Studies of deconfined matter at the LHC with ALICE A. Andronic – GSI Darmstadt on behalf of the ALICE Collaboration • Introduction: hot QCD (quark-gluon) matter; ALICE apparatus • Hadrons with light-flavor (u,d,s) and the QCD phase diagram • Quarkonium and deconfined matter • Jet quenching (if time allows) • Summary 56th International Winter Meeting on Nuclear Physics - Bormio, Jan. 22-27 2018
Lattice QCD predicts a phase transition A. Andronic - ALICE 2 16 (ideal gas) non-int. limit quarks and gluons ε qg /T 4 = (16 + 7 8 12 N f ) π 2 12 30 N f =3 (u,d,s) HRG T c 8 3p/T 4 ε /T 4 3s/4T 3 4 hadrons (pions) T [MeV] ε had /T 4 = 3 π 2 30 0 130 170 210 250 290 330 370 ≃ 1000 billion K see e.g: A. Bazavov et al., arXiv:1701.04325 transition is a crossover, Y. Aoki et al., Nature 443 (2006) 675 T c ≃ 145-164 MeV, ε c ≃ (0 . 18 − 0 . 5) GeV/fm 3 , or (1.2-3.1) ε nuclear numerical solutions of QCD on a discrete space-time grid (sophisticated formalism, huge computers)
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How to ”simulate” in laboratory the early Universe? A. Andronic - ALICE 4 hadronic phase QGP and and freeze-out hydrodynamic expansion initial state pre-equilibrium hadronization t ≃ 10 − 23 s, V ≃ 10 − 40 m 3 1. initial collisions ( t ≤ t coll = 2 R/γ cm c ; R Pb ≃ 7 fm) 2. thermalization: equilibrium is established ( t � 1 fm/c = 3 × 10 − 24 s) 3. expansion ( ∼ 0 . 6 c ) and cooling ( t < 10-15 fm/ c ) ...deconfined stage? 4. hadronization (quarks and gluons form hadrons) 5. chemical freeze-out: inelastic collisions cease; particle identities (yields) frozen 6. kinetic freeze-out: elastic collisions cease; spectra are frozen ( t + = 3-5 fm/c)
What are the ”control parameters” A. Andronic - ALICE 5 • Energy of the collision (per nucleon pair, √ s NN ) • Centrality of the collision (number of “participating” nucleons, N part ) [at high energies geometric concepts valid: “participant-spectator” picture] measured in percentage of the geometric cross section ( σ AB = π ( R A + R B ) 2 ) NB: we sort the collisions offline, based on detector signals coll inel Pb-Pb =2.76 TeV ( =63 mb) s σ , N NN NN 3 10 part N part N N coll ...while often taking as reference the measurement in proton-proton collisions (at the same energy), for 2 10 “hard probes” (pQCD) scaled by the number of col- lisions corresponding to the given centrality class 10 80-90 70-80 60-70 50-60 40-50 30-40 20-30 10-20 0-10 Centrality range (% of ) σ PbPb
The accelerator complex at CERN A. Andronic - ALICE 6
The accelerator complex at CERN A. Andronic - ALICE 7
The ALICE apparatus A. Andronic - ALICE A. Andronic - ALICE 8 8 arXiv:1402.4476 ALICE Collaboration: 37 countries, 176 institutions, 1800 members
Nucleus-nucleus collisions at the LHC A. Andronic - ALICE 9 a picture of a central collision (about 3200 primary tracks in | η | < 0 . 9 ); “Camera”: Time Projection Chamber [ 5 m length, 5 m diam.; 500 mil. pixels; we take a few 100 pictures per second (and are preparing to take 50000) ]
Nucleus-nucleus collisions: energy density A. Andronic - ALICE 10 16 (GeV) ALICE Preliminary E T : transverse energy ALICE PRC94(2016)034903 14 (energy built from p T ) CMS STAR 12 〉 /2 PHENIX ε LHC ≃ 20 − 40 GeV/fm 3 part NA49 10 E802/E917 N (much above ε c ) WA98 8 〈 / 〉 a ln( /b) η s NN 6 /d b a s T E 4 d ε FAIR � 1 GeV/fm 3 〈 2 (around ε c ) 0 3 2 4 1 10 10 10 10 (GeV) s NN ALI-PREL-118376 self-similar (Hubble-like) homogeneous (hydrodynamic) expansion of the fireball in the longitudinal (beam) direction (”Bjorken model”, J.D. Bjorken, PRD 27 (1983) 140 ) d E T 1 1 Energy density: ε = cτ A T d y - A T = πR 2 : transverse area (Pb-Pb: A T = 154 fm 2 ) - τ ≃ 1 fm/ c : formation time (establishing the equilibrium) ... not measurable!
