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ATLAS Heavy Ion Physics

ATLAS Heavy Ion Physics. Andrzej Olszewski (INP PAN Kraków) for the ATLAS Collaboration. Heavy Ion Studies with the ATLAS Detector. Building of ATLAS detector is progressing well First pp collisions in 2008 LHC physics program includes four weeks of heavy ion physics running per year

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ATLAS Heavy Ion Physics

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  1. ATLAS Heavy Ion Physics Andrzej Olszewski (INP PAN Kraków) for the ATLAS Collaboration

  2. Heavy Ion Studies with the ATLAS Detector • Building of ATLAS detector is progressing well • First pp collisions in 2008 • LHC physics program includes four weeks of heavy ion physics running per year • The primary collision system is Pb+Pb at 5.5. TeV/n,considered also p+Pb and p+p at 5.5 TeV • Heavy Ion beams expected to be commissioned in 2009, first significant heavy ion running in 2009/2010 Andrzej Olszewski, INP, Kraków

  3. RHIC: Energy 200 GeV/n observations • Strong quenching of high transverse momentum particles • Near-Perfect liquid behavior of a collective motion in medium • Collective motion of hadrons generated at parton level • Parton saturation manifested in low multiplicity of final hadrons • Discovery of two new forms of QCD matter • sQGP – strongly coupled Quark-Gluon Plasma • CGC – a saturated gluon initial state (QGP-source) • LHC: Energy 5.5 TeV/n opportunities • Initial energy density ~5 times higher • Lifetime of a quark-gluon plasma much longer • Large rates of hard probes over a broad kinematical range Heavy Ion Collisions at LHC Era of quantitative experimental exploration of thermal QCD Andrzej Olszewski, INP, Kraków

  4. ATLAS Acceptance Muons from , J/, Z0 decays Heavy quarks, quarkonia High pT probes Tracking particles with pT 1.0 GeV/c Global event characterization Unprecedented acceptance for A+A physics both in pT and rapidity, with full azimuthal coverage Andrzej Olszewski, INP, Kraków

  5. ATLAS Heavy Ion Program • Measure dNch/d, dET/d (total+EM) • Characterize gross properties of initial state • Test saturation predictions • Measure charged, inclusive , 0 elliptic flow • Probe early collective motion of (s/t/w)QGP • Measure jets, jet fragmentation, -Jet, di-jet, … • Precision tomography of QGP & its properties • Medium effects in jet quenching • Measure quarkonia production rates via +- decays • Probe Debye screening in medium • Study low x hard processes in p-p, p-A • Study factorization violations, saturation Andrzej Olszewski, INP, Kraków

  6. Nch(|| < 3) dNch/d|=0 3200 (HIJING, no quenching) Histogram – true Nch Points – reconstructed Nch 10% <3% dNch/d|=0 6000 (HIJING, with quenching) Reconstruction errors ~5% Global Event Characterization Day-one measurements: Nch, dNch/d, ET, dET/d, b Tracklets in pixel detector Single Pb+Pb event, b =0-1fm Andrzej Olszewski, INP, Kraków

  7. y’ Fourier expansion of the azimuthal distribution of particles: y x’ Data Type V2 (R) R Hit clusters, Pixel layer 1 0.042 Hit clusters, Pixel layer 2 0.036 Hit clusters, Pixel layer 3 0.032 x EM Barrel Calo 0.029 V2=0.042 b EM EndCap Calo 0.031 Isotropic radial flow EM FCAL Calo 0.036 Anisotropic flow -R HAD FCAL Calo 0.025 v1: directed v2: elliptic Elliptic Flow Generated v2 = 0.05 Distribution of azimuthal angle (v2) vs true reaction plane position, R View of a A+A collision with impact parameter b 0 Correlation of signals with flow Andrzej Olszewski, INP, Kraków

  8. =0 Event Plane Method Flow v2 vs  • Method: v2cos[2(-R)] • Reaction plane estimated from flow • Reconstructed flow is close to theinput 5% flow • Reconstructed v2is flat against , Nch • Remaining difference (~10%) is due to non - flow correlations • and will be accounted for by MC • corrections  Flow v2 vs Nch Nch Andrzej Olszewski, INP, Kraków

  9. Lee-Yang-Zeroes Method Andrzej Olszewski, INP, Kraków

  10. Jet quenching Jet  x  = 0.0028 x 0.1 All too wide for single photons Background Jet Studies Goal is to determine medium properties. • LHC: Copious hard radiation in high Q2 final-state • parton showers • Both an opportunity and a challenge • Understanding jet quenching more difficult • Potentially: time-dependent probe of medium • Resolving hard radiation in jets a must! Fine segmentation of first EM sampling layer helps • Need to measure jet shapes: • Fragmentation function using tracking • Core ET and jet profile using calorimeters • Neutral leading hadrons using EM calorimeters Andrzej Olszewski, INP, Kraków

  11. Jet Energy Resolution Study of different event samples embeddedinto central Pb+Pb HIJING (b=0-2 fm) Results obtained using a standard pp cone algorithm Another possibility is studied − Fast KT Jet Finder Andrzej Olszewski, INP, Kraków

