1. Probing the hot, dense QCD matter with the ATLAS experiment at the LHC Jiangyong Jia Stony brook University and BNL

2. Space-time history of heavy ion collisions 2 initial statepre-equilibrium QGP & expansion Phase transition Freeze-out HEPHI

3. Probe the properties of Quark Gluon Plasma Bulk hadrons ： Thermodynamic and hydrodynamic properties T, μ, EOS, viscosity, etc. Usually close to equilibrium Hard probes ： Transport properties Energy loss and broadening, screening length etc. Usually far from equilibrium 3 x z y hadrons J/Ψ  e  AGS 5 GeVSPS 17 GeVRHIC 200 GeV LHC 2760-5500 GeV hadrons J/Ψ, Υ,c,b  e  hadrons J/Ψ,Υ,c,b  e  

4. 4 LHC Heavy Ion Data-taking Design: Pb+Pb at √s NN =5.5 TeV (1 month per year) Nov. 2010: 60M PbPb at √s NN =2.76 TeV Nov. 2011: >1 Billion at √s NN =2.76 TeV

5. ATLAS detector & Pb+Pb measurement 5 |η|<5 |η|<2.5

6. Bulk hadrons: hydrodynamic flow 6 x z y Centrality: the amount overlap, percentile of cross-section or number of participants (N part ) Reaction plane(RP): orientation of the matter, defined by beam & impact parameter direction. Φ

7. anisotropic expansion: elliptic flow Pressure converts initial asymmetry into momentum anisotropy 7 x z y ϕ Φ

8. Generalize into harmonic flow (v n ) Anisotropic distribution generalized by Fourier series Related to initial spatial fluctuations of nucleons v n and correlations between the  n probe initial geometry and expansion mechanism 8 22 33 44

9. Flow coefficients: v n (n,η,p T,cent) Features of Fourier coefficients. v n coefficients are ~boost invariant. v n coefficients rise and fall with p T. v n coefficients rise and fall with centrality. 9 1203.3087 Measured by correlating single particle ϕ with global Φ n.

10. Ridge and Cone in two-particle correlation Once the “ridge” and “cone” were thought due to “jet-medium” interactions….. 10 Au+Au at RHIC √s=200 GeV 3-4 x 1-2 GeV Ridge Jet 1 Jet 2 Double hump or cone

11. Fourier expansion of 2PC 11 Long range structures exhausted by the first six harmonics v 1,1 -v 6,6 |Δη|>2 Important to check the factorization relation 1203.3087

12. Check factorization 2PC v n Factorization works well for n=2-6 Break down of v 1,1 is due to global momentum conservation 12 1203.3087

13. Reconstruct 2PC via single particle v n “ridge” and “cone” reproduced by the single particle v n. They are consequences of global event properties –not due to jet fragmentation!! 13 From 2PC method From single v n method 1203.3087

14. Connection to cosmology 14 22 33 44 Infer initial geometry fluctuation via observation in momentum space “little” bang “big” bang

15. “Acoustic” damping of harmonic flow Treat as sound wave seeded by the hot spot. Sound horizon fixed at freezeout Damping of the second peak sensitive to viscosity 15 ATLAS Data compared with 1106.3243 (Shuryak) 4πη/s=0 4πη/s=1 4πη/s=1.9

16. v 1,1 (p T a,p T b ) and v 1 (p T ) story Factorization of v 1,1 to v 1 breaks due to momentum conservation CMB is dominated by dipole component from Doppler shift of observer. Extract v 1 via two component fit 16 Red Points: v11 data Black line : Fit to functional form Blue line: momentum conservation component 1203.3087

17. Extracted v 1 (p T ) Significant v 1 values observed: p T dependence similar to other v n Comparable to v 3 : significant dipole moment in initial state 17 1203.3087

18. Reaction Plane correlations Further insights can be obtained by studying correlations between the  n : The procedure can be generalized to measure correlations involving three or more planes: One way to think of the three-plane correlations is as combination of two plane correlations  2  4  6 =  4  2  6  2   2  4  6 =  4  2  6  2  Thus three plane correlations are the correlation of two angles relative to the third. 18 arXiv:1203.5095 arXiv:1205.3585 http://cdsweb.cern.ch/record/1451882

19. Two-plane correlations 19

20. Three-plane correlations 20 “2-3-5” correlation Rich centrality dependence patterns are observed “2-4-6” correlation“2-3-4” correlation

21. Expectation from Glauber model Plane directions in configuration space Expected to be strongly modified by medium evolution in the final state 21 arXiv:1011.1853, 1203.5095 1205.3585 Correlation

