The Heavy Ion Physics Program with ATLAS at the LHC

1. The Heavy Ion Physics Program with ATLAS at the LHC Nathan Grau Columbia University, Nevis Labs On behalf of the ATLAS Heavy Ion Working Group Nathan Grau, WWND 2007

2. The ATLAS HI Working Group Nathan Grau, WWND 2007

3. 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 Nathan Grau, WWND 2007

4. 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 • p0, K, L, f, J/y, e, etc. • Single particle suppression is large at high-pT • p0, K, L, f, J/y, e, etc. • Two-particle azimuthal correlation suppression and shape modification • Near-side and Away-side • Color Glass Condensate • Slow rise of dN/dh 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 Nathan Grau, WWND 2007

5. The ATLAS Detector Nathan Grau, WWND 2007

6. The ATLAS Detector: h Coverage • Full azimuthal acceptance in all detectors • Unprecedented pseudorapidity coverage for A+A Nathan Grau, WWND 2007

7. Global Observables • Particle and Energy density: dN/dh, dET/dh • Extend root-s dependence of dN/dh: test CGC • Azimuthal Anisotropy: v2, etc. • What happens to v2/e at higher root-s? Nathan Grau, WWND 2007

8. Tracking with the Inner Detector Reconstructed tracks with |h|<1 • Inner detector has full azimuthal coverage within |h|<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. Nathan Grau, WWND 2007

9. Preliminary Tracking to lower pT Minimum bias p+p • Work extending pT reach important for p+p and A+A. • dN/dh in both cases • v2 in A+A • Ongoing with high energy and heavy ion participation. Efficiency: red/black Fake rate: red/green Nathan Grau, WWND 2007

10. dN/dh via Tracklets a la PHOBOS f h 1. Truth tracks2. “B-Layer” Hits 3. Layer 1 Hits 4. Matched Tracklets Measurement of track density flat with truth density Nathan Grau, WWND 2007

11. STAR, PRL 93 (2004) 252301 Jet Physics with ATLAS • See W. Holzmann’s talk for all of the details RAA interm. pT correlations -h correlations high pT correlations Nathan Grau, WWND 2007

12. ATLAS Calorimetry Hadronic Barrel EM Barrel Forward EM EndCap Hadronic EndCap Nathan Grau, WWND 2007

13. 1 2 3 4 5 6 Longitudinal Segmentation: 3-d Jets Sampling of a 100 GeV jet (no background) Note the h-f region is 0.8x0.8: a typical jet size Nathan Grau, WWND 2007

14. Jet Single f slice 0.1 rad Background Photon Isolation and Identification • Barrel EMCal front layer finely segmented in h for vectoring H  gg events and p0 rejection. • Example of jet embedded in central b=2 fm HIJING event. Nathan Grau, WWND 2007

15. Jet Single f slice 0.1 rad All too wide for single photons Back ground Photon Isolation and Identification • Barrel EMCal front layer finely segmented in h for vectoring H  gg events and p0 rejection. • Example of jet embedded in central b=2 fm HIJING event. Nathan Grau, WWND 2007

16. Single f slice 0.1 rad g-jet event embedded EM Layer 1 ET (GeV)  Photon Isolation and Identification • Barrel EMCal front layer finely segmented in h for vectoring H  gg events and p0 rejection. • Example of jet embedded in central b=2 fm HIJING event. Nathan Grau, WWND 2007

17. g/p0 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 Nathan Grau, WWND 2007

18. g/p0 Separation • Rejection of p0 with appropriate cuts on previous variables • Efficiency in p+p is ~90%, flat with ET and h Nathan Grau, WWND 2007

19. Jet Position Resolutions • From standard R=0.4 seeded cone algorithm • Results are important for studies of hard radiation in jets (sub-jets). Nathan Grau, WWND 2007

20. h Jet Energy Resolution • Energy resolution as a function of ET and h • Important for studies of jet RAA, fragmentation functions, etc. Nathan Grau, WWND 2007

21. 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,h,centrality) • Azimuthal ET distribution in different barrel EM calorimeter layers (|h|<1.5) Presampler Strip layer (front) Middle Layer Back Layer h x f 0.025 x 0.025 0.003 x 0.1 0.05 x 0.025 Nathan Grau, WWND 2007

22. Reaction Plane Resolution Comparison of subevents Comparison to true YRP • In measuring the physical v2 you must correct by the resolution: v2 = v2meas/res • Resolution measurement from the Barrel (|h|<1.5), Endcap (3.2<|h|<1.5), and Forward (4.9 < |h| < 3.2) calorimeters • Extremely good resolution Nathan Grau, WWND 2007

23. RHIC SPS Heavy Flavor Physics A. Bickley Hard Probes 2006 • Lattice Calculations indicates bounds states melt at different temperatures • But suppression of J/y similar between SPS and RHIC… Nathan Grau, WWND 2007

24. Muon Spectrometer • Coverage up to |h|<2.7 • Low background because the spectrometer is behind the calorimeters Nathan Grau, WWND 2007

25. Heavy Flavor Bound State Measurements • Both charm and bottom states should be accessible to through the m+m- decay channel Nathan Grau, WWND 2007

26. Resolution and Acceptance for U • Good mass resolution • Large acceptance • Loss of efficiency near h~0 due to material. Nathan Grau, WWND 2007

27. Possiblity of cc • cc measurements important because of feeddown to J/y. • Couple the J/y measurements with the photon isolation capabilities of the calorimeter should make the cc measurement possible. • Measurements of many states necessary to pin down temperature. Nathan Grau, WWND 2007

28. 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) • sE/E ~ 15-20%, sx,y ~ 1-2 mm Nathan Grau, WWND 2007

29. Low-x Measurements from ZDC • Measurement of forward mesons in the gg decay channel. • The p0 in the ZDC at very low x – possibly into the saturation region. Nathan Grau, WWND 2007

30. Summary of Physics • Covered in this talk: • Bulk observables • dN/dh, v2 • Inclusive jets and γ+jets • Spectra, hard radiation • Quarkonia (Υ and J/ψ) • Possibility of cc • Low-x physics • For the future: • Ultraperipheral collisions • Heavy quarks (esp. b physics) • Z+jet, jet-jet correlations Nathan Grau, WWND 2007

31. 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, USA 2 Charles University, Prague 3 Columbia Unversity, Nevis Laboratories, USA 4 University of Geneva, Switzerland 5 IHEP, Russia 6 IFJ PAN, Krakow, Poland 7 Iowa State University, USA 8 JINR, Dubna, Russia 9 MePHI, Moscow, Russia 10 Chemistry Department, Stony Brook University, USA 11 Yale University, USA Nathan Grau, WWND 2007