ZEUS fits-report: FL session Feb 2009 A.M.Cooper-Sarkar and C. Gwenlan • Report on fitting new FINAL data: • e- CC (175pb-1: P=0.30 71pb-1, P=-0.27 104pb-1)(DESY-08-177) • e- NC (169pb-1, P=+0.29, P=-0.27)(DESY-08-202) • HER(Ep=920,44.5pb-1), MER(Ep=575, 7.1pb-1), LER(Ep=460, 14.0pb-1) reduced cross-sections (DESY-08-666!!!) • THIS TALK-- Improvement to PDF uncertainties • On Friday High Q2 talk- Electroweak parameters • What are we planning before DIS09?- to include NC and CC e+ polarised data
Adding New NC and CCe- data to ZEUS-JETS fit → ZEUS-pol fit This takes 509 data points up to 760 data points Quadratic 2 (NEW) (NEW) Remember we have shown this before with preliminary e- data- this is now final PDFs from the new fit compared to published ZEUS-JETS fit – central values of the PDFs do not change much…..
The d-flavour sector is less well known- hence we look forward to CCe+ data (NEW) The xuv PDF uncertainties are reduced at high-x ….. as expected since NC and CC e- cross-sections are both u dominated However some other uncertainties increase marginally- this can always happen when OFFSETing correlated errors
Adding HER, MER, LER data to ZEUS-pol fit → ZEUS-pol-FL fit ! This takes 760 data points up to 922 data points Quadratic 2 PDFs from the new fit compared to the ZEUS-pol fit (showing just impact of HER,MER,LER data) – central values of the PDFs do not change much….
Quadratic Errors All systematics added in quadrature (i.e. no treatment for correlations) impact of LER,MER,HER data on low-x sea and low-x gluon is clearly visible
Offset method However using the OFFSET method to account for correlated systematic errors this is less clear. The new HER,MER, LER data reduce the uncertainties on the low-x sea- as expected since this is the kinematic region of the data and the data relate DIRECTLY to the sea. The relationship of the gluon is less direct - Gluon uncertainty at very low x is reduced, but uncertainty band wider at higher x
Summary/questions • The new HER, MER, LER data has impact on the fit • I doubt that ZEUS wants to reconsider the use of its traditional OFFSET method in favour of Hessian or Quadratic at this stage • But the combination of this with the H1 data could be dramatic