Transcript Student Colloquium at WSU (Fall 2006) (ppt-format)

Link to cosmology
A QCD/QGP/RHIC primer
The discovery of the sQGP
Towards the most fundamental questions
The Big Bang In The Laboratoy:
How Black Can It Get ?
Rene Bellwied
Wayne State University
([email protected])
A mass problem of universal proportion



The stars and gas in most galaxies
move much quicker than expected
from the luminosity of the galaxies.
In spiral galaxies, the rotation curve
remains at about the same value at
great distances from the center (it is
said to be ``flat'').
This means that the enclosed mass
continues to increase even though
the amount of visible, luminous
matter falls off at large distances
from the center.

Something else must be adding to the gravity of the
galaxies without shining. We call it Dark Matter !
According to measurements it accounts for > 90% of the
mass in the universe.
The cosmic connection of RHI physics
The universe is accelerating according to the latest Supernova results
SNAP:
Supernova
Accelerating
Probe
Witten’s ‘Cosmic Separation of phases’ (Phys.Rev.D 30 (1984) 272)
basic parameter: mass
What do we know about atomic substructure ?
What do we know about quark masses ?
Why are quark current masses so
different ?
Can there be stable (dark) matter
based on heavy quarks
There is no answer to these
questions.
There likely will be no answer to
these questions !
Nature’s constants:
-Speed of light, Electric charge,
Quark current masses
Very little is known, very little can be explained
Standard model is symmetric
All degrees of freedom are massless
Electro-weak symmetry breaking
via Higgs field (Dm of W, Z, g)
Mechanism to generate current quark
masses
(but does not explain their magnitude)
Chiral symmetry breaking
via dynamical quarks
Mechanism to generate constituent
quark masses
(but does not explain hadronization)
We can’t answer the question of mass
generation at the most fundamental level,
but can we answer the question of mass
generation at the nuclear level ?
Theory:
Quantum
Chromo
Dynamics
The fundamental problem: how is baryonic mass generated
Based on quark interactions (5+10+10 = 935 MeV/c2) ?
The main features of Quantum
Chromodynamics (QCD)



Confinement
 At large distances the effective coupling between quarks is large,
resulting in confinement.
 Free quarks are not observed in nature.
Asymptotic freedom
 At short distances the effective coupling between quarks decreases
logarithmically.
 Under such conditions quarks and gluons appear to be quasi-free.
(Hidden) chiral symmetry
 Connected with the quark masses
 When confined quarks have a large dynamical mass - constituent mass
 In the small coupling limit (some) quarks have small mass - current
mass
Analogies and differences between QED and QCD
to study structure of an atom…
electron
…separate constituents
nucleus
Imagine our understanding of atoms or QED if we
could not isolate charged objects!!
neutral atom
ToConfinement:
understandfundamental
the strong
force and the phenomenon of confinement:
& crucial (but not understood!) feature of strong force
- colored
objects (quarks)
have  energy
in normal
vacuum
Create and study
a system
of deconfined
colored
quarks
(and gluons)
quark-antiquark pair
created from vacuum
quark
“white” proton
(confined quarks)
Strong color field
“white” 0
“white”
proton
Force
grows
with separation(confined
!!!
quarks)
A mechanism of hadronization in vacuum:
String Fragmentation
High momentum current mass quark pair forms flux tube in a
collision = string of energy (string tension) i.e. dynamical quark field
which fragments into hadrons when string tension becomes too large.
Describes e+e- and p-pbar and p-p collisions well.
Hadronization in medium (i.e. during universe expansion) could be
different because medium might affect the mechanism.
Theoretical and computational (lattice) QCD
In vacuum:
- asymptotically free quarks have current mass
- confined quarks have constituent mass
- baryonic mass is sum of valence quark constituent masses
Masses can be computed as a function of the evolving coupling
Strength or the ‘level of asymptotic freedom’, i.e. dynamic masses.
But the universe was not a vacuum at the time of hadronization,
it was likely a plasma of quarks and gluons. Is the mass generation
mechanism the same ?
The temperature dependent running
coupling constant as and its effect on
mass generation above Tc
O.Kaczmarek et al. (thermal mass, LQCD)
(hep-lat/0406036)
1.05 Tc
1.5 Tc
3 Tc
12 Tc
6 Tc
in an expanding system: interplay between
distance and temperature
Massive partons above Tc
e.g. P.Levai and U.Heinz
(hep-ph/9710463)
One goal: Proving asymptotic freedom
in the laboratory.
Gross, Politzer, Wilczek win
2004 Nobel Prize in physics
for the discovery of
asymptotic freedom in the
theory of the strong
interaction

