Impact-parameter dependent Color Glass Condensate dipole model and new combined HERA data

The impact-parameter dependent color glass condensate (b-CGC) dipole model is based on the Balitsky-Kovchegov nonlinear evolution equation and improves the Iancu-Itakura-Munier dipole model by incorporating the impact-parameter dependence of the saturation scale. Here we confront the model to the recently released high precision combined Hadron Electron Ring Accelerator (HERA) data and obtain its parameters. The b-CGC results are then compared to data at small x for the structure function, the longitudinal structure function, the charm structure function, exclusive vector meson (J/ψ, ϕ, and ρ) production and deeply virtual Compton scattering. We also compare our results with the impact-parameter dependent saturation (IP-Sat) model. We show that most features of inclusive deep inelastic scattering and exclusive diffractive data, including the Q2, W, |t|, and x dependence, are correctly reproduced in both models. Nevertheless, the b-CGC and the impact-parameter dependent saturation (IP-Sat) models give different predictions beyond the current HERA kinematics, namely for the structure functions at very low x and high virtualities Q2, and for the exclusive diffractive vector meson and deeply virtual Compton scattering production at high t. This can be traced back to the different power-law behavior of the saturation scale in x and to a different impact-parameter b dependence of the saturation scale in these models. Nevertheless, both models give approximately similar saturation scales QS<1 GeV for the proton in HERA kinematics, and also both models lead to the same conclusion that the typical impact parameter probed in the total γ*p cross section is about b≈2–3 GeV-1. Our results provide a benchmark for further investigation of QCD at small x in heavy ion collisions at RHIC and the LHC and also at future experiments such as an electron-ion collider and the LHeC.

Note:

21 pages, 31 figures; v3: results unchanged, more comparison with HERA data added, one plot and references added. The version to appear in PRD

13.60.Hb
12.38.Bx
impact parameter: dependence
scale: saturation
model: dipole
p: structure function: longitudinal
structure function: charm
heavy ion: scattering
DESY HERA Stor
deeply virtual Compton scattering

References(137)

Figures(31)

[1]

Semihard Processes in QCD

- Phys.Rept. 100 (1983) 1-150,
- Phys. Rep. 100 ( 1983) 1-150
•
DOI:
- 10.1016/0370-1573(83)90022-4

[1]

A. H and J-W. Qiu

- Nucl.Phys. 268 (1986) 427

[1]

Parton saturation at small x and in large nuclei

Alfred H. Mueller
(
- Columbia U.
)

- Nucl.Phys.B 558 (1999) 285-303
•
e-Print:
- hep-ph/9904404
•
DOI:
- 10.1016/S0550-3213(99)00394-6

[2]

Computing quark and gluon distribution functions for very large nuclei

Larry D. McLerran
(
- Minnesota U.
)
,
Raju Venugopalan
(
- Minnesota U.
)

- Phys.Rev.D 49 (1994) 2233-2241
•
e-Print:
- hep-ph/9309289
•
DOI:
- 10.1103/PhysRevD.49.2233

[2]

Gluon distribution functions for very large nuclei at small transverse momentum

Larry D. McLerran
(
- Minnesota U.
)
,
Raju Venugopalan
(
- Minnesota U.
)

- Phys.Rev.D 49 (1994) 3352-3355
•
e-Print:
- hep-ph/9311205
•
DOI:
- 10.1103/PhysRevD.49.3352

[2]

Green's functions in the color field of a large nucleus

Larry D. McLerran
(
- Minnesota U.
)
,
Raju Venugopalan
(
- Minnesota U.
)

- Phys.Rev.D 50 (1994) 2225-2233,
- Phys. Rev. D50 (1994) 2225-2233, and Minnesota Univ. Minneapolis - TPI-MINN-94-07-T (94/02,rec.Feb.) 21 p. (407292) Minnesota Univ. Minneapolis - NUC-MINN-94-02-T (94/02,rec.Feb.) 21 p
•
e-Print:
- hep-ph/9402335
•
DOI:
- 10.1103/PhysRevD.50.2225