1

ATLAS Status ReportLHCC 17 February 2010

D Charlton (Birmingham), J Boyd (CERN)

Technical Aspects were Covered in Pre-Meeting with Referees Yesterday

Data Taken, Detector & TriggerCalorimetry, Jets & EM objects

Muons and Inner Detector TrackingMinimum Bias Analysis

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First collisions 23 NovemberFirst stable beams 6 December2009 data complete 16 December

Total collision candidate events: 9.2 x 105, ~ 21 μb-1 In stable beam conditions: 5.4 x 105, ~ 12 μb-1 With ID+solenoid on, good data quality: 3.8 x 105, ~ 9 μb-1

Short periods at 2.36 TeV ~ 34k collision events(without stable beam conditions: ID not fully on)

Data-taking efficiency ~90%

Only high pT tracks shown

2009 Collision Data

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Luminosity

Instantaneous luminosity ℒ derived from:Main 2009 measures:

● MBTS two-side coincidence trigger rate● LAr offline event selection (coincidence of

in-time endcap E deposits)Relative measurements also from:

● Dedicated LUCID forward detectors● FCal total energy measurement

Overall ℒ scale uncertainty ~ 30%

Specific luminosity ~ constant during stable fills, as expected

LUCID detector, ±17m from IPLuminosity Cerenkov Integrating Detector

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Luminosity

Instantaneous luminosity ℒ derived from:Main measures:

● MBTS two-side coincidence trigger rate● LAr offline event selection (coincidence of

in-time endcap E deposits)Relative measurements also from:

● Dedicated LUCID forward detectors● FCal total energy measurement

Overall ℒ scale uncertainty ~ 30%

Specific luminosity ~ constant during stable fills, as expected

LUCID detector, ±17m from IPLuminosity Cerenkov Integrating Detector

Overlay: Fcal total E measurement vs time

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Level-1 Trigger

Main 2009 collision trigger: hit in either arm of minimum-bias trigger scintillators (MBTS) 2.09<|η|<3.84

Higher ET triggers also active, eg:

● Lowest threshold jet trigger in 0.4x0.4 ηxф

● Lowest threshold EM trigger, on pairs of 0.1x0.1 ηxф EM cells

L1calo algorithms use 1 GeV bit-step and in 2009 a tight noise suppression

L1 muon trigger active, statistics very low

Offline: anti-kT(0.4)

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High-Level Trigger

Rapid commissioning on collision data:● Run systematically offline on data from 20

November (splashes) onwards● HLT infrastructure run online from the start to

provide event streaming● Real HLT menu run online from 25 November in

pass-through mode, e.g. online beamspot determination available from level-2

● Active event rejection started on 6 December for specific physics analysis requirement

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Active event rejection introduced at the HLT from 6 December● beam pickup level-1 trigger (prescaled by 20)● ID activity required at HLT (~104 rejection)

Provides a sample to measure MBTS efficiency

Further HLT commissioning will be required in 2010 for high-ET object trigger signatures

High-Level Trigger Rejection

Stable beamsL1 BPTX activatedHLT activated

L2 rejection

Sampling 5%

Level-1 collision trigger (MBTS)

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Detector Readiness - Summary

High operational fractions of all detector systems

Minor repairs/maintenance during technical stop:

● Barrel toroid current lead repairs

● Solenoid cooling circuit cleaned

● Maintenance of cooling and gas systems

● Minor detector cabling fixes

● Additional supports installed for future install'n of more small EE muon chambers

CSC muon chamber readout continuing its commissioning ATLAS is ready for 2010 data-taking

● Taking combined cosmic data since 2 February

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Prompt Data Processing and DistributionMB/sper day

Total data throughput through the Grid (Tier0, Tier-1s, Tier-2s)

Beam splashes

First collisions

Nov. Dec.

