RHIC Physics and the importance of particle identification

1. RHIC Physics and the importance of particle identification R. Bellwied (Wayne State University)

2. Did we serve up the perfect liquid ?(The AIP Science Story of 2005) • “The truly stunning finding at RHIC that the new state of matter created in the collisions of gold ions is more like a liquid than a gas gives us a profound insight into the earliest moments of the universe. The possibility of a connection between string theory, cosmology and RHIC collisions is unexpected and exhilarating. It may well have a profound impact on the physics of the twenty-first century.” said Dr. Raymond L. Orbach, Director of the DOE Office of Science. • “Once again, the physics research sponsored by the Department of Energy is producing historic results,” said Secretary of Energy Samuel Bodman. “The DOE is the principal federal funder of basic research in the physical sciences, including nuclear and high-energy physics. With today’s announcement we see that investment paying off.”

3. To understand the strong force and the phenomenon of confinement: Create and study a system of deconfined colored quarks (and gluons) quark-antiquark pair created from vacuum Analogies and differences between QED and QCD to study structure of an atom… electron …separate constituents Imagine our understanding of atoms or QED if we could not isolate charged objects!! nucleus neutral atom Confinement: fundamental & crucial (but not understood!) feature of strong force - colored objects (quarks) have  energy in normal vacuum quark Strong color field Force grows with separation !!! “white” 0 (confined quarks) “white” proton (confined quarks) “white” proton

4. Generating a deconfined state • Present understanding of Quantum Chromodynamics (QCD) • heating • compression •  deconfined color matter ! Hadronic Matter (confined) Nuclear Matter (confined) Quark Gluon Plasma deconfined !

5. Expectations from Lattice QCD /T4 ~ # degrees of freedom confined: few d.o.f. deconfined: many d.o.f. TC ≈ 173 MeV ≈ 21012 K ≈ 130,000T[Sun’s core] C  0.7 GeV/fm3

6. The phase diagram of QCD Early universe quark-gluon plasma critical point ? Tc Temperature colour superconductor hadron gas nucleon gas nuclei CFL r0 Neutron stars vacuum baryon density

7. PHOBOS BRAHMS RHIC Au+Au @ sNN=200 GeV PHENIX STAR AGS TANDEMS Relativistic Heavy Ion Collider (RHIC) 1 km v = 0.99995c

8. Study all phases of a heavy ion collision If the QGP was formed, it will only live for 10-22 s !!!! BUT does matter come out of this phase the same way it went in ???

10. The STAR Experiment 450 scientists from 50 international institutions Conceptual Overview

11. Actual Collision in STAR TPC QGP signatures: strangeness enhancement, early collectivity partonic degrees of freedom, energy loss in medium

12. Canonical suppression increases with increasing strangeness Strangeness yields from pp to AA LandX are not flat Production not well modeled by Npart (correlation volume)

13. Y Directed flow Elliptic flow Time X Elliptic(anisotropic)flow – a strong indicator of early collectivity Flow Y Out-of-plane In-plane Reaction plane Flow X Dashed lines: hard sphere radii of nuclei

14. Elliptic flow described by fluid dynamics

15. Λ->p+π(64%) • Kμν (63%) • Kππ0 (21%) Charged -> positive+negative (V0) Charged -> charged + neutral (Kink) Kink analysis in STAR L = baryon (q-q-q) = u-d-s K = meson (q-qbar) = ubar-s or u-sbar

16. Constituent quarks might be relevant

17. Fate of jets in heavy ion collisions? idea: p+p collisions @ same sNN = 200 GeV as reference p p ?: what happens in Au+Au to jets which pass through medium? • Prediction: scattered quarks radiate energy (~ GeV/fm) in the colored medium: • decreases their momentum (fewer high pT particles) • “kills” jet partner on other side ? Au+Au

18. High pt suppression at RHIC • strange RCP well behaved • all particles have same RCP for pT>~5 GeV: dominance of fragmentation? • no flavor dependence in fragmentation region ?

19. An unexpected liquid phase with very drastic thermodynamic properties ? liquid ? The ideal liquid requires very strong interaction cross sections, vanishing mean free path and sudden thermalization (in less than 1 fm/c). Perturbative calculations of gluon scattering lead to long equilibration times (> 2.6 fm/c) and very small v2 The state above Tc can not be simple mass less partons = constituent quarks Liquid

20. First time in Heavy-Ion Collisions a system created which, at low pt ,is in quantitativeagreement with ideal hydrodynamic model. The new phase behaves like an ideal liquid. But are the degrees of freedom partonic ? A novel ideal liquid behavior

21. ? An example: lower viscosity bound in strong quantum field theory Motivated by calculation of lower viscosity bound in black hole via supersymmetric N=4 Yang Mills theory in AdS (Anti deSitter) space (conformal field theory) 400 times less viscous than water,10 times less viscous than superfluid helium !

22. An example: thermalization through Hawking mechanism Black holes emit thermalized Hawking radiation due to strongly varying accelerator gradients on both sides of the event horizon (splitting of e+e- pair from virtual photons). RHIC collisions might have black-hole like gradients due to very different gluon densities inside and outside the fireball (leads to a-gradients). This might explain sudden thermalization

23. Conclusions • We have successfully created • the Quark Gluon Plasma, an • early universe phase of matter, • which might still exist in black • holes. Surprisingly it behaves • like a perfect liquid !! • Now we need to understand its exciting properties: • low viscosity • rapid equilibration (thermalization) • novel hadron formation mechanisms • jet quenching and medium reaction • temperature determination • degrees of freedom

24. 5-10 GeV static electron ring recirculating linac injector RHIC e-cooling EBIS BOOSTER AGS LINAC A three prong approach: improved facility expanded facility higher energy The future is bright EoS of sQGP QCD, CGC, QGP wQGP (?) LHC (2008-2020 ?): Large Hadron Collider with ALICE, CMS, ATLAS heavy ion programs RHIC-II (2008-2013): Upgrades to STAR & PHENIX QCDLab (2013---): A high luminosity RHIC with eA and AA detectors