV7 < N LCW R = 0.6tAnti-k
= 8 TeVsPythia Dijet, = 21⟩µ⟨
ATLAS Simulation Preliminary
Uncorrected
Corrected
|η|0 0.5 1 1.5 2 2.5 3 3.5
[GeV
]P
VN∂
Tp∂
-1
0
1
2
3
4
5 < 320 GeVtrueT
p≤160
< 24PV7 < N LCW R = 1.0tAnti-k
= 8 TeVsPythia Dijet, = 21⟩µ⟨
ATLAS Simulation Preliminary
Uncorrected
Corrected
� 0.5− 2GeV/vtx before correction with large dependency on R
� < 0.2GeV/vtx after jet-area correction� and no dependency on R
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 11
Jet Area Method � Residual Corrections� jet area method reduces mostly pile-up
from additional calorimeter clusters notbelonging to the hard scatter
� inside the jets belonging to the hardscatter the noise suppression is reduced –the pile-up overlaps with the signal
� this can be addressed by a residualcorrection after the jet area basedcorrection• linear fits to preco⊥ − ptrue⊥ vs. NPV (〈µ〉)• most relevant in forward direction
� dependency of pjet⊥ on in-time pile-up: NPV
for fixed 〈µ〉 and out-of-time pile-up: 〈µ〉for fixed NPV
• before, after jet area and after residual correction
• for AntiKt jets with R = 0.4
• small improvement for in-time pile-up
• large improvement in the forward region for out-of-timepile-up
|η|
0 0.5 1 1.5 2 2.5 3 3.5 4
[G
eV
]P
VN∂/
Tp∂
0.4
0.2
0
0.2
0.4
0.6
0.8
1ATLAS Simulation Preliminary
Pythia Dijets 2012
LCW R=0.4t
antik
Before any correctionA subtraction×ρAfter
After residual correction
|η|
0 0.5 1 1.5 2 2.5 3 3.5 4
[G
eV
]⟩
µ⟨∂/T
p∂
0.4
0.2
0
0.2
0.4
0.6
0.8
1ATLAS Simulation Preliminary
Pythia Dijets 2012
LCW R=0.4t
antik
Before any correctionA subtraction×ρAfter
After residual correction
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 12
Jet Area Method � p⊥ Resolution
� p⊥ resolution for jets in simulated di-jetevents• uncorrected
• offset corrected
• jet area corrected
� as a function of in-time pile-up, NPV
� as a function of out-of-time pile-up, 〈µ〉• for 20 GeV < ptrue⊥ < 30 GeV
• |η| < 2.4
� jet area method improves resolutionw.r.t. previous offset method
� still local pile-up fluctuations cause RMSto remain rising with NPV and 〈µ〉
PVN
5 10 15 20 25 30
) [G
eV
]tr
ue
T
pre
co
TR
MS
(p
5
6
7
8
9
10
11
12
13ATLAS Simulation Preliminary
=8 TeVsPythia Dijet
LCW R=0.6tantik
< 30 GeVtrue
T p≤20
| < 2.4η|
uncorrected
) correctionPV
, N⟩µ⟨f(
A correction×ρ
⟩µ⟨
5 10 15 20 25 30 35 40
) [G
eV
]tr
ue
T
pre
co
TR
MS
(p
5
6
7
8
9
10
11
12
13ATLAS Simulation Preliminary
=8 TeVsPythia Dijet
LCW R=0.6tantik
< 30 GeVtrue
T p≤20
| < 2.4η|
uncorrected
) correctionPV
, N⟩µ⟨f(
A correction×ρ
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 13
Jet Area � Jet Multiplicity
� pile-up subtraction with jet area method reduces amount of pile-upinside jets
� but also suppresses jets with pjet⊥ < ρ× Ajet
⟩µ⟨
