The hottest matter on earth: a look at the
Relativistic Heavy Ion Collider
outline
Science questions which define our goals
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 plasmadoes this really happen???
Such matter existed just after the Big Banghow does this stuff “work”?
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*
Early universe was a quark-gluon plasma for a few microseconds after Big Bang
Probably also in the core of neutron stars
*Plasma: conducting material, but chargesshield each other, making it ~ neutralusually has a high temperature/density
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? why more matter than antimatter today?
equation of state of nuclear matter 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
Uncovering nature’s secrets is not easy!
Large collaborationsPHENIX has ~500incl. Stony Brookmany countries!
“small” experimentshave > 50 people!
Use connected computing around the world! transfer data over the internet centrally located software libraries meetings span 3 continents
post slides on the webcirculate agendas, questions by emaileveryone phones in
Complex events require selections
RHIC makes many collisions per secondcan’t afford to write them all to tapetape bandwidth is ~ 20 MB/sec
(would fill 20 GB disk in < 20 min)
select the interesting ones - in real time!use the electronics + computing to
collect, collate, calculate & trigger take THIS
one!
Collect the Data!Collect the Data!
Collect the Data!
All 4 experimentshave fast, customelectronics
+ multiple layers of computing inside
PHENIX trigger coordinator:J. Nagle
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
What do we want 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 plasma:equation of state (energy vs. pressure)how is energy transported in the plasma?
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
Adding all particles under the curve, find ~ 5000 charged particles
These all started in a volume ~ that of a nucleus!
(~ longitudinal velocity)
Central Au+Aucollisions
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”
Something new at RHIC?
Compare to a baseline, or controluse nucleon-nucleon collision at same energy
Au + Au collisionsare a superpositionof N-N reactions(modulo effect ofnuclear binding orcollective motions)
Hard scattering processes scale asnumber of N-N binary collisions <Nbinary>
so expect: YieldA-A = YieldN-N . <Nbinary>
nucleons
From Federica Messer
Compare momentum spectra
Compiled by A. Drees
N-N collision at sNN = 130 GeV
Au+Au
Nbinary = 905central
Nbinary = 20peripheral
Phys. Rev. Lett. 88, 022301 (2002)
Deficit observed in central collisions
Charged deficit seen by both STAR & PHENIX
0
charged
central coll central
pp
/Yield N
Yield
transverse momentum (GeV/c)
Phys. Rev. Lett. 88, 022301 (2002)
charged is fromanalysis byF. Messer ofStony Brook
STARpreliminary
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 quark gluon plasma binding dissolves 2 D mesons
u, d, s
cu, d, s
c
J/ suppression observed at CERN
Fewer J/ in Pb+Pb than expected!
But other processes affect J/ tooso interpretation is still debated...
J/yield
How about at RHIC?
PHENIX looks for J/ e+e- and
There is the electron.
A needle in a haystack
must find electron without mistaking a pion for an electron at the level of one in 10,000
We use specialdetector to tagthe electrons
“RICH”
Prof. Tom Hemmickof Stony Brook
We do find the electrons
Electron enriched sample (using RICH)
All tracks
Energy/Momentum
PHENIX sees some “extra” electrons
they come from charm quarks c D meson
e + K +
J/ analysis is underway now
0 ee
ee, ee
0ee, 3
0ee, ee
conversion
ee
ee
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 by 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 thermal radiation:
Rate, energy of the radiated particles determined by temperature
NB: , e, interact only electromagnetically they exit the collision without further interaction
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
What have we learned?
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…
What’s next??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 dependenceare jets quenched & J/ suppressed???
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?
pT (GeV)
Hydrodynamics is not explosive enough!
D. Teaney & J. Burward-Hoy
Mysteries II
If jets from light quarks are quenched, shouldn’t charmed quarks be suppressed too?
nucl-ex/0202002
PHENIX at RHIC
2 Central spectrometers2 Forward spectrometers3 Global detectors
Philosophy: optimize for signals / sample soft physics
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.
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