Introduction to Relativistic Heavy Ion Collision Physics

1
Introduction to Relativistic Heavy Ion Collision
Physics

• Huan Z. Huang
• ???
• Department of Physics and Astronomy
• University of California, Los Angeles
• Oct 2006 _at_Tsinghua

http//hep.tsinghua.edu.cn/talks/Huang/
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Two Puzzles of Modern Physics
-- T.D.Lee

• Missing Symmetry all present theories are based
  on symmetry, but most symmetry quantum numbers
  are NOT conserved.
• Unseen Quarks all hadrons are made of quarks,
  yet NO individual quark has been observed.

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Vacuum As A Condensate

• Vacuum is everything but empty!
• The complex structure of the vacuum and the
  response of the vacuum to the physical world
  breaks the symmetry.
• Vacuum can be excited!

We do not understand vacuum at all !
4
A Pictorial View of Micro-Bangs at RHIC
Huge Stretch Transverse Expansion High
Temperature (?!)
Nuclei pass thru each other lt 1 fm/c
Thin Pancakes Lorentz g100
The Last Epoch Final Freezeout-- Large Volume
AuAu Head-on Collisions ? 40x1012 eV 6
micro-Joule Human Ear Sensitivity 10-11 erg
10-18 Joule A very loud Bang, indeed, if E?
Sound
Vacuum Engineering !
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High Energy Nucleus-Nucleus Collisions
Physics 1) Parton distributions in nuclei 2)
Initial conditions of the collision 3) a new
state of matter Quark-Gluon Plasma and its
properties 4) hadronization
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Kinematic Variables
Rapidity Pseudo-rapidity Transverse
Momentum Transverse Mass
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Useful Expressions
Feymann xF Bjorken x Light-cone x
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Cross Sections
Number of Reactions
sTotal
Number of Beam Particles X Scattering Center /
Area
Dimension L2
sTotal sinel sel
SD Singly Diffractive ND Non-Diffractive
sinel sSD sND
Differential Cross Section
Question differential cross section vs total
cross section?
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Invariant Cross Sections
Invariant Differential Cross Section
E d3s/d3p ?
Invariant Multiplicity Density
E d3n/d3p ?
Experimental Considerations Efficiency,
Acceptance, Decay
Correction, Target-out Correction.
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Order of Magnitude
Geometrical CS pp pr2 p(1fm)2 32 mb AuAu
Collisions Rau 1.2 A1/3 6.98 fm
pbmaxp(2R)2 6 barn 1 barn 10-24 cm2
Regge Theory stotalXS0.0808
YS-0.4525 p-pbar 21.70 98.39 mb p-p
21.70 56.08 mb Pomeron
r,w,f,a,. HIJING minijet production
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Luminosity at Collider
NB2 B v / U
L
A
B ? Number of bunches per beam NB ? Number of
particles per bunch v ? velocity of particles U ?
circumference of the ring A ? beam cross section
at the collision
Relativistic Heavy Ion Collider
eN? Invariant Transverse 95 Emittance b ? the
beta function
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RHIC Numbers
RHIC Design Au Beam proton Beam B 57
NB 109 1011 L 2x1026
1x1031 cm-2s-1 200 GeV 500 GeV
Collision Rate L x s 1200 Hz 0.7 MHz
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RHIC Complex
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Relativistic Heavy Ion Collider --- RHIC
AuAu 200 GeV N-N CM energy Polarized pp up to
500 GeV CM energy
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Building Blocks of Hadron World
Molecules
Atoms
Nucleus
Electrons
Proton
Neutron
Hyperons
(uud)
(udd)
(s)
Strong interaction is due to color charges and
mediated by gluons. Gluons carry color charges
too.
Baryon Density r baryon number/volume normal
nucleus r0 0.15 /fm3 0.25x1015
g/cm3 Temperature, MeV 1.16 x 1010 K 10-6
second after the Big Bang T200 MeV
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Energy Scale and Phase Transition
Entity Energy Dimension Physics Bulk
Property P/T Atom 10s eV 10-10
m Ionization e/Ion Plasma No Nucleus 8 MeV
10-14 m Multifrag. Liquid-Gas Y(?) QCD 200 MeV
10-15 m Deconfine. QGP Y(?) EW 100 GeV
10-18 m P/CP Baryon Asymmetry Y(?) GUT 10
15-16 GeV Supersymmetry TOE 1019
GeV Superstring
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Salient Feature of Strong Interaction
Asymptotic Freedom Quark
Confinement
????? 300 B.C. ????,????,????
Take half from a foot long stick each day, You
will never exhaust it in million years.
QCD
Quark pairs can be produced from vacuum No free
quark can be observed
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QCD on Lattice
Transition from quarks to hadrons DOF ! QGP
not an ideal Boltzmann gas !
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Lattice current status

