Quark fragmentation in the -vacuum
arXiv:1006.2132 · doi:10.1103/PhysRevLett.106.042001
Abstract
The vacuum of Quantum Chromodynamics is a superposition of degenerate states with different topological numbers that are connected by tunneling (the -vacuum). The tunneling events are due to topologically non-trivial 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 non-trivial QCD background. We find that even though QCD globally conserves $\p$ and $\cp$ symmetries, two new kinds of $\p$-odd fragmentation functions emerge. They generate interesting dihadron correlations: one is the azimuthal angle correlation usually referred to as the Collins effect, and the other is the $\p$-odd correlation that vanishes in the cross section summed over many events, but survives on the event-by-event basis. Using the chiral quark model we estimate the magnitude of these new fragmentation functions. We study their experimental manifestations in dihadron production in collisions, and comment on the applicability of our approach in deep-inelastic scattering, proton-proton and heavy ion collisions.
4 pages, 2 figures
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