1. QCD Fragmentation Functions for Hard Hadron Production ( with emphasis on charged-hadron/pion ratio) HIC03, Montreal, Canada, Jun 27, 2003 Xiaofei Zhang Kent State University X. F. Zhang, et al., PRL, 89,272301 (2002) X. F. Zhang, et al, hep-ph/0306227 (2003) based on work:

2. New phenomena at RHIC Charged hadron and pion are different!

3. Enhancement of p/ π, h/π Uncertainty in Fragmentation Functions (FF-s) A simple model to explain h/π enhancement from pQCD this talk: 0-10% 60-92%

4. pQCD for hard hadron production p hadron FF-s are important for hadron production

5. Phase space of fragmentation in pp collisions 8GeV 4GeV 16GeV X. Zhang, et. al., PRL, 89,272301 (2002)

6. 91.2 GeV full light q charm bottom

7. β=0.8β KKP 27.8 GeV β= β KKP β=0.8β KKP β=β KKP β=0.5β KKP Large z part of FF-s and p/π ratio in pp Large z part of FF-s have significant effect on p/π

8. FF-s and p/π ratio at RHIC pQCD x~0.01, gluon PDF-s become very important Gluon FF-s dominate Large z part of gluon FF-s are even less certain, especially for proton! FF sets

9. Charged-hadron to pion ratio in pp mimic higher twist effect using Kretzer FF-s h/π in pp at RHIC can be described by pQCD

10. * Croinin effect in p+A : R pA >1, for p T >2 GeV * At fixed target energies, Cronin effect is not universal ; heavier particle, larger enhancement p>k>π J. W. Cronin et al., Phys. Rev. D 11,3105 (1975) * Cronin effects in pA collisions k T broadening * k T effects: mimic power correction -- power correction is larger for proton than pion -- more phase space for dynamic broadening A simple model for h/π enhancement in Au+Au K T broadening is non-universal for different particles Simple model Assume suppression factors cancel approximately L(b) place of hard collisions

11. h/π enhancement in Au+Au, more central, larger L(b), more enhancement of charged-haron/pion X.F. Zhang and G. Fai, hep-ph/0306227

12. Cronin effects in dAu Difference of R dAu for charged-hadron and pion are reasonably described using the same parameters EKS anti-shadowing

13. Intrinsic k T mimics power corrections, systematic study of power correction is needed A simple model based on the non-universal k T broadening of different particles can explain both Direct prediction of this model: enhancement of h/ π in d+Au h/ π enhancement in central Au+Au collisions Difference of R dAu for pion and charged hadron Can it explain the difference of R AA between charged-hadron and pion?