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Letter of Intent for Heavy I on Physics with the ATLAS Detector ATLAS Collaboration

Letter of Intent for Heavy I on Physics with the ATLAS Detector ATLAS Collaboration. Heavy Ion Physics at RHIC. Evidence that possibly two new forms of QCD matter have been discovered:. sQGP – strongly coupled Quark-Gluon Plasma CGC – a saturated gluon initial state (QGP-source).

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Letter of Intent for Heavy I on Physics with the ATLAS Detector ATLAS Collaboration

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  1. Letter of IntentforHeavy Ion Physics with the ATLAS DetectorATLAS Collaboration LHCC, May 12, 2004

  2. Heavy Ion Physics at RHIC Evidence that possibly two new forms of QCD matter have been discovered: • sQGP – strongly coupled Quark-Gluon Plasma • CGC – a saturated gluon initial state (QGP-source) • AuAu @sNN = 200 GeV • dN/dη in AuAu @sNN = 200 GeV • high-pT suppression vs. y in dAu @sNN = 200 GeV Workshop organized by RIKEN BNL Research Center „New Discoveries at RHIC – The Strongly Interactive QGP” May 14-15, 2004 at BNL LHCC, May 12, 2004

  3. Empirical evidence for QGP at RHIC Jet quenchingin AuAu as predicted by pQCD (unquenching in dAu) Bulk matter collectivity • hydrodynamic limit is reached • matter produced is equlibrated • consistent with QCD EoS (lattice) • matter behaves like an ideal fluid PRL91,(2003) excellent probes for verifying QCD ! Hard processes  LHCC, May 12, 2004

  4. From RHIC to LHC sNN : 200 GeV 5,500 GeV Which of the RHIC concepts will still be valid at LHC?? Super-hot QCD – Will we see a weakly coupled QGP?? • Initial state fully saturated (CGC) • Enormous increase of high-pT processes over RHIC • Plentiful heavy quarks (b,c) LHC RHIC SPS LHCC, May 12, 2004

  5. ATLAS A Superb Detector for High-pT Studies LHCC, May 12, 2004

  6. ATLAS as a Heavy Ion Detector 1. High Resolution Calorimeters • Hermetic coverage up to || < 4.9 • Fine granularity (with longitudinal segmentation) High pT probes (jets, jet shapes, jets correlations) • Large Acceptance Muon Spectrometer • Coverage up to || < 2.7 Muons from , J/, Z0 decays • Inner Detector (Si Tracker) • Large coverage up to || < 2.5 • Finely segmented pixel and strip detectors • Good momentum resolution Tracking particles with pT 1.0 GeV/c Heavy quarks(b), quarkonium suppression(J/,, ’) 2.+ 3. 1.& 3. Global event characterization (dNch/dη, dET/dη, flow), jets LHCC, May 12, 2004

  7. Studies of the Detector Performance • Constraint:No modifications to the detector, with the exception • of trigger software and forward instrumentation • Simulations:HIJING event generator, dNch/dη = 3200 • Full (GEANT-3) simulations of the detector response • Large event samples: • |η|< 3.2 impact parameter range: b = 0 - 15fm • |η|< 5.1 impact parameter range: b = 10 - 30fm LHCC, May 12, 2004

  8. Central Pb+Pb Collision (b<1fm) • About 75,000 stable particles • ~ 40,000 particles in ||  3 • CPU – 6 h per central event (800MHz) • Event size 50MB (without TRT) Nch(|η|0.5) LHCC, May 12, 2004

  9. 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) In average: ~ 2 GeV/Tower ~ .3 GeV/Tower LHCC, May 12, 2004

  10. Single Pb+Pb event, b =0-1fm 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 • Constrain model prediction; indispensable for all physics analyses LHCC, May 12, 2004

  11. Collision Centrality Use 3 detector systems to obtain impact parameter: Pixel&SCT, EM-Cal HAD-Cal Resolution of the estimated impact parameter ~1fm for all three systems. LHCC, May 12, 2004

  12. Track Reconstruction • Pixel and SCT detectors • pT threshold of 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 ~5% Momentum resolution ~ 3% (2% - barrel, 4-5% end-caps) LHCC, May 12, 2004

  13. Heavy Quark Production Motivation: Heavy quarks may radiate less energy in the dense medium (dead-cone effect) than light quarks. • Open beauty: • Use ppWHlbb events overlayed • on HIJING bckground • Search for a displaced vertex in the • Inner Detector Rejection factor against u-jets ~ 100 for b-tagging efficiency of 25% Should be improved when combined with soft-muon tagging in the Muon Spec. LHCC, May 12, 2004

  14. Jet Reconstruction • Sliding window algorithm,    = 0.4  0.4, • after subtracting the average pedestal of (50 11) GeV • Accepted if ET(window) > 40 GeV Di-jet event from PYTHIA in pp: pThard=55GeV Di-jet reconstructed in PbPb Di-jet embedded in PbPb before pedestal subtraction Di-jet embedded in PbPb after pedestal subtraction LHCC, May 12, 2004

  15. Reconstruction – 280 GeV jet HIJING jet (counted as fake) HIJING jet LHCC, May 12, 2004

  16. Jet Reconstruction Jet energy resolution Correct plot is needed! Angular resolution for 70 GeV jets (~2  resolution in pp) Efficiency > 80% for ET >40GeV Energy resolution xx% at ET= 40 GeV LHCC, May 12, 2004

