1. QuarkNet 2006 Lets go smash some Atoms! Peripheral Collision:Central Collision Head-On Collision: Largest # of Nucleons Participate Glancing Collision: Small # of Nucleons Participate

2. QuarkNet 2006 Measuring Collision Centrality Data Trigger signal Peripheral Collision:  Small number of participating nucleons Central Collision  Large N part Lets Focus on the most head-on collisions, where expect the most interesting things to happen.

3. QuarkNet 2006 Looking at one gold+gold collision. Beamline creates over 5000 charged particles! (~600 at ~ 90 o to beamline) 90 o  ~ +0.5

4. QuarkNet 2006 Did we reach critical energy density? Total energy released in  =1 is ~ 1000 GeV Initial Energy Density Estimate,  ~ 5 GeV/fm 3 Max initial overlap volume Look at all produced particles in a Central ‘Head-on’ Collision Lets do a “FOOM estimate” (coffee napkin estimate) Energy Density = Total Energy/Volume ~ 1000GeV/200 fm 3  = 1  So the answer is YES, we are above the critical value of ~0.7

5. QuarkNet 2006 What Are We producing? 1. Matter and Antimatter

6. QuarkNet 2006 Matters of Matter and Anti-Matter Tracking in the spectrometer Alternate 2T magnetic fields Energy loss and momentum + Matter Anti-Matter K-K- p -- K+K+ p ++

7. QuarkNet 2006 Antimatter/Matter Particle Ratios p/p K – /K +  Approaching equal production of matter and anti-matter! A+A central collisions RHIC

8. QuarkNet 2006 What Are We producing? 1. Matter and Antimatter 2. A “liquid” with quark DoFs

9. QuarkNet 2006 Liquid or Gas? Animation courtesy of Brookhaven National Laboratory

10. QuarkNet 2006 Look More Closely: Emission Patterns Animation by Jeffrey Mitchell (Brookhaven National Laboratory) What happens in a peripheral collision?

11. 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

12. QuarkNet 2006 b (reaction plane) View along beamline  Emission patterns follow the shape of the overlap region.

13. QuarkNet 2006 Fourier analysis of emission patterns. Extract n=2, elliptic flow Study v 2 Increasing Collision Centrality  Find significant values of v 2 for peripheral collisions.  Behaving like a liquid (collectively)

14. QuarkNet 2006 Elliptic Flow for different particles PRC 72 (05) 014904 200 GeV Au+Au min-bias  v 2 is different for different particles

15. QuarkNet 2006 Elliptic Flow: Quark Scaling! solid: STAR open: PHENI X PRL91(03)  v 2 matches when scaled by the number of quarks

16. QuarkNet 2006 What Are We Producing? 1. Matter and Antimatter 2. A “liquid” with quark DoFs 3. The “Perfect” fluid

17. 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 2 HONEY WATER CANNON BALL RACES WINNER is #1: Or in more precise terms v 1 > v 2

18. QuarkNet 2006 Study of High Momentum Particles 0.2<y   <1.4 Momentum distributions of charged particles

19. 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.

20. QuarkNet 2006 Ratio of gold-gold to proton-proton Peripheral Central Mid-Central  We “lose” high momentum (speed) particles for Central Collisions Comparing High Momentum particles

21. 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!

22. QuarkNet 2006 “Fast” Probes of Dense Matter a “jet” proton + proton collisions Can calculate the “jet” cross section very precisely with QCD

23. QuarkNet 2006 Jets at RHIC p+p  jet+jet (STAR@RHIC) Au+Au  ??? (STAR@RHIC) nucleon parton jet Find this… STAR …in this

24. QuarkNet 2006 Azimuthal Jet Distributions in Au+Au Au+Au Peripheral Trigger “jet” Opposite “jet” STAR p+p

25. QuarkNet 2006 Azimuthal Jet Distributions in Au+Au Au+Au central Trigger “jet” Opposite “jet” is MISSING in Au+Au STAR p+p

26. QuarkNet 2006 Jet “Quenching” in Au+Au collisions Proton + ProtonCentral Au + Au  The second “jet” seems to disappear in central Au+Au collisions

27. QuarkNet 2006 Jet Quenching in our QCD matter Animation by Jeffrey Mitchell (Brookhaven National Laboratory)

28. 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)

29. 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?

30. 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).