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The Physics of

Società Italiana di Fisica – Congresso 2008. The Physics of. Andrea Dainese INFN – Legnaro for the ALICE Collaboration. The Physics of. High -density QCD with heavy nuclei at LHC. Layout. Physics of high-density QCD with heavy nuclei, from SPS and RHIC to LHC. Physics performance.

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The Physics of

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  1. Società Italiana di Fisica – Congresso 2008 The Physics of Andrea Dainese INFN – Legnaro for the ALICE Collaboration Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  2. The Physics of High-density QCD with heavy nuclei at LHC Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  3. Layout Physics of high-density QCD with heavy nuclei, from SPS and RHIC to LHC Physics performance • Observables: • soft physics • hard probes ALICE detector layout Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  4. Temperature Baryonic density U. Heinz High-density QCD in the final state of the collision: the Quark Gluon Plasma F.Ceradini high temperature high energy density low baryonic density Pb Pb • Explore QCD phase diagram: • High temp. (>LQCD ~200 MeV) • Low baryonic density (<< r0) • Lattice QCD predicts phase transition at Tc~170 MeV • Quark confinement removed • From hadronic to partonic d.o.f.  High energy density QCD medium (“Quark-Gluon Plasma”) of “weakly”-interacting gluons Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  5. New (unknown) regime of QCD: when gluons are numerous enough (low-x) & extended enough (low-Q2) to overlap  Saturation: (i) Standard DGLAP (linear) approach to PDF evolution invalid nonlinear gluon-gluon fusion balances gluon splitting (ii) Factorisation assumptions (pert. QCD) invalid parton scattering not incoherent Enhanced in the nucleus: factor A1/3 (6) more gluons per unit transverse area High-density QCD in the initial state of the collision:Saturation at low-x • Initial state: high-p nucleus = set of gluons with pg distribution according to PDF g(xBjorken,Q2), with x=pg/pN and Q2 the scale of the process (~ “area” of the gluon) • HERA DIS (ep) data: strong rise of xg(x,Q2) at low-x & low-Q2 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  6. 10 1 CERN-SPS:a glimpse of the new QCD medium • > 1990: fixed target Pb-Pb collisions at s = 17 GeV • Energy density e up to 3 GeV/fm3 (> ec ~ 1 GeV/fm3) • Experiments observe the two historical signatures of the QGP formation: Enhancement in multi-strange baryon yields (NA57, NA49)  partonic system Suppression of J/y yield (NA50, NA60)  large colour-charge density melts cc NA57 NA60 NA50 Factor 20 for  E.Scomparin 1 10 100 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  7. BNL-RHIC:first properties of the new QCD medium • > 2000: Au-Au collisions at s = 200 GeV • Energy density up to 5-15 GeV/fm3 • Major findings of the 4 RHIC experiments (BRAHMS, PHENIX, PHOBOS, STAR) in a nut-shell: • Jet quenching: high-momentum partons lose energy (much more than expected?) due to interaction with the medium • factor 4-5 suppresion for p • little suppression for g(medium blind) Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  8. BNL-RHIC:first properties of the new QCD medium • > 2000: Au-Au collisions at s = 200 GeV • Energy density up to 5-15 GeV/fm3 • Major findings of the 4 RHIC experiments (BRAHMS, PHENIX, PHOBOS, STAR) in a nut-shell: • Jet quenching: high-momentum partons lose energy (much more than expected?) due to interaction with the medium • Strong collective flow, well described by hydro-dynamical models • Quark recombination dominates over fragmentation in hadron production at intermediate monenta wQGP (weakly-coupled) sQGP (strongly-coupled) gas of gluons  liquid of gluons Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  9. Central collisions SPS RHIC LHC study of: s (GeV) 17 200 5500 dNch/dy 430 700 1-3103 hotter e (GeV/fm3) 3 5-10 15- 60  3 - 6 bigger Vf(fm3) 103 7x103 2x104  3 longer-lived tQGP (fm/c) < 1 1.5- 4.0 4-10 “fire-balls” of QCD medium Heavy-ion Physics at LHC LHC: factor 30 jump in w.r.t. RHIC Lessons from RHIC: 1) look for collectivity in flow/recombination  low-pT, PID 2) use hard partons to probe medium  c, b, jets (+ ref: g,W,Z0) 3) potential surprises ... Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  10. increasing s Novel aspects of HI Physics at LHC (1) Probe unexplored small-x region • bulk of partons at x < 10-3 • reach down to 10-6 at forward rapidity • Gluon dynamics (PDF) poorly known, in the proton: in the nucleus (huge saturation?): “terra incognita” Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  11. First snapshot of small-x gluons: Charged multiplicity • “The hadron multiplicity measurements at the LHC will enable us to understand the nature of multi-particle production and the origin of parton evolution at high energies” – D. Kharzeev 14/05/2007 • Estimates prior to RHIC: dNch/dy ~ 2000 – 8000 • ALICE designed for 6000 – 8000 dNch/dh ~ 2000-2500 Eskola et al., saturation model dNch/dh ~ 1200 Kharzeev et al., Color Glass Condensate: Collision of 2 classical saturated fields (full parton coherence) Day-1 measurement M.Nicassio Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  12. Novel aspects of HI Physics at LHC (2) QCD medium: perfect liquid or perfect gas? • Much higher temperature and lifetime at LHC w.r.t. RHIC • sQGP (strongly-coupled) at RHIC;wQGP (weakly-coupled) at LHC? phase transition: pion gas  QGP sQGP wQGP? “terra incognita” • - HARD PARTON QUENCHING  e • QUARKONIA AND PHOTONS  T Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  13.  2000 Novel aspects of HI Physics at LHC (3) Large hard cross sections  New probes of the medium: • b quarks • high-ET jets • W, Z0 High pT pions 10 w.r.t. RHIC Heavy quarks: 100 Jets at the LHC: ET2 GeV 20 GeV100 GeV 200 GeV 100/event 1/event106/month 4x104/month Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  14. Parton Energy Loss by • medium-induced gluon radiation • collisions with medium gluons QCD: u,d,s: m~0, CR=4/3 (difficult to tag at LHC) g: m=0, CR=3 > E loss, dominant at LHC c: m~1.5 GeV, CR=4/3 small m, tagged by D’s b: m~5 GeV, CR=4/3 large mass, < E loss QCD medium Hard Probes of the Medium q: colour triplet • Parton Energy Loss by • medium-induced gluon radiation • collisions with medium gluons g: colour octet Q: colour triplet Real photon: colourless Medium-blind, Control Virtual photon/W: colourless Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  15. medium-sensitive and medium-blind probe in same measurement Beauty energy loss:Use W-decay muons as a reference single m RCP(pt) beauty W beauty W First observation of b energy loss at LHC? Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  16. Parton Energy Loss by • medium-induced gluon radiation • collisions with medium gluons QCD: u,d,s: m~0, CR=4/3 (difficult to tag at LHC) g: m=0, CR=3 > E loss, dominant at LHC c: m~1.5 GeV, CR=4/3 small m, tagged by D’s b: m~5 GeV, CR=4/3 large mass, < E loss QQ (y,): colour singlet/octet object QCD medium Hard Probes of the Medium q: colour triplet • Parton Energy Loss by • medium-induced gluon radiation • collisions with medium gluons g: colour octet Q: colour triplet Dissociation? Real photon: colourless Medium-blind, Control Virtual photon/W: colourless Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  17. enhanced regeneration enhanced suppression 30 SPS RHIC LHC Quarkonia at the LHC • Comparison of suppression for different quarkonia states  T/Tc • Open question from RHIC: • J/ suppression (colour screening) & regeneration (recombination) ? T > 3 TC LHC? RHIC SPS •  would melt only at LHC • ’ TD ~ J/ TD • Small  regeneration • ’ can unravel J/ • suppression VS regeneration Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  18. The ALICE Detector Size: 16 x 26 meters Weight: 10,000 tons |h| < 0.9, B = 0.5 T TPC + silicon tracker g,e, p, K, p identification -4 < h < -2.5 muons ALICE Collaboration: >1000 people, 30 countries, ~80 Institutes Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  19. Ready to move in! Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  20. Ready to move TPC (largest ever) installed, ITS moving in Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  21. MUON arm: largest dipole ever Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  22. Ready to start! Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  23. ALICE commissioning with cosmics Inner Tracking System Time Projection Chamber Inner Tracking System Muon Spectrometer A.Rossi A.Silenzi  alignment and calibration Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  24. Physics Performance(selected examples) Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  25. statistical hadronization / recombination STAR@RHIC baryons mesons L0pK- Pb-Pb central 13 reconstructed L/event 300 Hijing events 11-12 GeV Identified Particle Spectra • Chemical composition of particle prod. • test of statistical hadronization scenario • strangeness enhancement • resonance in-medium mod. • Interplay between energy loss and hadronization scenario (recombination in medium vs fragmentation in vacuum) • RCP: central-to-peripheral ratio • baryon/meson ratios F.Riggi Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  26. D0 Kp • D+ Kpp Ds KKp D*  D0p D0 Kpr LcpKp under study • B  e+X B5 pr. BJ/yee under study Open heavy-flavour in ALICE D0Kp in Pb-Pb D+Kpp in pp Be +X in Pb-Pb Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  27. probes colour-charge dep. of QCD energy loss probes mass dep. of QCD energy loss Heavy-to-light ratios in ALICE 1 year at nominal luminosity (107 central Pb-Pb events, 109 pp events) Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  28. di-muon -4<h<-2.5 ITS (vertexing) TPC (tracking) TRD (e/p id) J/y family  family di-electron |h|<0.9 e e m m MUON (tracking,id) Mμμ(GeV/c) Mμμ(GeV/c) Quarkonia in ALICE Measured both in the di-electron (midrapidity, TRD) and di-muon (forward rapidity, MUON) channel Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  29. non-quenched jet g quenched jet Medium-modified jet fragmentation via g-jet correlations Decrease of leading particle pT Increase of number of low-pT particles Study jet FF(z), where z=pT/Eg Search for depletion at z1 and enhancement at z0 Jet: TPC+EMCAL g: PHOS g Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  30. Conclusions • The Large Hadron Collider with Pb nuclei will be: • a HARD PROBES machine • a SMALL-X machine • (not a black holes machine .... ;) • Explore new territories in high-density QCD • ALICE is ready for the challenge Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  31. LHC is up and running! Beam1 circulated in LHC (Sept 10, 10:25:28) Beam2-gas event in ALICE Inner Tracker (Sept 12) ... almost ... Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  32. Back-up Slides Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  33. Centrality measurement in ALICE brec(fm) sb ~ 1fm Event by event determination of the centrality : Zero degree hadronic calorimeters (ZDC) + electromagnetic calorimeters (ZEM) EZDC , EZEM Nspec Npart Impact parameter (b) bgen (fm) reconstructed generated sNpart ~15 Npart Npart Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  34. electron D & B: Expected pt coverage 1 year at nominal luminosity (107 central Pb-Pb events, 109 pp events) D0 Kp B  e + X Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  35. Resolution mainly provided by the 2 layers of silicon pixels < 60 mm (rf) for pt > 1 GeV/c Invariant mass analysis Charm reconstruction: D0 K-p+ • Exclusive reconstruction: ideal to study RAA • Large combinatorial background (dNch/dy=2-3103 in central Pb-Pb!) • Main selection: displaced-vertex selection • pair of opposite-charge tracks with impact parameters ~100mm • good pointing of reconstructed D0 momentum to the primary vertex Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  36. rec. track e Primary Vertex B X d0 Beauty via displaced electrons • ALICE has excellent electron identification capabilities (TRD + TPC) • Displaced electrons from B decays can be tagged by an impact parameter cut Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  37. charm beauty Cartoon Heavy quark production at LHC:a probe of small-x gluons • Probe small-x region with HQs at low pT and/or forward y • Charm production at low pT: Q2 (4mc2 ~5 GeV2) ~ Qs2 • Down to x~10-4 with charm at y=0, x~10-6 at y4 • Large pert. yields: ~0.1 cc/ev in pp, ~100 cc/ev in Pb-Pb PYTHIA charm Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

  38. Low-x at LHC: forward J/y in ALICE (2.5 <|h|< 4) • J/ measurement in m-spectrometer  xg(x) at x2~10-5 : ds/dy J/: NLO CEM, varying PDFs pp @ 14 TeV QQbar: Sensitive to different PDFs and DGLAP versus CGC predictions (Note: mJ/~Qs at the LHC) Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese

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