Hot andPrecision Dense Extraction QCD Matterof QGP Properties Unraveling the Mysterieswith Quantified of the Strongly Uncertainties Interacting Quark-Gluon-Plasma

A CommunitySteffen White Paper A. Basson the Future of Relativistic Heavy-Ion Physics in the US arXiv:1605.03954 Jonah E. Bernhard

J. Scott Moreland Jia Liu Ulrich Heinz + many other collaborators Introduction Phases of Matter

Ordinary Matter: • phases determined by (electro- magnetic) interaction • apply heat & pressure to study phase-diagram

3 Phases of Matter

Ordinary Matter: Phases of QCD matter: • phases determined by (electro- • heat & compress QCD matter: magnetic) interaction ‣collide heavy atomic nuclei • apply heat & pressure to study • numerical simulations: phase-diagram ‣solve partition function (Lattice)

3 Heating & Compressing QCD Matter

The only way to heat & compress QCD matter under controlled laboratory conditions is by colliding two heavy atomic nuclei! Heating & Compressing QCD Matter

ALICE experiment @ CERN: The only way to heat & compress QCD matter under controlled laboratory conditions is by colliding two heavy atomic nuclei!

• 1000+ scientists from 105+ institutions • dimensions: 26m long, 16m high, 16m wide • weight: 10,000 tons two more experiments w/ Heavy-Ions: • CMS, ATLAS Heating & Compressing QCD Matter

ALICE experiment @ CERN: typical Pb+Pb collision @ LHC: The only way to heat & compress QCD matter under controlled laboratory conditions is by colliding two heavy atomic nuclei!

• 1000+ scientists from 105+ institutions • 1000s of tracks • dimensions: 26m long, 16m high, 16m wide • task: reconstruction of final state to • weight: 10,000 tons characterize matter created in collision two more experiments w/ Heavy-Ions: • CMS, ATLAS Time Evolution of a Heavy-Ion Collision

hadronic phase QGP and and freeze-out hydrodynamic expansion initial state

pre-equilibrium hadronization

• Initial State: • QGP and hydrodynamic expansion: - fluctuates event-by-event - proceeds via 3D viscous RFD - classical color-field dynamics - EoS from Lattice QCD

• Pre-equilibrium: • hadronic phase & freeze-out - rapid change-over from glue-field dominated - interacting hadron gas initial state to thermalized QGP - separation of chemical and - time scale: 0.15 to 2 fm/c in duration kinetic freeze-out - significant conceptual challenges! Time Evolution of a Heavy-Ion Collision

hadronic phase QGP and and freeze-out hydrodynamic expansion initial state

pre-equilibrium hadronization

• Initial State: • QGP and hydrodynamic expansion: - fluctuates event-by-event - proceeds via 3D viscous RFD Principal- classical Challenges color-field of dy Probingnamics the QGP -withEoS Heavy-Ionfrom Lattice Collisions:QCD • time-scale of the collision process: 10-24 seconds! [too short to resolve] • characteristic length scale: 10-15 meters! [too small to resolve] • Pre-equilibrium: • hadronic phase & freeze-out • confinement: quarks & gluons form bound states, experiments don’t observe them directly - rapid change-over from glue-field dominated - interacting hadron gas ‣computationalinitial state to modelsthermalized are QGP need to connect the experiments to QGP properties! - separation of chemical and - time scale: 0.15 to 2 fm/c in duration kinetic freeze-out - significant conceptual challenges! Modeling of Heavy-Ion Collisions microscopic transport models based (viscous) relativistic fluid dynamics: on the Boltzmann Equation: • transport of macroscopic degrees of freedom • transport of a system of microscopic particles • based on conservation laws: • all interactions are based on binary scattering p + f (p, r, t)= C(p, r, t) t E r 1 processes Tik = uiuk + P (ik + uiuk) 2 u + u u i k k i 3 ik · diffusive transport models based on the Langevin Equation: + u ik · • transport of a system of microscopic particles in (plus an additional 9 eqns. for dissipative flows) a thermal medium • interactions contain a drag term related to the properties of the medium and a noise term hybrid transport models: representing random collisions • combine microscopic & macroscopic degrees p(t + t)=p(t) v t+(t)t of freedom 2T · • current state of the art for RHIC modeling

6 Modeling of Heavy-Ion Collisions microscopic transport models based (viscous) relativistic fluid dynamics: on the Boltzmann Equation: • transport of macroscopic degrees of freedom • transport of a system of microscopic particles • based on conservation laws: • all interactions are based on binary scattering p + f (p, r, t)= C(p, r, t) t E r 1 processes Tik = uiuk + P (ik + uiuk) 2 u + u u i k k i 3 ik · diffusive transport models based on the Langevin Equation: + u ik · • transport of a system of microscopic particles in (plus an additional 9 eqns. for dissipative flows) a thermal medium • interactions contain a drag term related to the properties of the medium and a noise term hybrid transport models: representing random collisions • combine microscopic & macroscopic degrees p(t + t)=p(t) v t+(t)t of freedom 2T · • current state of the art for RHIC modeling

