Search for Sub-GeV Axion-Like Particles at EBES Pilot Run Using 4 GeV Positron Beam at KEK LINAC

Takahiro Fusayasu; Tomoya Iizawa; Fumihito Ikeda; Akimasa Ishikawa; Masako Iwasaki; Hiroshi Iwase; Takahiro Kawahara; Aoi Masaki; Fusashi Miyahara; Yu Morikawa; Yuichi Okayasu; Toshiyuki Ono; Hidetoshi Otono; Yasuhito Sakaki; Takumi Seino; Yuta Shimasaki; Taikan Suehara; Yosuke Takubo; Shusaku Tsumura; Kosuke Uemura; Yifu Zhang

arXiv · 2605.07108

Search for Sub-GeV Axion-Like Particles at EBES Pilot Run Using 4 GeV Positron Beam at KEK LINAC

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Abstract

We report the results of a search for sub-GeV axion-like particles (ALPs) using pilot run data from the Electron Beam-dump Experiment at KEK LINAC Switching Yard 3 (EBES). The data were collected in December 2023 with a 4 GeV positron beam and correspond to $1.3\times10^{14}$ positrons on target. In the pilot run setup, a tungsten beam dump and a single PbO calorimeter were used. We consider ALP production via the Primakoff process induced by bremsstrahlung photons in the beam dump, followed by the decay $a\toγγ$. The background was estimated with a data-driven method, and a signal region was defined such that the expected background yield is below 0.1 events. No events were observed after unblinding. Upper limits at the 90% confidence level were derived in the ALP mass-coupling plane, extending the experimental coverage into a region of parameter space not explored by previous searches.

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Takahiro Fusayasu, Tomoya Iizawa, Fumihito Ikeda, Akimasa Ishikawa, Masako Iwasaki, Hiroshi Iwase, Takahiro Kawahara, Aoi Masaki, Fusashi Miyahara, Yu Morikawa, Yuichi Okayasu, Toshiyuki Ono, Hidetoshi Otono, Yasuhito Sakaki, Takumi Seino, Yuta Shimasaki, Taikan Suehara, Yosuke Takubo, Shusaku Tsumura, Kosuke Uemura, Yifu Zhang. 2026-05-08. Search for Sub-GeV Axion-Like Particles at EBES Pilot Run Using 4 GeV Positron Beam at KEK LINAC. https://arxiv.org/abs/2605.07108

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