# Presentation: 501882

## The nucleus at a trillion degrees

- David Morrison
- Brookhaven National Laboratory

## Where can we find it?

- early universe ... tough. very tough.
- high energy nuclear collisions.
- creates only very small quantities of stuff
- the created stuff is _very_ short-lived
- requires a big accelerator
- requires complex detectors
- tough ... but doable

## Some terminology

**Some terminology**

## High energy nuclear collision

**High energy nuclear collision**

- contracted by effects of special relativity

- impact parameter

## Slide 5

## Aftermath of a collision

**Aftermath 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

## Corona: 106 K

- Corona: 106 K

- Center: 107 K

- Surface: 6000 K

- Solar and Heliospheric Observatory (SOHO) satellite

## Planck distribution

- describes intensity
- as a function of the
- wavelength of the
- emitted radiation

- “Blackbody” radiation
- is the spectrum of radiation
- emitted by an object at
- temperature T

-   E  p

## Determining temperature

**Determining temperature**

- From transverse momentum distribution deduce temperature of about 120 MeV

## Energy density

- A typical approach
- use calorimeters to measure energy emitted from collision
- estimate the volume of the collision
- obtain energy densities ranging up to several GeV/fm3

## Calorimeters in PHENIX

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

**Calorimeters in PHENIX**

## 5 GeV/fm3. 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:

## Slide 13

## Chemical equilibrium

- 2H2O + energy  2H2 + O2

- time

- concentration of O2

- equilibrium concentration will depend on intensive quantities: T, p

- t1

- t2

## Not just your usual quarks

- Not exactly the way I think of them ...

- Ordinary matter made of **up** and **down** quarks

## Chemical 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 deeper

**One way to dig even deeper**

- hadron

- hadron

- possible for “knock-on” collisions of partons
- seen in high-energy physics experiments since mid-1970’s
- a real particle physics phenomenon that can be used to probe the trillion degree material we create

## Force between two quarks

- Compare to gravitational force at Earth’s surface

- Quarks exert 16 metric tons of force on each other!

- quark

- quark

- gluons

## A “jet” of particles

- as connection between quarks breaks up, most of the motion stays close to direction of the original quarks
- the fragmented bits appear as “normal” subatomic particles
- pions, kaons, ...

- kaon

- pion

- pion

- pion

## Slide 20

## Slide 21

## An algorithm

**An algorithm**

- a way to locate the running of the bulls in Pamplona, Spain:
- start by finding one high-momentum bull
- look others moving in roughly the same direction
- if the bull density is high, you might reconsider the place you’ve chosen to stand

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

## Case study: opacity of fog

**Case study: opacity of fog**

- “is this thing on?”

- if you detect one beam, at least know the source is on
- intensity of the “other” beam tells you a lot

## angle away from initial high momentum particle

- angle away from initial high momentum particle

- intensity

- same direction

- opposite direction

## The matter we make ...

- is fantastically hot
- has incredible energy density
- only exists for an instant, but shows many signs of equilibrium
- some properties are more straightforward to explain in language of partons
- very, very “sticky” – partons lose lots of energy trying to get through it
- being studied in dozens of ways – lots of new results anticipated at Quark Matter ‘04!

## Slide 26