Each transport model relies on roughly a dozen physics parameters to describe the time-evolution of the collision and its final state. These physics parameters act as a representation of the information we wish to extract from RHIC & LHC. 6 QCD Transport Coefficients: Shear Viscosity QCD Transport Coefficients: Shear Viscosity

shear and bulk viscosity are defined as the coefficients in the expansion of the stress tensor in terms of the velocity fields: 2 T = ⇤u u + P ( + u u ) ⇥ u + u u +⌅ u ik i k ik i k ⇤i k ⇤k i 3 ik⇤ · ik⇤ · ⇥ QCD Transport Coefficients: Shear Viscosity

shear and bulk viscosity are defined as the coefficients in the expansion of the stress tensor in terms of the velocity fields: 2 T = ⇤u u + P ( + u u ) ⇥ u + u u +⌅ u ik i k ik i k ⇤i k ⇤k i 3 ik⇤ · ik⇤ · ⇥

assuming matter to be quasi-particulate in nature:

microscopic kinetic theory: unitary limit on cross sections η is given by the rate of momentum suggests a lower bound for η transport 1 p¯ 4⇥ p¯3 np¯⇥f = ⇤tr 2 3 3⇤tr p¯ ⇤ ⇥ 12⇥

• viscosity decreases with increasing cross section (forget molasses!) • for viscous RFD, the microscopic origin of viscosity is not relevant! QCD Transport Coefficients: Shear Viscosity

shear and bulk viscosity are defined as the coefficients in the expansion of the stress tensor in terms of the velocity fields: 2 T = ⇤u u + P ( + u u ) ⇥ u + u u +⌅ u ik i k ik i k ⇤i k ⇤k i 3 ik⇤ · ik⇤ · ⇥

assuming matter to be quasi-particulate in nature:

microscopic kinetic theory: unitary limit on cross sections η is given by the rate of momentum suggests a lower bound for η transport 1 p¯ 4⇥ p¯3 np¯⇥f = ⇤tr 2 3 3⇤tr p¯ ⇤ ⇥ 12⇥

• viscosity decreases with increasing cross section (forget molasses!) • for viscous RFD, the microscopic origin of viscosity is not relevant!

The determination of the QCD transport coefficients is one of the key goals of the US relativistic heavy-ion effort! Collision Geometry: Elliptic Flow

• two nuclei collide rarely head-on, but mostly with an offset: Reaction z plane

only matter in the overlap area y gets compressed and heated up

x Collision Geometry: Elliptic Flow

• two nuclei collide rarely head-on, but mostly with an offset: Reaction z plane

only matter in the overlap area y gets compressed and heated up

x

elliptic flow (v2): • gradients of almond-shape surface will lead to preferential emission in the reaction plane • asymmetry out- vs. in-plane emission is quantified by nd 2 Fourier coefficient of angular distribution: v2 Ø vRFD: good agreement with data for very small η/s Temperature Dependence of η/s what can ordinary matter, e.g. He or H2O teach us about η/s?

He

H2O

• η/s has minimum & discontinuity at TC Temperature Dependence of η/s what can ordinary matter, e.g. temperature dependence of η/s in QCD can be estimated in low- and high-temperature limit: He or H2O teach us about η/s? • low temperature: chiral pions • high temperature: QGP in HTL approximation

He pQCD/HTL AdS/CFT vRFD

H2O terra incognita

• η/s has minimum & L.P. Csernai, J.I. Kapusta & L. McLerran: Phys. Rev. Lett. 97: 152303 (2006) M. Prakash, M. Prakash, R. Venugopalan & G. Welke: Phys. Rept. 227, 321 (1993) discontinuity at TC P. Arnold, G.D. Moore & L.D. Yaffe: JHEP 05: 051 (2003) The Challenge of a rigorous Model to Data Comparison

Model Parameter: experimental data: eqn. of state π/K/P spectra shear viscosity yields vs. centrality & beam initial state elliptic flow pre-equilibrium dynamics HBT thermalization time charge correlations & BFs quark/hadron chemistry density correlations particlization/freeze-out The Challenge of a rigorous Model to Data Comparison

Model Parameter: experimental data: eqn. of state π/K/P spectra shear viscosity yields vs. centrality & beam initial state elliptic flow pre-equilibrium dynamics HBT thermalization time charge correlations & BFs quark/hadron chemistry density correlations particlization/freeze-out The Challenge of a rigorous Model to Data Comparison

Model Parameter: experimental data: eqn. of state π/K/P spectra shear viscosity yields vs. centrality & beam initial state elliptic flow pre-equilibrium dynamics HBT thermalization time charge correlations & BFs quark/hadron chemistry density correlations particlization/freeze-out • large number of interconnected parameters w/ non-factorizable data dependencies • data have correlated uncertainties • develop novel optimization techniques: Bayesian Statistics and MCMC methods • transport models require too much CPU: need new techniques based on emulators • general problem, not restricted to RHIC Physics →collaboration with Statistical Sciences Precision Cosmology

comparison of Planck 2015 temperature power Planck EE+lowP Planck TE+lowP spectrum with the ΛCDM cosmological model: Planck TT+lowP Planck TT,TE,EE+lowP 6000

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