Cosmics

End data-taking

In steady-state 2010 operation, “calibration loop” will be introduced● express-stream (~5%) reconstructed promptly at Tier-0● wait ~36h for semi-automatic calibration updates before starting bulk reconstruction

● e.g. beamspot, channel maps derived from express processing● reconstructed bulk data available after ~48h, improved quality

Data reconstructed & exported promptly

Typically ~4h from DAQ to Tier-2, including reconstruction time

Excellent performance of Tier sites for data processing and analysis

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Reprocessing

“Fast reprocessing” campaign started just after data-taking ended in December → most plots shown today

● consistent reconstruction code● updated ID alignment constants…

Monte Carlo samples also reprocessed with same reconstruction version

Reprocessing performed at Tier-1 sites according to the ATLAS computing model

A second reprocessing was started on Friday last week → now largely done

● Uses software version for first 2010 data-taking Nine Tier-1s participating

Flexible re-allocation between Tier-1 sites possible

Jobs/day

First collision data reprocessing campaign

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Calorimetry

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LAr CalorimeterRaw cell energy distributions

● simulation quality is very good● full angular range including FCal

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Tile Calorimeter

Raw cell energy distributionsIncludes 2.36 TeV data

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events with2 jets pT> 7 GeV

JetsMBTS trigger (rather open)

Simulation normalised to data

Uncalibrated energies(EM scale)

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Calorimeter Response to Isolated Tracks

Sample of isolated hadrons● 0.5<p

T<10 GeV, |η|<0.8

● No track within ΔR=0.4

E(ΔR<0.1)/pa powerful tool to test

simulation of calorimeter response to single hadrons

Remarkable quality of simulation: very promising for detailed understanding of jet energy calibration

A pay-off from the many years of test-beam studies and detailed comparisons to G4 simulation (models, material, etc)

Uncalibrated energies(EM scale)

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Missing-ET

METyMETx

900 GeV and 2.36 TeV dataResolution of the two components

vs. total ET sum

Uncalibrated energies(EM scale)

EM scaleEM scale EM scale

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Photon candidates with pT>2.5 GeV

● Fraction of energy in first layer, f1

(longitudinal shower development)● Lateral shower width in middle EM

layer, w2

● Average η profile in front-layer strips● Shower width computed over three

cells in first layer ws3

Good description of the data both in depth and transverse profiles

Calorimeter shower shape variables

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Photon candidates with pT>2.5 GeV

● Fraction of energy in first layer, f1

(longitudinal shower development)● Lateral shower width in middle EM

layer, w2

● Average η profile in front-layer strips● Shower width computed over three

cells in first layer ws3

Good description of the data both in depth and transverse profiles

Calorimeter shower shape variables

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Diphoton Mass Distributions

Two photon candidates● p

T(γ)>0.4 GeV, p

T(γγ)>0.9 GeV

● Calibrated cluster energies

Tighter kinematic cuts, including:● p

T(γ)>0.6 GeV, p

T(γγ)>1.5 GeV

Remove clusters with matched tracks

Widths and positions well described by simulation

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Conversions

Reconstructed conversion radius● clean conversion sample● Dalitz decays separable● pay-off for detailed assay of

ID material

Reconstruct here using tracks with hits in silicon detectors

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Conversions

Reconstructed conversion radius● clean conversion sample● Dalitz decays separable● pay-off for detailed assay of

ID material

Reconstruct here using tracks with hits in silicon detectors

π0 mass peak with one converted photon

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Electron Identification

Electron candidates reconstructed from EM clusters with a matched track p

T>0.5 GeV

Track-based distributions well described by sum of hadron and conversion-electrons:

● few pixel hits on tracks● Strong discrimination even at these

low-pT for transition radiation hits

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Electron Identification

Electron candidates reconstructed from EM clusters with a matched track p

T>0.5 GeV

Track-based distributions well described by sum of hadron and conversion-electrons:

● few pixel hits on tracks● Strong discrimination even at these

low-pT for transition radiation hits

Conversions with particle ID on other leg: see onset of transition radiation, as expected

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Electron Identification

Electron candidates reconstructed from EM clusters with a matched track p

T>0.5 GeV

Track-based distributions well described by sum of hadron and conversion-electrons:

● few pixel hits on tracks● Strong discrimination even at these

low-pT for transition radition hits

Looking to the future: starting to test forward electron selection

Beyond tracking acceptance:

2.5 < |η| < 4.9(EMEC, HEC, FCal)

Fraction of energy, fem

,

deposited in EM layers

Mainly photons at high fem

Towards an extended acceptance for Z→ee and

H→eeee…

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EM shower lateral radius

and evolution of its mean value with

track incident angle

Towards Tau IdentificationPure background

sample useful to test modelling of τ ID

variables at low pT

ET

cone (0.1<ΔR<0.2)

ET

cone (ΔR<0.4)

Muon Spectrometer

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Muon candidates – data / MC comparisons

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Muoncandidatesveryforwardandlowmomentumat900GeV–thresholdPT>2.5GeV.

