Cao Z.Aharonian F.Bai Y.X.Bao Y.W.Bastieri D.Bi X.J.Bi Y.J.Bian W.Bukevich A.V.Cai C.M.Cao W.Y.Cao Z.Chang J.Chang J.F.Chen A.M.Chen E.S.Chen G.H.Chen H.X.Chen L.Chen L.Chen M.J.Chen M.L.Chen Q.H.Chen S.Chen S.H.Chen S.Z.Chen T.L.Chen X.B.Chen X.J.Chen Y.Cheng N.Cheng Y.D.Chu M.C.Cui M.Y.Cui S.W.Cui X.H.Cui Y.D.Dai B.Z.Dai H.L.Dai Z.G.DanzengluobuDiao Y.X.Dong X.Q.Duan K.K.Fan J.H.Fan Y.Z.Fang J.Fang J.H.Fang K.Feng C.F.Feng H.Feng L.Feng S.H.Feng X.T.Feng Y.Feng Y.L.Gabici S.Gao B.Gao C.D.Gao Q.Gao W.Gao W.K.Ge M.M.Ge T.T.Geng L.S.Giacinti G.Gong G.H.Gou Q.B.Gu M.H.Guo F.L.Guo J.Guo X.L.Guo Y.Q.Guo Y.Y.Han Y.A.Hannuksela O.A.Hasan M.He H.H.He H.N.He J.Y.He X.Y.He Y.Hernández-Cadena S.Hou B.W.Hou C.Hou X.Hu H.B.Hu S.C.Huang C.Huang D.H.Huang J.J.Huang T.Q.Huang W.J.Huang X.T.Huang X.Y.Huang Y.Huang Y.Y.Ji X.L.Jia H.Y.Jia K.Mahidol University2026-05-252026-05-252026-05-08Physical Review Letters Vol.136 No.18 (2026)00319007https://repository.li.mahidol.ac.th/handle/123456789/116842We report the first detection of gamma-ray emission up to ultrahigh-energy (UHE; >100 TeV) emission from the prototypical gamma-ray binary system LS I +61° 303 using data from the Large High Altitude Air Shower Observatory. It is detected with significances of 9.2σ in the Water Cherenkov Detector Array (WCDA, 1.4-30.5 TeV) and 6.2σ in the Kilometer Square Array (KM2A, 25-267 TeV); in KM2A alone we identify 16 photonlike events above 100 TeV against an estimated 5.1 background events, corresponding to a 3.8σ detection. These results provide compelling evidence of extreme particle acceleration in LS I +61° 303. Furthermore, we observe orbital modulation at 3.9σ confidence level, between 25 and 100 TeV, with a hint that the orbital modulation is energy dependent. These features can be understood in a composite scenario in which leptonic and hadronic processes jointly contribute.Physics and AstronomyArticleSCOPUS10.1103/7xhp-tff72-s2.0-10503918125410797114