The dynamical breaking of chiral symmetry in QCD is caused by nonperturbative interactions on a distance scale ρ ∼ 0.3 fm, much smaller than the typical hadronic size R ∼ 1 fm. These short-distance interactions influence the intrinsic transverse momentum distributions of partons and their correlations at a low normalization point. We study this phenomenon in an effective description of the low-energy dynamics in terms of chiral constituent quark degrees of freedom, which refers to the large-N c limit of QCD. The nucleon is obtained as a system of constituent quarks and antiquarks moving in a self-consistent classical chiral field (relativistic mean-field approximation, or chiral quark-soliton model). The calculated transverse momentum distributions of constituent quarks and antiquarks are matched with QCD quarks, antiquarks and gluons at the chiral symmetry-breaking scale ρ -2. We find that the transverse momentum distribution of valence quarks is localized at pT 2∼R-2 and roughly of Gaussian shape. The distribution of unpolarized sea quarks exhibits a would-be power-like tail ∼1/p T2 extending up to the chiral symmetry-breaking scale. Similar behavior is observed in the flavor-nonsinglet polarized sea. The high-momentum tails are the result of short-range correlations between sea quarks in the nucleon's light-cone wave function, which are analogous to short-range N N correlations in nuclei. We show that the nucleon's light-cone wave function contains correlated pairs of transverse size ρ ≪ R with scalar-isoscalar (Σ) and pseudoscalar-isovector (Π) quantum numbers, whose internal wave functions have a distinctive spin structure and become identical at pT2∼ρ-2 (restoration of chiral symmetry). These features are model-independent and represent an effect of dynamical chiral symmetry breaking on the nucleon's partonic structure. Our results have numerous implications for the transverse momentum distributions of particles produced in hard scattering processes. Under certain conditions the nonperturbative parton correlations predicted here could be observed in particle correlations between the current and target fragmentation regions of deep-inelastic scattering.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics