Status of ATLAS and preparation for the Pb-Pb runQM 2009, Knoxville

Jiří Dolejší Charles University Prague

for the ATLAS collaboration

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Performance & experience 2008

Single beam splash event on September 10th, 2008: particles from a beam hitting the collimator 140 m from ATLAS.

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Performance & experience 2008

Muon detectors

Calorimeters

Inner detector

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Inner detector2008: Cosmic run from September 14th:

Pixels: •Efficiency of about 98.4%•Optolinks tuned to 80Mbit/s

SCT: •99% of SCT Barrel and 97% of SCT EndCaps were operated•99% of all modules operational•99.8% strips alive

TRT:•97% of channels reading out•~99% of electronics working•2.9 M tracks collected in TRT

Repairs, prospects for 2009:•Cooling repairs & improvements•Restart during May 09

SCT

Pixels

TRT

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Inner detector – performance illustrations:

Display of cosmic ray event going through the SCT and pixel detector (notice low noise)

Alignment of upper and lower halves of cosmic tracks expressed in difference of d0 – distance to vertex. Tracks are selected to have pT > 2 GeV. Tracks are required to have a hit in the Pixel B layer, 3 Pixel hits and in total 7 Silicon hits.

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CalorimetersLiquid argon calorimeter:Successful operation in 2008: •97% power supplies OK•99.92% channels workingProspects for 2009:•Power supplies repaired, monitoring improved•Everything will be in place and ready to go by the end of AprilTile calorimeter:•Power supplies & controls: 99.2% OK•98.6% cells alive •Calibration ready or being commissioned, cell equalization within a few %. Tasks for 2009:•Further tuning of the 137Cs cell inter-calibration, monitoring of PMT stability, data quality monitoring.

Energy summed over 100 splash events in EM Presampler

ATLAS Preliminary

Liquid argon calorimeter- illustration of performance:

The 8-fold structure induced by the toroid endcap is clearly visible at large radius (layers S1, S2, S3).

The 16-fold structure is due to additional matter and shielding at low radius (Presampler PS).

The sum of 100 splash events from Sept. 10th

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up

down

ATLAS Preliminary

Tile calorimeter - illustration of performance:

This picture shows the 8-fold structure in of the beam splash events recorded on the 10th of September. The structure is due to the End Cap toroid material in front of TileCal for particles coming from the C-side. The up -down asymmetry is also due to the material in front of the detector.

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up

down

ATLAS Preliminary

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Tile calorimeter – test beam results: The response to electrons –

Tilecal EM scale factor (1.050±0.003 pC/GeV)

The energy resolution for pions impinging on the calorimeter at |η| =0.35, as a function of the beam energy. Data (full circles) are in reasonable agreement ‚with MC simulation results (open squares).

222

)%2.07.5()%9.09.52(

beamEE

ATLAS Preliminary

ATLAS Preliminary

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Monitored Drift Tubes•98.5% chambers operational•98.3% channels working•Aim: 99.8% after shutdown

Muon system

MDT, CSC: precision tracking;

TGC, RPC: trigger, coordinate

Cosmic muon map reconstructed by off-line RPC standalone muon monitoring projected on surface (y=81m).

ATLAS Preliminary

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Forward detectors

LUCID (Luminosity CerenkovIntegrating Detector) at 17 m

2009: ZDC (Zero Degree Calorimeter ) at 140 m,

2010: ALFA (Absolute Lumi-nosity for ATLAS) at 240 m

LUCID is a running detector in advanced status of commissioning; nevertheless, some consolidation and repairs are ongoing during the shutdown period

LUCID signal, Sept. 10, 2008

Important for heavy ions, significant contribution from HI

group

Data acquisition – cosmic events

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ATLAS Preliminary

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Heavy Ion Physics with the ATLAS Detector at the LHC

Some selected results from the forthcoming Physics Performance Report

More in parallel talks:

•Jets by Nathan Grau•Quarkonia & Z0 by Marzia Rosati•Direct photons by Mark Baker

ATLAS calorimetry - full azimuthal acceptance

Tracking in 2T solenoid

MuonsPhotons

Jets

100 GeV jet depositing energy

Overview of ATLAS acceptance

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Tracking

Tracking efficiency and fake rate in || < 1 extracted from a sample of central(b=2 fm) HIJING events produced with quenching effects turned off in the ATLAS tracking system.Acceptable efficiency of about 70%, negligible fake rate above 1 GeV/c

Top: Tracking efficiency as a function of pseudorapidity for tracks with 3 < pT < 8 GeV extracted from the same central sample of events. Bottom: Fake rate as function of pseudo-rapidity for the same tracks as above.Negligible dependence on

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ATLAS Preliminary ATLAS Preliminary

Elliptic Flow

Transverse momentum dependence of the reconstructed v2: •from the event plane method (squares)•two-particle correlations (stars)•the Lee-Yang Zeros method (triangles)•input flow as extrapolated from RHIC data (line)Thanks to complete azimuthal coverage we can well reproduce the input, different methods offer sensitivity to non-flow effects

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ATLAS PreliminaryPb+Pb s = 5.5 TeV/A

b = 2.3 fm b=7.0 fm b=10.7 fm

Jets … elucidating the jet energy loss

Parallel talk by Nathan Grau

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Fragmentation function: D(z)

Reliable reconstruction of D(z):Reconstructed tracks with pT > 2 GeV matching calorimeter jets

The scale of possible modifications of fragmentation function – comparison of PYTHIA and PYQUENWe can measure jet quenching of the size simulated by PYQUEN

ATLAS PreliminaryATLAS Preliminary

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Dimuon Measurements … quarkonia, Z0

Parallel talk by Marzia Rosati

Background muons from open charm and beauty decays, from hadron in-flight decays before absorption in the calorimeter and from punch-through hadrons which can be reconstructed as muons.

Error bars show statistical errors only.

Di-muon invariant mass distribution as expected for one month of data, taking into account acceptance and efficiency, for decay muons in the barrel region only (|| < 1). 19 000 in one month running at nominal luminosity (0.5 nb-1)

ATLAS Preliminary

Mass Resolution 120 MeV, sufficient the separate states

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Direct Photons & Photon-Jet Correlations

Parallel talk by Mark D. Baker

The performance of the shower shape cuts and isolation cuts on PYTHIA di-jets embedded into b = 2 fm Pb+Pb events:

Background greatly suppressed!

ATLAS Preliminary

ATLAS Preliminary

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Summary

•ATLAS is fully operational, recorded several hundred million cosmic events

•Ongoing activities enable further detector improvements, calibration, refinement of monitoring, software tools

•Extensive preparations for Pb+Pb program show a promissing performance of ATLAS for heavy ion beams.

•We will participate in initial p+p data taking to get reference data for heavy ion program and to tune the analysis techniques.

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Sources of further information

ATLAS Public Results

https://twiki.cern.ch/twiki/bin/view/Atlas/AtlasResults

The ATLAS Experiment at the CERN Large Hadron Collider

The ATLAS Collaboration, G Aad et al 2008 JINST 3 S08003