the phase diagram of nuclear matter oumarou njoya
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The Phase Diagram of Nuclear Matter
Oumarou Njoya
Outline
Motivations for studying QCD phase transitions Introduction to QCD Mapping the phase diagram Experimental considerations Summary
Motivations
The Big bang Theory Neutron stars Discovery of strong force
Forces and structures in Nature
Gravityone “charge” (mass)
force decreases with distance
m1 m2
Electromagnetismtwo “charges” (+ / -)
force decreases with distance
+ -
+ +
Atom
Atomic nuclei and the “nuclear” force
Nuclei composed of:protons (+ electric charge)
neutrons (no electric charge)
Do not fly apart!? “nuclear force”overcomes electrical repulsion
determines nuclear reactions(stellar burning, bombs…)
arises from fundamental strong force (#3)
acts on color charge of quarks
proton
neutron
quark
What is QCD?
Quantum chromo-dynamics
A theory of the strong (or nuclear, or color) force.
Closely modeled on QED but with three conserved color charges:
Quarks: r, g, b
Anti quarks: anti-red, anti-green, anti-blue.
Quarks scatter by exchanging gluons, which carry color and anticolor.
More QCD Only colour singlet states can exist as free particles.
Hadrons are colour singlet. Mesons: Baryons:
Confinement (r ~ 1fm) Chiral symmetry
Having to do with quark masses Asymptotic freedom (r → 0)
Strong interaction becomes weaker at high energy Relativistic hot gas
Strong color fieldEnergy grows with separation !!!
Confinementto study structure of an
atom…
“white” proton
nucleus
electron
quark
quark-antiquark paircreated from vacuum
“white” proton(confined quarks)
“white” 0
(confined quarks)
Confinement: fundamental & crucial (but not well understood!) feature of strong force
- colored objects (quarks) have energy in normal vacuum… QCD
neutral atom
QCD Thermodynamics Relativistic kinematics of free gas. Partition function:
bosons
fermions
A simple model Ideal gas of massless pions. Stefan-Boltzmann
From hadrons to quarks and gluons Chiral symmetry argument
Massless u and d implies chirally symmetric Lagrangian. Spontaneous symmetry breaking in ground state.
Symmetry conserved at high T.
Expect phase transition. (akin to Curie point in a ferromagnet).
Pisarski-Wilzeck: 1st order transition
Tricritical point Evidence suggests 1st order at high T
and low μB
At low T: nuclear matter
Crossover and critical point Crossover for μB = 0. (Lattice QCD) Critical point
Coexisting phases along 1st order line, similar to that of liquid in condensed matter physics
Low-T high- μB: ordered quark phases exist
Locating the critical point Theoretically simple (singularity of partition
function).
Importance sampling and sign problem. Lattice QCD.
Lattice QCD Quarks and gluons are studied on a discrete space-
time lattice
Solves the problem of divergences in pQCD calculations (which arise due to loop diagrams)
The lattice provides a natural momentum cut-off
Recover the continuum limit by letting a 0
• There are two order parameters
aa
Ns3 N
pmax
a
, pmin
Ns a
1. The Polyakov Loop L ~ Fq2. The Chiral Condensate ~ mq
pure gauge = gluons only
1 s2
Order Parameters Deconfinement measure:
Palyokov loop
Effective quark mass Energy density є at
deconfinement
The phase diagram of QCDTe
mpe
ratu
re
baryon density
Neutron stars
Early universe
nucleinucleon gas
hadron gas
quark-gluon plasma
Tc
0
critical point ?
vacuum
Generating a deconfined state
Nuclear Matter(confined)
Hadronic Matter(confined)
Quark Gluon Plasmadeconfined !
Present understanding of Quantum Chromodynamics (QCD)
heating
compression deconfined color matter
RHIC BRAHMSPHOBOS
PHENIXSTAR
AGS
TANDEMS
Relativistic Heavy Ion Collider (RHIC)
1 km
v = 0.99995c = 186,000 miles/sec
A few methods Hadron radiation
Electromagnetic radiation
Dissipation of a passing quarkonyum beam (fancy for Debye screening in nuclear matter)
Energy loss of a passing jet.
Hadron radiation Formed at the transition surface between hot matter and
physical vacuum. At Tc local hadronization occurs. Mostly pions, kaons,
nucleons and anti-nucleons.
Study of relative abundances gives us information about hadronization temperature.
Electromagnetic radiation Spectra of photons and leptons provide
information about the state of the medium at the time they were formed.
Consider for illustration μ+μ- formation
Summary Mapping the QCD phase diagram is important for
understanding the early evolution of the universe and the physics of neutron star.
QCD thermodynamics suggests a well-defined transition from hadronic matter to a plasma of deconfined quarks and gluons.
The nature and the origin of the transition at high needs to be clarified further.
The properties of the QGP can be explored through hard probes. Certainly, lots of new physics await discovery.
Bibliography M. Stephanov, [arXiv:hep-lat/0701002v1] Helmut Satz, [arXiv:0903.2778v1 [hep-ph]] Peter G Jones, Introduction to QCD,
rhic.physics.wayne.edu/~bellwied/classes/phy7070/QCD-lecture.ppt
Slides 5,8,17,18 were borrowed from Gang Wang (UCLA).
Thank you!
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