  12. Quarkonia suppression Color screening prevents various ψ, , χ states to be formed when T→Tc to QGP (color screening length < size of resonance) • Measurements of suppression patterns in production of heavy quarkonia states are an ideal thermometer for the plasma • Important to separate (1s) and (2s) states! Andrzej Olszewski, INP, Kraków

  13. +-reconstruction Low momentum muons measured by tagged ID tracks Identified by coincidence with track segment in -spectrometer ||  2 For |η| < 2 (12.5% acc+eff) we expect 15K /month of 106s at L=41026 cm-2 s-1 Andrzej Olszewski, INP, Kraków

  14. J/+-reconstruction ||  2.5, pT  1.5 GeV We expect 8K to 100K J/+- per month of 106s at L=41026 cm-2 s-1 A trigger with muon pT >1.5 GeV is more efficient if torroidal field is reduced for HI runs. The mass resolution is 15% worse but we gain a factor 2-3 in statistics Andrzej Olszewski, INP, Kraków

  15. π0 acceptance Low-x Physics with ZDC • ZDC will be used for centrality and Ultraperipheral(- and -nucleon) Pb+Pb collisions • ZDC reconstructs also neutral particles at very high rapidities:physics processes at very low x, e.g. Color Glass Condensate Andrzej Olszewski, INP, Kraków

  16. Summary • ATLAS Heavy Ion physics program addresses primary physics questions of interest at the LHC • Global observables, including elliptic flow, should be accessible from day-one, even with a very low luminosity (early scheme) • Jet physics is very promising with Atlas unique capabilities of measuring isolated direct photons, separating jets from heavy ion background, measuring jet shapes, hard radiation components • Z+jet, γ+jet, jet-jet correlations • Heavy-quarkonia physics with capabilityto measure and separate and ’,J/ using a specially developed  tagging method • Low-x physics & Ultra-peripheral collisions • Heavy quarks (esp. b physics) Andrzej Olszewski, INP, Kraków

  17. BACKUPS Andrzej Olszewski, INP, Kraków

  18. Summary of Ions The desired species for a systematic HI study are as follow In addition different colliding energies would provide for the study of different energy densities. Andrzej Olszewski, INP, Kraków

  19. Calorimeters Granularity • ATLAS calorimeters covers a large pseudo-rapidity range |h|<5.0 • Both EM and Hadronic calorimeters are segmented longitudinally in several compartments. • The first section of the EM calorimeter is finely segmented in eta strips. EM Barrel and Endcap Hadronic Tile Hadronic LAr Forward Calorimeter Andrzej Olszewski, INP, Kraków

  20. Examples of Calorimeter Performance The above performance was achieved with test beam modules Andrzej Olszewski, INP, Kraków

  21. Detector Occupancies b = 0 – 1fm Calorimeters ( |η|< 3.2 ) Si detectors: Pixels < 2% SCT < 20% TRT: too high, unusable (limited usage for PbPb collisions is under investigation) Muon Chambers: 0.3 – 0.9 hits/chamber (<< pp at 1034 cm-2 s-1) On average: ~ 2 GeV/Tower ~ .3 GeV/Tower Andrzej Olszewski, INP, Kraków

  22. Efficiency Ghosts Fakes Track Reconstruction • Pixel and SCT detectors • Threshold pT 1 GeV • Tracking cuts: • At least 10 hits out of 11(13) available in the barrel (end-caps) • All three pixel hits • At most 1 shared hits • 2/dof > 4 For pT: 1 -10 GeV/c: efficiency ~ 70 % fake rate <1% Momentum resolution ~ 3% (2% - barrel, 4-5% end-caps) Andrzej Olszewski, INP, Kraków

  23. Jet Studies with Tracks • Jets with ET = 100 GeV • Track pT > 3 GeV Momentum component perpendicular to jet axis Fragmentation function dN/djT broader in PbPb than in pp (background fluctuations) PbPb  HIJING-unquenched  pp Andrzej Olszewski, INP, Kraków

  24. Isola d'Elba, HCP 2007 Andrzej Olszewski, INP, Kraków 25 How to measure ? • Global method (A): use tracks fully traversing the -spectrometer, which allows momentum measurement in the standalone -spectrometer, then associate with ID tracks through a global fit. • Tagging method (B): select ID tracks whose extrapolation coincide with a track segment in the -spectrometer. • Advantage of A over B: better p measurement (true for Z0,not J/, ), better purity. • Advantage of B over A: lower p threshold => better acceptance (3 instead of 4 GeV). • For this study, A+B are used, with a priority to method A when possible. Selection of pairs with at least one  from method A. Andrzej Olszewski, INP, Kraków

  25. +-reconstruction || 2 For |η| < 2 (12.5% acc+eff)we expect 15K /month of 106s at L=41026 cm-2 s-1 A di-muon trigger study is under way Andrzej Olszewski, INP, Kraków

  26. J/+-reconstruction ||2.5, pT1.5 GeV We expect 8K to 100K J/+- per month of 106s at L=41026 cm-2 s-1 If a trigger is possible forward with a muon pT >1.5 GeV, we gain a factor 4 in statistics…A solution might be to reduce the toroidal field for HI runs Andrzej Olszewski, INP, Kraków

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