0 5 10 15 20 25 30 35 40
> 2
0 G
eVT
, p⟩je
tN⟨
2
2.5
3
3.5
4
4.5
5
5.5
6
⟩µ⟨0 5 10 15 20 25 30 35 40
Dat
a/M
C
0.90.95
11.05
1.1
MC, No Correction
Data, No Correction
MC, Area Correction
Data, Area Correction
PreliminaryATLAS
+ jets µµ →Z
LCW R = 0.4tanti-k
2.1≤| η |≤0.0 � jet multiplicity as function of 〈µ〉in Z→ µµ+ jets events beforeand after pile-up correction• pile-up correction improves
data/MC agreement• reduced µ dependency
� still some jets remain due tolocalized pile-up fluctuations
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 14
Jet Vertex Fraction
� track-based observables can help to remove those jets� the Jet Vertex Fraction (JVF)
JVF(jet,PVj) =
∑k
p⊥(trackjetk ,PVj)∑n
∑l
p⊥(trackjetl ,PVn)
• counts fraction of p⊥-sum of alltracks associated to the jet and agiven vertex over thetrack-p⊥-sum for all vertices forthat jet
• properties of JVF assuming onehard vertex w.r.t. this vertex:� 0 for pile-up� 1 for the hard scatter signal� −1 for jets without associatedtracks
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 15
Jet Vertex Fraction � Performance
� Z→ ee + jets events to identify onehard PV with leptons
� check in MC the JVF distributionfor jets from the hard scatter andfrom pile-up
Jets JVF
1 0.5 0 0.5 1
Je
ts/0
.05
210
310
410
510
Pileup jets
Hardscatter jets
ATLAS Simulation Preliminary
ee + jets→Z
, R=0.4, LC+JEStAntik
2.4≤|η<50 GeV, |T
p≤20
Jets JVF
-1 -0.5 0 0.5 1
Jets
/0.0
5
310
410 <15µMC <15µData
<25µ ≤MC 15<25µ ≤Data 15
25≥µMC 25≥µData
ATLAS Preliminary ee + jets→Z
, R=0.4, LCW+JEStAnti-k>20 GeV
T|<2.5, pη|
Jets JVF
-1 -0.5 0 0.5 1
Dat
a/M
C
0.60.8
11.21.4
� compare JVF in data and MC fordifferent µ• for larger µ the peak at JVF = 0
rises• MC reproduces data distributions
quite well
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 16
Jet Vertex Fraction � Performance
⟩µ⟨
0 5 10 15 20 25 30 35 40
> 2
0 G
eVT
, p⟩je
tN⟨
2
2.2
2.4
2.6
2.8
3
3.2
⟩µ⟨0 5 10 15 20 25 30 35 40
Dat
a/M
C
0.960.98
11.021.04
⟩µ⟨0 5 10 15 20 25 30 35 40
Dat
a/M
C
0.960.98
11.021.04
MC, No JVF Cut
Data, No JVF Cut
MC, |JVF| > 0.25
Data, |JVF| > 0.25
MC, |JVF| > 0.50
Data, |JVF| > 0.50
JVF Uncertainty
PreliminaryATLAS
+ jets µµ →Z
LCW+JES R = 0.4tanti-k
2.1≤| η |≤0.0
� use JVF to suppress pile-up:
� jet multiplicity for two |JVF | cuts inZ→ µµ+ jets data and MCcompared to no cut vs. 〈µ〉• |JVF| > 0.25
� reduces pile-up jet alreadysignificantly
• |JVF| > 0.5� the dependency on µ vanishes
• both lead to good data/MCagreement
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 17
Jet Shapes ATLAS-CONF-2013-85
� pile-up subtraction for jet shapes (arXiv:1211.2811) is an extension ofthe jet area correction approach beyond the p⊥ of the jet• first ingredient is the ghost’s 4-vectors
