1. Uncertainties of Parton Distributions
(II) Results
Sept 2003
PHYSTAT

2. Estimate the uncertainty on the predicted cross section for ppbar  W+X at the Tevatron collider.
global c2
local c2’s
Sept 2003
PHYSTAT

3. Each experiment defines a “prediction” and a “range”.
This figure shows the Dc2 = 1 ranges.
Sept 2003
PHYSTAT

4. This figure shows broader ranges for each experiment based on the “90% confidence level” (cumulative distribution function of the rescaled c2).
Sept 2003
PHYSTAT

5. The final result is an uncertainty range for the prediction of sW.
Survey of swBln predictions (by R. Thorne) …
PDF set
energy
swBln [nb]
PDF uncert
Alekhin
Tevatron
2.73
 0.05
MRST2002
2.59
 0.03
CTEQ6
2.54
 0.10
LHC
215.
 6.
204.
 4.
205.
 8.
Sept 2003
PHYSTAT

6. How well can we determine the value of aS( MZ ) from Global Analysis?
For each value of aS, find the best global fit. Then look at the c2 value for each experiment as a function of aS.
Sept 2003
PHYSTAT

7. Each experiment defines a “prediction” and a “range”.
This figure shows the Dc2 = 1 ranges.
Particle data group (shaded strip) is 0.1170.002.
The fluctuations are larger than expected for normal statistics. The vertical lines have Dc2global=100,
as(MZ)=0.11650.0065
Sept 2003
PHYSTAT

8. Gluon and U quark at Q2 = 10 GeV2.
Uncertainties of the PDF’s themselves (only interesting to the model builders)
Gluon and U quark at Q2 = 10 GeV2.
Sept 2003
PHYSTAT

9. Comparing “alternate sets”
red – CTEQ6.1
blue – Fermi2002 (H1, BCDMS, E665)
Gluon at Q2 = 10 GeV2
U quark at Q2 = 10 GeV2
Sept 2003
PHYSTAT

10. CTEQ error band with MRST2002 superimposed
Q2 = 10 GeV2
Sept 2003
PHYSTAT

11. Uncertainties of LHC parton-parton luminosities
Provides simple estimates of PDF uncertainties at the LHC.
Sept 2003
PHYSTAT