1. Anti-particle to Particle Ratios in Cu+Cu Collisions @ RHIC Vasundhara Chetluru University of Illinois, Chicago For the collaboration Division of Nuclear Physics, Nashville October 27th, 2006

2. PHOBOS EXPERIMENT Vasundhara Chetluru DNP Nashville, Oct 27 2006 2 Burak Alver, Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard Bindel, Wit Busza (Spokesperson), Vasundhara Chetluru, Edmundo García, Tomasz Gburek, Joshua Hamblen, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Chia Ming Kuo, Wei Li, Willis Lin, Constantin Loizides, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed, Christof Roland, Gunther Roland, Joe Sagerer, Peter Steinberg, George Stephans, Andrei Sukhanov, Marguerite Belt Tonjes, Adam Trzupek, Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter Walters, Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Bolek Wysłouch ARGONNE NATIONAL LABORATORYBROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOWMASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWANUNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLANDUNIVERSITY OF ROCHESTER PHOBOS Collaboration

3. PHOBOS EXPERIMENT Vasundhara Chetluru DNP Nashville, Oct 27 2006 3 Outline Ratios measurement PHOBOS detector. Particle identification using PHOBOS Corrections Results & Conclusions

4. PHOBOS EXPERIMENT Vasundhara Chetluru DNP Nashville, Oct 27 2006 4 Identified particle ratios h -/+ : identified anti-particle/particle count per event GA : Geometric Acceptance ε : Efficiency, Feed-down, Absorption

5. PHOBOS EXPERIMENT Vasundhara Chetluru DNP Nashville, Oct 27 2006 5 PHOBOS Detector

6. PHOBOS EXPERIMENT Vasundhara Chetluru DNP Nashville, Oct 27 2006 6 Acceptance Z Z Backward Bending Forward Bending 90% contour

7. PHOBOS EXPERIMENT Vasundhara Chetluru DNP Nashville, Oct 27 2006 7 Different field settings near mid-rapidity Z Z For a given bending direction Ratios are measured independently for different bending directions. B1B1 B2B2

8. PHOBOS EXPERIMENT Vasundhara Chetluru DNP Nashville, Oct 27 2006 8 Particle identification Pions Kaons Protons Deuterons Electrons

9. PHOBOS EXPERIMENT Vasundhara Chetluru DNP Nashville, Oct 27 2006 9 Detector Acceptance Decay particles produced from the heavier particles. Absorption of the particles by the detector material and production of the particles from the detector.

10. PHOBOS EXPERIMENT Vasundhara Chetluru DNP Nashville, Oct 27 2006 10 Absorption Correction p T GeV/C Absorption co-efficient Protons Antiprotons Absorption correction is particle dependent.

11. PHOBOS EXPERIMENT Vasundhara Chetluru DNP Nashville, Oct 27 2006 11 Particle Ratio Results

12. PHOBOS EXPERIMENT Vasundhara Chetluru DNP Nashville, Oct 27 2006 12 Summary Proton ratios are constant with in errors as a function of centrality. As the collision energy increases, we observe that the antiproton to proton ratios increases. –Contribution from pair production becomes more dominant than baryon transport.