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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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Wen chen chang institute of physics academia sinica

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

Outline

  • Evidences for the Existence of Sea Quarks

  • Flavor Asymmetry of Sea Quarks

  • Theoretical Interpretations

  • Intrinsic Sea Quark & Light-cone 5q Model

  • Current & Future Experiments

  • Conclusion


Deep inelastic scattering

Deep Inelastic Scattering

Q2 :Four-momentum transfer

x : Bjorken variable (=Q2/2Mn)

n : Energy transfer

M : Nucleon mass

W : Final state hadronic mass

  • Scaling

  • Valence quarks

  • Quark-antiquark pairs


Sum rules

Sum Rules

J.I. Friedman, Rev. Mod. Phys. Vol. 63, 615 (1991)


Constituent quark model

Constituent Quark model

  • Axial vector current matrix elements:

  • Scalar density matrix elements:

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


Sum rules1

Sum Rules

J.I. Friedman, Rev. Mod. Phys. Vol. 63, 615 (1991)


Gottfried sum rule

Gottfried Sum Rule

Assume an isotopic quark-antiquark sea,

GSR is only sensitive to valance quarks.


Measurement of gottfried sum

Measurement of Gottfried Sum

New Muon Collaboration (NMC), Phys. Rev. D50 (1994) R1

SG = 0.235 ± 0.026

( Significantly lower than 1/3 ! )


Explanations for the nmc result

Explanations for the NMC result

  • Uncertain extrapolation for 0.0 < x < 0.004

  • Charge symmetry violation

  • in the proton

Need independent methods to check the asymmetry, and to measure its x-dependence !


Drell yan process

Drell-Yan Process

Acceptance in Fixed-target Experiments


Light antiquark flavor asymmetry

Light Antiquark Flavor Asymmetry

  • Naïve Assumption:

  • NMC (Gottfried Sum Rule)

  • NA51 (Drell-Yan, 1994)

NA 51 Drell-Yan confirms

d(x) > u(x)


Light antiquark flavor asymmetry1

Light Antiquark Flavor Asymmetry

  • Naïve Assumption:

  • NMC (Gottfried Sum Rule)

  • NA51 (Drell-Yan, 1994)

  • E866/NuSea (Drell-Yan, 1998)


Deep inelastic neutrino scattering

Deep-Inelastic Neutrino Scattering


Strange quark in the nucleon

Strange Quark in the Nucleon

CCFR, Z. Phys. C 65, 189 (1995)


Strange quark and antiquark in the nucleon

Strange Quark and Antiquark in the Nucleon

NuTeV, PRL 99, 192001 (2007)


Strange quarks from si charged kaon dis production

Strange Quarks from SI Charged-Kaon DIS Production

x(s+s)

HERMES, Phys. Lett. B 666, 446 (2008)


Hermes vs ccfr and ct10

HERMES vs. CCFR and CT10


Nontrivial qcd vacuum animation of the action density in 4 dimensions

Nontrivial QCD VacuumAnimation of the Action Density in 4 Dimensions

http://www.physics.adelaide.edu.au/theory/staff/leinweber/VisualQCD/QCDvacuum/welcome.html


Origin of u x d x perturbative qcd effect

Origin of u(x)d(x): Perturbative QCD effect?

  • Pauli blocking

    • guu is more suppressed than gdd 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)

The valence quarks affect the gluon splitting.


Origin of u x d x non perturbative qcd effect

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.

n

The pion cloud is a source of antiquarks in the protons and it lead to d>u.


Flavor asymmetry of the nucleon sea and the connection with the five quark components

  • Meson Cloud Model (Signal and Thomas, 1987)

  • Chiral Field (Burkardt and Warr , 1992)

  • Baryon-Meson Fluctuation (Brodsky and Ma , 1996)

  • Perturbative evolution (Catani et al., 2004)


Spin and flavor are connected

Spin and Flavor are Connected

J.C. Peng, Eur. Phys. J. A 18, 395–399 (2003)


Flavor asymmetry of the nucleon sea and the connection with the five quark components

  • HERMES (PRD71, 012003 (2005))

  • COMPASS (NPB 198, 116, (2010))

  • DSSV2008 (PRL 101, 072001 (2008))

Light quark sea helicity densities

are flavor symmetric.


Origin of sea quarks

Origin of Sea Quarks

  • It is generally agreed that the observed flavor asymmetry mostly resulted from theintrinsic sea quarks.

  • For further investigation, it will be good toseparate their contributions.


Flavor non singlet quantity

: Flavor Non-singlet Quantity

  • is a flavor-non-singlet (FNS) quantity.

  • Extrinsic sea quarks vanish at 1st order in s .

  • Non-perturbative models are able to describe the trend.

  • Greater deviation is seen at large-x valence region.

  • No model predicts


Intrinsic sea flavor non singlet variables

Intrinsic Sea & Flavor Non-singlet Variables

  • Select a non-perturbative model with a minimal set of parameters.

  • Construct the x distribution of flavor non-singlet quantities: , , at the initial scale.

  • After a QCD evolution with the splitting function PNS to the experimental Q2 scale, make a comparison with the data.


