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

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Presentation on theme: "Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 1 The Physics of Andrea Dainese INFN – Legnaro for the ALICE Collaboration Società Italiana di Fisica."— Presentation transcript:

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

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

3 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 Observables: soft physics hard probes ALICE detector layout Physics performance

4 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 4 High-density QCD in the final state of the collision: the Quark Gluon Plasma Pb Temperature Baryonic density U. Heinz Explore QCD phase diagram: High temp. (>  QCD ~200 MeV) Low baryonic density (<<  0 ) Lattice QCD predicts phase transition at T c ~170 MeV Quark confinement removed From hadronic to partonic d.o.f.  High energy density QCD medium (“Quark-Gluon Plasma”) of “weakly”-interacting gluons high temperature high energy density low baryonic density  F.Ceradini

5 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 5 High-density QCD in the initial state of the collision: Saturation at low-x Initial state: high-p nucleus = set of gluons with p g distribution according to PDF g(x Bjorken,Q 2 ), with x=p g /p N and Q2 the scale of the process (~ “area” of the gluon) HERA DIS (ep) data: strong rise of xg(x,Q 2 ) at low-x & low-Q 2 (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 A 1/3 (  6) more gluons per unit transverse area New (unknown) regime of QCD: when gluons are numerous enough (low-x) & extended enough (low-Q 2 ) to overlap  Saturation:

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

7 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/fm 3 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  little suppression for  (medium blind)

8 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/fm 3 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

9 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 9 Heavy-ion Physics at LHC LHC: factor 30 jump in w.r.t. RHIC hotter bigger study of: longer-lived “fire-balls” of QCD medium 4-101.5- 4.0< 1  QGP (fm/c) 2x10 4 7x10 3 10 3 V f (fm 3 ) 15- 605-103  (GeV/fm 3 ) 1-3  10 3 700430dN ch /dy 550020017  s (GeV) LHCRHICSPS Central collisions  3  3 - 6 Lessons from RHIC: 1) look for collectivity in flow/recombination  low-p T, PID 2) use hard partons to probe medium  c, b, jets (+ ref: ,W,Z 0 ) 3) potential surprises...

10 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”

11 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: dN ch /dy ~ 2000 – 8000 ALICE designed for 6000 – 8000 dN ch /d  ~ 2000-2500 dN ch /d  ~ 1200 Kharzeev et al., Color Glass Condensate: Eskola et al., saturation model Collision of 2 classical saturated fields (full parton coherence) Day-1 measurement  M.Nicassio

12 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 12 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 - HARD PARTON QUENCHING   - QUARKONIA AND PHOTONS  T Novel aspects of HI Physics at LHC (2) sQGPwQGP? “terra incognita”

13 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 13 Novel aspects of HI Physics at LHC (3) Large hard cross sections  New probes of the medium: b quarks high-E T jets W, Z 0 RHICLHC charm10100 beauty0.055  10  100 w.r.t. RHIC  2000 High p T pions E T 2 GeV 20 GeV 100 GeV 200 GeV 100/event 1/event 10 6 /month 4x10 4 /month Jets at the LHC: Heavy quarks:

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

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

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

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

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

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

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

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

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

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

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

25 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 25 statistical hadronization / recombination 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) R CP : central-to-peripheral ratio baryon/meson ratios STAR@RHIC Pb-Pb central 300 Hijing events    pK - 13 reconstructed  /event 11-12 GeV baryons mesons  F.Riggi

26 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 26 Open heavy-flavour in ALICE D 0  K  D +  K  D s  KK  D*  D 0  D 0  K   c   Kp under study B  e+X B   5 pr. B  J/  ee under study D 0  K  in Pb-Pb D +  K  in pp B  e +X in Pb-Pb

27 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 27 Heavy-to-light ratios in ALICE 1 year at nominal luminosity (10 7 central Pb-Pb events, 10 9 pp events) probes colour-charge dep. of QCD energy loss probes mass dep. of QCD energy loss

28 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 28 ITS (vertexing) TPC (tracking) TRD (e/  id) MUON (tracking,id)  e e  Quarkonia in ALICE Measured both in the di-electron (midrapidity, TRD) and di-muon (forward rapidity, MUON) channel J/  family  family M μμ (GeV/c) di-electron |  |<0.9 di-muon -4<  <-2.5

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

30 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

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

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

33 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 33 Centrality measurement in ALICE Event by event determination of the centrality : Zero degree hadronic calorimeters (ZDC) + electromagnetic calorimeters (ZEM) E ZDC, E ZEM N spec N part Impact parameter (b )  b ~ 1fm b gen (fm) b rec (fm) reconstructed N part generated  Npart ~15

34 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 34 electron D & B: Expected p t coverage 1 year at nominal luminosity (10 7 central Pb-Pb events, 10 9 pp events) D 0  K  B  e + X

35 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 35 Charm reconstruction: D 0  K -  + Exclusive reconstruction: ideal to study R AA Large combinatorial background (dN ch /dy=2-3  10 3 in central Pb-Pb!) Main selection: displaced-vertex selection pair of opposite-charge tracks with impact parameters ~100  m good pointing of reconstructed D 0 momentum to the primary vertex Invariant mass analysis < 60  m (r  ) for p t > 1 GeV/c Resolution mainly provided by the 2 layers of silicon pixels

36 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 36 Beauty via displaced electrons Primary Vertex B e X d0d0 rec. track ALICE has excellent electron identification capabilities (TRD + TPC) Displaced electrons from B decays can be tagged by an impact parameter cut

37 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 37 Heavy quark production at LHC: a probe of small-x gluons Probe small-x region with HQs at low p T and/or forward y Charm production at low p T : Q 2 (4m c 2 ~ 5 GeV 2 ) ~ Q s 2 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 Cartoon charm beauty PYTHIA charm

38 Cogresso SIF 2008, Genova, 24.09.2008 Andrea Dainese 38 Low-x at LHC: forward J/  in ALICE (2.5 <|  |< 4) J/  measurement in  -spectrometer  xg(x) at x 2 ~10 -5 : d  /dy J/  : NLO CEM, varying PDFs QQbar: Sensitive to different PDFs and DGLAP versus CGC predictions (Note: m J/  ~Q s at the LHC) pp @ 14 TeV

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