Measure deconfinement and chiral symmetry restoration under
the conditions of maximum particle or energy density.
What can we do in the laboratory ?
a.) Re-create the conditions as close as possible to the Big
Bang, i.e. a condition of maximum density and minimum
volume in an expanding macroscopic system.
Is statistical thermodynamics applicable ?
b.) Measure a phase transition, characterize the new phase,
measure the de-excitation of the new phase into ‘ordinary’
matter – ‘do we come out the way went in ?’
(degrees of freedom, stable or metastable matter,
homogeneity)
c.) Learn about hadronization (how do particles acquire
mass) – complementary to the Higgs search but with the
same goal. The relevant theory is Quantum Chromo
Dynamics
Going back in time…
Age
0
10-35 s
Energy
1019 GeV
1014 GeV
Matter in universe
grand unified theory of all forces
1st phase transition
(strong: q,g + electroweak: g, l,n)
10-10 s
102 GeV
2nd phase transition
(strong: q,g + electro: g + weak: l,n)
10-5 s
0.2 GeV
3 min.
0.1 MeV
RIA & FAIR
RHIC, LHC &(strong:hadrons
FAIR + electro:g + weak: l,n)
6*105 years 0.3 eV
Now
(15 billion years)
3rd phase transition
3*10-4 eV = 3 K
nuclei
atoms
Generating a deconfined state
Present understanding of
Quantum Chromodynamics (QCD)
• heating
• compression
 deconfined color matter !
Hadronic
Nuclear
Matter
Matter
Quark
Gluon
Plasma
(confined)!
deconfined
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
A phase transition into what ?


With the liquid-gas phase transition established (ground state
liquid drop nuclei transition to a hadron gas) the question was:
What comes next ? A weakly interacting plasma.
Edward Shuryak (1971) : name it the Quark Gluon Plasma
Cabibo-Parisi, PLB59 (1975) G.Baym, NSAC-LRP (1983)
The phase diagram of QCD
Temperature
Early universe
critical point ?
quark-gluon plasma
Tc
colour
superconductor
hadron gas
nucleon gas
nuclei
CFL
r0
vacuum
baryon density
Neutron stars
Relativistic Heavy Ion Collider (RHIC)
PHOBOS
PHENIX
1 mile
Au+Au @ sRHIC
NN=200 GeV
BRAHMS
STAR
v = 0.99995c
AGS
TANDEMS
Study all phases of a heavy ion collision
If the QGP was formed, it will only live for 10-21 s !!!!
BUT does matter come out of this phase the same way it went in ???
Step 1: Proving the existence of a new phase of matter
Can we prove that we have a phase that
behaves different than elementary pp collisions ?
Three steps:
a.) prove that the phase is partonic
b.) prove that the phase is collective
c.) prove that the phase characteristics are different from the QCD
vacuum
How do we determine medium properties ?
(by producing probe and medium in the same collision)

We are producing ‘soft’ and ‘hard’ matter. An arbitrary distinction is
coming from the applicability of pQCD which is generally set to pT
> 2 GeV/c (hard). Below 2 GeV/c we expect thermal bulk matter
production.
Medium: The bulk of the particles; dominantly soft
production and possibly exhibiting some phase.
 Probe: Particles whose production is calculable,
measurable, and thermally incompatible with (distinct
from) the medium (hard production)


