Heavy Ion Physics with the ATLAS Detector for the ATLAS Collaboration

1. Heavy Ion Physics with the ATLAS Detectorforthe ATLAS Collaboration Sebastian White Brookhaven National Lab Winter Workshop on Nuclear Dynamics

2. Jet Physics with ATLAS Strikman,Vogt &SNW -Gyulassy & Vitev Winter Workshop on Nuclear Dynamics

3. Studies of the Detector Performance • Using existing ATLAS detector and (mostly) algorithms developed for pp @L=1034 (~24 interactions @40Mhz) • Simulations:HIJING event generator, dNch/dh = 3200 • Full GEANT simulations of the detector response • Large event samples: • |h|< 3.2 impact parameter range: b = 0 - 15fm (27,000 events) • |h|< 5.1 impact parameter range: b = 10 - 30fm (5,000 events) Winter Workshop on Nuclear Dynamics

4. Simulation DataFlow Winter Workshop on Nuclear Dynamics

5. ATLAS Inner Tracking (to |h|<2.5 ) Pixel+SCT=11 layers(2-3+8) TRT=39 layers Winter Workshop on Nuclear Dynamics

6. Tracking Reconstruction Full ATLAS Simulation -2.5<h<2.5 Tile Calorimeter threshold cut will have excellent rejection. Detailed reconstruction with pTthr = 300 MeV/c Track 10 of 11 planes. Most fakes in forward directions. Winter Workshop on Nuclear Dynamics

7. Tracking Resolution Full ATLAS Simulation Plot shows the average reconstruction resolution. dpt/pt=2% in barrel, larger in endcaps -2.5<h<2.5 Winter Workshop on Nuclear Dynamics

8. State of the art EM+Had calorimeter! -Highly segmented. -4 depth segments -200k EM channels. -LAr to |h|<4.9 Winter Workshop on Nuclear Dynamics

9. EM Calorimeter Segmentation Winter Workshop on Nuclear Dynamics

10. Jet Reconstruction Energy in 0.1x0.1 tower in the EM and HAD calorimeter for |h|<3.2. Most of the energy is in the EM calorimeter due to soft particles ranging out. Hadronic calorimeter is relatively quiet even in b=0 HIJING events! Energy in 0.1x0.1 tower as function of h. Full ATLAS Simulation Winter Workshop on Nuclear Dynamics

11. 55 GeV Jet PYTHIA + HIJING overlayed event. PYTHIA only After average background subtraction For lower jet energies we found that it is easier to find jets if the first EM compartment is not included. Later the energy from the 1st compartment is recovered. The Result ! Winter Workshop on Nuclear Dynamics Full ATLAS Simulation

12. Jet Reconstruction Efficiency Full ATLAS Simulation Very promising results with high jet reconstruction efficiency! A “good” jet is defined as the one that finds a match in the generated event within a cone radius of 0.2. Fakes are the ones that do not fulfill the requirement. Fakes include HIJING jets. Track matching may reduce the number of “real” fakes. Winter Workshop on Nuclear Dynamics

13. Jet Reconstruction sh,f=.045,.035 Winter Workshop on Nuclear Dynamics

14. Jet Energy Resolution Excellent jet energy resolution. Energy resolution is close to a high luminosity L~1034 proton-proton run. This fact also means that large contingent of high energy ATLAS participants are interested in working on these issues. Winter Workshop on Nuclear Dynamics Full ATLAS Simulation

15. Weight=7000T diameter=22m Width=44m Winter Workshop on Nuclear Dynamics

16. Quarkonia Suppression Color screening prevents formation of various  states when T>Tcfor the phase transition 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)! Winter Workshop on Nuclear Dynamics

17. Upsilon Reconstruction   +– • Overlay  decays on top of HIJING events. • Use combined info from ID and m-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 to the vertex for the best 2 association. Winter Workshop on Nuclear Dynamics

18. Upsilon Reconstruction Barrel only (|| <1) A compromise has to be found between acceptance and mass resolution to clearly separate upsilon states. || <1 || <2.5 Acceptance 4.9% 14.1% +efficiency Resolution 123 MeV147 MeV S/B 1.30.5 Purity 94-99%91-95% For a 106s run with Pb+Pb at L=41026 cm-2 s-1 we expect 104 events in |h| < 1.2 (6% acc+eff). - a study is under way (mass =53 MeV). J/  +– Winter Workshop on Nuclear Dynamics

19. Diffractive Physics with ATLAS • ATLAS Coverage • Forward Instrumentation • ATLAS reach in jj and gj Pro-E model of ZDC for ATLAS and full simulation of Energy response

20. Lessons from Run IV:PHENIX J/y and high mass e+e- Photoproduction PHENIX implemented trigger for small cross section UPC physics ~10 M events collected (seeG.Baur et al. Nucl-th/03070310) Winter Workshop on Nuclear Dynamics

21. Probing small x structure in the Nucleus with gN->jets, heavy flavor. di-jet photoproduction-> parton distributions,x2 by g with momentum fraction, x1 4pt2/s=x1*x2 <y>~ -1/2*ln(x1/x2) Signature: rapidity gap in g direction(FCAL veto) x1 x2 ATLAS coverage to |h|<5 units. Pt ~2 Gev “rapidity gap” threshold Analogous upc interactions and gap structure diffractive Non-diffractive Winter Workshop on Nuclear Dynamics

22. Event yields from a 1 month HI (Pb-Pb) run at Nominal Luminosity. Counts per bin of dpt=2 GeV dx2/x2=+/- 0.25 M.Strikman, R.Vogt, SNW Winter Workshop on Nuclear Dynamics

23. Collision Hall at start of installation( Feb. 04) Winter Workshop on Nuclear Dynamics

24. Location,location,location Winter Workshop on Nuclear Dynamics

25. US-ATLAS Heavy Ion Group S. Aronson, K. Assamagan, M.Baker,H. Gordon, M. Levine, P. Nevski, H. Takai, P.Steinberg, S. White Brookhaven National Laboratory J. Nagle-University of Colorado B. Cole-Columbia University +Bern, CERN, Geneva, Prague,Cracow… -LOI submitted to LHCC by the full ATLAS collaboration in May ‘04 -Broad range of physics and simulation activities now under way Atlas.ch/standardmodel/HeavyIons Winter Workshop on Nuclear Dynamics

26. 280 GeV event Preliminary efficiency numbers show that jet reconstruction efficiency is larger than 90% above 50 GeV. Below 50 GeV the efficiency lowers to approximately 75% with an increase in the number of “ghosts”. Remember we are using b=0 HIJING events as our test case. Winter Workshop on Nuclear Dynamics Full ATLAS Simulation

27. c a b d Motivation: High-pT Results from RHIC Jet quenching observed in AuAu as predicted by pQCD: (unquenching in dAu) Hard processes: excellent probes to test QCD! PRL91, (2003) Winter Workshop on Nuclear Dynamics

28. Heavy ion Physics with the ATLAS Detector -Introductory- we come from a program at RHIC which has been productive beyond our expectations. Much of the physics has been driven by experimental opportunities due to large multi-purpose detectors. Key experimental tools have been excellent tracking coverage with particle identification, powerful calorimetry (electromagnetic in the central region-PHENIX,STAR EMC; Hadronic in the forward region ZDC/SMD and Pcal in the forward region). Many aspects of Heavy Ion physics evolving now; heavy flavors, UPC, jet studies at the highest pt. Winter Workshop on Nuclear Dynamics