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Relativistic Heavy Ion Physics: the State of the Art. Barbara V. Jacak Stony Brook Feb. 15, 2002. outline. Science goals of the field Structure of nuclear matter and theoretical tools we use Making super-dense matter in the laboratory the Relativistic Heavy Ion Collider - PowerPoint PPT Presentation
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Relativistic Heavy Ion Physics: the State of the Art
outline
Science goals of the field
Structure of nuclear matter and theoretical tools we use
Making super-dense matter in the laboratory the Relativistic Heavy Ion Collider
experimental observables &what have we learned already?
Next steps...
Studying super-dense matter by creating a little bang!
Structure ofatoms, nuclei,and nucleons
At very high energyshatter nucleons into a cloud of quarks and gluons
Expect a phase transition to a quark gluon plasma
Such matter existed just after the Big Bang
At high temperature/density
Quarks no longer bound into nucleons ( qqq ) and mesons (qq )
Phase transition quarks move freely within the volume
they become a plasma
* Such matter existed in the early universefor a few microseconds after Big Bang
* Probably also in the core of neutron stars
Phase Transition
we don’t really understandhow process of quark confinement workshow symmetries are broken by nature
massive particles from ~ massless quarks transition affects evolution of early universe
latent heat & surface tension matter inhomogeneity in evolving universe? more matter than antimatter today?
equation of state compression in stellar explosions
Quantum ChromoDynamics
Field theory for strong interaction among colored quarksby exchange of gluons
Works pretty well...
Quantum Electrodynamics (QED)for electromagnetic interactionsexchanged particles are photons
electrically uncharged QCD: exchanged gluons have “color”charge
a curious property: they interact among themselves
+ +…
This makes interactions difficult to calculate!
Transition temperature?
QCD “simplified”: a 3d grid of quark positions & summing the interactions
predicts a phase transition:
Karsch, Laermann, Peikert ‘99/T4
T/Tc
Tc ~ 170 ± 10 MeV (1012 °K)
~ 3 GeV/fm3
So, we need to create a little bang in the lab!
Use accelerators to reach highest energy vBEAM = 0.99995 x speed of light at RHICcenter of mass energy s = 200 GeV/nucleonSPS (at CERN) has s 18 GeV/nucleonAGS (at BNL) s 5 GeV/nucleon
Use heaviest beams possiblemaximum volume of plasma~ 10,000 quarks & gluon in fireball
Experimental method
Look at region between the two nuclei for T/density maximum
RHIC is first dedicated heavy ion collider
10 times the energy previously available!
Collide two nuclei
RHIC at Brookhaven National Laboratory
Relativistic Heavy Ion Collider started operations in summer 2000
4 complementary experiments
STAR
What do we need to knowabout the plasma?
Temperatureearly in the collision, just after nuclei
collide
Densityalso early in the collision, when it is at its
maximum
Are the quarks really free or still confined?
Properties of the quark gluon plasmaequation of state (energy vs. pressure)how is energy transported in the plasma?
When nuclei collide at near the speed of light, a cascade of quark & gluon
scattering results….
In Heavy Ion Collisions
101044 gluons, q, q’s gluons, q, q’s
Is energy density high enough?
4.6 GeV/fm3
YES - well above predicted transition!50% higher than seen before
PRL87, 052301 (2001)
dy
dE
cRT
Bj 22
11
02
R2
2c
Colliding system expands: Energy tobeam direction
per unitvelocity || to beam
Density: a first look
Central Au+Aucollisions
Adding all particles under the curve, find ~ 5000 charged particles
These all started in a volume ~ that of a nucleus!
