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Production of K+K− pairs through the decay of ϕ mesons

Xin-Nan Zhu1,2,3,*, Xin-Li Sheng4,†, and Defu Hou1,‡

  • 1Institute of Particle Physics and Key Laboratory of Quark and Lepton Physics (MOS), Central China Normal University, Wuhan 430079, China
  • 2Institut für Theoretische Physik, Johann Wolfgang Goethe–Universität, Max-von-Laue-Strasse 1, D–60438 Frankfurt am Main, Germany
  • 3Helmholtz Research Academy Hesse for FAIR, Campus Riedberg, Max-von-Laue-Strasse 12, D–60438 Frankfurt am Main, Germany
  • 4Università degli studi di Firenze and INFN Sezione di Firenze, Via Giovanni Sansone 1, I-50019 Sesto Fiorentino (Florence), Italy

  • *Contact author: zxn19980402@mails.ccnu.edu.cn
  • †Contact author: sheng@fi.infn.it
  • ‡Contact author: houdf@ccnu.edu.cn
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Phys. Rev. D 112, 056011 – Published 11 September, 2025

DOI: https://doi.org/10.1103/7s6h-r457

Abstract

We develop a theoretical framework for the production of K+K− pairs through the decay of ϕ mesons produced from a thermal background, based on the Nambu-Jona-Lasinio (NJL) model. The differential production rate of K+K− is related to the self-energy of the ϕ meson, incorporating the contributions of the quark loop at leading order and the kaon loop at next-to-leading order in the 1/Nc expansion. We numerically evaluate the invariant mass spectrum of the K+K− pair both in vacuum and at finite temperature. The inclusion of the kaon loop results in a finite width of the spectrum, improving agreement with experimental data. We also investigate the spin alignment of the ϕ meson induced by its motion relative to the thermal background. In the NJL model with only chiral condensates, we find that deviations from the unpolarized limit of 1/3 are negligible.

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Phys. Rev. D 112, 056011– Published 11 September, 2025
  • Received 18 April 2025
  • Accepted 22 August 2025
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