Azimuthal asymmetries of back-to-back ${\pi }^{\pm }-({\pi }^0,\eta ,{\pi }^{\pm })$ pairs in $e^{+}{e}^{-}$ annihilation

Abstract

This work reports the first observation of azimuthal asymmetries around the thrust axis in $e^{+}{e}^{-}$ annihilation of pairs of back-to-back charged pions in one hemisphere, and ${\pi }^0$ and $\eta$ mesons in the opposite hemisphere. These results are complemented by a new analysis of pairs of back-to-back charged pions. The ${\pi }^0$ and $\eta$ asymmetries rise with the relative momentum $z$ of the detected hadrons as well as with the transverse momentum with respect to the thrust axis. These asymmetries are sensitive to the Collins fragmentation function $H_1^{\perp }$ and provide complementary information to previous measurements with charged pions and kaons in the final state. In particular, the $\eta$ final states will provide additional information on the flavor structure of $H_1^{\perp }$. This is the first measurement of the explicit transverse-momentum dependence of the Collins fragmentation function from Belle data. It uses a dataset of 980.4~fb${}^{-1}$ collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV.

arXiv comment31 pages, 14 figures, submitted to PRD

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