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Centrality Dependence of Pseudorapidity Distributions in d+Au collisions at √s = 200GeV

Centrality Dependence of Pseudorapidity Distributions in d+Au collisions at √s = 200GeV. Richard S Hollis University of Illinois at Chicago For the collaboration. Collaboration (October 2004).

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Centrality Dependence of Pseudorapidity Distributions in d+Au collisions at √s = 200GeV

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  1. Centrality Dependence of Pseudorapidity Distributions in d+Au collisions at √s = 200GeV Richard S Hollis University of Illinois at Chicago For the collaboration

  2. Collaboration (October 2004) Burak Alver, Birger Back,Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Abigail Bickley, Richard Bindel, Wit Busza (Spokesperson), Alan Carroll, Zhengwei Chai, Vasundhara Chetluru, Patrick Decowski, Edmundo García, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Clive Halliwell, Joshua Hamblen, Ian Harnarine, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Jay Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo, Wei Li, Willis Lin, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland, Joe Sagerer, Iouri Sedykh, Wojtek Skulski, Chadd Smith, Peter Steinberg, George Stephans, Andrei Sukhanov, Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter Walters, Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Alan Wuosmaa, Bolek Wysłouch ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER

  3. Outline • d+Au Centrality • New Results • Shapes • Limiting Fragmentation • Integrated Yield • Limiting Fragmentation Revisited • Conclusion

  4. Detector Au Analysis Apparatus: 4p Multiplicity Array Central Octagon Barrel 6 Rings at higher (Pseudo) Rapidity Trigger Apparatus: Paddles → One Hit on Each Array is the Minimum-Bias Trigger d

  5. d+Au Event Selection Shapes agree reasonably in High multiplicity region • Event Selection • Clean-up by requiring a valid silicon vertex • Efficiency • Used a shape matching algorithm between Data and Simulations (HIJING or AMPT) • Efficiency includes Trigger and Vertex finding efficiency • Estimated to be ~83% Hijing + GEANT Data Data inefficient for peripheral events EOct is the summed charge deposited in the Octagon detector

  6. d+Au Centrality • Centrality • Correct for efficiency • Divide data into 20% bins • Centrality binning • Used ERing • Least auto-correlation bias (from Data and MC studies) Primary Trigger (Scintillator)Paddles Octagon Rings Rings η Schematic Plot not to scale

  7. Data: arXiv:nucl-ex/0409021 Gold-going hemisphere Deuteron-going hemisphere • Five Centrality Classes • Each of 20% cross-section • Brief Observations • Increase centrality • Total number of particles grows • Asymmetry grows • Mean η shifts to Gold-going hemisphere

  8. “Rest” position of the gold nucleus Limiting Fragmentation:Measuring the Total Yield • Limiting Fragmentation: • Yield of particles is the same close to the beam rapidity of the target nucleus • Independent of energy • Can shift our distributions by the beam rapidity of the gold. • Lends guidance to extrapolate the total charged-particle yield 50-70% Central p+Emulsion ○ 38.7GeV □ 23.7GeV ∆ 19.4GeV ◊ 11.2GeV ╬ 6.7GeV

  9. Integrated Yields:Nch scaled by Npart/2 • d+Au Data • consistent with p+p (UA5) • Lower than the PHOBOS Au+Au data • ~20-25% lower • Compared to the 50% most central Au+Au

  10. Integrated Yields:Nch(d+Au) scaled by Nch(p+p) • Scale by p+p for comparison with lower energy data • All data fall on a common line • RA = 0.5*<Npart>

  11. Limiting Fragmentation:Revisited • Close to the deuteron beam rapidity • Same Limiting fragmentation observations • Departure point from the limiting curve • Determined by kinematics • Collision Energy • Can compare the limiting slopes in both rest frames • invert the η+ytarget figure “Rest” position of the deuteron nucleus

  12. Limiting Fragmentation:Limiting Curves • Limiting curve 50-70% centrality class • Similar (yield/η) slope • both target and projectile • Limiting curves offset from each other in η space ~1 unit • SIMILAR limiting slopes only for peripheral centrality classes!

  13. Limiting Fragmentation:Departure Points in dNch/dη-space By eye, departure point from limiting curve different 38.7GeV → large uncertainty in the departure point.

  14. Limiting Fragmentation:Departure Points in dNch/dη-space Scale Scale (a) distribution such that the deuteron peak is the same as the gold peak (equalize the dashed lines) ~20% increase

  15. Limiting Fragmentation:Departure Points in dNch/dη-space Scale By eye, departure point from the limiting curve relatively the same

  16. Conclusions • Detailed centrality dependence of d+Au collisions • Total yield scaled by 0.5<Npart> • consistent with p+p data • Lower than Au+Au data (top 50%) • Observe consistency with lower energy data • Total yield / p+p • Limiting fragmentation regions • Relative departure points from the limiting curve are the same in the gold and deuteron rest frames.

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