Search for Axionlike Particles Produced in e(+)e(-) Collisions at Belle II

Abstract

We present a search for the direct production of a light pseudoscalar a decaying into two photons with the Belle II detector at the SuperKEKB collider. We search for the process e(+)e(-) -˃ gamma a, a -˃ gamma gamma in the mass range 0.2 ˂ m(a) ˂ 9.7 GeV/c(2) using data corresponding to an integrated luminosity of (445 +/- 3) pb(-1). Light pseudoscalars interacting predominantly with standard model gauge bosons (so-called axionlike particles or ALPs) are frequently postulated in extensions of the standard model. We find no evidence for ALPs and set 95% confidence level upper limits on the coupling strength g(a gamma gamma) of ALPs to photons at the level of 10(-3) GeV-1. The limits are the most restrictive to date for 0.2 ˂ m(a) ˂ 1 GeV/c(2).