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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+eγa, aγγ in the mass range 0.2 < ma < 9.7 GeV/c2 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 gaγγ of ALPs to photons at the level of 10−3 GeV−1. The limits are the most restrictive to date for 0.2< ma < 1 GeV/c2 .

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Abudinén, F., Adachi, I., Aihara, H., Akopov, N., Aloisio, A., Ameli, F., Anh Ky, N., Asner, D. M., Aushev, T., Aushev, V., Babu, V., Baehr, S., Bahinipati, S., Bambade, P., Banerjee, Sw., Bansal, S., Baudot, J., Becker, J., Behera, P. K., … Zhukova, V. I. (2020). Search for Axionlike particles produced in . Physical Review Letters, 125(16).

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