RHIC Physics and the RHIC Physics and the importance of particle identificationimportance 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 fieldForce grows with separation !!!

Analogies and differences between QED and QCDto 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 paircreated 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 Plasmadeconfined !

Present understanding of Quantum Chromodynamics (QCD)• heating• compression deconfined color matter !

Expectations from Lattice QCD/T4 ~ # degrees of freedom

confined:few d.o.f.

deconfined:many d.o.f.

TC ≈ 173 MeV ≈ 21012 K ≈ 130,000T[Sun’s core]C 0.7 GeV/fm3

The phase diagram of QCDT

em

per

atu

re

baryon density

Neutron stars

Early universe

nucleinucleon gas

hadron gascolour

superconductor

quark-gluon plasmaTc

0

critical point ?

vacuum

CFL

RHIC BRAHMSPHOBOS

PHENIXSTAR

AGS

TANDEMS

Relativistic Heavy Ion Collider (RHIC)

1 km

v = 0.99995c

Au+Au @ sNN=200 GeV

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 ???

microexplosions femtoexplosions

s 0.1 J 1 J

1017 J/m3 5 GeV/fm3 = 1036 J/m3

T 106 K 200 MeV = 1012 K

rate 1018 K/s 1035 K/s

The STAR Experiment 450 scientists from 50 international institutions

Conceptual Overview

Conceptual Overview

Actual Collision in STAR TPC

QGP signatures: strangeness enhancement, early collectivitypartonic degrees of freedom, energy loss in medium

Strangeness yields from pp to AA

Production not well modeled by Npart (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

Reactionplane

In-planeOu

t-o

f-p

lan

e

Y

XFlow

Flo

w

Y

XTime

Directed flow Elliptic flow

Elliptic flow described by fluid dynamics

Kink analysis in STAR Λ->p+π(64%) Charged -> positive+negative (V0)

Kμν (63%)Kππ0 (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 collisions @ same sNN = 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 pT particles) “kills” jet partner on other side

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 ?

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 Tc 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 pt ,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 createdthe Quark Gluon Plasma, anearly universe phase of matter,which might still exist in black holes. Surprisingly it behaveslike 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 brightA three prong approach:

improved facility expanded facility higher energy

                                                    

LHC (2008-2020 ?): Large Hadron Colliderwith ALICE, CMS, ATLAS heavy ion programs

RHIC-II (2008-2013):Upgrades toSTAR & PHENIX

EoS of sQGP QCD, CGC, QGP wQGP (?)

QCDLab (2013---):A high luminosityRHIC with eA andAA detectors

AGS

BOOSTER

RHIC

e-cooling

LINAC

EBIS

recirculating linac injector

5-10 GeV static electron ring