Heavy Ions at LHC R. Lietava The University of Birmingham 0 - PowerPoint PPT Presentation

Heavy Ions at LHC R. Lietava The University of Birmingham 0

Outlook  QGP  Event characterisation  Soft probes  I nterferom etry  Multiplicity, Transverse energy, Energy density  Flow and correlations  Hard Probes  Quarkonia  Jet quenching  High pt suppression ( h - ,D0 ,J/ ψ , γ,Z ,...)  Reconstructed jets  Sum m ary 23/ 11/ 2011 Birmingham

Quantum ChromoDynamics (QCD) QCD confinement – free quarks never observed ! QCD vacuum not well understood. Heavy ions – study QCD at high temperature and density 23/ 11/ 2011 Birmingham

Quark Gluon Plasma  Latice QCD: transition hadrons -> quarks and gluons QGP is not ideal gas ! ε π   2 T 4 7 = = +   p g g B F   3 8 90 g B =8 c *2 s =16 g F =3 f *3 c *2 s *2 a =36  Relativistic Heavy Ion Collider (RHIC):  Macroscopic liquid:  System size > mean free path  System lifetime > relaxation time  Perfect: shear viscosity/ entropy ~ 0  LHC :  System is bigger, denser, hotter  Abundant production of hard probes 23/ 11/ 2011 Birmingham

LHC Heavy Ion Program LHC Heavy Ion Data-taking Design: Pb + Pb at √ s NN = 5.5 TeV (1 month per year) Nov. 2010: Pb + Pb at √ s NN = 2.76 TeV • LHC Collider Detectors - ATLAS - CMS - ALICE 23/ 11/ 2011 Birmingham

Pb–Pb Luminosity B.Wyslouch, CMS, EPIC2011 Delivered integrated luminosity ~ 9 µ b -1 Luminosity achieved L = 2–3 x 10 25 cm -2 s -1 ATLAS very similar to CMS ALICE recorded ~ 50% due to TPC dead time 23/ 11/ 2011 Birmingham

Heavy Ion Collision Centrality Controls the volume and shape of the system Multiplicity and energy of produced particles are correlated with geometry of collisions. Measured distribution: • Track multiplicity • Transverse energy • Forward energy b Participants Variables: (10) • impact parameter => Collisions • participants • collisions (18) • percentile of x section Plane perpendicular y Beam direction to beam direction x 23/ 11/ 2011 Birmingham

Centrality selection ALICE S.White, ATLAS, EPIC2011 B.Wyslouch, CMS,EPIC2011 M.Nicassio, ALICE, EPIC2011 23/ 11/ 2011 Birmingham

Soft Probes  Interferometry of identical particles  Charged particle multiplicity , E T , ε  Transverse momentum spectra  Radial flow  Anisotropic flow 8

System size  Spatial extent of the particle emitting source extracted from interferometry of identical bosons  Two-particle momentum correlations in 3 orthogonal directions -> HBT radii (R long , R side , R out )  Size: twice w.r.t. RHIC  Lifetime: 40% higher w.r.t. RHIC ALICE: PLB696 (2011) 328 ALICE: PLB696 (2011) 328 9 9 F.Prino,SQM2011

Multiplicity, E T and ε  Particle Production and Energy density ε:  Produced Particles: dN ch / d η ≈ 1600 ± 7 6 ( syst) ≈ 30,000 particles in total, ≈ 400 times pp !  somewhat on high side of expectations (tuned to RHIC)  growth with energy faster in AA  E 1 dE Energy density ε > 3 x RHI C (fixed τ 0, ) ε τ = =  T ( ) CMS, QM2011 τ V A dy  Tem perature + 3 0 % 0 23/ 11/ 2011 Birmingham

Charged particle spectra Radial Flow • K, π, p spectra 0-5% central collisions • Very clear flattening and higher tails at √ s NN =2.76 TeV • Quantify with blastwave parameter studies: radial flow β =v 0 /c and freezout temperature T fo β = 0.66 T fo ~110 MeV L.Barnby , ALICE, EPIC2011 23/ 11/ 2011 Birmingham

Anisotropic Flow  Fourier expansion in azimuthal distribution: dN 1 dN ( ) = + ϕ − ψ + ϕ − ψ + 1 2 v cos( ) 2 v cos( 2 ( )) ... ϕ π 1 1 2 2 p dp dyd 2 p dp dy T T T T  φ – azimuthal angle In non-central collisions participant area is not azimuthally symmetric: system evolution transfer this anisotropy from coordinate space to momentum space v 1 - direct flow v 2 - elliptic flow, dominant for system Collision Plane : symmetric wrt Collision Plane 12 - Defined by Beam and Impact Parameter

Elliptic flow - v 2 Adopted from R.Snellings 23/ 11/ 2011 Birmingham

Physics of elliptic flow Elliptic flow depends on:  Initial conditions  Fluid properties  Equation of state  Shear viscosity η = < > λ =< > σ Shear viscosity: n p p / Small viscosity η = > large cross section σ = > strongly interacting fluid 23/ 11/ 2011 Birmingham

R.Snellings, ALICE 23/ 11/ 2011 Birmingham Heavy ions in LHC: experimental 15 EPIC Bari