Comparisonofcombinedmuoncandidates(requiringtrackingandmuonspectrometerhits)betweendataandMC.

NiceagreementwithinthelimitedstaKsKcs(50muoncandidates).

The Inner Detector

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The900GeVdataprovideslotsoflowPTtracksoriginaKngfromthecentreofthedetectortocommissiontheInnerDetector.

(overlayofmanyevents)

Tracking - data / MC comparisons ExcellentdescripKonofthedatabytheMC

Numberofpixelhitsontrackversusη/ϕ

NumberofSCThitsontrackversusη/ϕ

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‐CorrectMCforbeamspotposiKonandsize‐SimulaKngthedetectorconfiguraKonasusedindatataking

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x residual [mm]-0.2 -0.1 0 0.1 0.2

nu

mb

er

of

hits o

n t

racks

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000MC perfect alignment

=65%core

m, f!=23core

!m, !=0core!

Collision data alignment

=66%core

m, f!=28core

!m, !=0core!

ATLASPreliminaryPixel Barrel

x residual [mm]-0.2 -0.1 0 0.1 0.2

nu

mb

er

of

hits o

n t

racks

0

500

1000

1500

2000

2500

3000

3500

4000 MC perfect alignment

=83%core

m, f!=20core

!m, !=0core!

Collision data alignment

=79%core

m, f!=22core

!m, !=0core!

ATLASPreliminaryPixel EC

x residual [mm]-0.2 -0.1 0 0.1 0.2

nu

mb

er

of

hits o

n t

racks

0

5000

10000

15000

20000

25000 MC perfect alignment

=75%core

m, f!=36core

!m, !=0core!

Collision data alignment

=73%core

m, f!=41core

!m, !=0core!

ATLASPreliminarySCT Barrel

x residual [mm]-0.2 -0.1 0 0.1 0.2

nu

mb

er

of

hits o

n t

racks

0

2000

4000

6000

8000

10000

12000

14000

16000MC perfect alignment

=77%core

m, f!=38core

!m, !=0core!

Collision data alignment

=74%core

m, f!=42core

!m, !=0core!

ATLASPreliminarySCT EC

Unbiased Hit Residuals after Alignment

PixelBarrel23μm28μm

PixelEC20μm22μm

SCTBarrel36μm41μm

SCTEC38μm42μm

MCperfectalignmentCollisionalignment

TheseresidualstakeintoaccountalignmentandintrinsicresoluKon‐dominatedbymulKplesca\eringinthissample.

Bigimprovementinalignmentwithcollisiondataespeciallyforendcapswherecosmicsarenotsouseful.ApproachingtheperfectlyalignedMCresidualsalready!Finalclusteringstrategyshouldimprovewidthsfurther.

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GooddescripKonofthedatabytheMCfortheimpactparameterdistribuKons.

[mm]0

d-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

Num

ber

of T

racks

0

20

40

60

80

100

120

140

160

180

200

220

310!

Data

ND MC MinBias

[mm]0

d-4 -2 0 2 4N

um

be

r o

f T

racks

310

410

510

610 = 900 GeVs

) [mm]! sin(0z-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

Num

ber

of T

racks

0

20

40

60

80

100

120

140

310!

= 900 GeVs

Data

ND MC MinBias

) [mm]! sin(0

z-10 -5 0 5 10N

um

be

r o

f T

racks

210

310

410

510

610

Impact parameters - data / MC comparisons

Tracking – strange particles

Detailedstudiesoftrackingefficiency,momentumscaleandmomentumresoluKonongoingusingstrangeparKcledecays(KS).

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Pixel dE/dx

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UsingtheparKcleIDfeaturesofthepixeldetector.

