Diquark Induced Short-Range Nucleon-Nucleon Correlations \& the EMC Effect

Abstract

Diquark formation across a short-range nucleon-nucleon pair is proposed as the underlying QCD physics of short-range correlations (SRC) in nuclei. SRC pairs have been proposed as the cause of distorted quark behavior in nuclei; experimentally observed quark momentum distribution distortions termed the EMC effect. The strong spatial overlap of SRC pairs brings nucleon constituents within range of inter-nucleon QCD potentials and any bonds formed - such as the diquark bond - affects their distributions. In this SRC model, diquarks form in the $3_{\mathrm{C}}\otimes 3_{\mathrm{C}}\to {\bar{3}}_{\mathrm{C}}$ channel of $\mathrm{SU}(3{)}_{\mathrm{C}}$ acting on valence quarks from highly overlapping nucleon wavefunctions. The most energetically favorable diquark is a valence $u$ quark from one nucleon with a valence $d$ quark from the other in a spin-0 state bound together via continual single gluon exchange and an attractive quantum chromodynamics short-range potential. Formation of a new scalar isospin-singlet $[ud]$ diquark across a NN pair is proposed as the primary QCD-level theoretical foundation for SRC models of distorted structure functions in $\mathrm{A}\ge 3$ nuclei. Contributions from the higher mass spin-1 isospin triplet states $(ud)$, $(uu)$ and $(dd)$ are possible, with the spin-1 $(ud)$ diquark proposed as a higher mass but viable structure function distortion mechanism for the spin-1 ground state deuteron. Predictions are made for lepton scattering experiments on ${}^3\mathrm{H}$ and ${}^3\mathrm{He}$ nuclear targets, with implications for the coefficients of the 3-valence quark Fock states in the nucleon wavefunction.

Comments: Version accepted for publication in Nuc.Phys.A