gµ = g⊥[cosφ, sinφ, sinhy , coshy ] with area Ag = 1/νg
• their addition during the jet forming change jet shapes V(ρ, g⊥)slightly
• by varying the ghost’s transverse momentum scale g⊥ the effect onany shape can be evaluated
• and eventually subtracted
� instead of subtracting the average ρ× Ajet from the jet p⊥ thecorresponding subtraction is done for the ghosts• measured shape: V(ρ = ρ0, g⊥ = 0)
• desired shape: V(ρ = 0, g⊥ = 0)
• correction principle: V(ρ+ δ, g⊥) = V(ρ, g⊥ + δ × Ag)
• evaluate: V(ρ = 0, g⊥ = 0) = V(ρ = ρ0, g⊥ = −ρ0 × Ag)
� calculated with first 3 terms of Taylor expansion
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 18
Jet Shapes � Performance� several shapes tested in 2012 data and MC
• splitting scale√
dij = min(p⊥,i , p⊥,j )∆Rij , with the distance
of two subjets ∆Riji = 1, j = 2 for the last two sub-jets in jet forming
• N-subjettinessτN =
∑k p⊥,kmin(∆R1,k , ...,∆RN,k )/
∑k p⊥,k R, close
to 0 if the jet can be described by N or less sub-jets• ratios of τN , τij = τi/τj• energy-energy correlations (EEC) of the jet constituents,
C(β)1 =
(∑i<j p⊥,i p⊥,j (∆Rij )
β)/(∑
k p⊥,k)2
� examples for di-jet events� corrected shapes closer to truth
0 20 40 60 80 100 120 140
Jets
/ 3
.2 G
eV
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
610×
MC: Uncorrected
MC: Corrected
Data: Uncorrected
Data: Corrected
Truth-particle jets
ATLAS Preliminary -1 L dt = 20.3 fb∫=8 TeV, s
dijets (Herwig++) LCW jets with R=1.0
tanti-k
< 300 GeVjet
T p≤200
[GeV]12
d0 20 40 60 80 100 120 140
Data
/ M
C
0.60.8
11.21.4
0 0.1 0.2 0.3 0.4 0.5 0.6
Jets
/ 0
.014
0
10
20
30
40
50
60
70
80
310×
MC: Uncorrected
MC: Corrected
Data: Uncorrected
Data: Corrected
Truth-particle jets
ATLAS Preliminary -1 L dt = 20.3 fb∫=8 TeV, s
dijets (Herwig++) LCW jets with R=1.0
tanti-k
< 300 GeVjet
T p≤200
1τ
0 0.1 0.2 0.3 0.4 0.5 0.6
Data
/ M
C0.60.8
11.21.40 0.2 0.4 0.6 0.8 1 1.2 1.4
Jets
/ 0
.032
0
10
20
30
40
50
60
70
310×
MC: Uncorrected
MC: Corrected
Data: Uncorrected
Data: Corrected
Truth-particle jets
ATLAS Preliminary -1 L dt = 20.3 fb∫=8 TeV, s
dijets (Herwig++) LCW jets with R=1.0
tanti-k
< 300 GeVjet
T p≤200>0.01
1τcorr
21τ
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Data
/ M
C
0.60.8
11.21.4
0 0.05 0.1 0.15 0.2 0.25
Je
ts /
0.0
06
0
0.02
0.04
0.06
0.08
0.1
0.12
0.146
10×
MC: Uncorrected
MC: Corrected
Data: Uncorrected
Data: Corrected
Truth-particle jets
ATLAS Preliminary -1 L dt = 20.3 fb∫=8 TeV, s
dijets (Herwig++) LCW jets with R=1.0
tanti-k
< 300 GeVjet
T p≤200
(3)
1C
0 0.05 0.1 0.15 0.2 0.25
Data
/ M
C
0.60.8
11.21.4
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 19
Jet Shapes � µ Dependence� shapes before and after
correction for different µ
� for di-jet events with500GeV < p⊥ < 600GeV