22. Predictions from hydrodynamic models Significant correlations are generated dynamically. Strong constraints to the model assumptions, in particular the viscosity. 22 Teaney and Yan in preparation

23. Hard probes: single hadron,μ, jets, Z/W/γ, Quarkonium 23

24. Single hadron suppression Quantify suppression with central/peripheral ratio normalized by Ncoll 24 “Enhancement” from flow Jet quenching Transition region

25. Single muon from c, b decay Open heavy flavor production measured via c,b  μ ±. Probing jet quenching of the c/b jets Expect less quenching than light quark jet and gluon jet. But no difference seen between heavy and light jet fragments at RHIC. 25

26. Extracting the heavy flavor muon yield 26

27. Suppression of heavy flavor muons Evaluate Rcp using 60-80% peripheral reference  Factor of 2.0-2.5 relative suppression in 0-10%  Independent of muon p T  Trend different from inclusive hadron suppression 27

28. Full jets probes Beyond di-jet asymmetry!  Suppression of single jet yield  Jet fragmentation function, jet shape, j T distributions  multi-jet final states.  All of above relative to the reaction plane 28 PRL ~140 citations

29. Single jet suppression Single jet yield suppressed by x2 Smooth vs pT and centrality 29 ‣ Error bars: sqrt of diagonal elements of covariance matrix ‣ Systematic errors Black band: fully correlated Red boxes: partially correlated

30. Jet suppression vs radius Evaluate jet radius dependence of Rcp  correlated error cancels in the ratio Modest but significant increase for larger R  broadening? 30

31. Jet suppression vs radius Evaluate jet radius dependence of Rcp  correlated error cancels in the ratio Modest but significant increase for larger R  broadening? Models predicting strong R dependence ruled out. 31

32. Modification of jet shape? p T cut to suppress underlying event, bg subtracted. No strong modification of jet fragmentation between central and peripheral collisions. Suggest energy lost by jet appears at large angle wrt jet axis 32

33. Eletro-weak probes Isolated gamma, Z/W yield are not expected to be modified at final state, but can be affected by nuclear pdf (shadowing, isospin etc) However low p T gamma (upto 50 GeV) might be generated by the QCD matter. Important baseline for jet quenching measurement Unbiased tagging on away-side color probes : γ-jet, Z-jet etc. 33

34. Isolated gamma measurement w/ 2011 data Measured using isolation and shower shape cuts  75% purity Consistent with NLO QCD multiplied by Ncoll 34 https://cdsweb.cern.ch/record/1451913

35. Z measurement w/ 2011 data Z yield scales with N coll Similar story for W 35

36. Quarkonium and dimuon continuum 36 By yifei Dilepton enhancement belowρ: Chiral symmetry restoration Melting of heavy quarkonia states: Debye screening, recombination IS & Jet quenching via Z, Z-tagged jet decay of correlated ccbar,bbar or q + q -  l + l - : Initial state, jet quenching Strangeness enhancements, flow etc ω, ϕ J/ψ ψ’ψ’ Υ b  J/ Ψ+x Analyses in progress.. But need manpower

37. J/Ψ suppression from RUN 2010 data Clean J/Ψ peak in central Pb+Pb collisions J/Ψ p T >6.5 GeV, because eloss of muon in calorimeter Less suppressed than inclusive hadrons 37 R cp 5μb -1

38. Summary Flow coefficients v n and Φ n correlations probe the geometry of the created matter and subsequent hydrodynamic evolution. Significant harmonic flow measured for v 1 -v 6  constraints on viscosity. Factorization from v n,n to v n valid for n=2-6  non-flow is small. v 1,1 is consistent with dipolar flow v 1 plus global momentum conservation. Naturally explains the exotic ridge and cone-like structures in 2PC Correlation between flow angle Φ n probes into dynamics of hydro-evolution Jet quenching of color probes provides insight on energy loss Single particle/jet suppression consistent with radiative energy loss Energy lost by jets seems to be redistributed to large angle. Heavy flavor jet suppression seems to be similar to light flavor. Electro-weak probes constrains the initial condition Effect of nuclear pdf and other initial state effects are small Jet suppressions are mostly due to final state effects 38

39. Opportunities We are just at the beginning, a lot more to do. Measure γ-jet, Z-jet, multi-jet final state Understand the medium response, final state direct photons b-jets, b-tagged dijets, b  J/Ψ heavy quarkonium, Drell-Yan Flow and correlations of above with geometry. Ultra-peripheral physics p+A base line measurement  2012 Most measurements above can be done.  Precision determination of pdf  Saturation physics, cold nuclear matter effects Full energy Pb+Pb run  2014 and beyond x6.5 luminosity and much larger cross sections. 39 x42