Saturation and BFKL dynamics in the HERA data at small-x

Abstract

We show that the HERA data for the inclusive structure function F 2 (x, Q 2 ) for x ≤ 10 −2 and 0.045 ≤ Q 2 ≤ 45 GeV 2 can be well described within the color dipole picture, with a simple analytic expression for the dipole-proton scattering amplitude, which is an approximate solution to the non-linear evolution equations in QCD. For dipole sizes less than the inverse saturation momentum 1/Q s (x), the scattering amplitude is the solution to the BFKL equation in the vicinity of the saturation line. It exhibits geometric scaling and scaling violations by the diffusion term. For dipole sizes larger than 1/Q s (x), the scattering amplitude saturates to one. The fit involves three parameters: the proton radius R, the value x 0 of x at which the saturation scale Q s equals 1GeV, and the logarithmic derivative of the saturation momentum λ. The value of λ extracted from the fit turns out to be consistent with a recent calculation using the next-to-leading order BFKL formalism.

Electromagnetic signatures of the color glass condensate: dileptons

“…This has been done in [21] and a comparison to the HERA data on structure functions has been performed. It is shown in [21] that one can fit the HERA data in the kinematic region Q 2 < 50 GeV 2 and x bj < 0.01.…”

“…This has been done in [21] and a comparison to the HERA data on structure functions has been performed. It is shown in [21] that one can fit the HERA data in the kinematic region Q 2 < 50 GeV 2 and x bj < 0.01. Furthermore, this ansatz has a simple form which includes the right anomalous dimension in the extended scaling region [22,23], unlike some previous parameterizations of the dipole cross section [24].…”

“…The form of the saturation scale Q 2 s is taken to be Q 2 s ≡ (x 0 /x) λ GeV 2 with x 0 , λ, N 0 determined from fitting the HERA data on proton structure function F 2 . We refer the reader to [21] for details of the fit. In case of a nucleus, we make the assumption that the saturation scale of the nucleus is Q 2 sA ≡ A 1/3 Q 2 sp .…”

High density QCD through eletromagnetic probes

“…(9) in the correlator function C(l T , x 2 , A) is performed by means of the saturation scale Q s (x 2 , A). We employed the GBW parametrization [20] to obtain the x dependence of the saturation scale (Q 2 s = (x)(x 0 /x) λ ), and the parameters have been taken from the dipole cross section extracted from the fit procedure by CGCfit [30] parametrization. The nuclear radius, which appears in the Eq.…”

“…The nuclear radius, which appears in the Eq. (9), is taken from the parametrization which has the form, R A = 1.2A 1/3 f m, while the proton radius (for pp calculations) is taken from the fit [30] (R p = 0.6055 f m).…”