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Probing the neutrino mass through semileptonic meson decays

Damir Bečirević1,*, Claire Chevallier1,†, Svjetlana Fajfer2,3,‡, Nejc Košnik2,3,§, and Lovre Pavičić3,∥

  • *Contact author: damir.becirevic@ijclab.in2p3.fr
  • †Contact author: claire.chevallier@ijclab.in2p3.fr
  • ‡Contact author: svjetlana.fajfer@ijs.si
  • §Contact author: nejc.kosnik@ijs.si
  • ∥Contact author: lovre.pavicic@ijs.si
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Phys. Rev. D 114, 035005 – Published 4 August, 2026

DOI: https://doi.org/10.1103/793f-29kk

Abstract

We argue that a detailed analysis of semileptonic decays can test the possibility of a massive neutrino. The key observable, related to the forward–backward asymmetry, is exactly zero for a massless neutrino but becomes nonzero if the neutral lepton is heavy and interacts with Standard Model fields via lefthanded operators. For righthanded interactions, this quantity differs significantly from zero even for a massless righthanded neutrino. We demonstrate this explicitly using the example of a pseudoscalar meson decaying into another pseudoscalar meson. A similar discussion applies to decays into a vector meson, with an additional subtlety addressed in this work.

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Phys. Rev. D 114, 035005– Published 4 August, 2026
  • Received 30 March 2026
  • Accepted 14 July 2026
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