Q p [GeV] -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

]2

cm

-1d

E/d

x [

Me

V g

0

1

2

3

4

5

6

7

8

9

10

1

10

210

ATLAS Preliminary

900 GeV Collisions p

K

π

Pixel dE/dx

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dE/dxforprotoncandidatesselectedusingtheΛ(Λ)invariantmass.‐

UsingtheparKcleIDfeaturesofthepixeldetector.

Pixel dE/dx

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dE/dxforprotoncandidatesselectedusingtheΛ(Λ)invariantmass.‐

UsingtheparKcleIDfeaturesofthepixeldetector.

dE/dxdominatedbypionsforsidebands

Event with Two Primary Vertices

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Charged particle multiplicity analysis •  Analysisoverview

–  Useall900GeVdatatakenwithstablebeamsandwithtrigger,trackingdetectors,andsolenoidoperaKonal•  ~9μb‐1ofdatafrom13runstakenbetweenDec6‐15,2009

–  ChoosetomeasureprimarychargedparKclesinthephasespace•  PT>500MeV,|η|<2.5

–  Foranalysispresentedhereweshowfor|η|<2.2aswearesKllworkingonthefinalhighηmaterialcorrecKons

–  Requireeventshaveatleastoneofthesetracksandareconstructedprimaryvertex

–  Select:330kevents/1.9Mtracks•  BeambackgroundesKmatedbylookingateventstakeninunpairedbunchestobe<10‐4of

selectedevents

•  WithinourphasespacewemeasurefullyinclusiveinelasKcdistribuKonstoavoidanymodeldependence–  FacilitatedirectcomparisonswithMCmodels–  Correctforourtrigger,vertexing&trackingefficiencytothehadronlevel–  DonotcorrectfordiffracKonorextrapolateoutsideourphasespace

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FirstpublicpresentaKonoftheseresults!

SelNoVtxN

1 2 3 4 5 6 7 8 9 10 11 12

Trigger

Effic

iency

0.98

0.985

0.99

0.995

1

= 900 GeVsData,

Analysis overview - Trigger •  WeuseadedicatedMinimumBiastrigger

–  ±3.56mfromIP(2.09<|η|<3.84)

–  32scinKllaKngcounters–  Require>0hitsoneitherside(veryinclusive)

•  Measurethetriggerefficiencyfromdata–  Usinganorthogonaltrigger–  BeamcrossingsignalsfrompickupsatL1

–  RequirePixel/SCThitsandaloosetrackinHigherLevelTrigger(looserthananalysisrequirement)

•  TriggerEfficiencywithrespecttotheanalysisselecKonisextremelyhigh

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Nobiasesw.r.ttrackη,PT,…VerylowsystemaKcuncertainty(<0.3%).

MinBiasTriggerScinKllators

No.ofselectedtracks

d0 [mm]

-10 -8 -6 -4 -2 0 2 4 6 8 10

Tra

cks

10

210

310

410

510

SecondariesPrimariesData

d0 [mm]

-10 -8 -6 -4 -2 0 2 4 6 8 10

Tra

cks

10

210

310

410

510

SelNoVtxN

1 2 3 4 5 6 7 8 9 10

Vert

ex E

ffic

iency

0.6

0.7

0.8

0.9

1

= 900 GeVsData,

Analysis Overview – Vertexing & Secondaries •  Requireareconstructedprimaryvertex

–  Require>2tracksinvertex(PT>150MeV)

–  Vertexingefficiencymeasuredfromdata•  SystemaKcuncertainty<0.1%

–  ~100%fornumberofselectedtracks>4

• Toremovesecondariesrequire:• |d0|<1.5mm• |z0sinθ|<1.5mm

• Bothd0,z0w.r.tprimaryvertex• RemainingsecondariesesKmatedusingtailsintheimpactparameterdistribuKontobe~2%ofselectedtracks

No.ofselectedtracks(PT>500MeV)

[GeV]T

p

2 4 6 8 10 12 14 16 18 20

sel

!

0.4

0.5

0.6

0.7

0.8

0.9

1

=900 GeVsND MC MinBias

Systematic uncertainty

!

