Intrinsic transverse momentum and QCD vacuum structure

Recent theoretical work has shown the existence of non-perturbative short-range correlations between partons caused by the dynamical breaking of chiral symmetry in QCD [1]. The light sea quarks in the nucleon wave function exist in correlated pairs with transverse size $\ll$ 1 fm, much smaller than the nucleon's valence quark size. This effect broadens the transverse momentum-dependent (TMD) distribution of sea quarks and defines the natural boundary of perturbative QCD evolution. The non-perturbative parton correlations can be studied experimentally in measurements of hadron correlations in semi-inclusive DIS (COMPASS, EIC), and in exclusive meson production processes (JLab 12 GeV). They also influence the rate of multiparton processes in high-energy nucleon-nucleon collisions (LHC). \\[4pt] [1] P.~Schweitzer, M.~Strikman, C.~Weiss, JHEP 1301 (2013) 163.