The nucleus at a The nucleus at a trillion degreestrillion degrees

David MorrisonDavid Morrison

Brookhaven National LaboratoryBrookhaven National Laboratory

Where can we find it?Where can we find it?

early universe … tough. very tough.early universe … tough. very tough. high energy nuclear collisions.high energy nuclear collisions.

creates only very small quantities of stuffcreates only very small quantities of stuff the created stuff is the created stuff is veryvery short-lived short-lived requires a big acceleratorrequires a big accelerator requires complex detectorsrequires complex detectors tough … but doabletough … but doable

quarkshadrons

mesons baryons

pions,kaons,

...

protons,neutrons,

...

nucleons

protons neutrons

partons

quarks gluons

Some terminologySome terminology

High energy nuclear collisionHigh energy nuclear collision

contracted by effects of special relativity

impact parameter

Aftermath of a collisionAftermath of a collision

As seen by STAR experiment at RHIC

End-on view of high energy gold-gold

collision

• more than 5000 particles• you only see the charged particles here (there are also lots of neutral particles)• your eye doesn’t really see particle momenta, correlations, distributions

QuickTime™ and aSorenson Video decompressorare needed to see this picture.

Corona: 106 K

Center: 107 K

Surface: 6000 KSolar and Heliospheric Observatory (SOHO) satellite

Planck distributiondescribes intensityas a function of thewavelength of theemitted radiation

“Blackbody” radiation is the spectrum of radiation

emitted by an object attemperature T

E p

inte

nsity

transverse momentum

Systematic Errors not shown

Phobos Preliminary

Determining temperatureDetermining temperature

From transverse momentum

distribution deduce temperature of about 120 MeV

Energy densityEnergy density

A typical approachA typical approach use calorimeters to measure energy emitted use calorimeters to measure energy emitted

from collisionfrom collision estimate the volume of the collisionestimate the volume of the collision

obtain energy densities ranging up to obtain energy densities ranging up to several GeV/fmseveral GeV/fm33

Energy density in highest energy head-on Au+Au collisions – more than 5 GeV/fm3

Calorimeters in PHENIXCalorimeters in PHENIX

5 GeV/fm5 GeV/fm33. Is that a lot?. Is that a lot?Last year, the U.S. used about 100 quadrillion BTUs of energy:

At 5 GeV/fm3, this would fit in a volume of:

Or, in other words, in a box of the following dimensions:

Chemical equilibriumChemical equilibrium

2H2O + energy 2H2 + O2

time

conc

entr

atio

n of

O2

equilibrium concentration will depend on intensive quantities: T, p

t1 t2

Not just your usual quarksNot just your usual quarks

Not exactly the way I think of them …

Ordinary matter made of up and down quarks

Chemical equilibriumChemical equilibrium

With enough time, forward and reverse reactions will drive system to chemical equilibrium. Abundances will only depend on temperature and chemical potential.

One way to dig even deeperOne way to dig even deeper

hadron

hadron possible for “knock-possible for “knock-

on” collisions of on” collisions of partonspartons

seen in high-energy seen in high-energy physics experiments physics experiments since mid-1970’ssince mid-1970’s

a real particle physics a real particle physics phenomenon that can phenomenon that can be used to probe the be used to probe the trillion degree material trillion degree material we createwe create

Force between two quarksForce between two quarks

Compare to gravitational force at Earth’s surface

Quarks exert 16 metric tons of force on each other!

quark quarkgluons

A “jet” of particlesA “jet” of particles

as connection as connection between quarks between quarks breaks up, most of breaks up, most of the motion stays the motion stays close to direction of close to direction of the original quarksthe original quarks

the fragmented bits the fragmented bits appear as “normal” appear as “normal” subatomic particlessubatomic particles pions, kaons, …pions, kaons, …

kaon

pion

pion

pion

An algorithmAn algorithm a way to locate the a way to locate the

running of the bulls in running of the bulls in Pamplona, Spain:Pamplona, Spain:

1.1. start by finding one high-start by finding one high-momentum bullmomentum bull

2.2. look others moving in look others moving in roughly the same directionroughly the same direction

3.3. if the bull density is high, if the bull density is high, you might reconsider the you might reconsider the place you’ve chosen to place you’ve chosen to standstand

The next step is simple: just replace “bull” by “particle”

Case study: opacity of fogCase study: opacity of fog

““is this thing on?”is this thing on?” if you detect one if you detect one beam, at least know beam, at least know the source is onthe source is on

intensity of the “other” intensity of the “other” beam tells you a lotbeam tells you a lot

Pedestal&flow subtracted

angle away from initial high momentum particle

inte

nsity

same direction opposite direction

The matter we make …The matter we make …

is fantastically hotis fantastically hot has incredible energy densityhas incredible energy density only exists for an instant, but shows many signs only exists for an instant, but shows many signs

of equilibriumof equilibrium some properties are more straightforward to some properties are more straightforward to

explain in language of partonsexplain in language of partons very, very “sticky” – partons lose lots of energy very, very “sticky” – partons lose lots of energy

trying to get through ittrying to get through it being studied in dozens of ways – lots of new being studied in dozens of ways – lots of new

results anticipated at Quark Matter ‘04!results anticipated at Quark Matter ‘04!

Heavy-Ion Physics(materia in extremis)