Measure bulk matter properties to determine global properties
(collectivity, equilibration, timescales)
Measure the modification of high pt probes to determine specific
properties of the matter produced (jet tomography)
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:
 “quenches” high pT particles
 “kills” jet partner on other side
?
Au+Au
RAA and high-pT suppression
STAR, nucl-ex/0305015
pQCD + Shadowing + Cronin
energy
loss
pQCD + Shadowing + Cronin + Energy Loss
Deduced initial gluon density at t0 = 0.2 fm/c dNglue/dy ≈ 800-1200
 ≈ 15 GeV/fm3, eloss = 15*cold nuclear matter (compared to HERMES eA)
(e.g. X.N. Wang nucl-th/0307036)
The matter is BLACK (opaque) !
?
Pedestal&flow subtracted
Energy that goes in
doesn’t come out !!
That does not happen
in hadronic matter
Au+Au
Bulk matter properties: elliptic (anisotropic) flow –
No elliptic flow,
Mid-peripheral
Central
collision strong radial flow
Out-of-plane
Flow
a strong indicator of early collectivity
with velocity b
Reaction
plane
Flow
Y
In-plane
X
Directed flow
Elliptic flow
Dashed lines: hard
sphere radii of nuclei
Y
Time
X
Flow described by hydrodynamics (WSU)
Strong collective flow:
elliptic and radial
expansion with
mass ordering
Hydrodynamics:
strong coupling,
small mean free path,
lots of interactions
NOT plasma-like
For the first time: 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 ?
An unexpected liquid phase with very drastic
thermodynamic properties ?
plasma
liquid ?
gas
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
massless partons
Identified particles at intermediate pt (WSU)
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two groups, baryons and mesons, which seem to approach each other
around 5 GeV/c
coalescence/recombination provides a description ~1.5 - 5 GeV/c
constituent (massive ?) quark scaling for hadron production
Recombination vs. Fragmentation
(a different hadronization mechanism in medium than in
vacuum ?)
Recombination at moderate PT
Parton pt shifts to higher
hadron pt.
Recomb.
Fragmentation at high PT:
Parton pt shifts to lower
hadron pT
fragmenting parton:
ph = z p, z<1
recombining partons:
p1+p2=ph
Frag.
Summary of experimental observations
At RHIC we showed that Au+Au collisions create a
medium that is partonic, dense, dissipative and
exhibits strong collective behavior. The system
behaves like a liquid, i.e. ideal hydro, low viscosity,
strong coupling
 We observe suppression phenomena in single
Instead
of generating
a weakly
interacting
quark
gluon
particle
observables
and very
importantly
also
in
plasmathe
made
of free quarks
gluons, we have made a
correlations
(large and
acceptance)
strongly coupled liquid. What are the relevant degrees of
 We observe constituent quark scaling in v2 and
freedom at hadronization, i.e. shortly after the Big Bang ?
Rcp at ~ 2-5 GeV/c and gluon density scaling in
the energy production
 We observe strong collective behavior (flow) in
all bulk matter observables

Where do we go from here ?


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We found strong coupling where we expected weak
coupling (the sQGP, the ideal liquid)
We found evidence for massive sub-structures above
the critical temperature (constituent quarks or quasiparticles)
We found collective behavior above the critical
temperature.
- The degrees of freedom above Tc will form all
baryonic matter in the universe. Cosmologically the
system was sufficiently big to talk about a phase.
- How is baryonic mass generated ?
- Is the liquid state a ‘quantum black hole ?’
The Quark Gluon 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 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.
The ‘cosmic’ connection
a.) the equation of state of the QGP resembles
features of black hole physics.
b.) the degrees of freedom above Tc will be the
building blocks of hadronic matter in the universe.
Hadronization in matter might be different from
hadronization in vacuum.
c.) primordial fluctuations of conserved quantum
numbers around the critical point might lead to
measurable effects in the universe (matter-antimatter,
charge, and strangeness distribution)
An example: lower viscosity bound in
strong quantum field theory
Motivated by calculation of lower viscosity bound in a black hole via
supersymmetric N=4 Yang Mills theory in AdS (Anti deSitter) space (conformal
field theory)
String dual:
A thermodynamic quantity in strong quantum fields
can be calculated based on
first principles in a string theory
?
400 times less viscous than water,10 times less viscous than superfluid helium !
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
Conclusions
We have successfully created
the Quark Gluon Plasma, an
early universe phase of matter,
which might still exist in black
holes.
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
The future is bright
better facility
EoS of sQGP
A three prong approach:
expanded facility
QCD, CGC, QGP
5-10 GeV static
electron ring
higher energy
wQGP (?)
recirculating
linac injector
RHIC
EBIS BOOSTER
LINAC
ecooling
AGS
RHIC-II (2008-2013):
QCDLab (2013---):
Upgrades to
A high luminosity
STAR & PHENIX
RHIC with eA and
AA detectors
LHC (2008-2020 ?):
Large Hadron Collider
with ALICE, CMS,
ATLAS heavy ion
programs
The WSU-RHI group and its projects
a.) professors: Bellwied, Cormier, Pruneau, Voloshin
theory: Gavin
b.) postdocs: Ilya Selyuzhenkov (+2 in January)
c.) graduate students: Sarah LaPointe (Bellwied)
Muhamed Elnimr (Pruneau)
d.) former graduate students (Bellwied):
Ying Guo
Saugy Chakraborty
Sadek Nehmeh
Jeff Sheen
We are looking for 2-3 Ph.D. or Masters students !!
The WSU-RHI group and its projects (II)
a.) hardware projects:
Calorimeter in ALICE (Geneva)
new Silicon in STAR (BNL)
b.) analysis projects (Bellwied group):
heavy flavor detection in STAR (Sarah)
strangeness production in pp (STAR/ALICE)
medium response to strange particles (STAR/ALICE)
hadronization mechanism in pp and AA (STAR/ALICE)