RHIC Physics and the importance of particle identification R. Bellwied (Wayne State University)
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.”
Strong color field Force grows with separation !!! Analogies and differences between QED and QCD to study structure of an atom… “white” proton …separate constituents Imagine our understanding of atoms or QED if we could not isolate charged objects!! nucleus electron quark quark-antiquark pair created from vacuum “white” proton (confined quarks) “white” 0 (confined quarks) Confinement: fundamental & crucial (but not understood!) feature of strong force - colored objects (quarks) have energy in normal vacuum neutral atom To understand the strong force and the phenomenon of confinement: Create and study a system of deconfined colored quarks (and gluons)
Generating a deconfined state Nuclear Matter (confined) Hadronic Matter (confined) Quark Gluon Plasma deconfined ! Present understanding of Quantum Chromodynamics (QCD) heating compression deconfined color matter !
Expectations from Lattice QCD /T 4 ~ # degrees of freedom confined: few d.o.f. deconfined: many d.o.f. T C ≈ 173 MeV ≈ 2 K ≈ 130,000 T[Sun’s core] C 0.7 GeV/fm 3
The phase diagram of QCD Temperature baryon density Neutron stars Early universe nuclei nucleon gas hadron gas colour superconductor quark-gluon plasma TcTc 00 critical point ? vacuum CFL
RHIC BRAHMS PHOBOS PHENIX STAR AGS TANDEMS Relativistic Heavy Ion Collider (RHIC) 1 km v = c s NN =200 GeV
Study all phases of a heavy ion collision If the QGP was formed, it will only live for s !!!! BUT does matter come out of this phase the same way it went in ???
microexplosionsfemtoexplosions ss0.1 J 1 J J/m 3 5 GeV/fm 3 = J/m 3 T10 6 K200 MeV = K rate10 18 K/s10 35 K/s
The STAR Experiment 450 scientists from 50 international institutions Conceptual Overview
Actual Collision in STAR TPC QGP signatures: strangeness enhancement, early collectivity partonic degrees of freedom, energy loss in medium
Strangeness yields from pp to AA Production not well modeled by N part (correlation volume) Canonical suppression increases with increasing strangeness and are not flat
Elliptic (anisotropic) flow – a strong indicator of early collectivity Dashed lines: hard sphere radii of nuclei Reaction plane In-plane Out-of-plane Y X Flow Y X Time Directed flowElliptic flow
Elliptic flow described by fluid dynamics
Kink analysis in STAR Λ->p+π(64%) Charged -> positive+negative (V0) K μν (63%) K ππ0 (21%) Charged -> charged + neutral (Kink) = baryon (q-q-q) = u-d-s K = meson (q-qbar) = ubar-s or u-sbar
Constituent quarks might be relevant
Fate of jets in heavy ion collisions? p p ? Au+Au idea: p+p same s NN = 200 GeV as reference ?: 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 p T particles) “kills” jet partner on other side
High pt suppression at RHIC strange R CP well behaved all particles have same R CP for p T >~5 GeV: dominance of fragmentation? no flavor dependence in fragmentation region ?
An unexpected liquid phase with very drastic thermodynamic properties ? 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 T c can not be simple mass less partons = constituent quarks liquid ? Liquid
A novel ideal liquid behavior First time in Heavy-Ion Collisions a system created which, at low p t,is in quantitative agreement with ideal hydrodynamic model. The new phase behaves like an ideal liquid. But are the degrees of freedom partonic ?
400 times less viscous than water,10 times less viscous than superfluid helium ! ? 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)
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 -gradients). This might explain sudden thermalization
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 Conclusions
The future is bright A three prong approach: improved facility expanded facility higher energy LHC ( ?): Large Hadron Collider with ALICE, CMS, ATLAS heavy ion programs RHIC-II ( ): Upgrades to STAR & PHENIX EoS of sQGP QCD, CGC, QGP wQGP (?) QCDLab ( ): A high luminosity RHIC with eA and AA detectors AGS BOOSTER RHIC e- cooling LINAC EBIS recirculating linac injector 5-10 GeV static electron ring