1. Exploring Hot QCD Matter with ALICE PHENO11, Madison WIHot QCD Matter in ALICE1 Heavy Ion Collisions: what are we after? ALICE Overview ALICE results from 2010 Pb+Pb run Putting together RHIC and LHC: What have we learned about hot QCD matter ? Peter Jacobs, Lawrence Berkeley National Laboratory for the ALICE Collaboration

2. QCD Phase Diagram: qualitative view PHENO11, Madison WIHot QCD Matter in ALICE2 Temperature ~170 MeV Baryon chemical potential µ B ~few hundred MeV Deconfined Quark-Gluon Plasma

3. QCD thermodynamics: calculation PHENO11, Madison WIHot QCD Matter in ALICE3 T [MeV] QCD on the lattice (  B =0) Cross-over, not sharp phase transition (like ionization of atomic plasma) Slow convergence to non-interacting Steffan-Boltzmann limit What are the quasi-particles? “Strongly-coupled” plasma? RHIC LHC?

4. 4Hot QCD Matter in ALICE ALICE is the comprehensive heavy ion experiment at the LHC Design optimized for huge particle multiplicities of nuclear collisions ALICE PHENO11, Madison WI

5. ALICE vs ATLAS/CMS PHENO11, Madison WIHot QCD Matter in ALICE5 Requirements for heavy ion physics: measure large-scale collective phenomena: reconstruct complex hadronic events precise measurements of heavy flavor, photons, leptons, jets and jet fragments energy scale → robust tracking ~ 100 MeV – 100 GeV → calorimetry ~ 200 GeV low material budget near vertex particle ID: multiple detector technologies Requirements for Higgs/SUSY searches: missing energy signatures: hermetic coverage energy scale 10 GeV – 1 TeV tiny cross sections: high rate and rejection capabilities ALICE favors robust tracking, precision, and low mass over large acceptance, high rate, and huge dynamic range

6. November 7 2010: First Pb+Pb collisions at √s NN =2.76 TeV PHENO11, Madison WIHot QCD Matter in ALICE6

7. PHENO11, Madison WI7 Particle ID: TPC dE/dx Hot QCD Matter in ALICE Copious production of anti-nuclei

8. Tomography via  -conversions PHENO11, Madison WIHot QCD Matter in ALICE8 Inner material understood better than 10% Compare data and MC NLO (W. Vogelsang) M 

9. Charm in Pb+Pb PHENO11, Madison WI9Hot QCD Matter in ALICE J/ψ  μ + μ - D+K-D+K- D0K-+D0K-+

10. Heavy flavor in p+p: consistency check PHENO11, Madison WIHot QCD Matter in ALICE10 Compare directly measured electrons and electrons calculated from D-decay  good agreement at low p t (charm dominant)

11. Measuring collision geometry I PHENO11, Madison WIHot QCD Matter in ALICE11 Nuclei are “macroscopic”  characterize collisions by impact parameter Correlate particle yields from ~causally disconnected parts of phase space  correlation arises from common dependence on collision impact parameter

12. Measuring collision geometry II PHENO11, Madison WIHot QCD Matter in ALICE12 Forward neutrons Charged hadrons  ~3 Order events by centrality metric Classify into percentile bins of “centrality” HI jargon: “0-5% central” Glauber modeling N bin : effective number of binary nucleon collisions (~5-10% precision) N part : number of (inelastically) participating nucleons

13. ALICE Results I: hadron multiplicity PRL, 105, 252301 (2010), arXiv:1011.3916 √s NN =2.76 TeV Pb+Pb, 0-5% central, |η|<0.5 2 dN ch /dη / = 8.3 ± 0.4 (sys.) PHENO11, Madison WI13Hot QCD Matter in ALICE

14. dN ch /dη: model comparisons pp extrapolation pQCD-based MC Saturation PRL, 105, 252301 (2010), arXiv:1011.3916 dN ch /dη = 1584 ± 76 (sys.) √s NN =2.76 TeV Pb+Pb, 0-5% central, |η|<0.5 Energy density estimate (Bjorken): PHENO11, Madison WI14Hot QCD Matter in ALICE

15. dNch/dη: Centrality dependence PRL, 106, 032301 (2011), arXiv:1012.1657 Interpolation between 2.36 and 7 TeV pp Pb+Pb, √s NN =2.76 TeV 2.5% bins |η|<0.5 ALICE LHC scale RHIC scale RHIC peripheralcentral PHENO11, Madison WI15Hot QCD Matter in ALICE Striking centrality-independent scaling RHIC  LHC

