quarknet 2006 lets go smash some atoms! peripheral collision:central collision head-on collision:...
TRANSCRIPT
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QuarkNet 2006
Lets go smash some Atoms!
Peripheral Collision: Central Collision
Head-On Collision: Largest # of Nucleons Participate
Glancing Collision: Small # of Nucleons Participate
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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.
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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
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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
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QuarkNet 2006
What Are We producing?
1. Matter and Antimatter
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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
+
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QuarkNet 2006
Antimatter/Matter Particle Ratios
p/p
K–/K+
Approaching equal production of matter and anti-matter!
A+A central collisions
RHIC
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QuarkNet 2006
What Are We producing?
1. Matter and Antimatter2. A “liquid” with quark DoFs
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QuarkNet 2006
Liquid or Gas?
Animation courtesy of Brookhaven National Laboratory
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QuarkNet 2006
Look More Closely: Emission Patterns
Animation by Jeffrey Mitchell (Brookhaven National Laboratory)
What happens in a peripheral collision?
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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
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QuarkNet 2006
b (reaction plane)
View along beamline
Emission patterns follow the shape of the overlap region.
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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)
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QuarkNet 2006
Elliptic Flow for different particles
PRC 72 (05) 014904
200 GeV Au+Aumin-bias
v2 is different for different particles
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QuarkNet 2006
Elliptic Flow: Quark Scaling!
solid: STARopen:
PHENIX
PRL91(03)
v2 matches when scaled by the number of quarks
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QuarkNet 2006
What Are We Producing?
1. Matter and Antimatter2. A “liquid” with quark DoFs3. The “Perfect” fluid
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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
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QuarkNet 2006
Study of High Momentum Particles
mvp
0.2<y<1.4
Momentum distributions of
charged particles
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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.
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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
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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!
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QuarkNet 2006
“Fast” Probes of Dense Matter
a “jet”
a “jet”
proton + proton collisions
Can calculate the “jet” cross section very precisely with QCD
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QuarkNet 2006
Jets at RHIC
p+p jet+jet (STAR@RHIC)
Au+Au ??? (STAR@RHIC)
nucleon nucleonparton
jet
Find this…STARSTAR
…in this
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QuarkNet 2006
Azimuthal Jet Distributions in Au+Au
Au+Au Peripheral
Trigger “jet”
Opposite “jet”
STARSTARp+p
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QuarkNet 2006
Azimuthal Jet Distributions in Au+Au
Au+Au central
Trigger “jet”
Opposite “jet” is MISSING in Au+Au
STARSTAR p+p
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QuarkNet 2006
Jet “Quenching” in Au+Au collisions
Proton + Proton Central Au + Au
The second “jet” seems to disappear in central Au+Au collisions
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QuarkNet 2006
Jet Quenching in our QCD matter
Animation by Jeffrey Mitchell (Brookhaven National Laboratory)
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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)
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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?
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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).