wen chen chang institute of physics academia sinica
Download
Skip this Video
Download Presentation
Flavor Asymmetry of the Nucleon Sea and the Connection with the Five-Quark Components

Loading in 2 Seconds...

play fullscreen
1 / 46

Flavor Asymmetry of the Nucleon Sea and the Connection with the Five-Quark Components - PowerPoint PPT Presentation


  • 56 Views
  • Uploaded on

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.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Flavor Asymmetry of the Nucleon Sea and the Connection with the Five-Quark Components' - khan


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
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)
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)

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.

slide21

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)

slide23

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 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

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.
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)

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!
ad