Q 0 2 =4 GeV 2 - PowerPoint PPT Presentation

beverly-nunez
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Q 0 2 =4 GeV 2

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  1. Q02=4 GeV2 Q02=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

  2. 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 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 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 Low-x sea similar Gluon similar

  3. 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= 4Q2αS(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!