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The Heavy Ion Physics Program with ATLAS at the LHC

Nathan Grau

Columbia University, Nevis LabsOn behalf of the ATLAS Heavy Ion Working Group

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The ATLAS HI Working Group

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Outline

ATLAS Detector and Performance Up-to-date software, geometry of the as-built

detector Physics Program

Global observables, jet physics, quarkonia, and low-x physics

Something to take away: ATLAS ability for isolated photon identification

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The physics of HIC at the LHC Build on the strong base of work done at RHIC Strongly-coupled QGP (sQGP)

Azimuthal anisotropy is large at high-pT 0, K, , , J/, e, etc.

Single particle suppression is large at high-pT 0, K, , , J/, e, etc.

Two-particle azimuthal correlation suppression and shape modification Near-side and Away-side

Color Glass Condensate Slow rise of dN/d with energy in Au+Au Single particle suppression at forward rapidity in d+Au Searched for mono-jet production at forward rapidity in d+Au

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The ATLAS Detector

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The ATLAS Detector: Coverage

Full azimuthal acceptance in all detectors Unprecedented pseudorapidity coverage for A+A

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Global Observables Particle and Energy density: dN/d, dET/d

Extend root-s dependence of dN/d: test CGC

Azimuthal Anisotropy: v2, etc. What happens to v2/ at higher root-s?

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Tracking with the Inner Detector Inner detector has full

azimuthal coverage within ||<2.5 and consists of Pixel detector Silicon tracking

detector Transition radiation

tracker (occupancy too large for central Pb+Pb?)

Results from p+p tracking algorithm optimized for HI environment.

Reconstructed tracks with ||<1

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Tracking to lower pT

Work extending pT reach important for p+p and A+A. dN/d in both cases v2 in A+A

Ongoing with high energy and heavy ion participation.

Efficiency: red/blackFake rate: red/green

Preliminary

Minimum bias p+p

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dN/d via Tracklets a la PHOBOS

1. Truth tracks2. “B-Layer” Hits3. Layer 1 Hits4. Matched Tracklets

Measurement of track density

flat with truth density

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Jet Physics with ATLAS See W. Holzmann’s talk for all of the details

STAR, PRL 93 (2004) 252301

interm. pT interm. pT correlationscorrelations

high pT correlationshigh pT correlations

RRAAAA

-h correlations-h correlations

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ATLAS CalorimetryHadronic Barrel

Hadronic EndCap

EM EndCap

EM Barrel

Forward

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Longitudinal Segmentation: 3-d JetsSampling of a 100 GeV jet (no background)

1

2 3

4

5 6

Note the region is 0.8x0.8:a typical jet size

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Photon Isolation and Identification

Barrel EMCal front layer finely segmented in for vectoring H events and 0 rejection.

Example of jet embedded in central b=2 fm HIJING event.

Jet

Background

Single slice 0.1 rad

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Photon Isolation and Identification

Barrel EMCal front layer finely segmented in for vectoring H events and 0 rejection.

Example of jet embedded in central b=2 fm HIJING event.

Jet

Background

All too wide for single photons

Single slice 0.1 rad

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Photon Isolation and Identification

EM

Layer

1 E

T

(GeV

)

Single slice 0.1 rad

-jet event embedded

Barrel EMCal front layer finely segmented in for vectoring H events and 0 rejection.

Example of jet embedded in central b=2 fm HIJING event.

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/0 Separation Variables

Left: fractional energy deposited outside the cluster core in the strip layer

Right: Energy of a 2nd maximum peak in the strip layer

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/0 Separation

Rejection of 0 with appropriate cuts on previous variables

Efficiency in p+p is ~90%, flat with ET and

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Jet Position Resolutions

From standard R=0.4 seeded cone algorithm

Results are important for studies of hard radiation in jets (sub-jets).

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Jet Energy Resolution

Energy resolution as a function of ET and Important for studies of jet RAA, fragmentation

functions, etc.

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Azimuthal Anisotropy from Calorimeters Flow afterburner on HIJING events based on

Poskanzer and Voloshin [PRC 58 (1998) 1671] Simulated “physical” flow based on RHIC data

v2(pT,,centrality) Azimuthal ET distribution in different barrel EM

calorimeter layers (||<1.5)Presampler Strip layer (front) Middle Layer Back Layer

0.003 x 0.1 0.025 x 0.025 0.05 x 0.025 x

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Reaction Plane Resolution

In measuring the physical v2 you must correct by the resolution: v2 = v2

meas/res Resolution measurement from the Barrel (||<1.5), Endcap

(3.2<||<1.5), and Forward (4.9 < || < 3.2) calorimeters Extremely good resolution

Comparison to true RP Comparison of subevents

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Heavy Flavor Physics

Lattice Calculations indicates bounds states melt at different temperatures

But suppression of J/ similar between SPS and RHIC…

SPSRHIC

A. Bickley Hard Probes 2006

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Muon Spectrometer

Coverage up to ||<2.7 Low background because the spectrometer is

behind the calorimeters

Muon Chamber # hits/chamber

Barrel Inner (=0.2) 0.3

Middle (=0.2) 0.5

Outer (=0.2) 0.5

End Cap (=2.0) 0.9

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Heavy Flavor Bound State Measurements

Both charm and bottom states should be accessible to through the +- decay channel

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Resolution and Acceptance for Good mass

resolution Large acceptance Loss of efficiency

near ~0 due to material.

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Possiblity of c

c measurements important because of feeddown to J/. Couple the J/ measurements with the photon isolation

capabilities of the calorimeter should make the c measurement possible.

Measurements of many states necessary to pin down temperature.

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Zero Degree Calorimeter Contribution from the Heavy Ion effort Single highly segmented EMCal module and hadronic

calorimeter modules Expected response (for 1-7 TeV neutrons)

E/E ~ 15-20%, x,y ~ 1-2 mm

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Low-x Measurements from ZDC Measurement of

forward mesons in the decay channel.

The 0 in the ZDC at very low x – possibly into the saturation region.

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Summary of Physics Covered in this talk:

Bulk observables dN/d, v2

Inclusive jets and γ+jets Spectra, hard radiation

Quarkonia (Υ and J/ψ) Possibility of c

Low-x physics For the future:

Ultraperipheral collisions Heavy quarks (esp. b physics) Z+jet, jet-jet correlations

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ATLAS Heavy Ion Working Group A. Ajitanand10, A. Angerami3, G. Atoian11, M. Baker1, P. Chung10, B. Cole3, R. Debbe1,

A. Denisov5, J. Dolejsi2, N. Grau3, J. Hill7, W. Holzmann3, V. Issakov11, J. Jia10, H. Kasper11, R. Lacey10, A. Lebedev7, M. Leltchouk3, A. Moraes1, R. Nouicer1, A.

Olszewski6, A. Poblaguev11, V. Pozdnyakov8, M. Rosati7, L. Rosselet4, M. Spousta2, P. Steinberg1, H. Takai1, S. Timoshenko9, B. Toczek6, A. Trzupek6, F. Videbaek1, S.

White1, B. Wosiek6, K. Wozniak6, M. Zeller11

1 Brookhaven National Laboratory, USA2 Charles University, Prague

3 Columbia Unversity, Nevis Laboratories, USA4 University of Geneva, Switzerland

5 IHEP, Russia6 IFJ PAN, Krakow, Poland

7 Iowa State University, USA8 JINR, Dubna, Russia

9 MePHI, Moscow, Russia10 Chemistry Department, Stony Brook University, USA

11 Yale University, USA