Quark fragmentation in the $\theta$-vacuum

Abstract

The vacuum of Quantum Chromodynamics is a superposition of degenerate states with different topological numbers that are connected by tunneling (the $\theta$-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 $\sim \cos ({\varphi }_1+{\varphi }_2)$ usually referred to as the Collins effect, and the other is the $\p$-odd correlation $\sim \sin ({\varphi }_1+{\varphi }_2)$ 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 $e^{+}{e}^{-}$ collisions, and comment on the applicability of our approach in deep-inelastic scattering, proton-proton and heavy ion collisions.

4 pages, 2 figures

References in corpus (6)

• The Chiral Magnetic Effect
• An Improved Experimental Limit on the Electric Dipole Moment of the Neutron
• Charge separation induced by P-odd bubbles in QCD matter
• Measurement of Azimuthal Asymmetries in Inclusive Production of Hadron Pairs in e+e- Annihilation at \sqrt{s} = 10.58 GeV
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Cited by in corpus (1)

• Azimuthal correlations from transverse momentum conservation and possible local parity violation