1. Identification of Upsilon Particles Using the Preshower Detector in STAR Jay Dunkelberger, University of Florida

2. Outline Quarks, Confinement, and QGP Relativistic Heavy Ion Collider and the STAR experiment Heavy Quarkonia STAR’s Electromagnetic Calorimeter and Preshower detector Summary

3. Quarks Building blocks for hadrons Come in six flavors Interact via the strong force, which is mediated by gluons Are found bound as triplets in baryons, or pairs in mesons Free quarks and gluons are never observed because of the nature of the strong force (confinement)

4. Deconfinement and QGP At extremely high temperatures ( >10¹² K) quarks are no longer confined to specific baryons or mesons New deconfined state of matter called Quark-Gluon Plasma is formed The QGP is thought to have existed in our universe up to 10 ⁻⁵ seconds after the Big Bang

5. Relativistic Heavy Ion Collider (RHIC) Located at Brookhaven National Laboratory on Long Island Can collide Au nuclei at energies of up to 200 GeV per nucleon-nucleon pair At these energy densities it is possible for the QGP to be formed briefly

6. The STAR Detector Gold nuclei collide in the center of the detector STAR is able to record about 100 of the thousands of events per second Decisions are made at the hardware and software levels as to which data are recorded for analysis

7. STAR Detector Systems Solenoid Magnet Establishes uniform magnetic field parallel to the beam axis Time Projection Chamber Records hits that are later reconstructed into tracks for charged particles that can be used to identify particles and determine their momentum Electromagnetic Calorimeter Measures the energies of electromagnetically interacting particles, can detect neutral particles (e.g. photons) Preshower Detector Helps distinguish between hadrons and electrons in the EM calorimeter

8. Au + Au Collision at STAR

9. J/ψ Particle Neutral meson composed of a charm anti-charm pair Has a rest mass of about 3.1 GeV/c² A suppression of J/ψ is expected in QGP compared to binary scaling of data from proton-proton collisions Suppression has already been observed at lower energies At RHIC energies recombination of J/ψ is possible

10. Upsilon Particle Consists of a bottom anti-bottom pair Rest mass is about 9.5 GeV/c² Like J/ψ it is expected that Y production will be suppressed in the QGP, but Y is much heavier than J/ψ so recombination is not likely Comparing J/ψ and Y yields could provide important evidence for the formation of QGP

11. Finding Upsilon Particles Look for Y particles that decay to e ⁺ e ⁻ pair Combinatorially create opposite-sign pairs and generate invariant mass plot Create like sign pairs to generate background c²) Subtract out the background and look for a peak at the Y mass (~9.5 GeV/c²)

12. BEMC Towers 21 layers of scintillator and lead Particles that interact by EM force start showers in lead plates which shows up as light in scintillator Light signals are carried away by fiber optic cables, and converted to digital values At layer five is the Shower Maximum Detector First two layers serve as Preshower detector

13. Preshower Detector (BPRS) First two layers are read out separately from the rest of the tower Using Preshower data we can greatly reduce hadronic background About 84% of electrons will shower in the first two layers of the BEMC, compared to only about 6% of hadrons Rough estimates showed a two times improvement in relative electron yield BPRS is currently being commissioned as a part of the STAR detector

14. Particle Identification

15. Comparing Yields: No BPRS dE/dx as measured in TPC (2 GeV/c < p < 3 GeV/c)

16. Comparing Yields: with BPRS dE/dx as measured in TPC (2 GeV/c < p < 3 GeV/c)

17. Commissioning the BPRS The BPRS has not yet been incorporated as a part of STAR’s analysis One task was to modify the preexisting status table package to include BPRS data Status tables are stored in a database so analyzers know which towers are giving good data for a given run A graph of the raw ADC values taken from the BPRS detector

18. Summary and Future Work Heavy quarkonia can be useful in gathering information about the QGP STAR’s Preshower detector gives a method for effectively screening out hadrons from our data Need to run our upsilon analysis on a full data set

19. Acknowledgements Dr. Saskia Mioduszewski Dr. Rory Clarke Matt Cervantes STAR Collaboration Cyclotron Institute, Texas A&M University