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Recent ALICE Results From Heavy-Ion Collisions at the LHC

Recent ALICE Results From Heavy-Ion Collisions at the LHC. Grigory Feofilov (St.Petersburg State University) for the ALICE Collaboration Report at the 15th Lomonosov Conference on Elementary Particle Physics , Moscow State University, 24 August 2011. Outline:. Introduction

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Recent ALICE Results From Heavy-Ion Collisions at the LHC

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  1. Recent ALICE Results From Heavy-Ion Collisions at the LHC Grigory Feofilov (St.Petersburg State University) for the ALICE Collaboration Report at the 15th Lomonosov Conference on Elementary Particle Physics, Moscow State University, 24 August 2011

  2. Outline: • Introduction • Experimental results • charged-particle multiplicity density • charged particle elliptic flow, • suppression of charged particle production at large pt • two-pion Bose--Einstein correlations (HBT) • ongoing analyses : strange and heavy-flavour particle production, prompt D meson R_AA, ridge • Summary

  3. ”Relativistic heavy ion physics” : a bit of history A.M. Baldin 1971: the 1st relativistic nuclear beams with an energy of 4.2 AGeV at the synchrophasotron at the LHE, JINR. One of the 1st studies of nuclear effects in the high energy interactions off nuclei A.M. Baldin et al. Sov.J. Nucl.Phys.18,41 (1973) A.M. Baldin ,”Heavy Ion Interactions at High Energies”,report at AIP Conf. Proc. 26, 621 (1975) BEVALAC(1974), SPS(1976), RHIC(2000), LHC(2009)

  4. QGP …J. C, Collins and M. J. Perry -1975, …E.Shuryak 1978… Early expectations: QGP like an ideal gas of quarks and gluons Lattice QCD QGP Hadron gas Lattice QCD results for the energy density / T^4 as a function of T/Tc F. Karsch, Lect. Notes Phys. 583 (2002) 209. Phys. Lett. B78 (1978) 150

  5. RHIC : Several surprises • Rather low multiplicity of charged particles dNch/dη(η=0)∼600for central collisions)  showing some coherence in particle production (collectivity effects) • Elliptic flow for non-central collisions strongly interacting matter behaving as a liquid with very low viscosity (almost ideal fluid) - sQGP. • Large radial flow velocity ~ 0.7 c (p_t ∼ 1.5–2 GeV/c), • Early thermalization times 0.6-1.0 fm/c- from hydro calculations • Energy densities at thermalization time: ~ 5.4 GeV/fm3 - 9.0 GeV/fm3 • The strong suppression of high-pt particle production “jet tomography” on the initial dense matter with “beams” of quarks and gluons. • …the list is not exhausted…(J/psi production?, (anti)baryon to pion excess at intermediate pT (2 — 5 GeV/c)?…, ridge long-range phenomenon…) see: BNL -73847-2005 Formal Report, April 18, 2005 5

  6. LHC: A new journey! • LHC started accelerating • Pb beams on 04.11. 2010: • √sNN = 2.76 TeV • The 1st collisions on 07.11.2010; • After ~ 3 weeks:∼108 recorded • events in ALICE+ATLAS+CMS • The 1st ALICE paper 17.11.2010: • on multiplicities in central collisions, • arXiv:1011.3916 [nucl-ex]. • Now ~ 6 ALICE papers are devoted to Pb-Pb results

  7. K. Aamodt et al. (ALICE), JINST, 3 , S08002 (2008)

  8. Charged-particle multiplicity density at mid-rapidity in central Pb-Pb collisions at sqrt(sNN)= 2.76 TeV:

  9. Charged-particle multiplicity density at mid-rapidity in central Pb-Pb collisions at √sNN = 2.76 TeV:: Multiplicity: • is essential to estimate • the initial energy density and it is the 1st important constraint for the models! Comparison of ALICE measurement with model predictions. • Bjorken energy density: 2.8 x RHIC for 5% of most central collisions arXiv:1011.3916 [nucl-ex]. Phys. Rev. Lett. 105 (2010) 252301

  10. Charged-particle multiplicity density at mid-rapidity in central Pb-Pb collisions at √sNN = 2.76 TeV:: Empirical extrapolation pQCD-inspired MC Initial-state gluon density saturation models Some other approaches ALICE measurement and model predictions ] arXiv:1011.3916 [nucl-ex]. Phys. Rev. Lett. 105 (2010) 252301

  11. Charged particle pseudo-rapidity density per participant pair for central nucleus-nucleus and non-single diffractive pp (pp) collisions , as a function of √sNN • an increase of about • a factor 1.9 relative to pp collisions at similar collision energies, • an increase of about • a factor 2.2 to central Au-Au collisions at √sNN= 0. 2 TeV ! • Faster growth with √sNN in AA than in pp! • Logarythmic extrapolation is ruled out • Important constraint for the models! arXiv:1011.3916 [nucl-ex]. Phys. Rev. Lett. 105 (2010) 252301 11

