Exploring Hot QCD Matter with ALICE Peter Jacobs, Lawrence Berkeley National Laboratory for the ALICE Collaboration • Heavy Ion Collisions: what are we.
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Exploring Hot QCD Matter with ALICE Peter Jacobs, Lawrence Berkeley National Laboratory for the ALICE Collaboration • 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 ? PHENO11, Madison WI Hot QCD Matter in ALICE 1 QCD Phase Diagram: qualitative view Temperature Deconfined Quark-Gluon Plasma ~170 MeV ~few hundred MeV Baryon chemical potential µB PHENO11, Madison WI Hot QCD Matter in ALICE 2 QCD thermodynamics: calculation QCD on the lattice (mB=0) Slow convergence to non-interacting Steffan-Boltzmann limit What are the quasi-particles? “Strongly-coupled” plasma? 4 T 2 4 gDOF T 30 RHIC LHC? Cross-over, not sharp phase transition (like ionization of atomic plasma) T [MeV] PHENO11, Madison WI Hot QCD Matter in ALICE 3 ALICE ALICE is the comprehensive heavy ion experiment at the LHC Design optimized for huge particle multiplicities of nuclear collisions PHENO11, Madison WI Hot QCD Matter in ALICE 4 ALICE vs ATLAS/CMS 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 ALICE favors robust • energy scaletracking, 10 GeV –precision, 1 TeV and low mass over large acceptance, high rate, and huge rangecapabilities • tiny cross sections: high ratedynamic and rejection PHENO11, Madison WI Hot QCD Matter in ALICE 5 November 7 2010: First Pb+Pb collisions at √sNN=2.76 TeV PHENO11, Madison WI Hot QCD Matter in ALICE 6 Particle ID: TPC dE/dx PHENO11, Madison WI Copious production of anti-nuclei Hot QCD Matter 7 in ALICE Tomography via g-conversions Compare data and MC Inner material understood better than 10% NLO (W. Vogelsang) PHENO11, Madison WI MggHot QCD Matter in ALICE 8 Charm in Pb+Pb D0K-+ J/ψμ+μ- D+K-++ PHENO11, Madison WI Hot QCD Matter in ALICE 9 Heavy flavor in p+p: consistency check Compare directly measured electrons and electrons calculated from D-decay good agreement at low pt (charm dominant) PHENO11, Madison WI Hot QCD Matter in ALICE 10 Measuring collision geometry I 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 PHENO11, Madison WI Hot QCD Matter in ALICE 11 Measuring collision geometry II Forward neutrons • Order events by centrality metric • Classify into percentile bins of “centrality” HI jargon: “0-5% central” Charged hadrons h~3 PHENO11, Madison WI Glauber modeling • Nbin: effective number of binary nucleon collisions (~5-10% precision) • Npart: number of (inelastically) participating nucleons Hot QCD Matter in ALICE 12 ALICE Results I: hadron multiplicity PRL, 105, 252301 (2010), arXiv:1011.3916 √sNN=2.76 TeV Pb+Pb, 0-5% central, |η|<0.5 PHENO11, Madison WI 2 dNch/dη / <Npart> = 8.3 ± 0.4 (sys.) Hot QCD Matter in ALICE 13 dNch/dη: model comparisons PRL, 105, 252301 (2010), arXiv:1011.3916 √sNN=2.76 TeV Pb+Pb, 0-5% central, |η|<0.5 dNch/dη = 1584 ± 76 (sys.) pQCD-based MC Saturation pp extrapolation Energy density estimate (Bjorken): PHENO11, Madison WI Hot QCD Matter in ALICE 14 dNch/dη: Centrality dependence PRL, 106, 032301 (2011), arXiv:1012.1657 2.5% bins ALICE RHIC Pb+Pb, √sNN=2.76 TeV RHIC scale LHC scale |η|<0.5 Interpolation between 2.36 and 7 TeV pp peripheral central Striking centrality-independent RHICLHC Hot QCD Matter in scaling ALICE PHENO11, Madison WI 15 dNch/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 PHENO11, Madison WI Pb+Pb, √sNN=2.76 TeV Albacete and Dumitru (arXiV:1011.5161): • Most sophisticated saturation model: evolution, running coupling • Captures full centrality dependence…? Hot QCD Matter in ALICE 16 Collective Flow of QCD Matter Initial spatial anisotropy Final momentum anisotropy py px z y y x 2 2 x Interaction of constituents v2 y +x 2 2 2 2 px py 2 2 px + py Elliptic flow PHENO11, Madison WI Hot QCD Matter in ALICE 17 Elliptic flow v2: LHC vs RHIC PRL 105, 252302 (2010) Striking similarity of pT-differential v2 at RHIC and LHC PHENO11, Madison WI Hot QCD Matter in ALICE 18 Shear viscosity in fluids Shear viscosity characterizes the efficiency of momentum transport Large quasi-particle interaction cross section s Strongly-coupled matter Small shear viscosity perfect liquid” AdS/CFT and kinetic theory: absolute lower bound PHENO11, Madison WI Hot QCD Matter in ALICE 19 Elliptic flow: data vs. viscous hydrodynamic modeling e.g. Song, Bass, and Heinz, arXiv:1103.2380 pT-differential pT-integrated central peripheral Preferred values: h/s(RHIC)=0.16, h/s(LHC)=0.20 PHENO11, Madison WI Hot QCD Matter in ALICE 20 Shear viscosity: expectations from QCD Analytic: Csernai, Kapusta and McClerran PRL 97, 152303 (2006) Lattice: H. Meyer, PR D76, 101701R (2007) Chiral limit, resonance gas pQCD w/ running coupling 1/4 Lattice QCD Temperature (MeV) If T PHENO11, Madison WILHC > TRHIC, expect h/s(LHC) > h/s(RHIC) Hot QCD Matter in ALICE 21 Jet quenching Radiative energy loss in QCD (multiple soft scattering): Plasma transport coefficient: Total medium-induced energy loss: Apr 4, 2011 LHC News - Sonoma State 22 Jet quenching via leading charged hadron suppression Phys. Lett. B 696 (2011) p+p reference at 2.76 TeV: interpolated peripheral central PHENO11, Madison WI pT Hot QCD Matter in ALICE pT 23 Jet quenching: RHIC vs. LHC Phys. Lett. B 696 (2011) Qualitatively similar, quantitatively different Where comparable, LHC quenching is larger higher color charge density Apr 4, 2011 LHC News - Sonoma State 24 0 vs charged hadrons/RHIC vs LHC RHIC/LHC charged hadrons RHIC 0, h, direct g High pT dependence qualitatively different: • different quenching mechanisms? • consequence of steeper incl spectrum at RHIC? (near phase space limit…) Hot QCD Matter in ALICE 25 PHENO11, Madison WI Jet quenching: comparison to pQCD-based models 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) Apr 4, 2011 Newsformalism? - Sonoma State • something missing LHC in the 26 Summary and Outlook 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… PHENO11, Madison WI Hot QCD Matter in ALICE 27