Hydrodynamics and v 2  comparison of identified particles v 2 (p T ) with hydro prediction – mass splitting described (calculation by C Shen et al.: arXiv: 1105.3226 [ nucl-th] )  Protons are to be understood  23/ 11/ 2011 Birmingham

Fluctuations  v 3 “ideal” shape of participants’ overlap  is ~ elliptic  in particular: no odd harmonics expected  participants’ plane coincides with event plane but fluctuations in initial conditions:   participants plane != event plane Matt Luzum (QM 2011)  v 3 (“triangular”) harmonic appears [ B Alver & G Roland, PRC81 (2010) 054905] v 2 and indeed, v3 != 0 !  v 3 has weaker centrality dependence  than v 2 v 3 ALICE: PRL 107 (2011) 032301 23/ 11/ 2011 Birmingham

Higher harmonics S.White, ATLAS, EPIC2011 • v n+1 < v n • v n+1 less centrality dependent than v n M.Issah, CMS, EPIC2011 dN 1 dN ( ) = + ϕ − ψ + ϕ − ψ + 1 2 cos( ) 2 cos( 2 ( )) ... v v ϕ π 2 2 3 3 p dp dyd 2 p dp dy T T T T v n – information on viscosity, n > 2 23/ 11/ 2011 Birmingham

2 Particle Correlations and Flow  Fourier expansion in azimuthal distribution: dN ( ) = + ∆ ϕ + ∆ ϕ + 1 2 v cos( ) 2 v cos( 2 ) ... ∆ ϕ 1 2 d = A T  I f flow dom inates than: v v * v i i i Flow Fourier coefficients ∆ ϕ = ϕ − ϕ T A 23/ 11/ 2011 Birmingham

Flow vs Non-Flow Correlations  Compare single calculated values with global fit  To some extent, a good fit suggests flow-type correlations, while a poor fit implies non- flow effects  v 2 to v 5 factorize until p T ~ 3-4 GeV/ c, then jet-like correlations dominate  v 1 factorization problematic (influence of away- side jet) Jan Fiete Grosse-Oetringhaus – ALICE 23/ 11/ 2011 Birmingham

Anisotropic Flow Summary  Centrality and p t dependences of various v n constraint  initial conditions (CGC vs Glauber)  viscosity – η / s  There is no hydro calculation (yet) describing simultaneously data on v 2 and v 3 ,… .  2 particle correlations consistent with flow for p T < 3-4 GeV/ c 23/ 11/ 2011 Birmingham

Speaking of which… Full Fourier decom position of the CMS pp ridge? 23/ 11/ 2011 Birmingham

The nuclear modification factor  quantify departure from binary scaling in AA  ratio of yield in AA versus reference collisions  e.g.: reference is pp  R AA Yield 1 = ⋅ AA R AA Yield Nbin pp AA or peripheral AA  R CP (“central to peripheral”)  … Nbin Yield AA, periph = AA, central ⋅ R cp Yield Nbin AA, periph AA, central 23/ 11/ 2011 Birmingham

Quarkonia suppression  In the plasma phase the interaction potential is expected to be screened beyond the Debye length λ D (analogous to e.m. Debye screening):  Charmonium (cc) and bottonium (bb) states with r > λ D will not bind; their production will be suppressed  Recombination of cc and bb regenerates quarkonia 24

J/ ψ @ LHC: forward y, low p T  LHC: 2.5 < y < 4, p T > 0 (ALICE)  Less suppression than RHI C : 1.2 < y < 2.2, p T > 0 (PHENIX)  As suppressed as RHIC: | y| < 0.35. pT > 0 (PHENIX) Yield 1 = ⋅ AA R AA Yield Nbin pp AA Recombination ? Ginés Martínez – ALICE (QM2011) 23/ 11/ 2011 Birmingham

J/ ψ @ LHC: central y, high p T Yield 1 = ⋅ LHC: | y| < 2.4, p T > 6.5 GeV/ c (CMS) prompt J/ ψ AA  R AA Yield Nbin pp AA CMS: PAS HIN-10-006 ATLAS: PLB 697 (2011) 294  m ore suppressed than RHI C:  | y| < 1. pT > 5 GeV/ c (STAR) inclusive J/ ψ 23/ 11/ 2011 Birmingham

Υ ( 1 S) suppression CMS: PAS HIN-10-006 23/ 11/ 2011 Birmingham

Υ (2S+3S) suppression  additional suppression for Υ (2S+ 3S) w.r.t. Υ (1S) ? CMS: arXiv: 1105.4894 23/ 11/ 2011 Birmingham

Quarkonia Summary  Υ and J/ψ suppressed by same amount ?  Suppression depends on y and pt  the future runs should allow us to establish quantitatively the complete quarkonium suppression(/ recombination?) pattern  high statistic measurements  open flavour baseline / contamination  pA baseline 23/ 11/ 2011 Birmingham

Jets in medium h Leading hadron Fragmentation c radiated radiated gluons gluons a b p a = x a P p b = – x b P d heavy nucleus heavy nucleus Key prediction : jets are quenched • collisional energy loss (Bjorken) • radiative energy loss (Wang and Gyulassy) 30 J .D. Bjorken Fermilab preprint PUB- 82/ 59- THY (August 1982). X.- N. Wang and M. Gyulassy, Phys . Rev . Lett . 68 (1992) 1480