Nucleon Sea Structure and the Five-Quark Components Wen-Chen Chang Institute of Physics, Academia Sinica, Taiwan Jen-Chieh Peng University of Illinois at Urbana-Champaign, USA Baryons2013 International Conference on the Structure of Baryons June 24th - 28th 2013 1
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Nucleon Sea Structure and the Five-Quark Components Wen-Chen Chang Institute of Physics, Academia Sinica, Taiwan Jen-Chieh Peng University of Illinois.
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1
Nucleon Sea Structure and the
Five-Quark Components
Wen-Chen ChangInstitute of Physics, Academia Sinica, Taiwan
Jen-Chieh Peng University of Illinois at Urbana-Champaign, USA
Baryons2013International Conference on the Structure of
Baryons June 24th - 28th 2013
Outline
• Evidences of nucleon sea• Flavor Asymmetry of light sea quarks• Structure of strange quarks• Intrinsic sea quarks in light-front 5q model• Sea quarks in lattice-QCD• Prospect• Conclusion
2
Deep Inelastic Scattering
3
Q2 :Four-momentum transferx : Bjorken variable (=Q2/2Mn)n : Energy transferM : Nucleon massW : Final state hadronic mass
Assume a symmetric quark-antiquark sea,GSR is only sensitive to valance quarks.J.I. Friedman, Rev. Mod. Phys. Vol. 63, 615 (1991)
6
Gottfried Sum Measured by NMC
SG = 0.235 ± 0.026
New Muon Collaboration (NMC), Phys. Rev. D50 (1994) R1
SG is significantly lower than 1/3 !
Explanations for the NMC result
7
• Uncertain extrapolation for 0.0 < x < 0.004
• Charge symmetry violation
• in the proton,( )n p n pu d d u
( ) ( )u x d x1
0( ( ) ( )) 0.148 0.04d x u x dx
Need independent methods to check the asymmetry, and to measure its x-dependence !
d u
224 1[ ( ) ( ) ( ) ( )]
9 t b t bb t b t
de q x q x q x q x
dx dx x x s
( )1
1 ( ) 1 ( )4 ( )| 1 1
2 2 2( ) ( ) ( ) ( )1
4 ( ) ( )
b t
bpd
t tbx x
ppb t t t
b t
d xd x d xu x
d x d x u x u xu x u x
Drell-Yan Process
8
Acceptance in Fixed-target Exps.
Light Anti-quark Flavor Asymmetry
Naïve Assumption:
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NA51 (Drell-Yan, 1994)
NMC (Gottfried Sum Rule)
NA 51 Drell-Yan confirms d(x) > u(x)
Light Anti-quark Flavor Asymmetry
Naïve Assumption:
10
NA51 (Drell-Yan, 1994)
E866/NuSea (Drell-Yan, 1998)
NMC (Gottfried Sum Rule)
Origin of u(x)d(x): Perturbative QCD effect?
• Pauli blocking• guu is more suppressed than gdd in the proton since
p=uud (Field and Feynman 1977)
• pQCD calculation (Ross, Sachrajda 1979)
• Bag model calculation (Signal, Thomas, Schreiber 1991)
• Chiral quark-soliton model (Pobylitsa et al. 1999)• Instanton model (Dorokhov, Kochelev 1993)• Statistical model (Bourrely et al. 1995; Bhalerao 1996)• Balance model (Zhang, Ma 2001)
11
The valence quarks affect the gluon splitting.
G 𝑞𝑞
Origin of u(x)d(x): Non-perturbative QCD effect?
• Meson cloud in the nucleons (Thomas 1983, Kumano 1991):
Sullivan process in DIS.
• Chiral quark model (Eichten et al. 1992; Wakamatsu 1992): Goldstone bosons couple to valence quarks.
12Pion cloud is a source of antiquarks in the protons and it lead to d>u.
0; : : 4 : 3 : 2q q
0; : : 2 :1: 0p N
n
13
( ) ( ) vs. Theoretical Modelsd x u x
Strange Quark in the Nucleon:Deep-Inelastic Neutrino Scattering
Short Range Structure of HadronExtrinsic Sea Intrinsic SeaGluon splitting in leading twist Gluon fusion & light quark
scattering (higher-twist)
Perturbative radiation Non-perturbative dynamicsCP invariant Possible CP non-invariantFast fluctuation With a longer lifetimeOf small x Of large x (valence-like)Strong Q2 dependent Small Q2 dependent
21Hoyer and Brodsky, AIP Conf. Proc. 221, 238 (1990)
Intrinsic Sea:•Non-perturbative•Origin of flavor asymmetry of light sea quarks•With x^-1/2 small-x behavior from the Reggeon exchange
Disconnected Sea(u, d quarks and heavy quarks)
Intrinsic Sea:•Non-perturbative•Peaked at medium x (~ 0.1)•Meson cloud or the Reggeon exchangeExtrinsic Sea:•Perturbative•At small x•With x^-1 small-x behavior from the Pomeron exchange
• E906/SeaQuest at FNAL: flavor asymmetry of d-bar/u-bar at large x region.
• MINERνA at FNAL: x-dependence of nuclear effects for sea quarks.
• JLAB-12 GeV: transverse spatial distribution of sea quarks.• Kaon-induced DY experiment at J-PARC: s and s-bar.• Electron-Ion Collider (EIC): sea quark distributions and their
spin structure.
• Heavy sea quarks:• Open-charm production at forward rapidity, e.g. fixed-target
experiment at LHC. • Higgs production at large xF at LHC.
d/u From E906/SeaQuest at FNAL
Ratio of Drell-Yan cross sections
(in leading order—E866 data analysis confirmed in NLO)
Global NLO PDF fits which include E866 cross section ratios agree with E866 results
Fermilab E906/Drell-Yan will extend these measurements and reduce statistical uncertainty.
E906 expects systematic uncertainty to remain at approx. 1% in cross section ratio. 46
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Future Prospect (Theoretical) • Intrinsic sea for hyperons and mesons? • Intrinsic gluons in the nucleons? • Connection between the 5-quark model and the
meson-cloud model? • Connection between the 5-quark model and lattice
QCD? • Spin-dependent observables of intrinsic sea?
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Conclusion
• Using DIS, Drell-Yan and SIDIS processes, the structure of sea quarks in the nucleon are explored.
• The measured x distributions of (d-u), (s+s) and (u+d-s-s) could be reasonably described by the light-front 5q Fock states. The probabilities of the intrinsic 5q states of light sea quarks are extracted.
• The intrinsic or valence-like sea quarks are deeply connected with the non-perturbative QCD. More accurate data will be available in the coming experiments at FNAL, JLAB, LHC, J-PARC and EIC.