QuarkNet 2006

Lets go smash some Atoms!

Peripheral Collision: Central Collision

Head-On Collision: Largest # of Nucleons Participate

Glancing Collision: Small # of Nucleons Participate

QuarkNet 2006

Measuring Collision Centrality

Data

Trigger signal

Peripheral Collision:

Small number of participating nucleons

Central Collision

Large Npart

Lets Focus on the most head-on collisions, where expect the most interesting things to happen.

QuarkNet 2006

Looking at one gold+gold collision.

Beamline

creates over 5000 charged particles!(~600 at ~ 90o to beamline) 2c

Em

90o~ +0.5~ +0.5

QuarkNet 2006

Did we reach critical energy density?

Total energy released in =1 is ~ 1000 GeV

Initial Energy Density Estimate, ~ 5 GeV/fm3

32 200~)1(~ fmfmRMax initial overlap volume

Look at all produced particles in a

Central ‘Head-on’ Collision

Lets do a “FOOM estimate” (coffee napkin estimate)

1000~all

d

dN

GeVE 1~

Energy Density = Total Energy/Volume ~ 1000GeV/200 fm3

= 1

So the answer is YES, we are above the critical value of ~0.7

QuarkNet 2006

What Are We producing?

1. Matter and Antimatter

QuarkNet 2006

Matters of Matter and Anti-Matter

•Tracking in the spectrometer•Alternate 2T magnetic fields•Energy loss and momentum

+

Matter

Anti-MatterK-

p

-

K+

p

+

QuarkNet 2006

Antimatter/Matter Particle Ratios

p/p

K–/K+

Approaching equal production of matter and anti-matter!

A+A central collisions

RHIC

QuarkNet 2006

What Are We producing?

1. Matter and Antimatter2. A “liquid” with quark DoFs

QuarkNet 2006

Liquid or Gas?

Animation courtesy of Brookhaven National Laboratory

QuarkNet 2006

Look More Closely: Emission Patterns

Animation by Jeffrey Mitchell (Brookhaven National Laboratory)

What happens in a peripheral collision?

QuarkNet 2006

Particle emission patterns

Peripheral Collisions: Overlap “hot spot” looks like an almond.

If they do – can learn more about timescales of the “cooling” process and help us distinguish between liquid and gas behavior

Do the particle emission patterns reflect this initial shape?

Reaction plane

x

z

y

QuarkNet 2006

b (reaction plane)

View along beamline

Emission patterns follow the shape of the overlap region.

QuarkNet 2006

Fourier analysis of emission patterns.

)(cos21)( Rn

R

nvd

dN

Extract n=2, elliptic flow

Study v2

Increasing Collision Centrality

Find significant values of v2 for peripheral collisions. Behaving like a liquid (collectively)

QuarkNet 2006

Elliptic Flow for different particles

PRC 72 (05) 014904

200 GeV Au+Aumin-bias

v2 is different for different particles

QuarkNet 2006

Elliptic Flow: Quark Scaling!

solid: STARopen:

PHENIX

PRL91(03)

v2 matches when scaled by the number of quarks

QuarkNet 2006

What Are We Producing?

1. Matter and Antimatter2. A “liquid” with quark DoFs3. The “Perfect” fluid

QuarkNet 2006

Thinking about Fluids…

What is the difference between the behavior of Water and Honey?

Devise an experiment to study this…

2 baby cannons

1

2HONEYHONEY

WATERWATER

CANNON BALL RACESCANNON BALL RACES

WINNER is #1: Or in more precise terms v1 > v2

QuarkNet 2006

Study of High Momentum Particles

mvp

0.2<y<1.4

Momentum distributions of

charged particles

QuarkNet 2006

Need a “Benchmark momentum”

• We are colliding gold + gold nuclei and believe we have created a new state of matter in the large overlap region of the collisions.

• For our benchmark we use collisions of only one proton on another proton where no such overlap exists.

QuarkNet 2006

Rati

o o

f g

old

-gold

to p

roto

n-p

roto

n

Peripheral Central Mid-Central

We “lose” high momentum (speed) particles for Central Collisions

Comparing High Momentum particles

QuarkNet 2006

Where have all the fast particles gone?

They are only missing for central heavy-ion collisions. Could it be direct evidence we have created the quark-gluon-plasma that somehow either slows particles down or just makes much less high-momentum ones?

Can do an even more detailed check→ use direct signature of back-to-back JETS!

QuarkNet 2006

“Fast” Probes of Dense Matter

a “jet”

a “jet”

proton + proton collisions

Can calculate the “jet” cross section very precisely with QCD

QuarkNet 2006

Jets at RHIC

p+p jet+jet (STAR@RHIC)

Au+Au ??? (STAR@RHIC)

nucleon nucleonparton

jet

Find this…STARSTAR

…in this

QuarkNet 2006

Azimuthal Jet Distributions in Au+Au

Au+Au Peripheral

Trigger “jet”

Opposite “jet”

STARSTARp+p

QuarkNet 2006

Azimuthal Jet Distributions in Au+Au

Au+Au central

Trigger “jet”

Opposite “jet” is MISSING in Au+Au

STARSTAR p+p

QuarkNet 2006

Jet “Quenching” in Au+Au collisions

Proton + Proton Central Au + Au

The second “jet” seems to disappear in central Au+Au collisions

QuarkNet 2006

Jet Quenching in our QCD matter

Animation by Jeffrey Mitchell (Brookhaven National Laboratory)

QuarkNet 2006

“Jet Quenching” in Central Au+Au Collisions

• Opposite jets seen in:– Proton + Proton collisions– Deuteron + Gold collisions– Peripheral Gold + Gold

• Opposite jets missing in only one place:– Central Gold + Gold

Something interesting is happening (has not seen before)

QuarkNet 2006

Emerging Experimental Consensus: We have created a “state of matter” with a relevant energy density above the predicted QCD critical point and appears to have the following features:

• Emits large numbers of produced particles.

• In a relatively “baryon-free” environment (approaching equal matter and anti-matter production).

• Behaves collectively (like a fluid)• Is very strongly interacting and has the

ability to significantly affect the characteristics of jet fragmentation and production of high momentum particles.

Is it “the” Quark Gluon Plasma?

QuarkNet 2006

Final Thoughts

• In the brief moment of a relativistic heavy-ion collision, we have created a “different” form of matter with very interesting properties. Only time will tell what it is and what it will teach us about the strong interaction.

• It is an extremely exciting time.

• Research at RHIC will continue “full speed ahead”.

• Another exciting new accelerator at CERN (LHC) will come “alive” next year (and also study heavy ion collisions).