Scientists of the Laboratory of Theoretical Physics at JINR, scientific centres, and universities of Chile, Germany, and Russia presented the results of the experiment to search for dark sector particles in decays of neutral mesons in the NA64 experiment at the Super Proton Synchrotron (SPS) at CERN.

We consider an experiment to search for dark sector particles in invisible (or semi-invisible) decays of neutral mesons M⁰=π⁰, ?, ?′, ?, ? 2 (1270), which produced the charge-exchange reactions π-+(A,Z)→M⁰+(A,Z-1);M⁰→ invisible of high-energy pions (or kaons) on a nuclei target in the NA64 experiment at the CERN SPS. This reaction chain would lead to a striking signature of the signal event—the complete disappearance of the beam energy in the setup. Using data obtained from the measurements at IHEP (Protvino) and Fermilab (Batavia) we show that the integral cross sections ? for the production of the M⁰_s slightly deviate from the phenomenological formula σ~Z^2/3, where ? is the nuclei charge. In particular, we present the formulas for the differential and integral cross sections that explicitly depend on the Mandelstam and ? variables. Derived formulas are used to predict the M⁰ yield as a function of beam energy for several target nuclei, and to estimate the projection sensitivity for the proposed search in the dark vector portal model. Sensitivity to different decay modes of M⁰_s is explored.

Read the full text of this paper via the link. JINR is represented in the list of authors by Senior Researcher of the Laboratory of Theoretical Physics Alexey Zhevlakov.