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

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 LABORATORYBROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS, KRAKOWMASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWANUNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLANDUNIVERSITY OF ROCHESTER

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 StateFinal State Interactions

Centrality Dependence The more collisions a participating nucleon suffers the greater the baryon number transport to mid-rapidity PeripheralCentral d+Au:Au+Au: N coll = # collisions, N part = # participants, N d part = # deuteron participants

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

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

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

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

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

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%

Systematic Uncertainties Kaon and Proton Ratios: –Centrality Measure: 2% –Kinematic Acceptance (p T 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%

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

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

Model Comparison 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 d+Au

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/

Backup Slides

Raw Particle Yields TriggerCentrality % Evts (M) -- ++ K-K- K+K+ ppEvt (M) -- ++ K-K- K+K+ pp dAVertex dAVertex dAVertex dAVertex dAPeriph dAPeriph dAVertex: 30M evts; required T0 coincidence and |vz|<50cm dAPeriph: 20M evts; required dAVertex and Paddle occupancy <50%

Final Particle Ratios TriggerCentrality %  -  /  +  K -  /  K + p/pp/p dAVertex (1.3)0.995    0.07   0.04  0.04 dAVertex (1.8)1.004    0.03   0.02  0.03 dAVertex (1.8)1.008    0.02   0.02  0.03 dAVertex (2.0)1.016    0.03   0.02  0.03 dAPeriph (1.3)0.996    0.04   0.03  0.03 dAPeriph (1.6)1.014    0.03   0.02  0.03 Au+Au0-12~    0.03   0.02  0.03 Superscript = statistical uncertainty; Subscript = systematic uncertainty

Trigger Elements Normal Trigger: (dAVertex) –30M events collected –required T0 coincidence and |vz|<50cm Peripheral Trigger: (dAPeriph) –20M events collected –required dAVertex and Paddle occupancy <50% Negative Paddles Positive Paddles dAu x z PP PNT0NT0P Positive T0s Negative T0s

Energy (arb. units) Pseudorapidity Glauber Calculation Hijing Hulthen w.f.  inelastic = 41mb Full GEANT Simulation HIJING Simulation dN/d  Trigger% Centrality  N coll  dAVertex (1.7)2.2(1.3)0.20 dAVertex (3.0)4.0(1.8)0.61 dAVertex (3.6)6.1(1.8)0.78 dAVertex0-1016(4.0)8.1(2.0)0.84 dAPeriph (1.7)2.2(1.3)0.18 dAPeriph (2.7)3.7(1.6)0.24 Measuring Centrality in d+Au

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 (E Ring ) : agree within 1% –Kinematic distributions  p T ,  p T 2  and  y  : agree within 2%

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! 