Shining light on the dark sector: search for axion-like particles and other new physics in photonic final states with FASER
Roshan Mammen Abraham, X. Ai, J. K. Anders, C. Antel, A. Ariga, T. Ariga, Jeremy Atkinson, F. U. Bernlochner, Emma Bianchi, Tobias Boeckh, Jamie Boyd, Lydia Brenner, A. M. Burger, F. Cadoux, R. Cardella, D. Casper, Charlotte Cavanagh, X. Chen, Eunyeong Cho, Dhruv Chouhan, A. Coccaro, Stephane Débieux, M. D’Onofrio, Ansh Desai, Sergey Dmitrievsky, Radu Dobre, Sinead Eley, Yannick Favre, D. E. Fellers, Jonathan L. Feng, Carlo Alberto Fenoglio, D. Ferrère, Max Fieg, Wissal Filali, Elena Firu, Edward Karl Galantay, Ali Garabaglu, S. M. Gibson, S. González-Sevilla, Y. Gornushkin, C. B. Gwilliam, D. Hayakawa, Michael Holzbock, S.‐C. Hsu, Z. Hu, G. Iacobucci, Tomohiro Inada, Luca Iodice, S. Jakobsen, Hans Ludwig Joos, E. Kajomovitz, H. Kawahara, Alex Keyken, Felix Kling, Daniela Köck, P. Kontaxakis, U. Köse, Rafaella Kotitsa, S. Kuehn, T. Kugathasan, L. J. Levinson, K. Li, Jinfeng Liu, Yi Liu, Margaret S. Lutz, J. C. MacDonald, Chiara Magliocca, Toni Mäkelä, Lawson McCoy, J. A. Mcfayden, Andrea Pizarro Medina, Matteo Milanesio, Théo Moretti, Mitsuhiro Nakamura, Toshiyuki Nakano, Laurie Nevay, K. Ohashi, H. Otono, Lorenzo Paolozzi, Brian Petersen, Titi Preda, M. T. Prim, M. Queitsch-Maitland, Hiroki Rokujo, André Rubbia, Jorge Sabater-Iglesias, Osamu Sato, P. Scampoli, Kristof Schmieden, M. Schott, A. Sfyrla, D. Sgalaberna, M. Shamim, Savannah Shively, Yosuke Takubo, Noshin Tarannum, O. Theiner, E. Torrence, Oscar Ivan Valdes Martinez, S. Vasina
Abstract
A bstract The first FASER search for a light, long-lived particle decaying into a pair of photons is reported. The search uses LHC proton-proton collision data at $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 13 . 6 TeV collected in 2022 and 2023, corresponding to an integrated luminosity of 57 . 7 fb − 1 . A model with axion-like particles (ALPs) dominantly coupled to weak gauge bosons is the primary target. Signal events are characterised by high-energy deposits in the electromagnetic calorimeter and no signal in the veto scintillators. One event is observed, compared to a background expectation of 0 . 44 ± 0 . 39 events, which is entirely dominated by neutrino interactions. World-leading constraints on ALPs are obtained for masses up to 300 MeV and couplings to the Standard Model W gauge boson, g aWW , around 10 − 4 GeV − 1 , testing a previously unexplored region of parameter space. Other new particle models that lead to the same experimental signature, including ALPs coupled to gluons or photons, U(1) B gauge bosons, up-philic scalars, and a Type-I two-Higgs doublet model, are also considered for interpretation, and new constraints on previously viable parameter space are presented in this paper.