� correction reduces µdependence and movescorrected data close to MCtruth
[GeV]12d
0 20 40 60 80 100 120 140
Arb
itra
ry N
orm
aliz
atio
n
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
Truth-particle jets
Uncorrected Data
9≤⟩µ⟨≤4
17≤⟩µ⟨≤12
31≤⟩µ⟨≤24
ATLAS Preliminary -1 L dt = 20.3 fb∫=8 TeV, s
dijets (Herwig++) LCW jets with R=1.0
tanti-k
< 600 GeVjet
T p≤500
[GeV]12d
0 20 40 60 80 100 120 140
Arb
itra
ry N
orm
aliz
atio
n
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
Truth-particle jets
Corrected Data
9≤⟩µ⟨≤4
17≤⟩µ⟨≤12
31≤⟩µ⟨≤24
ATLAS Preliminary -1 L dt = 20.3 fb∫=8 TeV, s
dijets (Herwig++) LCW jets with R=1.0
tanti-k
< 600 GeVjet
T p≤500
√
32τ0 0.2 0.4 0.6 0.8 1 1.2 1.4
Arb
itra
ry N
orm
aliz
atio
n
0
0.05
0.1
0.15
0.2
Truth-particle jets
Uncorrected Data
9≤⟩µ⟨≤4
17≤⟩µ⟨≤12
31≤⟩µ⟨≤24
ATLAS Preliminary -1 L dt = 20.3 fb∫=8 TeV, s
dijets (Herwig++) LCW jets with R=1.0
tanti-k
< 600 GeVjet
T p≤500
leading jets > 30 GeV
jetcorr m
> 0.121
τcorr
32τ0 0.2 0.4 0.6 0.8 1 1.2 1.4
Arb
itra
ry N
orm
aliz
atio
n
0
0.05
0.1
0.15
0.2
Truth-particle jets
Corrected Data
9≤⟩µ⟨≤4
17≤⟩µ⟨≤12
31≤⟩µ⟨≤24
ATLAS Preliminary -1 L dt = 20.3 fb∫=8 TeV, s
dijets (Herwig++) LCW jets with R=1.0
tanti-k
< 600 GeVjet
T p≤500
leading jets > 30 GeV
jetcorr m
> 0.121
τcorr
10 15 20 25 30
[G
eV
]⟩
12
d⟨
40
45
50
55
60
65
70MC: Uncorrected
MC: Corrected
Data: Uncorrected
Data: Corrected
Truth-particle jets
ATLAS Preliminary -1 L dt = 20.3 fb∫=8 TeV, s
dijets (Herwig++) LCW jets with R=1.0
tanti-k
< 600 GeVjet
T p≤500
10 15 20 25 30
Data
/ M
C
0.90.95
11.05
1.1
⟩µ⟨10 15 20 25 30
0.80.9
11.11.2 MC Corrected / Truth-particle jets
Data Corrected / Truth-particle jets
√
� average shapes for same events vs. µ
� splitting scale√
d12 as typical example� also for the average shapes thecorrection removes µ dependence andimproves agreement with non pile-up truth
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS � BOOST, 12-16. Aug 2013, Flagstaff, AZ 20
Conclusions
� Pile-up reached in 2012 unprecedented levels in ATLAS• even surpassed design levels at the beginning of some fills
� It will become even larger after the long shutdown� Methods to subtract and to suppress pile-up have been improved for the
2012 data� Corrections:• corrections are mainly based on jet areas and the median transverse
momentum density in the event• works as p⊥ subtraction for jets• and also with ghost subtraction approach for jet shapes
� Suppression:• direct suppression by adapting the calorimeters noise definition• track based suppression with the jet vertex fraction to identify jets
with mostly pile-up� similar methods also used for missing transvere momentum
measurements
S. Menke, MPP Munchen � Pile-Up in Jets in ATLAS BOOST, 12-16. Aug 2013, Flagstaff, AZ 21