Upsilon Particles in High-Energy Au+Au Collisions

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/Y 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. 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 Physics Motivation

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

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 thedynamics 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/Y (cc) • Bottomonium • Upsilon (bb)

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

12. b b Upsilon Particle • Bottom (Upsilon) is much more rare than charm (J/Y) • 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)

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 J/Y Simulation Upsilon Simulation Decays to electron, positron Decays to electron, positron Experimental Approach STARsim Program

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/Y 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