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

sel

"

0.4

0.5

0.6

0.7

0.8

0.9

1

=900 GeVsND MC MinBias

Systematic uncertainty

•  Tracksforanalysis

–  PT>500MeV

•  WeseeexcellentdescripKonofdatabyMCsowecantakethetrackingefficiencyfromMC

–  NocorrecKonstoefficiency–  Lotsofefforthasgoneintoassessing

systemaKcuncertaintyduetodiscrepanciesbetweendata/MC•  HitmulKpliciKes(seeearlierplots)

•  Individualsystemtrackletefficiencies(data/MC)

•  KSstudiesindata/MC

–  OverallsystemaKc~3%incentralregion

Analysis Overview – Tracking eff.

!-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

reco

"

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

nominal

10%

20%

Analysis Overview – Material studies ‐ Alotofstudiesonunderstandingthedetectormaterialfromdata

‐ Investmentforthefuture‐ MajorityoftrackinginefficiencyfrommaterialinteracKons‐ LargestsystemaKcontrackingefficiencyfromuncertaintyonmaterialinthesimulaKon‐ BenefitfromcarefulweighingofthetrackingdetectorcomponentsbeforeinstallaKon‐ Expectphotonconversionstogiveusadetailedmapofmaterial

‐ Currentlynotenoughdatatogiveusrequiredprecision

MCstudiesofthetrackingefficiencywithuniformscalingupofthematerialby10and20%(inrad.length).

AllchargedparKclesNomaterialinteracKonsinSitracker

TodemonstratesensiKvityoftheefficiencytomaterial

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‐ KSstudiestoconstraintheamountofmaterialinthedetector‐DatafavoursthenominalMCandisinconsistentwiththeMCwith10%,20%addiKonalmaterial‐ ForsystemaKcwecurrentlytakethelargestdifferenceinefficiencybetweennominalMCandthe10%addiKonalmaterialMC

‐ Gives3%systemaKcuncertaintyontrackingefficiency

‐ Otherstudiesgiveconsistentresults

Analysis Overview – Material studies

Radius [mm]10 210

310

mean m

ass [M

eV

]0 S

K

493

494

495

496

497

498

499

500

Beam

Pip

e

Pix

el Layer-

0

Pix

el Layer-

1

Pix

el Layer-

2

SC

T L

ayers

DataMC (nominal)

MC (10%)MC (20%)

| < 1.5!|

=900 GeV)sMinimum Bias Events (

ATLAS Preliminary

)!

/ d

ch

)(dN

ev

(1/N

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5 1" ch

| < 2.5, N! > 500 MeV, | T

p

Data = 900 GeVs

PYTHIA ATLAS MC09PYTHIA ATLAS MC09c

PYTHIA DWPYTHIA Perugia0

PHOJET

ATLAS Preliminary

)!

/ d

ch

)(dN

ev

(1/N

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

!

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

Ratio

0.850.9

0.951

1.051.1

1.15 Data Uncertainties

MC / Data

!

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

Ratio

0.850.9

0.951

1.051.1

1.15

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Analysis overview - Results

‐ dN/dηdistribuKon‐ ShapeagreeswellwithsomePYTHIAtunes‐ ATLASdatashowshighervaluethenallMCs

‐ MCstunedindifferentregionofphasespace

Notesuppressed0ony‐axis

[GeV]T

p1 10

]-2

) [ G

eVT

dp

! /

dchN2

)(d T p

ev N"

1/(2

-910

-810

-710

-610

-510

-410

-310

-210

-1101

10

|<2.4!CMS NSD pp |

|<2.5!ATLAS pp |

= 900 GeVsATLAS Preliminary

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Analysis overview - Results

‐ ComparingPTdistribuKonwithCMSdata

‐ ThankstoCMSformakingthedataavailable(arXiv:1002.0621v1)

‐ ATLAS/CMStreatdiffracKveeventsindifferentways

Summary•  DuringthefirstrunATLAShasbeenworkingverywellfromdetectoroperaKontodataprocessing,distribuKonandanalysis

•  FirstcollisiondatahaveshownthatthedetectorperformanceisexcellentandremarkablywelldescribedbythesimulaKon(inthemostdifficultsovregime)

•  PreliminaryresultsoninclusivemeasurementsofchargedparKclemulKpliciKesat900GeVhavebeenpresented.Apaperwillbesubmi\edsoon.

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ATLASisverygratefultotheLHCteamfortheexcellentmachineperformanceandlooksforwardtohighenergydata!