Quark Gluon Plasma; in AA, pA and pp collisions? what can we learn - PowerPoint PPT Presentation

Quark Gluon Plasma; in AA, pA and pp collisions? what can we learn from that? Raimond Snellings Nikhef colloquium 2016 1

What happens when you heat and compress matter to very high temperatures and densities? Do we understand what QCD tells us? Quark Gluon Plasma (QGP) Electroweak phase transition QCD phase transition 100,000 x T core sun 2


 Lattice QCD and the Phase Diagram Early Universe 16 non-int. limit tions 
 12 HRG T c 8 3p/T 4 ε /T 4 3s/4T 3 Critical Point ? 4 tions, T [MeV] 0 130 170 210 250 290 330 370 t finite μ B hotQCD collab: arXiv:1407.6387 • at μ B =0 we have rather reliable calculations from the lattice • at larger μ B conflicting results from the lattice • for all cases the lattice calculations tell us (currently) very little about the (transport) properties of the matter • in case of a strongly interacting system, using e.g. the AdS/CFT correspondence, the energy density over 4 reaches about 70% of the non-interacting limit, not so different from lattice QCD! T • what are the relevant degrees of freedom? 3

How to connect observables to lattice QCD predictions? • try to create a large hot and dense system for which thermodynamics/hydrodynamics can be applied • collide heavy-ions at the highest energies possible 4

Our current picture pre-equilibrium flow? AdS/CFT? CGC? hadron cascade? 5

How to connect observables to lattice QCD predictions? • many of the quantities calculable on the lattice are difficult/ impossible to measure directly from the observed particle distributions • not well constrained contributions of e.g. initial conditions, different phases, hadronization, …. • need some extra reference of other well understood control parameters • pp collisions and pA collisions as reference? 6

How to connect observables to lattice QCD predictions? 6 = 6 = pp pA AA 6 = 6 = 7

The ratio of scaled pp, pA and AA ALICE, charged particles 1.8 p-Pb s = 5.02 TeV, NSD, | | < 0.3 η NN cms 1.6 Pb-Pb s = 2.76 TeV, 0-5% central, | | < 0.8 η NN Pb-Pb s = 2.76 TeV, 70-80% central, | | < 0.8 η 1.4 NN PbPb 1.2 , R 1 pPb 0.8 R 0.6 0.4 0.2 0 2 4 6 8 10 12 14 16 18 20 p (GeV/c) T ALI − PUB − 44351 The Jack fruit is much heavier than a comparable amount of grapes or mixed fruit 8

How to connect observables to lattice QCD predictions? • many of the quantities calculable on the lattice are difficult/ impossible to measure directly from the observed particle distributions • not well constrained contributions of e.g. different phases, hadronization, …. • need some extra reference of other well understood control parameters • pp collisions as reference, pA collisions as reference? • geometry as a control parameter? 9

A Heavy-Ion Collision spectators b participants UrQMD 10

The transverse plane Howard Wieman 11

Elliptic Flow Ollitrault 1992 Animation: Mike Lisa 1) superposition of independent p+p: momenta pointed at random relative to reaction plane b 12

Elliptic Flow 1) superposition of independent p+p: high density / pressure momenta pointed at random at center relative to reaction plane 2) evolution as a bulk system pressure gradients (larger in-plane) push bulk “out” à “flow” “zero” pressure in surrounding vacuum more, faster particles seen in-plane b 13

Elliptic Flow 1) superposition of independent p+p: v 2 = ⇥ cos 2( φ � Ψ R ) ⇤ = 0 N momenta pointed at random relative to reaction plane π 0 π /4 π /2 3 π /4 φ - Ψ RP (rad) 1.6 Normalized Counts 2) evolution as a bulk system v 2 = ⇥ cos 2( φ � Ψ R ) ⇤ 1.4 b ≈ 6.5 fm pressure gradients (larger in-plane) b ≈ 4 fm push bulk “out” à “flow” 1.2 1 more, faster particles seen in-plane 0.8 0.6 0.4 0 0.5 1 1.5 2 2.5 3 φ Ψ - (rad) lab plane 14

What do we measure? We do not know the reaction plane ψ R or in more general ψ n v n ⌘ h e in ( ϕ − Ψ n ) i We can calculate these observables only using correlations hh e in ( ϕ 1 − ϕ 2 ) ii = hh e in ( ϕ 1 ) iihh e in ( ϕ 2 ) ii + hh e in ( ϕ 1 − ϕ 2 ) i c i zero for symmetric detector when averaged over many events hh e in ( ϕ 1 − ϕ 2 ) ii = hh e in ( ϕ 1 − Ψ n − ( ϕ 2 − Ψ n )) ii hh e in ( ϕ 1 − Ψ n ) ih e − in ( ϕ 2 − Ψ n ) ii = h v 2 n i = when only ψ n correlations are present 15