(~ longitudinal velocity)
Observables IIDensity - use a unique probe
hadrons
q
q
hadronsleadingparticle
leading particle
schematic view of jet production
Probe: Jets from scattered quarks
Observed via fast leading particles orazimuthal correlations between the leadingparticles
But, before they create jets, the scatteredquarks radiate energy (~ GeV/fm) in thecolored medium
decreases their momentum fewer high momentum particles beam “jet quenching”
See talk by X.N. Wang
Deficit observed in central collisions
Charged deficit seen by both STAR & PHENIX
0
charged
central coll central
pp
/Yield N
Yield
See talk by F. Messer
transverse momentum (GeV/c)
Observables IIIConfinement
J/ (cc bound state)
produced early, traverses the medium
if medium is deconfined (i.e. colored)other quarks “get in the way”J/ screened by QGP binding dissolves 2 D mesons
u, d, s
cu, d, s
c
See talks of D. Kharzeev & J. Nagle
J/ suppression observed at CERN
Fewer J/ in Pb+Pb than expected!
But other processes affect J/ tooso interpretation is still debated...
RHIC data being analyzed now !
J/yield
Observables IV: Propertieselliptic flow “barometer”
Origin: spatial anisotropy of the system when created followed by multiple scattering of particles in evolving system spatial anisotropy momentum anisotropy
v2: 2nd harmonic Fourier coefficient in azimuthal distribution of particles with respect to the reaction plane
y2 x2 y2 x2
2cos2 v
x
y
p
patan
Almond shape overlap region in coordinate space
Large v2: the matter can be modeled hydrodynamics
STARPRL 86 (2001) 402
Hydro. CalculationsHuovinen, P. Kolb and U. Heinz
v2 = 6%: larger than at CERN or AGS!
pressure buildup explosionpressure generated early! early equilibration !?first hydrodynamic behavior seen
Observables VTemperature
Thermal dileptonradiation:
q
q
e-, -
e+, +
*
Thermal photonradiation:
g
q, q
Look for “thermal” radiationprocesses producing it:
Rate, energy of the radiated particles determined by temperature
NB: , e, interact electromagnetically only they exit the collision without further interaction
See talk of D. Kharzeev
Temperature achieved?
At RHIC we don’t know yet But it should be higher since the energy
density is larger
At CERN, photon and lepton spectra consistent with T ~ 200 MeV
WA98
NA50
photonspairs
The state of the art (and the outlook…)
unprecedented energy density at RHIC!high density, probably high temperaturevery explosive collisions matter has a stiff
equation of state
new features: hints of quark gluon plasma?large elliptic flow, suppression of high pT,J/ suppression at CERN?but we aren’t sure yet…
To rule out conventional explanations extend reach of Au+Au data compare p+p, p+Au to check effect of
cold nuclei on observables study volume & energy dependence
Mysteries...
How come hydrodynamics does so well on elliptic flow and momentum spectra of mesons & nucleons emitted
… but FAILS to explain correlations between meson PAIRS?not explosive enough!
See talk of J. Nagle
If jets from light quarks are quenched, shouldn’t charmed quarks be suppressed too?
pT (GeV)
Compare spectra to p+p collisions
Peripheral collisions (60-80% of geom):
~ p-p scaled by <N bin coll> = 20 6
central (0-10%):shape different (more exponential)below scaled p-p!(<N bin coll> = 905 96)
Did something new happen?
Study collision dynamics
Probe the early (hot) phase
Do the particles equilibrate?
Collective behaviori.e. pressure and expansion?
Particles created earlyin predictable quantityinteract differently withQGP and normal matterfast quarks, bound fast quarks, bound ccc pairs, s quarks, ...c pairs, s quarks, ...
+ thermal radiation!
matter box
vacuum
QGP
Thermal Properties
PCM & clust. hadronization
NFD
NFD & hadronic TM
PCM & hadronic TM
CYM & LGT
string & hadronic TM
measuring the thermal history
, e+e-,
+Kpn
d,Real and virtual photons from quark scattering is most sensitive to the early stages. (Run II measurement)
Hadrons reflect thermal properties when inelastic collisions stop (chemical freeze-out).
Hydrodynamic flow is sensitive to the entire thermal history, in particular the early high pressure stages.