• technical progress finer mesh size, physical
  quark masses, improved fermion actions
• phase-transition smooth, rapid cross-over
• EoS at finite µB in reach, but with large
  systematic uncertainties
• critical temperature TC?180 MeV

Fodor Katz, hep-lat/0110102
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Quark-Hadron Phase Transition
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(No Transcript)
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QGP micro-second after the Big Bang
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The Melting of Quarks and Gluons-- Quark-Gluon
Plasma --
Matter Compression Vacuum Heating
Deconfinement
High Temperature Vacuum -- high energy heavy
ion collisions -- the Big Bang
High Baryon Density -- low energy heavy ion
collisions -- neutron star?quark star
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QCD Phase Transition
What do experimental data points indicate and
how were these points obtained ?
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Nuclear Collision Geometry
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Number of Participant Nucleons

• Geometrical Interpretation of Observables
• A monotonic relation between the
  observable and
• collision centrality is
  assumed
• b) Estimate from direct measurement
• missing energy from Zero-degree
  calorimeter
• from dn/dy of protons.

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Directly Determining NPART

• Best approach (for fixed target!)
• Directly measure in a zero degree calorimeter
• (for AA
  collisions)
• Strongly (anti)-correlated with produced
  transverse energy

NA50
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Number of Participant Nucleons
c) Dynamical Model Tune to fit
experimental measurement From model
to convert measurement to impact parameter
and number of
participant nucleons Fluctuations
are included - - Physical picture is
biased to begin with
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Spectrum Fit
mT spectrum d2n/(2pmT)dmTdy vs (mT-m0) pT
spectrum d2n/(2ppT)dpTdy vs pT
Boltzmann mT Fit d2n/(2pmT)dmTdy mT
exp(-mT/slp) slp ? Slope Parameter Why is this
Boltzmann? d3n/d3p exp(-E/T) Invariant
Multiplicity Density Ed3n/d3p E exp(-E/T) E
mTcosh(y-ycm) d2n/(2pmT)dmTdy mT cosh(y-ycm)
exp(-mT cosh(y-ycm)/T) Slp depends on
rapidity for an isotropic thermal fireball slp
T/cosh(y-ycm) dn/dy
sy 0.7-0.8
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Naïve Expectations

• Thermal Isotropic Source ? mT Scaling
• p, K and proton have the same slope parameter
  e-E/T

Data show a large difference among these
particles ? Expansion
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Naïve Expectation 2
Slope parameter ? Temperature Rapidity density
dn/dy ? entropy or energy density
First Order Phase Transition
ltpTgt
QGP
Mixed
hadron
dn/dy
Collision dynamics much more complicated !!
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Collision Dynamics
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Bjorken Scaling
Bjorken Ansatz at sufficient high energy
there is a central-plateau structure for the
particle production as a function of the
rapidity variable.
dn/dy
y
Physics must be invariant under Lorentz-boost
1) Local thermodynamic quantity must be a
function of proper time
only. 2) Longitudinal velocity vz
z/t or y 0.5 ln ((tz)/(t-z))
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Bjorken Energy Density
E x DN
Energy density e
A x Dz
E ? average energy per particle A ? transverse
area of the collision volume Dz ? longitudinal
interval DN ? number of particles in Dz interval
vz z/t tanh y z t sinh y Dz t cosh y
Dy E mT cosh y
mT cosh y DN
e
A t cosh y Dy
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Initial Energy Density Estimate
PRL 85, 3100 (00) 91, 052303 (03) 88, 22302
(02), 91, 052303 (03)
200 GeV
130 GeV
PHOBOS
19.6 GeV
Pseudo-rapidity
Within hlt0.5 the total transverse momentum
created is 1.5x650x0.508 500 GeV from an
initial transverse overlap area of pR2 153
fm2 !
hminus Central AuAu ltpTgt0.508GeV/c pp
0.390GeV/c
Energy density e 5-30 e0 at early time
t0.2-1 fm/c !
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Ideas for QGP Signatures
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Ideas for QGP Signatures
Chiral Symmetry Restoration T 0, m(u,d,s)
gt 0 Spontaneous symmetry breaking Tgt 150
MeV, m0 Chiral symmetry restored Mass,
width and decay branching ratios of resonances
may be different in dense medium .
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F. Weber J.Phys. G27 (2001) 465
Models of Neutron Stars
Strangeness" of dense matter ? In-medium
properties of hadrons ? Compressibility of
nuclear matter ? Deconfinement at high baryon
densities ?
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The STAR Detector
1st year detectors
2nd year detectors
installation in 2002
installation in 2003
Coils
TPC Endcap MWPC
Silicon Vertex Tracker
Silicon Strip Detector
ZDC
ZDC
Vertex Position Detectors
Barrel EM Calorimeter
Central Trigger Barrel
TOF
RICH