Q02=4 GeV2 Q0

2=4 GeV2

ZEUS parametrization H1 parametrization

Nature of the parametrization forces the errors on the low-x valence distributions to be very small- better to compare U,D

Central values of the fits are very close- good news I

haven’t added the charm into the sea for H1, so it’s a bit low

Very similar χ2 ~ 500 for 584 points

ZEUS parametrisation

xf(x) = A xa (1-x)b (1+ c x)

For u,d valence, sea and glue

Au,Ad,Ag from sum rules, ad=au, cs=0

au=0.72 ± 0.04

bu=3.99 ± 0.13

cu=1.5 ±0.71

bd=5.18 ± 0.72

cd=2.54 ± 2.02

As=0.63 ± 0.02

as=-0.197 ± 0.004

bs=6.85 ± 0.71

ag= -0.128 ± 0.02

bg=11 ± 1

cg=-16 ± 5

H1 parametrisation

xf(x) = A xa (1-x)b (1+ c x) (no x3 term)

For U=u+c, D=d+s, Ubar, Dbar and glue AU,AD,Ag from sum-rules,

aU=aD=aUbar=aDbar,cUbar=cDbar=0

aU=-0.195±0.004

bU=3.5± 0.5

cU=31 ± 2

bD=4.5 ±

cD=34 ± 8

AUbar=AU,ADbar=AD

bUbar = 10.8 ± 0.5

bDbar = 2.7 ± 0.9

ag= -0.115 ± 0.03

bg= 11 ± 5

cg=12 ± 5

Gluon similar

Low-x

sea

simila

r

Max’s suggestion to free αS(MZ)

Back to ZEUS parametrisation

αS(MZ) =0.121 ± 0.003 χ2=500

Investigate scale dependence, renormalisation scale usually the biggest so start with that

Scale= 2 Q2 αS(MZ) =0.123 χ2=502

Scale= 4Q2 αS(MZ) =0.124 χ2=507

Scale= Q2/2 αS(MZ) =0.118 χ2=526

Scale= Q2/4 job blows up!

Scale dependence 0.002-0.003?

Not as bad as I thought!