  12. Centrality selection in ALICE Front view of ZDC ZN and ZP calorimeters VZERO: Front view of V0A and V0C arrays arXiv:1011.3916 [nucl-ex]. Phys. Rev. Lett. 105 (2010) 252301 12 K. Aamodt et al. (ALICE), JINST, 3 , S08002 (2008)

  13. Centrality dependence of the charged-particle multiplicity density at mid-rapidity in Pb–Pb collisions at √sNN =2.76 TeV • very similar centrality dependence at LHC and RHIC ! (Note 2 scales: “left” (for 2.76 TeV and “right” - for 200 GeV data) arXiv:1012.1657 [nucl-ex], 4 Feb 2011; Phys.Rev.Lett. 106 (2011) 032301 13

  14. Centrality dependence of the charged-particle multiplicity density at mid-rapidity in Pb–Pb collisions at √sNN =2.76 TeV Important constraint for the models! • Strong competition between the models! • Saturation models {Kharzeev et al.} are looking better … arXiv:1012.1657 [nucl-ex], 4 Feb 2011; Phys.Rev.Lett. 106 (2011) 032301 14

  15. Elliptic flow of charged particles in Pb-Pb collisions at √sNN =2.76 TeV: Tannebaum’06 Excintricity: 2- and 4-particle cumulant methods: v 2{2} and v 2{4} arXiv:1011.3914v1 [nucl-ex] 17 Nov 2010; Phys. Rev. Lett. 105 (2010) 252302 15

  16. Elliptic flow of charged particles in Pb-Pb collisions at √sNN =2.76 TeV: Differential elliptic flow vs. pt Integrated elliptic flow vs. centrality • the value of • v2(pt) does not • change within • uncertainties • from RHIC to LHC • Qualitatively similar • for all 3 centrality • classes. • CERN Press release, November 26, 2010: • “…confirms that the much hotter plasma produced at the LHC behaves as a very low viscosity liquid (a perfect fluid)…” arXiv:1011.3914v1 [nucl-ex] 17 Nov 2010; Phys. Rev. Lett. 105 (2010) 252302 16

  17. Elliptic flow of charged particles in Pb-Pb collisions at √sNN =2.76 TeV: • There is a continuous increase • in the magnitude of integrated elliptic flow measured in the 20-30% centrality class from RHIC to LHC energies. • This increase is higher than current predictions • from ideal hydrodynamic models arXiv:1011.3914v1 [nucl-ex] 17 Nov 2010; Phys. Rev. Lett. 105 (2010) 252302 17

  18. Higher harmonic anisotropic flow measurements Initial geometry fluctuations, a mean-free-path (lmf p) and higher harmonics, see: P.Sorensen,”The rise and fall of the ridge”, Nuclear Physics A 855 (2011) 229–232 18

  19. Higher harmonic anisotropic flow measurements of charged particles in Pb-Pb collisions at √sNN = 2.76 TeV: Intergrated v2, v3 and v4 vs. centrality {2} {2} {4} {2} • behavior of higher harmonics is different from that of v2{2} ! arXiv:1105.3865 ; CERN-PH-EP-2011-073. - 2011 19

  20. Higher harmonic anisotropic flow measurements of charged particles in Pb-Pb collisions at √sNN =2.76 TeV: ν2 ,ν3 ,ν4 ,ν5 vs. pt 30-40% centrality ν2 ν3 0-5% centrality ν3 • behavior of ν3 changes dramatically for very central collisions • hydrodynamic prediction for v3(pt) with ƞ/s = 0.08better than ƞ/s = 0.0 • no hydro calculation (yet) describing simultaneously data on v2and v3 … …analysis of the viscosity effects is in progress… ν2 20 arXiv:1105.3865 ; CERN-PH-EP-2011-073. - 2011

  21. Suppression of charged particle production at large pT in central Pb-Pb collisions at √sNN =2.76 TeV: RAA vs. Pt Data driven interpolation 900 GeV & 7 TeV or from NLO 7 TeV * NLO (2.76 TeV)/NLO(7 TeV) Nuclear modification factor RAA: RAA =1 if no nuclear effects 21 arXiv:1012.1004v1 [nucl-ex], 5 Dec 2010; Phys. Lett. B 696 (2011) 30-39

  22. Suppression of charged particle production at large pT in central Pb-Pb collisions at √sNN =2.76 TeV: • Strong centrality dependence • Small losses for peripheral • collisions • Minimum (~0.12) is reached • at pT ≈ 6-7 GeV/c • Strong rise above 6 GeV/c 0.9 TeV * NLO (2.76 TeV)/NLO(0.9 TeV) from 0.9 TeV * NLO (2.76 TeV)/NLO(0.9 TeV) arXiv:1012.1004v1 [nucl-ex], 5 Dec 2010; Phys. Lett. B 696 (2011) 30-39 22