  17. Jet Rates For a 106s run with Pb+Pb at L=41026 cm-2 s-1 we expect in |η| < 2.5: And also: ~106 + jet events with ET > 50 GeV ~500 Z0() + jets with ET > 40 GeV LHCC, May 12, 2004

  18. Jet Studies Goal is to determine medium properties. Jet quenching But, most energy is radiated INSIDE cone vacuum Salgado & Wiedemann hep-ph/0310079 in medium • Need to measure jet shapes: • Fragmentation function using tracking • Core ET and jet profile using calorimeters • Neutral leading hadrons using EM calorimeters LHCC, May 12, 2004

  19. Jet Studies with Tracks • Jets with ET = 100 GeV • Cone radius of 0.4 • Track pT > 3 GeV Fragmentation function Momentum component perpendicular to jet axis PbPb  HIJING-unquenched  pp dN/djT broader in PbPb than in pp Promising, but a lot of more work is needed! LHCC, May 12, 2004

  20. ETcore Measurements Energy deposited in a narrow cone around the jet axis: R < 0.11 (HADCal), R < 0.07 (EMCal) pp pp PbPb pp More work is needed to minimize effect of background fluctuations. <ETcore> sensitive to 10% change in ETjet LHCC, May 12, 2004

  21. Isolated Neutral Hadrons Select jets that have an isolated neutral cluster along the axis (~1% of the total jet sample) pp pp pp Further studies of large samples of jets embedded into PbPb events are needed. Cluster ET sensitive to small change in ETjet LHCC, May 12, 2004

  22. Quarkonia Suppression Color screening prevents various ψ, , χ states to be formed when T→Tcfor the PT to QGP (color screening length < size of resonance) QGP thermometer Upsilon family(1s) (2s) (3s) Binding energies (GeV) 1.1 0.54 0.2 Dissociation at the temperature ~2.5Tc ~0.9Tc ~0.7Tc Important to separate (1s) and (2s)! LHCC, May 12, 2004

  23. Upsilon Reconstruction   +– • Overlay  decayson top of HIJING events. • Use combined info from ID and μ-Spectrometer • Single Upsilons • HIJING background • Half ’s from c, b decays, half from π, K decays for pT>3 GeV. • Background rejection: • 2 cut • geometrical cut • pT cut. ,: differences between ID and µ-spectrometer tracks after back-extrapolation tothe vertex for the best 2 association. LHCC, May 12, 2004

  24. Upsilon Reconstruction Mass resolution vs. |η| of decayed ’s Acceptance & efficiency vs. |η| (used to estimate rate and S/B) A compromise has to be found between acceptance (overall rate of events) and mass resolution to clearly separate upsilon states. LHCC, May 12, 2004

  25. Upsilon Reconstruction Barrel only (|| <1) || <1 || <2.5 Acceptance 4.9% 14.1% +efficiency Resolution 123 MeV(147 MeV) S/B 1.3(0.5) Purity 94-99%(91-95%) Are all these numbers correct??? For a 106s run with Pb+Pb at L=41026 cm-2 s-1 we expect 104 events in |η| < 1.2 (6% acc+eff) LHCC, May 12, 2004

  26. J/ Reconstruction J/  +– - a study is under way • Large cross-section • σmass=53 MeV =>easy separation of J/ψ and ψ’ • good for J/ψ with pT > 4-5 GeV Full pT analysis is only possible in forward andbackward regions, but there thebackgroundis largest. LHCC, May 12, 2004

  27. Trigger and DAQ Interaction rate of 8 kHz for L = 1027 cm-2 s –1 Event size ~ 5 MB for central PbPb Data rate to storage ~300 Hz  MB  Output rate (after HLT) ~ 50 Hz for central events Minimum-bias trigger (LVL1) – use forward calorimeters (FCAL) - Triggering on the total ET in FCAL with a Trigger Tower threshold of 0.5 GeV selects 95% of the inelatsic cross-section. Triggering on events with b < 10 fm - use full ATLAS Calorimetry High Level Triggers (ATLAS T/DAQ) - jet trigger, di-muon trigger Jet rate ~ 40 Hz for ET threshold = 50 GeV ~ 0.1 Hz for ET threshold = 100 GeV LHCC, May 12, 2004

  28. Ultra-Peripheral Nuclear Collisions • High-energy - and -nucleon collisions • Measurements of hadron structure at energies > HERA • Di-jet and heavy quark production • Tagging of UPC using Zero Degree Calorimeters • (ongoing work on design and integration with the accelerator instrumentation) Proton-Nucleus Collisions • Link between pp and AA physics • Study of the nuclear modification of the gluon distribution at low xF. • Study of the jet fragmentation function modification • Full detector capabilities will be available. • L~1030 translates to about 1MHz interaction rate (compare to 40 MHz in pp) LHCC, May 12, 2004

  29. Summary • The Letter of Intent represents a first look into a heavy-ion • physics with the ATLAS detector. • The high granularity and large coverage of the calorimeter system, external muon spectrometer and tracking capabilities of the inner detector allow for a comprehensive study of high-pT phenomena and heavy quark production in heavy-ion collisions. • Studies of the detector performance are going on: • Optimization of algorithms for high-multiplicity environment • Study of the flow effects and its impact on the jet reconstruction • Study of pA collisions These first results already demonstrate a very good potential of the ATLAS experiment for heavy-ion studies and ensure its valuable and significant contribution to the LHC’s heavy-ion physics programme. LHCC, May 12, 2004

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