Particle identification A. Andronic - ALICE 11 dE/dx: truncated mean of 159 samples along a track; resolution: 5.8% lines: Bethe-Bloch parametrization particles and antiparticles are shown
Hadron yields A. Andronic - ALICE 12 π π - + y Matter and antimatter are 3 Pb-Pb s =2.76 TeV, 0-10% centrality /d 10 NN - + 0 N K K K produced in equal amounts in s Yield d 2 p Λ Λ 10 p φ high-energy Pb-Pb collisions + - Ξ Ξ 10 at the LHC + - Ω Ω 1 d d − 1 10 Mass hierarchy in production − 2 10 − 3 3 Data, ALICE Data, ALICE 10 3 He He 3 3 H H Λ Λ − 4 10 − 5 10 4 He 4 He − 6 10 arXiv:1710.07531
Hadron yields and statistical hadronization A. Andronic - ALICE 13 π π - + y Matter and antimatter are 3 Pb-Pb Pb-Pb s s =2.76 TeV, 0-10% centrality =2.76 TeV, 0-10% centrality /d 10 NN NN - + 0 N K K K s produced in equal amounts in Yield d 2 p Λ Λ 10 p φ high-energy Pb-Pb collisions + - Ξ Ξ 10 at the LHC + - Ω Ω 1 d d Best fit: − 1 10 T CF = 156 . 5 ± 1 . 5 MeV − 2 10 µ B = 0 . 7 ± 3 . 8 MeV − 3 3 10 Data, ALICE Data, ALICE 3 He He 3 3 V = 5280 ± 410 fm 3 H H Λ Λ − Statistical Hadronization Statistical Hadronization 4 10 chemical freeze-out − 5 10 4 He 4 He − 6 10 Laboratory creation of a piece of hot Universe when 10 µ s Data/Model 2 old, T ≃ 10 12 K 1.5 1 arXiv:1710.07531 0.5 arXiv:1710.09425 + + - + 0 - - 3 3 3 3 π π - φ Λ Λ Ξ Ξ Ω Ω 4 4 + K K K p p d d He He H H He He Λ s Λ
Thermal fit of hadron abundances A. Andronic - ALICE 14 � ∞ p 2 d p n i = N i /V = − T ∂ ln Z i = g i V ∂µ 2 π 2 exp[( E i − µ i ) /T ] ± 1 0 +1) π + Pb-Pb s =2.76 TeV 3 10 NN + J quantum nr. conservation ensured K /(2 0-10% centrality 2 10 p Λ via chemical potentials: y /d 10 - Ξ N µ i = µ B B i + µ I 3 I 3 i + µ S S i + µ C C i φ d 1 - Ω − 1 d 10 Latest PDG hadron mass spectrum − 2 10 (up to 3 GeV, 500 species) − 3 10 3 He 3 H Λ − 4 10 Data, ALICE ( N exp − N therm ) 2 Minimize: χ 2 = � − 5 Statistical Hadronization 10 i i i 4 σ 2 He total (after decays) − 6 10 i primordial N i : hadron yield ⇒ ( T , µ B , V ) − 7 10 0 0.5 1 1.5 2 2.5 3 3.5 4 Mass (GeV) The hadron abundances are in agreement with a chemically-equilibrated system ...but how can a loosely-bound deuteron “survive” at T=156 MeV?
Chemical freeze-out and the phase diagram of QCD A. Andronic - ALICE 15 − √ s NN (GeV) ← at LHC, remarkable “coincidence” 2760 200 20 5 2.3 with Lattice QCD results 200 T (MeV) Quark-Gluon Matter 180 at LHC ( µ B ≃ 0 ): purely-produced 160 (anti)matter ( m = E/c 2 ), as in the 140 Early Universe Hadronic Matter 120 µ B > 0 : more matter, from “rem- 100 Lattice QCD, T c nants” of the colliding nuclei Borsanyi et al.; HotQCD Collab. 80 Statistical Hadronization, T CF 60 Cleymans, Redlich µ B � 400 MeV: the critical point Vovchenko et al. 40 Becattini et al. awaiting discovery STAR Collab. 20 Andronic et al. Nuclei 0 2 3 1 10 10 10 µ B is a measure of the net-baryon µ B (MeV) density, or matter-antimatter asym- metry arXiv:1710.09425
Proton collisions at the LHC A. Andronic - ALICE 16 pp collision at 7 TeV, “photographed” by ALICE
Proton collisions at the LHC A. Andronic - ALICE 17 pp collision at 7 TeV, “photographed” by ALICE
Hyperon production - from small to large systems A. Andronic - ALICE 18 (big geometric) fireball in Pb–Pb reached with violent pp and p–Pb collisions (grand canonical) statistical description works well in Pb–Pb (with T of QCD phase boundary) is the same mechanism at work in small systems (at large multiplicities)? string hadronization models do not describe data well ...new ideas are being put forward Fischer, Sj¨ ostrand, JHEP 01 (2017) 140 “thermodynamical string fragmentation” ALI-PUB-106878 Nature Physics 13 (2017) 535
Fluctuations of relative hadron production A. Andronic - ALICE 19 − × 3 10 ALICE: 0-5% Pb-Pb (Identity Method), stat. uncertainty 3 Systematic uncertainty ] - quantified by η +K | |<0.8, 0.2< p <1.5 GeV/ c STAR: 0-5% Au-Au (TPC+TOF) + 2 η π ≥ ,K | |<1, , K: 0.2, <1.8 GeV/ p p c T ≥ - p: p 0.4, p <3.0 GeV/ c π T ν dyn [ A, B ] = + PRC92(2015)021901 + π 1 [ dyn � N A ( N A − 1) � + � N B ( N B − 1) � − 2 � N A N B � ν 0 � N A � 2 � N B � 2 � N A �� N B � × 10 the relative strength of fluctuations of 0 ] p ,p+ species A and B - relative strength of cor- - π − 2 + + π relations between species A and B [ dyn − 4 ν (event-by-event) ALICE Pb-Pb s = 2.76 TeV NN × 10 ν dyn [ A, B ] = 0 if A and B are produced in 0 ] - +K + a statistically independent way ,K − 2 p [p+ dyn − 4 ν arXiv:1712.07929 2 3 10 10 10 s (GeV) NN
Collective flow A. Andronic - ALICE 20 R. Snellings, arXiv:1102.3010 dN dϕ ∼ [1 + 2 v 1 · cos( ϕ ) + 2 v 2 · cos(2 ϕ ) + ... ] ϕ is azimuthal angle with respect to reaction plane v 2 = � cos(2 ϕ ) � we call elliptic flow , v 3 = � cos(3 ϕ ) � triangular flow (coefficients)
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