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.