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ZEUS fits-report -High Q2 session Feb 2009 A.M.Cooper-Sarkar and C. Gwenlan. Report on fitting FINAL new 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) Improvement to PDF uncertainties

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ZEUS fits-report -High Q2 session

Feb 2009

A.M.Cooper-Sarkar and C. Gwenlan

  • Report on fitting FINAL new 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)
  • Improvement to PDF uncertainties
  • Electroweak parameter fits: MW , MW/ GF ,MW/ g
  • Electroweak NC couplings: au ad vu vd
  • What are we planning before DIS09?- to include NC and CC e+ polarised data
  • Including the new HER, MER, LER was reported on Wednesday

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



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- NOTE the scale difference-

hence we look forward to CCe+ data


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


Electroweak parameter fits- go back to just ZEUS-pol

Now let MW be a free parameter of the fit, together with the PDF parameters How does MW enter the fit?

In the factor GF2 MW4/(Q2+MW2)2

Value of MW (=80.4 SM) Specifications of the fit

Little correlation between EW and QCD sector of fit


Can also fit BOTH GF and MW remember GF SM= 1.11639×10-5

Or we can fit a more general formalism: fit g and MW in g2 / (Q2 + MW2)2

such that g2=GF2 MW4 = 0.07542 for standard model

This is the most general way to present our data

THESE results are very similar to what we already presented as preliminary to conferences


F20= Σi Ai0(Q2) [xqi(x,Q2) + xqi(x,Q2)]

xF30= ΣiBi0(Q2) [xqi(x,Q2) - xqi(x,Q2)]

Ai0(Q2) = ei2 – 2 eivivePZ + (ve2+ae2)(vi2+ai2) PZ2

Bi0(Q2) = – 2 eiaiae PZ + 4ai aevi ve PZ2

F2P = ΣiAiP(Q2) [xqi(x,Q2) + xqi(x,Q2)]

xF3P= Σi BiP(Q2) [xqi(x,Q2) - xqi(x,Q2)]

AiP(Q2) = 2 eivi ae PZ - 2 ve ae (vi2+ai2) PZ2

BiP(Q2) = 2 eiaive PZ - 2 ai vi (ve2+ae2) PZ2

Now consider fits to electroweak NC couplings as well as PDF parameters

The total cross-section : σ = σ0 + P σP

The unpolarised cross-section is given by σ0 = Y+F20 + Y-xF30

The polarised cross-section is given by σP = Y+F2P + Y-xF3P

PZ >> PZ2 (γZ interference is dominant)

ve is very small (~0.04).

unpolarized xF3 ai,

polarized F2  vi


SM formalism ai = T3i , vi = T3i – 2ei sin2ƏW

Let ai and vi be free as well as PDFparameters. Perform fits with 4 NC EW parameters free

But the errors are not very informative since the contours are very asymmetric- see next slide.


au/vu ad/vd au/ad vu/vd contours: Final HERA-II e-

Note: these are RTVFN jobs (with jets)

We look forward to NC e+ polarised data to improve this.


au/vu ad/vd au/ad vu/vd contours: Prel Hera-II e-

Yes the final e- data do make things slightly worse than the preliminary- this is because we are sitting near a double minimum and the fit is very sensitive to it

But in compensation we are closer to the Standard Model !

And we are no worse off than H1 –see next slide

  • We have now repeated our preliminary work of Summer 2007 using the FINAL e- CC and NC data
  • If anything the FINAL data make things slightly worse for Electroweak parameter fits- we look forward to NCe+
  • The d- sector of the PDFs is the least well known – we look forward to CCe+
  • PS- in case no-one else is doing it…
what is going on with the hera combination pdf
What is going on with the HERA combination/ PDF
  • The HERA-I Data combination is FINAL.
  • We are re-fitting for PDFs to become HERAPDF1.0 not 0.1
  • This involves using RTVFN or ACOT heavy quark mass scheme NOT ZMVFN
  • And a move to QCDNUM17.02 for speed and high-x accuracy
  • H1 have some catching up to do on both points 3 and 4 BUT YES we are aiming for DIS09

YES ZEUS SVX95 is also in now

PLUS 3 proceedural errors for how the combination is done (4 last year)

110 errors from both experiments (43 last year)


Before averaging

After averaging

The change in input data is mostly at low Q2, so here’s how it looks

Enrico is checking


au/vu ad/vd au/ad vu/vd contours: Final HERA-II e-

Note: these are ZMVFN jobs (without jets)

We look forward to NC e+ polarised data to improve this.