Geometric scaling above the saturation scale
Mar, 200224 pages
Published in:
- Nucl.Phys.A 708 (2002) 327-352
e-Print:
- hep-ph/0203137 [hep-ph]
Report number:
- SACLAY-T02-027
Citations per year
Abstract: (Elsevier)
We show that the evolution equations in QCD predict geometric scaling for quark and gluon distribution functions in a large kinematical window, which extends above the saturation scale up to momenta Q 2 of order 100 GeV 2 . For Q 2 < Q 2 s , with Q s the saturation momentum, this is the scaling predicted by the Colour Glass Condensate and by phenomenological saturation models. For 1≲ln( Q 2 / Q s 2 )⪡ln( Q s 2 / Λ 2 QCD ), we show that the solution to the BFKL equation shows approximate scaling, with the scale set by Q s . At larger Q 2 , this solution does not scale any longer. We argue that for the intermediate values of Q 2 where we find scaling, the BFKL rather than the double logarithmic approximation to the DGLAP equation properly describes the dynamics. We consider both fixed and running couplings, with the scale for running set by the saturation momentum. The anomalous dimension which characterizes the approach of the gluon distribution function towards saturation is found to be close to, but lower than, one half.Note:
- 24 pages
- 11.10.Hi
- 12.38.Cy
- 11.55.Bq
- quantum chromodynamics
- momentum spectrum: parton
- scaling: geometrical
- color glass condensate
- Lipatov equation
- DGLAP equation
- integral equations: solution
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