Probing the hot, dense QCD matter with the ATLAS experiment at the LHC

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 HEP HI initial state pre-equilibrium QGP & expansion Phase transition Freeze-out

3. Probe the properties of Quark Gluon Plasma z y x AGS 5 GeV SPS 17 GeV RHIC 200 GeV LHC 2760-5500 GeV hadrons hadrons J/Ψ γ,e,μ hadrons J/Ψ,Υ,c,b γ,e,μ hadrons J/Ψ,Υ,c,b γ,e,μ, Z, W Full Jets • 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

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

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

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

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

8. Generalize into harmonic flow (vn) ε2 ε3 ε4 • Anisotropic distribution generalized by Fourier series • Related to initial spatial fluctuations of nucleons • vn and correlations between the Φn probe initial geometry and expansion mechanism

9. Flow coefficients: vn(n,η,pT,cent) • Measured by correlating single particle ϕ with global Φn. 1203.3087 • Features of Fourier coefficients. • vn coefficients are ~boost invariant. • vn coefficients rise and fall with pT. • vn coefficients rise and fall with centrality.

10. Ridge and Cone in two-particle correlation Au+Au at RHIC √s=200 GeV 3-4 x 1-2 GeV Jet2 Jet1 Double hump or cone Ridge Once the “ridge” and “cone” were thought due to “jet-medium” interactions…..

11. Fourier expansion of 2PC 1203.3087 |Δη|>2 Long range structures exhausted by the first six harmonics v1,1-v6,6 Important to check the factorization relation

12. Check factorization 2PC vn 1203.3087 Factorization works well for n=2-6 Break down of v1,1 is due to global momentum conservation

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

14. Connection to cosmology “little” bang ε2 ε3 Infer initial geometry fluctuation via observation in momentum space ε4 “big” bang

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

16. v1,1(pTa,pTb) and v1(pT)story 1203.3087 Red Points: v11 data Black line : Fit to functional form Blue line: momentum conservation component • Factorization of v1,1 to v1 breaks due to momentum conservation • CMBis dominated by dipole component from Doppler shift of observer. • Extract v1 via two component fit

17. Extracted v1(pT) 1203.3087 Significant v1 values observed: pT dependence similar to other vn Comparable to v3: significant dipole moment in initial state

18. Reaction Plane correlations http://cdsweb.cern.ch/record/1451882 arXiv:1203.5095 arXiv:1205.3585 • Further insights can be obtained by studying correlations between the Φn: • 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 • 2Φ2+4Φ4-6Φ6 = 4(Φ4-Φ2) -6(Φ6-Φ2) • -10Φ2+4Φ4+6Φ6 = 4(Φ4-Φ2) +6(Φ6-Φ2) • Thus three plane correlations are the correlation of two angles relative to the third.

19. Two-plane correlations

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

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

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

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

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

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.

26. Extracting the heavy flavor muon yield

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 muonpT Trend different from inclusive hadron suppression

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

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

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?

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.

32. Modification of jet shape? • pT 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

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 pT 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.

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

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

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

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

38. Summary • Flow coefficients vn and Φn correlations probe the geometry of the created matter and subsequent hydrodynamic evolution . • Significant harmonic flow measured for v1-v6constraints on viscosity. • Factorization from vn,n to vn valid for n=2-6non-flow is small. • v1,1 is consistent with dipolar flow v1 plus global momentum conservation. • Naturally explains the exotic ridge and cone-like structures in 2PC • Correlation between flow angle Φn 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

39. Opportunities x42 • 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.