title: Quark fragmentation in the θ vacuum.
abstract: QCD vacuum is a superposition of degenerate states with different topological numbers that are connected by tunneling (the θ vacuum). The tunneling events are due to configurations of gauge fields (e.g., the instantons) that induce local P-odd domains in Minkowski space-time. We study the quark fragmentation in this topologically nontrivial QCD background. We find that even though QCD globally conserves P and CP symmetries, two new kinds of P-odd fragmentation functions emerge. We study their experimental manifestations in dihadron production in e(+)e(-) collisions, and find two interesting dihadron correlations: the cos(ϕ(1)+ϕ(2)) correlation usually referred to as the Collins effect, and a P-odd ∼sin(ϕ(10+ϕ(2)) correlation that vanishes in the cross section summed over many events, but survives on the event-by-event basis.
authors.affiliation: RIKEN BNL Research Center, Brookhaven National Laboratory, Upton, New York 1197-5000, USA.
authors.forename: Zhong-Bo
authors.initials: ZB
authors.lastname: Kang
authors.forename: Dmitri E
authors.initials: DE
authors.lastname: Kharzeev