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8th Circum-Pan-Pacific Symposium on High Energy Spin Physics June 20-24, 2011 in Cairns, QLD, Australia. Wen -Chen Chang Institute of Physics, Academia Sinica. Flavor Asymmetry of the Nucleon Sea and the Connection with the Five-Quark Components. Outline.
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June 20-24, 2011 in Cairns, QLD, Australia
Institute of Physics, Academia Sinica
Q2 :Four-momentum transfer
x : Bjorken variable (=Q2/2Mn)
n : Energy transfer
M : Nucleon mass
W : Final state hadronic mass
The simplest interpretation of these failures is that the sQM lacks a quark sea.
Hence the number counts of the quark flavors does not come out correctly.
- Ling-Fong Li and Ta-Pei Cheng, arXiV: hep-ph/9709293
Assume an isotopic quark-antiquark sea,
GSR is only sensitive to valance quarks.
New Muon Collaboration (NMC), Phys. Rev. D50 (1994) R1
SG = 0.235 ± 0.026
( Significantly lower than 1/3 ! )
Need independent methods to check the asymmetry, and to measure its x-dependence !
Acceptance in Fixed-target Experiments
NA 51 Drell-Yan confirms
d(x) > u(x)
CCFR, Z. Phys. C 65, 189 (1995)
NuTeV, PRL 99, 192001 (2007)
HERMES, Phys. Lett. B 666, 446 (2008)
Origin of u(x)d(x): Perturbative QCD effect?
The valence quarks affect the gluon splitting.
Origin of u(x)d(x): Non-perturbative QCD effect?
Sullivan process in DIS.
The pion cloud is a source of antiquarks in the protons and it lead to d>u.
J.C. Peng, Eur. Phys. J. A 18, 395–399 (2003)
Light quark sea helicity densities
are flavor symmetric.
In the 1980’s Brodsky et al. (BHPS) suggested the existence of “intrinsic” charm (PLB 93,451; PRD 23, 2745).
Still No Conclusive Evidence…..
CTEQ Global Analysis
PRD 75, 054029
mc=1.5, ms=0.5, mu, md=0.3 GeV
is obtained numerically.
In the limit of a large mass for quark Q (charm):
Data of d(x)-u(x) vs. Light-Cone 5-q Model
W.C. Chang and J.C. Peng, arXiv: 1102.5631
Data of x(d(x)+u(x)-s(x)-s(x)) vs. Light-Cone 5-q Model
W.C. Chang and J.C. Peng, arXiv: 1105.2381,1102.5631
Tevatron 800 GeVFNAL E906/SeaQuest Experiment
Fixed Target Beam lines
Ratio of Drell-Yan cross sections
(in leading order—E866 data analysis confirmed in NLO)
p+p at sqrt(s)=500 GeV
Yang, Peng, and Groe-Perdekam, Phys. Lett. B 680, 231 (2009)
Very preliminary, not part of publication on the topic
Only muons (no electrons)
Uncertified systematic errors
J. Mans :: CMS EWK Measurements