QCD Fragmentation Functions for Hard Hadron Production ( with emphasis on charged-hadron/pion ratio)...
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Transcript of QCD Fragmentation Functions for Hard Hadron Production ( with emphasis on charged-hadron/pion ratio)...
QCD Fragmentation Functions for Hard Hadron Production
(with emphasis on charged-hadron/pion ratio)
HIC03, Montreal , Canada, Jun 27, 2003
Xiaofei ZhangXiaofei Zhang
Kent State UniversityKent State University
X. F. Zhang, et al. , PRL, 89,272301 (2002)
X. F. Zhang , et al , hep-ph/0306227 (2003)
based on work:
ddpdT
ddpdNR
Tpp
AB
TAB
AB /
/
New phenomena at RHIC
Charged hadron and pion are different!
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%
pQCD for hard hadron production
p
hadron
hadron
FF-s are important for hadron production
Phase space of fragmentation in pp collisions
8GeV
4GeV
16GeV
X. Zhang, et. al. , PRL, 89,272301 (2002)
91.2 GeVfull
light q
charm
bottom
β=0.8βKKP
27.8 GeV
β= βKKP
β=0.8βKKP
β=βKKP
β=0.5βKKP
Large z part of FF-s and p/π ratio in pp
Large z part of FF-s have significant effect on p/π
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
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
* Croinin effect in p+A : RpA>1, for pT>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 kT broadening
* kT 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
KT broadening is non-universal for different particles
Simple model
•Assume suppression factors cancel approximately
L(b)
place of hard collisions
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
Cronin effects in dAu
• Difference of RdAu for charged-hadron and pion are reasonably described using the same parameters
EKS anti-shadowing
Intrinsic kT mimics power corrections, systematic study of power correction is needed
A simple model based on the non-universal kT
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 RdAu for pion and charged hadron
Can it explain the difference of RAA betweencharged-hadron and pion?