  23. Suppression of charged particle production at large pt in central Pb-Pb collisions at √sNN =2.76 TeV: • results are qulitatively similar • to the STAR and PHENIX data • more “dramatic” behaviour • the medium formed in central • Pb-Pb collisions is denser than • at RHIC arXiv:1012.1004v1 [nucl-ex], 5 Dec 2010; Phys. Lett. B 696 (2011) 30-39 23

  24. Two-pion Bose--Einstein correlations (HBT) in central Pb-Pb collisions at √sNN =2.76 TeV: Pion HBT radii (for kT=0.3 GeV/c) vs. (dN/deta)^1/3 HBT radii (for 5% centrality) vs.kT arXiv:1012.1004v1 [nucl-ex], 5 Dec 2010; Phys. Lett. B 696 (2011) 30-39 24

  25. Two-pion Bose--Einstein correlations in central Pb-Pb collisions at √sNN =2.76 TeV: • Homogeneity-region volume 2 x RHIC (~ dNch/dh) arXiv:1012.4035v2 [nucl-ex]; Phys. Lett. B 696 ( 2011) 328-337 25

  26. Two-pion Bose--Einstein correlations in central Pb-Pb collisions at √sNN =2.76 TeV: • Decoupling time tf (~ Rlong) • 1.4 x RHIC (~ (dNch/dh)1/3) • tf(central PbPb) ~ 10–11 fm arXiv:1012.4035v2 [nucl-ex]; Phys. Lett. B 696 ( 2011) 328-337 26

  27. Ongoing analyses : strange and heavy-flavour particle production Signal of decays selected using displaced decay vertices at central rapidity |y|<0/8 (left) and decays in the forward muon spectrometer 2.5 < y < 4, (right). Pb-Pb collisions, arXiv:1106.1341v1 [nucl-ex]; 27

  28. Ongoing analyses :Prompt D meson R_AA  R_AA (0-20%) shows a suppression of about a factor of 4-5 for pt > 5 GeV/c  Prompt D meson and π+- R_AA are compatible. Z. Conesa del Valle, report at PANIC, 24 - 29 July 2011, Cambridge, MA, USA 28

  29. Ongoing analyses :J/psi supression (?) in Pb-Pb collisions at √sNN =2.76 TeV (preliminary) J/psi production is suppressed (factor ~2) independently on centrality  J/psi behavior is still a puzzle …!? 29

  30. Ongoing analyses :The two-particle azimuthal correlations, higher harmonics and ridges in Pb-Pb at ALICE PbPb central • .…the measured anisotropic flow Fourier coefficients give a natural description of these structures… • …See also numerous QM-2011discussionsonhigher harmonics • …the origin of this effect is still a puzzle… arXiv:1105.3865 ; CERN-PH-EP-2011-073. - 2011 30

  31. Summary and outlook • Themedium produced in Pb-Pb collisions at √sNN =2.76 TeV • at the LHC has in comparison to 200 GeV data at RHIC: • ~ 3 times larger energy density • ~ 2 times larger volume of homogenity region • ~ Larger lifetime ≈ +20% (≈ 10 fm/c) • It shows the properties of almost ideal liquid (like at RHIC) • It appears to be denser than at RHIC (suppression of high-pt • particles is stronger) • J/psi production is suppressed (factor ~2) - still a puzzle…? • “Ridge” structures in long-range azimuthal 2-particle correlations - another puzzle…? • 5 times increase in luminosity is expected in Pb-Pb in the end of 2011! • pA collisions in 2012 - ? • …… • We are entering a new and unexplored territory ! • Stay tuned!

  32. BACK-UP slides:

  33. Time Ptojection Chamber largest ever, novel features: 88 m3, l = 5 m, d = 5.6m 570 k channels drift gas Ne - CO2 – N2 (86/9/5) HV membrane (25 mm) 16 May 2006 First cosmic and laser tracks ! 33 Oct 2008 Split J. Schukraft

  34. Inner Tracking System (ITS) • Silicon Pixel Detector (SPD): • ~10M channels • 240 alignable vol. (60 ladders) • Silicon Drift Detector (SDD): • ~133k channels • 260 alignable vol. (36 ladders • Silicon Strip Detector (SSD): • ~2.6M channels • 1698 alignable vol. (72 ladders) SSD ITS total: 2198 alignable sensitive volumes  13188 d.o.f. SPD Adam Jacholkowski & Andrea Dainese SDD

  35. High pT Particle Correlations Associated pTt Δf Trigger ‘near’ side ‘away’ side UE Trigger Particle Trigger Particle: highest pT particle in event (pTt) Associate Particle: all the others (pTa)

  36. Jet Quenching (?) seen via Multiparticle Correlations ‘Autocorrelation’: d2Nch/dDhdDf (signal)/d2Nch/dDhdDf (mixed events) pp Pb PbPb peripheral pp 7 TeV CMS pp 7 TeV ‘near side ridge’ PbPb central PbPb central d2Nch/dDhdDf (signal)/d2Nch/dDhdDf (mixed events) • ‘near side ridge’: • - striking effect, not really understood • response of QGP to jet quenching ? • initial state gluon radiation ? • ???

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