Centrality Dependence of Charged Antiparticle to Particle Ratios from

1. Centrality Dependence of Charged Antiparticle to Particle Ratios from Abigail Bickley Univ. of Maryland, Chemistry Dept. for the Collaboration DNP, October 31, 2003

2. Collaboration Birger Back,Mark Baker, Maarten Ballintijn, Donald Barton, Bruce Becker, Russell Betts, Abigail Bickley, Richard Bindel,Wit Busza (Spokesperson), Alan Carroll, Patrick Decowski, Edmundo Garcia, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Stephen Gushue, Clive Halliwell, Joshua Hamblen,Adam Harrington,Conor Henderson, David Hofman, Richard Hollis, Roman Holynski, Burt Holzman, Aneta Iordanova,Erik Johnson,Jay Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo,Jang Woo Lee, Willis Lin, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland, Joe Sagerer, Pradeep Sarin, Iouri Sedykh, Wojtek Skulski, Chadd Smith, Peter Steinberg, George Stephans, Andrei Sukhanov, Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Robin Verdier, Gábor Veres, Frank Wolfs, Barbara Wosiek, Krzysztof Wozniak, Alan Wuosmaa, Bolek Wyslouch, Jinlong Zhang ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER

3. Motivation • In d+Au collisions little reinteraction is expected thus the ratios should reflect the initially produced yields • Recent results suggest conditions in Au+Au collisions are different than those observed in d+Au collisions • Do these different conditions influence the measured particle ratios? Initial State Final State Interactions

4. Peripheral Central Au+Au: d+Au: Ncoll = # collisions, Npart = # participants, Ndpart = # deuteron participants Centrality Dependence • The more collisions a participating nucleon suffers the greater the baryon number transport to mid-rapidity

5. Expect the p/p ratio to decrease with increasing number of • collisions; i.e with centrality p/p Ratio vs Centrality • If the total proton yield is equal to the sum of the transported and produced components 

6. Paddle T0 Paddle Rings T0 Spectrometer Rings Detector 2003 TOF Walls mini-pCal SPECTRIG pCal

7. Particle Identification • Cut bands lie 3 RMS deviations from the expected mean • Cutoffs minimize contamination from other particle species

8. Bend towards beampipe Bend away from beampipe d+Au d+Au Spectrometer Acceptance • Contours represent where the acceptance has fallen to 10% of the maximal value

9. Field Polarity: B- Field Polarity: B+  -  -  +  + Z Z  +  -  +  - near mid-rapidity near mid-rapidity Bending away from beampipe: h-B+, h+B- Magnetic Field Reversals Bending toward beampipe: h-B-, h+B+

10. Corrections • Protons: • Absorption  3.5% ± 1.4% (syst.) • Secondary  1.6% ± 0.3% (stat.) ± 0.2% (syst.) • Feed-down  -0.5% ± 1% (syst.) • Kaons: total correction <1% • Pions: total correction <0.5%

11. Systematic Uncertainties • Kaon and Proton Ratios: • Centrality Measure: 2% • Kinematic Acceptance (pT and y): 1% • Proton Ratios: • Dead & hot spectrometer channels: 0.5% • Spectrometer arm asymmetries: 1% • Polarity-dependent vertex correction: 1% • Pion Ratios: • Electron Contamination: < 0.1%

12. Colored points  d+Au Black points  Au+Au • -/+, K- /K+  d+Au ~ -/+, K- /K+  Au+Au • No evidence observed that final state effects in Au+Au collisions • modify the produced meson yields Particle Ratios vs Centrality

13. Colored points  d+Au Black points  Au+Au • Au+Au proton ratio is significantly lower than d+Au ratios • All d+Au particle ratios appear to be independent of centrality Particle Ratios vs Centrality

14. Model Comparison d+Au • Models agree with the expectation that baryon transport increases • with increasing  thus resulting in a decreased p/p ratio • Data does not exhibit this behavior

15. Conclusions • Do the different conditions in Au+Au and d+Au collisions influence the measured particle ratios? • d+Au and Au+Au  and K ratios are consistent  no evidence that final state interactions in Au+Au collisions modify the ratio of initially produced meson yields is observed • d+Au particle-antiparticle ratios show a surprising lack of centrality dependence • Results are in clear disagreement with AMPT, HIJING and RQMD predictions nucl-ex/0309013

16. Backup Slides

17. Raw Particle Yields • dAVertex: 30M evts; required T0 coincidence and |vz|<50cm • dAPeriph: 20M evts; required dAVertex and Paddle occupancy <50%

18. Final Particle Ratios Superscript = statistical uncertainty; Subscript = systematic uncertainty

19. x z Trigger Elements Negative T0s Negative Paddles Positive T0s Positive Paddles d Au T0N PN T0P PP • Normal Trigger: (dAVertex) • 30M events collected • required T0 coincidence and |vz|<50cm • Peripheral Trigger: (dAPeriph) • 20M events collected • required dAVertex and Paddle occupancy <50%

20. Measuring Centrality in d+Au HIJING Simulation dN/dh Energy (arb. units) Pseudorapidity • Glauber Calculation • Hijing 1.383 • Hulthen w.f. • inelastic = 41mb • Full GEANT Simulation

21. Raw Particle Ratios • Assumptions: the following must be the same for antiparticles and particles for each bending direction and centrality bin • Acceptance and tracking efficiency • Field strength (B+/B-) : agree within 0.2% • Centrality Fractions (ERing) : agree within 1% • Kinematic distributions • pT, pT2 and y : agree within 2%

22. Baryon Transport  • d+Au vs Au+Au comparison: • central d+Au > central Au+Au BUT !! • (p/p)central d+Au > (p/p)central Au+Au • Relative fraction of transported protons in central d+Au collisions is half that in central Au+Au collisions!