Intrinsic charm in light cone 5q model

“Intrinsic” Charm in Light-Cone 5q Model

In the 1980’s Brodsky et al. (BHPS) suggested the existence of “intrinsic” charm (PLB 93,451; PRD 23, 2745).

  • Dominant Fock state configurations have the minimal invariant mass, i.e. the ones with equal-rapidity constituents.

  • The large charm mass gives the c quark a larger x than the other comovinglight partons, more valence-like.


Experimental evidences of ic

Experimental Evidences of IC

arXiv:hep-ph/9706252

ISR

Still No Conclusive Evidence…..

CTEQ Global Analysis

PRD 75, 054029


Intrinsic sea 5q component

“Intrinsic” Sea 5q Component


Intrinsic sea 5q component1

“Intrinsic” Sea 5q Component

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

Data of d(x)-u(x) vs. Light-Cone 5-q Model

  • The shapes of the x distributions of d(x) and u(x) are the same in the 5-q model and thus their difference.

  • Need to evolve the 5-q model prediction from the initial scale  to the experimental scale at Q2=54 GeV2.

W.C. Chang and J.C. Peng, arXiv: 1102.5631


Data of x s x s x vs light cone 5 q model

Data of x(s(x)+s(x)) vs. Light-Cone 5-q Model

  • The x(s(x)+s(x)) are from HERMES kaon SIDIS data at <Q2>=2.5 GeV2.

  • Assume data at x>0.1 are originated from the intrinsic |uudss> 5-quark state.

W.C. Chang and J.C. Peng, arXiv: 1105.2381


Data of x d x u x s x s x vs light cone 5 q model

Data of x(d(x)+u(x)-s(x)-s(x)) vs. Light-Cone 5-q Model

  • The d(x)+u(x) from CTEQ 6.6.

  • The s(x)+s(x) from HERMES kaon SIDIS data at <Q2>=2.5 GeV2.

  • Assume

  • Probabilities of 5-q states associated with the light sea quarks are extracted.

W.C. Chang and J.C. Peng, arXiv: 1105.2381,1102.5631


Comparison of 5q probabilities

Comparison of 5q Probabilities


The light cone 5 q model

The Light-Cone 5-q Model

  • It is surprising that many FNS quantities can be reasonably described by such a naïve model with very few parameters (mass of quarks and the initial scale).

  • For completeness, this model should be extended to take into account:

    • Anti-symmetric wave function

    • Chiral symmetry breaking effect

    • Spin structure

    • Higher configuration of Fock states


Fnal e906 seaquest experiment

Main Injector 120 GeV

Tevatron 800 GeV

FNAL E906/SeaQuest Experiment

FermilabE906/SeaQuest

  • Data taking planned in 2010

  • 1H, 2H, and nuclear targets

  • 120 GeV proton Beam

Fermilab E866/NuSea

  • Data in 1996-1997

  • 1H, 2H, and nuclear targets

  • 800 GeV proton beam

  • Cross section scales as 1/s

    • 7x that of 800 GeV beam

  • Backgrounds, primarily from J/ decays scale as s

    • 7x Luminosity for same detector rate as 800 GeV beam

  • 50x statistics!!

Fixed Target Beam lines


D u from drell yan scattering

d/u From Drell-Yan Scattering

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.


Longitudinal and transverse view of e906 experimental area

Longitudinal and Transverse View of E906 Experimental Area


Run schedule

Run Schedule


Charged asymmetry of w at rhic

Charged Asymmetry of W at RHIC

p+p at sqrt(s)=500 GeV

Yang, Peng, and Groe-Perdekam, Phys. Lett. B 680, 231 (2009)


Flavor asymmetry of the nucleon sea and the connection with the five quark components

Kensuke’s talk on Monday


20 gev p t results

20 GeV PT Results

Caveats

Very preliminary, not part of publication on the topic

Only muons (no electrons)

Uncertified systematic errors

J. Mans :: CMS EWK Measurements


Future experiments

Future Experiments

  • COMPASS Polarized -induced DY experiment at CERN: spin structure of sea quark.

  • MINERνAat FNAL: x-dependence of nuclear effects for sea and valance quarks.

  • JLAB-12 GeV: transverse spatial distribution of partons.

  • (Polarized) DY experiment at J-PARC: d/u at very large-x region.

  • EIC at RHIC: sea quark distributions and their spin dependence.


Conclusion

Conclusion

  • Using DIS, Drell-Yan and SIDIS processes, the structure of sea quarks in the nucleon are explored.

    • A large asymmetry between d and u was found at intermediate-x regions.

    • No large asymmetry was observed between s and s.


Conclusion1

Conclusion

  • The observed large flavor asymmetry mostly resulted from the non-perturbative effects.

  • The measured x distributions of (d-u), (s+s) and (u+d-s-s) could be reasonably described by the light-cone 5q model. The probabilities of the intrinsic 5q states of light sea quarks are extracted.


Conclusion2

Conclusion

  • The sea quarks are connected with the non-perturbative feature of QCD. They could be the key to understand the confinement!


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