What do we measure? offline (b) CMS MinBias, 1.0GeV/c<p <3.0GeV/c (a) CMS PbPb s = 2.76 TeV, 220 ≤ N < 260 NN trk T trig 1 < p < 3 GeV/c T assoc 1 < p < 3 GeV/c T ) φ ∆ 1 φ pair ∆ , 2.8 η d N 0 η ∆ 2 2.6 ∆ d d R( -1 2.4 trig 1 N 4 4 4 2 2 4 ∆ ∆ φ -4 -2 0 φ 2 ( 2 r η 0 a ∆ d 0 i a η n ∆ 0 s -2 ) -4 In minimum bias pp collisions clear jet near and away side peak In PbPb long ridge structures on near and away side Signatures of correlations due to the initial stage (geometry) and in PbPb final state interactions (which translate spatial geometry into momentum space) 16

How do we quantify these ridges? offline (a) CMS PbPb s = 2.76 TeV, 220 N < 260 ≤ NN trk trig 1 < p < 3 GeV/c T assoc The long range correlations 1 < p < 3 GeV/c T can be characterised by the φ pair ∆ 2.8 d N η flow Fourier harmonics such as 2 2.6 ∆ d d 2.4 trig 1 v 2 , which is the most dominant N 4 4 ∆ φ 2 ( 2 r a d 0 i a η n ∆ 0 s -2 ) -4 dN pair 1 d ∆ φ = N assoc X [1 + 2 V n ∆ cos( n ∆ φ )] 2 π N trig n 17

Collective motion p 2 particle 1 coming from the resonance. Out of p 1 remaining M-1 particles there is only one which is coming from the same resonance, particle 2. Hence a probability that out of M particles we will select two coming from the same resonance is ~ 1/(M-1). From this we can draw a conclusion that for large multiplicity: • therefore to reliably measure flow: • not easily satisfied: M=200 v n >> 0.07 18

Collective motion cumulants allow us to see if there are multi-particle correlations in the system (cumulants nonzero only mathematical proof) 19

What do we measure? Build cumulants with multi-particle correlations (Ollitrault and Borghini, 2000) got rid of 2-particle correlations not related to collective flow however now we measure higher moment moments of the distribution mathematical framework to calculate these analytically developed at Nikhef and used by all RHIC and LHC experiments 20

What do we measure? if the fluctuations are small or for a special pdf we can say for any distributions that the various flow estimates follow: 21

Integrated v 2 0.12 2 v 0.1 0.08 0.06 v {2} 2 v {2} (same charge) 0.04 2 v {4} 2 v {4} (same charge) 2 v {q-dist} 2 0.02 v {LYZ} 2 v {EP} STAR 2 v {LYZ} STAR 2 0 0 10 20 30 40 50 60 70 80 centrality percentile 22

Collision energy dependence of elliptic flow as function of transverse momentum 0.25 {4} ALICE Phys. Rev. Lett. 105, 252302 (2010) 2 v STAR Phys. Rev. C. 86, 054908 (2012) charged particles, centrality 20-30% 0.2 0.15 0.1 ALICE 2.76 TeV STAR 200 GeV STAR 62.4 GeV STAR 39 GeV 0.05 STAR 27 GeV STAR 19.6 GeV STAR 11.5 GeV STAR 7.7 GeV 0 0 1 2 3 4 5 p (GeV/ c ) T 23

Collective behaviour 2 v 0.16 VISH2+1 Phys. Rev. C84, 044903 (2011) 0.14 centrality 10-20% 0.12 0.1 0.08 0.06 π K 0.04 p φ 0.02 Λ Ξ VISH2+1 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 p (GeV/ c ) T In a hydro picture particles have a common temperature and flow velocity at freeze-out. The difference in p T -differential elliptic flow depends mainly on one parameter: the mass of the particle 24

Hydrodynamic behaviour 2 v Hydro, s = 2.76 TeV NN 0.08 π p Hydro, s = 62.4 GeV NN 0.06 π p 0.04 centrality 0-10% MC Glauber, /s = 0.08 η 0.02 0 Chun Shen, private communication 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 p (GeV/ c ) T hydro picture particles have a common temperature and flow velocity larger radial flow increases mass splitting 25

Collision energy dependence of elliptic flow for particles with different masses STAR QM2014 ALICE arXiv:1405.4632 0.35 0.35 2 2 v v Au-Au s = 62.4 GeV (STAR Preliminary) Pb-Pb s = 2.76 TeV (ALICE Preliminary) NN NN 0.3 0.3 centrality 10-40% centrality 20-30% 0.25 0.25 0.2 0.2 0.15 0.15 + ± π π 0.1 0.1 0 + ± K K + K p p + p 0.05 0.05 + Λ Λ Λ - + + Ξ Ξ + Ξ 0 0 0 1 2 3 4 5 0 1 2 3 4 5 p (GeV/ c ) p (GeV/ c ) T T mass hierarchy follows hydrodynamic picture at low p T ! 26