Accepted author manuscript, 912 KB, PDF document
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Final published version
Research output: Contribution to Journal/Magazine › Journal article › peer-review
| Article number | 138513 |
|---|---|
| <mark>Journal publication date</mark> | 31/03/2024 |
| <mark>Journal</mark> | Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics |
| Volume | 850 |
| Number of pages | 1 |
| Pages (from-to) | 138513 |
| Publication Status | Published |
| Early online date | 13/02/24 |
| <mark>Original language</mark> | English |
A sample of 3984 candidates of the K +→π +γγ decay, with an estimated background of 291±14 events, was collected by the NA62 experiment at CERN during 2017–2018. In order to describe the observed di-photon mass spectrum, the next-to-leading order contribution in chiral perturbation theory was found to be necessary. The decay branching ratio in the full kinematic range is measured to be (9.61±0.17)×10 −7. The first search for production and prompt decay of an axion-like particle with gluon coupling in the process K +→π +a, a→γγ is also reported.