Elastic scattering of a quark from a color field: longitudinal momentum exchange

Jamal Jalilian-Marian (1)

1 CPHT - Centre de Physique Théorique [Palaiseau]

Perturbative QCD in the small Bjorken-x limit can be formulated as an effective theory known as the color glass condensate (CGC) formalism. The CGC formalism takes into account the dynamics of large gluon densities at small x and has been successfully applied to deep inelastic scattering (DIS) and particle production in high-energy hadronic and nuclear collisions in the small-x kinematic region. The effective degrees of freedom in CGC are Wilson lines which enter in the effective quark (and gluon) propagators and resum multiple soft scatterings from the small-x gluon field of the target. It is however known that the CGC effective theory breaks down when one probes the moderately large-x (high-pt) kinematics where collinear factorization and DGLAP evolution of parton distribution functions should be the right framework. Here we propose a general framework which may allow one to eventually unify the two approaches and to calculate perturbative QCD cross sections in both small and large Bjorken-x regions. We take the first step towards this goal by deriving an expression for the quark propagator in a background field which includes scatterings from both small- and large-x modes of the gluon field of the target. We describe how this quark propagator can be used to calculate QCD structure functions F2 and FL at all x and thus generalize the dipole model of DIS. We outline that this approach can also be used to extend the so-called hybrid approach to particle production in the forward rapidity region of high-energy hadronic and nuclear collisions to all x and pt regions and speculate on how one may apply the same techniques to extend the McLerran-Venugopalan effective action used in high-energy heavy-ion collisions to include high-pt physics.

Mots clés: energy: high; quark: propagator; energy: hadronic; quantum chromodynamics: perturbation theory; parton: distribution function; model: deep inelastic scattering; heavy ion: energy; gluon: density; factorization: collinear; heavy ion: scattering; model: dipole; color glass condensate; kinematics; Bjorken; nucleus; longitudinal momentum; structure function; elastic scattering; background field; effective action; DGLAP equation; Wilson loop; rapidity; hybrid; color

Domaines: Physique des Hautes Energies - Phénoménologie [hep-ph]; Physique Nucléaire Expérimentale [nucl-ex]; Physique Nucléaire Théorique [nucl-th]

Jamal Jalilian-Marian. Elastic scattering of a quark from a color field: longitudinal momentum exchange. Physical Review D, 2017, 96 (7), pp.074020. ⟨10.1103/PhysRevD.96.074020⟩. ⟨hal-01645957⟩