16. dN ch /dη vs. centrality: models PRL, 106, 032301 (2011), arXiv:1012.1657 Two-component models Soft (~Npart) and hard (~Ncoll) processes Saturation-type models Parametrization of the saturation scale with centrality Comparison to data DPMJET (incl. string fusion) stronger rise than data HIJING 2.0 (no quenching)  Strong centrality dependent gluon shadowing  Fine-tuned to 0-5% dN/dη Saturation models [12-14]  Most have too much saturation Pb+Pb, √s NN =2.76 TeV Albacete and Dumitru (arXiV:1011.5161): Most sophisticated saturation model: evolution, running coupling Captures full centrality dependence…? PHENO11, Madison WI16Hot QCD Matter in ALICE

17. Collective Flow of QCD Matter PHENO11, Madison WIHot QCD Matter in ALICE17 Initial spatial anisotropy x y z pypy pxpx Elliptic flow Final momentum anisotropy Interaction of constituents

18. Elliptic flow v 2 : LHC vs RHIC PHENO11, Madison WIHot QCD Matter in ALICE18 PRL 105, 252302 (2010) Striking similarity of p T -differential v 2 at RHIC and LHC

19. 19 Hot QCD Matter in ALICE Shear viscosity in fluids PHENO11, Madison WI Shear viscosity characterizes the efficiency of momentum transport Large quasi-particle interaction cross section   Strongly-coupled matter  Small shear viscosity  ” perfect liquid” AdS/CFT and kinetic theory: absolute lower bound

20. Elliptic flow: data vs. viscous hydrodynamic modeling PHENO11, Madison WIHot QCD Matter in ALICE20 e.g. Song, Bass, and Heinz, arXiv:1103.2380 p T -differential p T -integrated peripheralcentral Preferred values:  /s(RHIC)=0.16,  /s(LHC)=0.20

21. Shear viscosity: expectations from QCD PHENO11, Madison WIHot QCD Matter in ALICE21 Analytic: Csernai, Kapusta and McClerran PRL 97, 152303 (2006) Lattice: H. Meyer, PR D76, 101701R (2007) pQCD w/ running coupling Chiral limit, resonance gas 1/4  Lattice QCD Temperature (MeV) If T LHC > T RHIC, expect  /s(LHC) >  /s(RHIC)

22. Jet quenching 22 Total medium-induced energy loss: Plasma transport coefficient : Apr 4, 2011LHC News - Sonoma State Radiative energy loss in QCD (multiple soft scattering):

23. Jet quenching via leading charged hadron suppression PHENO11, Madison WIHot QCD Matter in ALICE23 Phys. Lett. B 696 (2011) peripheral central pTpT pTpT p+p reference at 2.76 TeV: interpolated

24. Jet quenching: RHIC vs. LHC Apr 4, 2011LHC News - Sonoma State24 Phys. Lett. B 696 (2011) Qualitatively similar, quantitatively different Where comparable, LHC quenching is larger  higher color charge density

25.  0 vs charged hadrons/RHIC vs LHC PHENO11, Madison WIHot QCD Matter in ALICE25 RHIC  0, , direct  RHIC/LHC charged hadrons High p T dependence qualitatively different: different quenching mechanisms? consequence of steeper incl spectrum at RHIC? (near phase space limit…)

26. Jet quenching: comparison to pQCD-based models Apr 4, 2011LHC News - Sonoma State26 X-F Che et al.,arXiv1102.5614 Horowitz and Gyulassy, arXiv1104.4958 Several formalisms  different treatments of medium, radiative/elastic e-loss Models calibrated at RHIC Scale energy density with charged multiplicity (factor~2) Models systematically predict too much quenching….? must measure p+p reference at 2.76 TeV (data now on tape) something missing in the formalism?

27. Summary and Outlook PHENO11, Madison WIHot QCD Matter in ALICE27 Initial LHC heavy ion run: machine and ALICE worked superbly First task is to rediscover and compare to the striking heavy ion phenomena found at RHIC qualitative similarities but quantitative differences consistent picture of strongly-coupled (low viscosity) fluid with high color-charge density (opaque to jets) discrepancies with models: requires some rethinking Next for ALICE: qualitative  quantitative quarkonia (deconfinement signature) charm full jets (newly commissioned large EMCal) correlations of many kinds…