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pp and d-Au at RHIC

pp and d-Au at RHIC. Fuming LIU (IOPP, Wuhan), Tanguy Pierog, Klaus Werner. Contents: Interesting data from RHIC High parton densities pp and d-Au results Conclusion. August 9-14, 2004, CCAST, Beijing. Interesting data from RHIC. The nuclear modification factor

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pp and d-Au at RHIC

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  1. pp and d-Au at RHIC Fuming LIU (IOPP, Wuhan), Tanguy Pierog, Klaus Werner • Contents: • Interesting data from RHIC • High parton densities • pp and d-Au results • Conclusion August 9-14, 2004, CCAST, Beijing

  2. Interesting data from RHIC The nuclear modification factor shows interesting features: • AuAu: much smaller than one for central collisions • d-Au: bigger than one for central collisions charged hadrons / 2 minimum bias STAR col. data F.M.Liu, CCAST, Beijing

  3. Centrality dependence of the nuclear modification factor from top to bottom: 0-20%, 20-40%, 40-60%, 60-88% Rapidity dependence of the nuclear modification factor from top to bottom: eta=0, 1, 2.2, 3.2 F.M.Liu, CCAST, Beijing

  4. Nuclear modification factor R > 1 implies that partons with higher density in d-Au than in pp involve the interactions. How to formulize and simulate this high parton densities in a Monte Carlo generator? F.M.Liu, CCAST, Beijing

  5. 2. High parton densities Parton-parton scattering: Scattering with many partons: rapidity plateau Same symbol for soft and hard. No nuclear effect  Nuclear modification factor R=1. F.M.Liu, CCAST, Beijing

  6. With high parton densities in target, a parton in projectile may interact with more partons in the target, e.g.: • elastic interaction interference with simple diagram and provide negative contrib. to cross section (screen) • Multiple ladders • Affects: • multiplicites • hadronization properties • Rapidity gap (high mass Diffraction) F.M.Liu, CCAST, Beijing

  7. We try to put all possibilities together • In a simple and transparent way; • Using only simple ladder diagrams between projectile and target; • Putting all complications into “projectile/target excitations”, to be treated in an effective way. The number of partons in projectile/target which can interact with a parton in target/projectile is the key quantity, we define it as Z p/T. F.M.Liu, CCAST, Beijing

  8. For the screen contribution: With reduced weight The contribution of simple diagram F.M.Liu, CCAST, Beijing

  9. Adding the screening diagram gives the contribution So we use Z should increase with collision energy, centrality and atomic number So we use with F.M.Liu, CCAST, Beijing

  10. For the diffractive contribution: The flat line represents a projectile excitation. For the multiple ladder contribution: A target excitation represents Several ladders F.M.Liu, CCAST, Beijing

  11. How to realize projectile/target excitation? • We suppose an mass distributed according to • For masses exceeding hadron masses, we take strings. • To realize the effects of high parton density, string properties are supposed to depend on Z , e.g.: with F.M.Liu, CCAST, Beijing

  12. The formalism: • Cut diagram technique • Strict energy conservation • Markov chains for numerics Our simulations tell that the number of “visible” Partons in projectile by a parton in target, F.M.Liu, CCAST, Beijing

  13. 3. proton-proton results a. multiplicity distribution: Left to right: contributions from 0, 1, >=2 Pomerons F.M.Liu, CCAST, Beijing

  14. 3. proton-proton results b. pseudo-rapidity distribution: PHOBOS data UA5 data Central ladders (Pom’s) Target excitations / Projectile excitations F.M.Liu, CCAST, Beijing

  15. 3. proton-proton resultsc. Transverse momentum distribution: data: PHENIX F.M.Liu, CCAST, Beijing

  16. 3. proton-proton resultsc. Transverse momentum distribution: At different rapidity regions, data: BRAHMS F.M.Liu, CCAST, Beijing

  17. 3. d-Au resultsa. pseudo-rapidity distribution: Minimum bias Centrality dependence Central ladders (N Pom > 1) Central ladder (N Pom =1) Target excitations / Projectile excitations # # F.M.Liu, CCAST, Beijing

  18. 3. d-Au resultsc. Transverse momentum distribution, the nuclear modification factor R. F.M.Liu, CCAST, Beijing

  19. The centrality dependence of nuclear modification factor R. F.M.Liu, CCAST, Beijing

  20. The rapidity dependence of nuclear modification factor R. F.M.Liu, CCAST, Beijing

  21. Some other good results • Results on identified hadrons, e.g. • The nuclear modification factor R for d-Au collisions as a function of transverse momentum • The particle ratios as a function of transverse momentum for pp and d-Au collisions • The number of triggered jets at near side and away side for pp and d-Au collisions. F.M.Liu, CCAST, Beijing

  22. Conclusions • Motivated by the recent RHIC data in pp and d-Au collisions, we study the behaviors of nuclear modification factor. • The behaviors change with collision energy and centrality (including the atomic numbers of projectile and target). • We simulate the R behavior for d-Au collisions successfully and find the high parton density plays the key role for it. • There are still something to do, e.g. adding the interactions of produced particles, to explain well the target side data of d-Au collision and explain Au-Au collisions. F.M.Liu, CCAST, Beijing

  23. Thanks !

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