Search for π0 decays to invisible particles


The NA62 experiment at the CERN SPS reports a study of a sample of 4 × 109 tagged π0 mesons from K+π+π0(γ), searching for the decay of the π0 to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of 4.4 × 109 is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model- independent upper limit on the branching ratio for the decay K+π+X, where X is a particle escaping detection with mass in the range 0.110–0.155 GeV/c2 and rest lifetime greater than 100 ps. Model-dependent upper limits are obtained assuming X to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs boson.

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Correspondence to L. Peruzzo or T. Spadaro.

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ArXiv ePrint: 2010.07644

Deceased (A. Zinchenko, A. Ostankov, V. Semenov, F. Hahn)

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The NA62 collaboration., Cortina Gil, E., Kleimenova, A. et al. Search for π0 decays to invisible particles. J. High Energ. Phys. 2021, 201 (2021).

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  • Beyond Standard Model
  • Exotics
  • Fixed target experiments
  • Rare decay