1. Upsilon Particles in High-Energy Au+Au Collisions Catie Talbert Austin College Texas A&M – Cyclotron Institute REU 2006 Mentor: Saskia Mioduszewski Grad Student: Matt Cervantes

2. Outline Physics Motivation – QGP Background –The Accelerator – RHIC –The Detector – STAR Theoretical/Experimental Approach –Suppression/Enhancement of J/  and Upsilon –STARsim Program Summary and Outlook

3. Physics Motivation Quarks –6 flavors –Interact in accordance with the strong force –Exist only in triplets (baryons) or paired with an anti- quark (mesons) –No free quarks

4. Physics Motivation Quark-Gluon Plasma (QGP) –Phase change that occurs at high energy densities –Quarks are so densely packed that they no longer recognize their own boundaries – they become “free” to move

5. Physics Motivation Where can we find QGP? –Thought to have existed shortly after the Big Bang –May also exist in (very dense) neutron stars –Re-create QGP at RHIC

6. The Accelerator – RHIC Relativistic Heavy-Ion Collider (RHIC) –2.4 mile circumference –200 GeV (.99995c) –Gold (Au) ions and protons The Detector – STAR Solenoidal Tracker at RHIC

7. The Detector – STAR STAR detector subsystems Solenoidal magnet Provides for a uniform axial magnetic field Time Projection Chamber Gives complete 3-D information of the particle tracks Electromagnetic Calorimeters Provides information on the energy deposited by e +/- and γ

8. STAR’s Mission To re-create the QGP and study the dynamics of quark matter by observing the particles resulting from the collisions

9. Theoretical Approach Quarkonium –Meson made up of a quark and its own anti-quark Charmonium –J /  cc) Bottomonium –Upsilon (bb)

10. Theoretical Approach Suppression of J/  –Compared to p+p collision (multiplied by # of nucleons) –During initial collision, charm (bottom) particles are produced –In QGP phase, deconfinement, quarkonium no longer bound, charm prefers to combine with a light quark –Suppression of charmonium was thought to be a signature of the QGP (original idea of Matsui, Satz)

11. Theoretical Approach Enhancement of J/  –RHIC has higher energies than previous experiments Increased initial charm production Increased chance to thermalize J/  can recombine –Possible increased charmonium count after QGP phase (Grandchamp, Rapp) New problem: –Suppression (deconfinement) and Enhancement (recombination)

12. Upsilon Particle Bottom (Upsilon) is much more rare than charm (J/  ) –Bottom quark is heavier than charm, takes more energy to make Because bottom quark is heavier, difficult to thermalize ENHANCEMENT not an issue Only a measure of suppression, disentangles new Suppression/Enhancement puzzle (Grandchamp, Rapp, Lumpkins, van Hees, Sun) b b

13. Experimental Approach Importance of STARsim Simulation –Upsilon is very rare particle, difficult to measure –We can insert simulated Upsilon particles into real events and then be able to search for them –This allows for a measure of detector efficiencies –Simulation allows us to set an upper limit on the production of Upsilon particles resulting from a collision

14. Experimental Approach STARsim Program J/  Simulation Decays to electron, positron Upsilon Simulation Decays to electron, positron Experimental Approach

15. Summary and Outlook Goal of RHIC/STAR to create and study QGP Because of complications with suppression and enhancement, Upsilon is important for understanding J/  data at RHIC and whether or not QGP is observed Simulation is critical for measurement of Upsilon

16. Summary and Outlook This summer we got STARsim up and running (!) for single particle generation Next step is to embed simulated Upsilon particle into real data from STAR

17. Acknowledgements Dr. Saskia Mioduszewski, Texas A&M Cyclotron Institute Matt Cervantes, Graduate Student, Texas A&M Cyclotron Institute STAR Collaboration