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

F.M.Liu, CCAST, Beijing2 1.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, Beijing3 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, Beijing4 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, Beijing5 2. High parton densities Parton-parton scattering: Same symbol for soft and hard. rapidity plateau Scattering with many partons: No nuclear effect  Nuclear modification factor R=1.

F.M.Liu, CCAST, Beijing6 With high parton densities in target, a parton in projectile may interact with more partons in the target, e.g.:  Multiple ladders Affects: multiplicites hadronization properties  elastic interaction interference with simple diagram and provide negative contrib. to cross section (screen)  Rapidity gap (high mass Diffraction)

F.M.Liu, CCAST, Beijing7 We try to put all possibilities together In a simple and transparent way; In a simple and transparent way; Using only simple ladder diagrams between projectile and target; Using only simple ladder diagrams between projectile and target; Putting all complications into “ projectile/target excitations ”, to be treated in an effective way. 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, Beijing8 The contribution of simple diagram For the screen contribution: With reduced weight

F.M.Liu, CCAST, Beijing9 So we use Z should increase with collision energy, centrality and atomic number with So we use Adding the screening diagram gives the contribution

F.M.Liu, CCAST, Beijing10 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, Beijing11 How to realize projectile/target excitation? We suppose an mass distributed according to We suppose an mass distributed according to For masses exceeding hadron masses, we take strings. 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.: To realize the effects of high parton density, string properties are supposed to depend on Z, e.g.: with

F.M.Liu, CCAST, Beijing12 The formalism: Cut diagram technique Cut diagram technique Strict energy conservation Strict energy conservation Markov chains for numerics Markov chains for numerics Our simulations tell that the number of “ visible ” Partons in projectile by a parton in target,

F.M.Liu, CCAST, Beijing13 3. proton-proton results a. multiplicity distribution : Left to right: contributions from 0, 1, >=2 Pomerons

F.M.Liu, CCAST, Beijing14 3. proton-proton results b. pseudo-rapidity distribution : UA5 data PHOBOS data Central ladders (Pom ’ s) Target excitations / Projectile excitations

F.M.Liu, CCAST, Beijing15 3. proton-proton results c. Transverse momentum distribution : data: PHENIX

F.M.Liu, CCAST, Beijing16 3. proton-proton results c. Transverse momentum distribution : At different rapidity regions, data: BRAHMS

F.M.Liu, CCAST, Beijing17 3. d-Au results a. pseudo-rapidity distribution : Central ladders (N Pom > 1) Central ladder (N Pom =1) Target excitations / Projectile excitations Minimum bias Centrality dependence # #

F.M.Liu, CCAST, Beijing18 3. d-Au results c. Transverse momentum distribution, the nuclear modification factor R.

F.M.Liu, CCAST, Beijing19 The centrality dependence of nuclear modification factor R.

F.M.Liu, CCAST, Beijing20 The rapidity dependence of nuclear modification factor R.

F.M.Liu, CCAST, Beijing21 Some other good results Results on identified hadrons, e.g. Results on identified hadrons, e.g. The nuclear modification factor R for d-Au collisions as a function of transverse momentum 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 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. The number of triggered jets at near side and away side for pp and d-Au collisions.

F.M.Liu, CCAST, Beijing22 Conclusions Conclusions Motivated by the recent RHIC data in pp and d-Au collisions, we study the behaviors of nuclear modification factor. 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). 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. 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. 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.

Thanks !