According to the current state of the theory of particle physics, the number of generations of leptons (and quarks) is three. In this case, however, the mass distribution of the three known leptons is such (m_e ~ 10⁰, m_μ ~ 10², m_𝜏 ~ 10³ MeV/c²), which often raises the hypothesis of the possible existence of a fourth anomalous lepton with a mass m_a ~ 10¹ MeV/c². Such a large difference in the masses of leptons is not fully explained at present.

In this paper, we directly test the hypothesis of the existence of a lepton with a mass m_a ~ 10¹/c².

Thus, a method is proposed for finding the mass of a charged particle by the spatial trace (track) left by it, passing through matter in a uniform magnetic field near the stopping point. In the projection of the spatial track onto a plane perpendicular to the direction of the field, the particle trajectory is approximated by a helix (“hadroida”), one of whose parameters is proportional to the particle mass. The initial energy of the particle does not matter for this problem. In accordance with the method, the mass of the particle is found.