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BRAHMS Identified Particle v 2 (p t ,y) Analysis S. J. Sanders, U. Kansas

This analysis explores the longitudinal behavior of RHIC reactions, specifically focusing on the changes in identified particle v2 as we go to forward angles. The study investigates the impact of rapidity on v2 and the factors influencing its integral behavior. Experimental arrangements, detector subsystems, and correction factors are considered. Comparison with other measurements and theoretical models is also discussed.

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BRAHMS Identified Particle v 2 (p t ,y) Analysis S. J. Sanders, U. Kansas

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  1. BRAHMS Identified Particle v2(pt,y) Analysis S. J. Sanders, U. Kansas

  2. BRAHMS explores the longitudinal behavior of RHIC reactions. What changes going to forward rapidities? PHOBOS BRAHMS 200 GeV Au+Au 0-5% Au+Au 5-10% 10-20% 20-30% 30-40% 40-50% From ~0 to ~3, dNch/d drops about 25%… …and v2 is reduced about 40%. How does identified particle v2(pT) change in going to forward angles?

  3. Flow Ring 3 Z = -11 cm BRAHMS Experimental Arrangement MRS Si Ring 1 Global Detectors Tile Ring 1 Flow Ring 2 FS Spectrometer arms measure identified particle v2, while global detectors determine reaction plane.

  4. Determining Reaction Plane with Multiple Detector Subsystems Experimental correction factors found in good agreement with Monte Carlo simulations.

  5. Avoiding Auto Correlations… MRS Events MRS at 90o MRS at 40o A restricted vertex range is used in the analysis to avoid auto correlations: z>-5 cm @ 90o and z>-20 cm @ 40o an 4o.

  6. STAR: Phys. Rev. C 72, 014904 (2005) / PHENIX: PRL 91, 182301(2003) (0-70%; ||<0.35) Precision measurements at mid-rapidity (not BRAHMS) Protons and kaons show delayed onset of v2 rise (consistent with hydrodynamic models)

  7. 90o BRAHMS Preliminary STAR 0-50% Charged Hadrons

  8. 40o BRAHMS Preliminary

  9. 4o BRAHMS Preliminary

  10. Comparison of 4o, 40o and 900 settings. No appreciable change observed above 1 GeV/c.

  11. How do we understand the integral v2 behavior? What else changes in going to forward rapidities? Pions must drive the behavior.

  12. Toy model: • All + • No y dependence of v2(pT) 90o Assumed v2 <pT>=478 MeV/c BRAHMS Preliminary Yield weighted v2 4o <pT>=379 MeV/c Integral v2(90o) = 0.040 Integral v2(4o) = 0.032 20% decrease

  13. Few models results available for particle identified v2, but… 4o AMPT (~ 4) AMPT provides reasonable description with “string melting” near mid rapidity (||<3) Lie-Wen Chen, Vincenzo Greco, Che Ming Ko, Peter F. Kolb Phys. Lett. B, 605(2005); private communication. BRAHMS Preliminary AMPT (~ 4)

  14. Conclusions • v2(pT>1) for identified pions, kaons and protons remains relatively constant from y=0 to y=3. • A significant fraction of the falloff observed for the integral v2 can be attributed to the y-dependence of <pT>.

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