# Presentation: 712826

## The Future of Heavy Ion Physics

- _The Future of __Heavy Ion Physics_

- Jamie Nagle, University of Colorado at Boulder

## What have we learned experimentally in the first five years at RHIC?

- What is the fundamental science of heavy ion physics in the next decade?

## Color Glass Condensate

- At high enough gluon density, we may find a universal description of the matter as a Color Glass Condensate.

- One can study this universal state of matter via
- Deep Inelastic Scattering, just one virtual parton at a time.
- One can do this via electron scattering or proton-nucleus reactions.

- _Color Glass Condensate_

## Experimental Data

- Suppression of forward hadrons consistent with saturation of low-x gluons.

- x ~ 10-3

- x ~ 10-2

- x ~ 10-1

- Centrality dependence and
- x dependence are being studied to test CGC.

-              Suppression Factor

## Mono-Jets?

- Complementary physics to e-A collider and LHC.
- What if instead of studying one virtual parton at a time, we hit the Color Glass with a hammer?

- _Mono-Jets?_

## The Hammer

- _The Hammer_

- 10,000 gluons, quarks, and antiquarks
- from the nuclear wavefunctions
- are made physical in the laboratory !
- What is the nature of this ensemble of partons?

## 26 TeV of Available Energy !

- Out of a maximum energy of 39.4 TeV in central Au-Au
- reactions, _26 TeV_ is made available for heating the system.
- Measures of transverse energy production indicate initial energy density far above lattice QCD transition value.

## What Happens to All That Energy?

-  ,  0,  K,  K*0(892), Ks0,  , p,  d,  0,  ,  ,
-  ,  *(1385),  *(1520),  ± ,  ,  D0, D±,  J/’s,
- (+ anti-particles) in equilibrium at T > 170 MeV

## How Does the Matter Behave?

- Simple answer is with a _very high degree of collectivity._

## Like a Perfect Fluid?

- First time hydrodynamics without any viscosity describes heavy ion reactions.

- *viscosity = resistance of liquid to shear forces (and hence to flow)

- Thermalization time _t=0.6 fm/c_ and ___=20 GeV/fm__3_

- _Like a Perfect Fluid?_

- v2

- pT (GeV)

## Analogy in Atomic System

- strongly interacting atom

- The RHIC fluid behaves like this, that is,     a strongly coupled fluid.

- _Analogy in Atomic System_

## String Theory and Black Hole Physics

- What could this have to do with quark gluon plasma physics?

- The Maldacena duality, know also as AdS/CFT correspondence, has opened a way to study the strong coupling limit using classical gravity where it is difficult even with lattice Quantum Chromodynamics.
- It has been postulated that there
- is a universal lower viscosity bound
- for all strongly coupled systems, as
- determined in this dual gravitational
- system.

## ?

- _Universal Viscosity Bound_

- Critical future goal to put the QCD data point on this plot

## How Do We Put the Point on the Plot?

- _How Do We Put the Point on the Plot?_

- Multi-Strange Baryons

- Charm and Beauty

- Charm and beauty measures with full kinematics gives us perfect fluid constraints.

## Quark Recombination

- _Quark Recombination_

## Calibrating Our Probes

- High Energy Probes are well described in
- Proton-Proton reactions by NLO Perturbative QCD.

## Probes of the Medium

- _Probes of the Medium_

## Probes of the Medium

- If the plasma is dense enough we expect the quark or gluon to be swallowed up.

- _Probes of the Medium_

## Experimental Results

- Scaling of photons shows excellent calibrated probe.
- Quarks and gluons disappear into medium, except consistent with surface emission.

- Survival Probability

- Size of Medium

## Jet Quenching !

- _Jet Quenching !_

- Azimuthal Angular Correlations

## Reaction of the Medium 

- _Reaction of the Medium _

- How does the near-perfect liquid react to this  large energy deposition?  Color shock wave?

## Changing the Conditions

- _Changing the Conditions_

## Deconfinement

- _Deconfinement_

- Lattice QCD makes a clear prediction for the onset of deconfinement.
- Different Quarkonia states test the degree
- of color screening and measure the temperature.

## Quarkonia Probes

- _Quarkonia Probes_

## Probing In-Medium Interactions

- _Probing In-Medium Interactions_

## Summary

- LHC Heavy Ion Program is likely to be very successful.
- The accelerating productivity of the RHIC program at this dedicated facility will continue to set the standard, against which other programs will be measured, for world class investigations into hot QCD.

- Excitation Function

- _Summary_

## Backup Slides

## Conclusions

- Gluon density well above lattice QCD predicted transition level and behaving as zero viscosity “perfect” liquid.

- This is not the traditionally thought of weakly-interacting gas of quarks and gluons (“the QGP”).

- This is the creation of a strongly-interacting
- Quark-Gluon Plasma (or Quark-Gluon Liquid).

- The next decade should be very exciting.
- 1.  Understanding perfect fluid behaviour.
- Understanding the nature of deconfinement and the
-     degrees of freedom

- _Conclusions_

## Gamma-Jet gives important information on modified fragmentation and precision studies of how the energy affects the medium.

## Thermalization of Energy

- If we look outside the traditional jet features, we see an extremely broadened set of particles with momentum not so different from <pT> of the bulk medium !

## Baryon Puzzle

- _Baryon Puzzle_

- More (anti) baryons than pions at moderate pT.
- Does not look like vacuum jet fragmentation.

- Proton-Proton

- Central Au-Au

- (anti)proton/pion

## Slide 32

## Slide 33

## Slide 34

## Slide 35

## Degrees of Freedom

- Critical measurement of thermal radiation to constrain temperature.

- _Degrees of Freedom_

## Quark Gluon Plasma

- 20 Year Old Plot:
- Very little know about matter beyond the boundary.
- Generic moniker of Quark-Gluon Plasma for this region.

## We now know a lot more....

- _We now know a lot more...._
- Rich Color Superconducting phases at high density.
- Lattice evidence for critical point.
- High temperature matter behaves as near-perfect fluid.
- Is it the Quark-Gluon Plasma?  As defined by experimental evidence.