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Strange sea asymmetry from global QCD fits

Update of the global QCD Fit Results on the strange sea asymmetry Impact on the NuTeV measurement. Strange sea asymmetry from global QCD fits. Benjamin Portheault on behalf of V. Barone, C. Pascaud, F. Zomer. DIS cross section data from BEBC, new CCFR , CDHSW.

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Strange sea asymmetry from global QCD fits

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  1. Update of the global QCD Fit Results on the strange sea asymmetry Impact on the NuTeV measurement Strange sea asymmetry from global QCD fits Benjamin Portheault on behalf of V. Barone, C. Pascaud, F. Zomer Benjamin Portheault

  2. DIS cross section data from BEBC, newCCFR, CDHSW Drell Yan data from E605, E772 and new from E866 is not constrained to have the same shape as also is allowed with the constraint New global QCD fit previously : hep-ph/9907512 Based on HERA I (H1,Zeus) data + NMC, BCDMS NLO QCD Fixed Flavour Scheme and Intrinsic strange sea : phenomenological meson-baryon fluctuation of the proton Benjamin Portheault

  3. fit results is slightly favoured with respect to (8 units for 2 more paramaters) Benjamin Portheault

  4. Constraints on Comes from high x cross section measurment (isoscalar target) Both CCFR and CDHSW provide high x data dimuon data (x<0.5) are not a direct constraint in this region no significant statistics, large background CDHSW neutrino data higher than CCFR agreement for antineutrino data x=0.65 En=110 GeV Benjamin Portheault

  5. Results on the strange sea asymmetry without CCFR, same asymmetry as in previous studies no CCFR all data using all data sets, the asymmetry is strongly reduced momentum asymmetry is compatible with zero Benjamin Portheault

  6. Impact on the partial allowing How favoured is the strange asymmetry ? CDHSW neutrino data decrease by 8 units CCFR E770 neutrino data increase by 6 units (E774 neutrino data decrease by 3 units) Dominant systematic uncertainty (flux normalisation) on CCFR neutrino data is fitted to –5.2 s (data is scaled up by 4%) with and without the strange asymmetry BUT : Kown problem in the y shape of the CDHSW data at low x (< 0.1) Solution in global analysis is to take both by default Benjamin Portheault

  7. The NuTeV NuTeV use a quantity related to (exact for an isoscalar target) NuTeV LEP EWWG a 3.1 s discrepancy Must be corrected for a target with a fractionnal neutron excess and if Benjamin Portheault

  8. Corrections to R- Kulagin hep-ph/0301045 : NLO correction (NuTeV : LO) neutron excess reduction strange asymmetry Compute these corrections using our pdfs and properly propagate the errors Benjamin Portheault

  9. Without CCFR (with the significant strange asymmetry ) no discrepancy All data included : 1.35 s discrepancy NuTeV reports : reduction is due to neutron excess correction (with CTEQ5 pdfs ) Benjamin Portheault

  10. Conclusion New global fit including the up-to-date DIS and Drell Yan data The strange sea asymmetry is found to be reduced by the recently analysed CCFR data Impact on the measurement : the neutron excess and the strange sea asymmetry reduce the NuTeV discrepancy but the effect of the latter is small but no access to NuTev detector effect Benjamin Portheault

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