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NuTeV Anomaly NuTeV Anomaly & & Strange-Antistrange Asymmetric Strange-Antistrange Asymmetric

Sea Sea Bo-Qiang MaBo-Qiang Ma Department of Physics, Peking UniversityDepartment of Physics, Peking University August 16, August 16, 2002004, talk at ICHEP04, Beijing4, talk at ICHEP04, Beijing

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In collaboration with Yong Ding PLB590(2004)216

hep-ph/0405178

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OutlineOutline

• The NuTeV anamoly and Paschos-Wolfenstein The NuTeV anamoly and Paschos-Wolfenstein

relation relation

• A brief review on strange-antistrange asymmetry of A brief review on strange-antistrange asymmetry of

the nucleon seathe nucleon sea

• The strange-antistrange asymmetry in the light-The strange-antistrange asymmetry in the light-

cone baryon-meson fluctuation mdelcone baryon-meson fluctuation mdel

• SummarySummary

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Weinberg Angle from Nuetrino DIS: Weinberg Angle from Nuetrino DIS: NuTeV AnamolyNuTeV Anamoly

• NuTeV Collaboration reported result, PRL88(02)091802

• Other electroweak processes

• The three standard deviations could be an indication of new physics beyond standard model if it cannot be explained in conventional physics

2sin 0.2227 0.0004w

2sin 0.2277 0.0013(stat) 0.0009(syst)w

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• The Paschos-Wolfenstein relation

• The assumptions for the P-W relationship a isoscalar target

b charge symmetry c symmetric strange and antistrange distributions

( ) ( ) ( ) ( )p np ns x s x s x s x ( ) ( ) ( ) ( )

p np nc x c x c x c x

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• Non-isoscalar target correction

a neutron excess correction (p<n) (S. Kumano (PRD66:111301,2002), the correction is small ; S. A. Kulagin (PRD67:091301,2003), gave the correction is -0.004 ;

S. Davidson et. al (JHEP,0202: 037,2002), no exactly correction. )

b nuclear shadowing and anti-shadowing effect

(S. Kuvalenko, I. Schmit and J.J,Yang (杨建军） (PLB546:68,2002), gave the correction changes its sign from -0.00098 to 0.00178; J. W, Qiu and I. Vitev (hep-ph/0401062), providing 2% for the discrepancy)

c EMC effect

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• Charge symmetry violation

Perturbative method a quark model (E. Sather, (PLB274:433,1992)) obtained the correction is -0.002, which could reduce the discrepancy 40% )

b twist two valence parton distributions (J. T. Londergan and A. W. Thomas, (PLB558:132,2003;PRD 67:111901, 2003)) obtained the result should remove roughly

one-third of the discrepancy)

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c comparing the structure functions (C. Boros, J. T. Londergan and A. W. Thomas (PRL81:4075,1998;PRD59:074021,1999) thought the CSV in the nucleon sea is predominant and much larger than the valence quarks)

d other calculations about CSV (B. Q. Ma (PLB274:111,1992); C. J. Benesh and T. Goldman (PRC55:441,1997) R. M. Davidson and M. Burkardt (PLB403:134,1997); C. J. Benesh and J. T. Londergan (PRC58:1218,1998) C. Boros, et. al (PLB468:161,1999) )

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non-perturbative method meson cloud model

F. G. Cao(曹福广 ) and A. I. Signal (PRC62:015203,2000),

found the CSV in both the valence quark distribution

and the nucleon sea are smaller (below 1%) than

most quark model predictions (2%-10%) and did not

give the correction to the discrepancy

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• Asymmetric strange-antistrange sea quark distributions

meson cloud model: F. G. Cao and A.I. Signal, PLB559(03)229

it is concluded that the asymmetry of the strange and anti-strange is small and could not affect the discrepancy

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The Strange-Antistrange AsymmetryThe Strange-Antistrange Asymmetry

The strange quark and antiquark distributions

are symmetric at leading-orders of

perturbative QCD( ) ( )s x s x

However, it has been argued that there is strange-antistrange distribution

asymmetry in pQCD evolution at three-loops from non-vanishing up and down

quark valence densities.

hep-ph/0404240, S.Catani et al.

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Strange-Antistrange AsymmetryStrange-Antistrange Asymmetry from Non-Perturbative Sourcesfrom Non-Perturbative Sources

• Meson Cloud Model A.I. Signal and A.W. Thomas, PLB191(87)205

• Chiral Field M. Burkardt and J. Warr, PRD45(92)958

• Baryon-Meson Fluctuation S.J. Brodsky and B.-Q. Ma, PLB381(96)317

( ) ( ) at large s x s x x

( ) ( ) at large s x s x x

( ) ( ) at large s x s x x

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Mechanism for S-Sbar asymmetryMechanism for S-Sbar asymmetry

s(x)=s(x)\_

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Strange-Antistrange Asymmetry Strange-Antistrange Asymmetry in phenomenological analysesin phenomenological analyses

• V. Barone et al. Global Analysis, EPJC12(00)243

• NuTeV dimuon analysis, hep-ex/0405037

• CTEQ Global Analysis, F. Olness et. al (hep-ph/0312323),

[ ( ) ( )] 0.002x s x s x dx

[ ( ) ( )] 0.0013 0.0016x s x s x dx

[ ( ) ( )] 0.001 0.004x s x s x dx With large uncertainties

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A brief commentA brief comment

More precision determinations of strange-antistrange asymmetry should be performed or some sensitive quantities should be used to measure the strangeness asymmetry

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Modified P-W relationship

• The cross section for neutrino-nucleon DIS

a for neutral current interaction

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b for charged current interaction

• The structure functions of neutral current

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• The structure functions of charged current

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• The modified P-W relation

-

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Strange-antistrange asymmetry

• In light-cone baryon-meson fluctuation model

• The dominant baryon-meson configuration for s-sbar

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Mechanism for S-Sbar asymmetryMechanism for S-Sbar asymmetry

( ) ( )s x s x

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• Proton wave functions

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• The momentum distributions

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• The probabilities

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The probabilities for meson-baryon fluctuation

• General case

• Our case

( )3% 6%

KP

( )4% 10%

KP

Brodsky & Ma, PLB381(96)317

Ma, Schmidt, Yang, EPJA12(01)353

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• The distributions for

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The results for

• For Gaussian wave function

• For power law wave function

However, we have also very large Qv (around a factor

of 3 larger) in our model calculation, so the ratio of

S‾/Qv is reasonable

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The results • For Gaussian wave function

the discrepancy from 0.005 to 0.0033(0.0009)

• For power law wave function

the discrepancy from 0.005 to 0.0036(0.0016)

Remove the discrepancy 30%-80%between NuTev and other values of Weinberg angle

0.0017 0.0041SR

0.0014 0.0034SR

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s(x)/sbar(x) asymmetry

s(x)/sbar(x) could be compatible with data by by including some intrinsic strange

sea contributions

CCFR and NuTeV experimental analyses break net zero strangeness ( ) ( )s x dx s x dx

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A Further Chiral Quark Model Study

• A further study by using chiral quark model also shows that this strange-antistrange asymmetry has a significant contribution to the Paschos-Wolfenstein relation and can explain the anomaly without sensitivity to input parameters.

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SummarySummary • Checked the influence due to strange-

antistrange asymmetry and derived the modified Paschos-Wolfenstein relation

• Conclude that the correction due to the strange-antistrange asymmetry might be important to explain the NuTeV anamoly