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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 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 Physics Motivation • Quarks – 6 flavors – Interact in accordance with the strong force – Exist only in triplets (baryons) or paired with an antiquark (mesons) – No free quarks 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 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 The Detector – STAR The Accelerator – RHIC •Solenoidal Tracker at RHIC • Relativistic Heavy-Ion Collider (RHIC) – 2.4 mile circumference – 200 GeV (.99995c) – Gold (Au) ions and protons 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 STAR’s Mission To re-create the QGP and study the dynamics of quark matter by observing the particles resulting from the collisions Theoretical Approach • Quarkonium – Meson made up of a quark and its own anti-quark • Charmonium – J/Y (cc) • Bottomonium – Upsilon (bb) Theoretical Approach • Suppression of 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) 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) 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) 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 Experimental Approach STARsim Program Upsilon Simulation Decays to electron, positron J/Y Simulation Decays to electron, positron 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 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 Acknowledgements • Dr. Saskia Mioduszewski, Texas A&M Cyclotron Institute • Matt Cervantes, Graduate Student, Texas A&M Cyclotron Institute • STAR Collaboration