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arXiv · 2501.14827

Proposal of the KOTO II experiment

Jung Keun Ahn·Antonella Antonelli·Giuseppina Anzivino·Emile Augustine·Laura Bandiera·Jianming Bian·Francesco Brizioli·Stefano De Capua·Gabriella Carini·Veronika Chobanova·Giancarlo D'Ambrosio·John Bourke Dainton·Babette Dőbrich·John Fry·Alberto Gianoli·Alexander Glazov·Mario Gonzalez·Martin Gorbahn·Evgueni Goudzovski·Mei Homma·Yee B. Hsiung·Tomáš Husek·David Hutchcroft·Abhishek Iyer·Roger William Lewis Jones·Mai Katayama·Yuto Kawata·Eun-Joo Kim·Chong Kim·Takeshi Komatsubara·Katsushige Kotera·Michal Kreps·Gianluca Lamanna·Cristina Lazzeroni·Samet Lezki·GeiYoub Lim·Sanghoon Lim·Chieh Lin·Farvah Mahmoudi·Victoria Martin·Karim Massri·Toru Matsumura·Luigi Montalto·Matthew Moulson·Hajime Nanjo·Matthew Needham·Siavash Neshatpour·Tadashi Nomura·Daiki Ogawa·Keita Ono·Monica Pepe·Letizia Peruzzo·Jacopo Pinzino·Dan Protopopescu·Claire Prouve·Thomas Reddel·Joseph Redeker·Daniele Rinaldi·Marco Romagnoni·Angela Romano·Armine Rostomyan·Jack Sanders·Diego Martínez Santos·Ivano Sarra·Artur Shaikhiev·Koji Shiomi·Ryota Shiraishi·Mattia Soldani·Marco Sozzi·Benjamin Stillwell·Yi-Ting Su·Joel Swallow·Yasuhisa Tajima·Adam Tomczak·Yu-Chen Tung·Yau Wah·Rainer Wanke·Hiroaki Watanabe·John Wendel·Tong Wu·Maresa Wynd·Guang Yang
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Abstract

The KOTO II experiment is proposed to measure the branching ratio of the decay $K_L\to\pi^0\nu\bar{\nu}$ at J-PARC. With a beamline to extract long-lived neutral kaons at 5 degrees from a production target, the single event sensitivity of the decay is $8.5\times 10^{-13}$, which is much smaller than the Standard Model prediction $3\times 10^{-11}$. This allows searches for new physics beyond the Standard Model and the first discovery of the decay with a significance exceeding $5\sigma$. As the only experiment proposed in the world dedicated to rare kaon decays, KOTO II will be indispensable in the quest for a complete understanding of flavor dynamics in the quark sector. Moreover, by combining efforts from the kaon community worldwide, we plan to develop the KOTO II detector further and expand the physics reach of the experiment to include measurements of the branching ratio of the $K_L\to\pi^0\ell^+\ell^-$ decays, studies of other $K_L$ decays, and searches for dark photons, axions, and axion-like particles. KOTO II will therefore obtain a comprehensive understanding of $K_L$ decays, providing further constraints on new physics scenarios with existing $K^+$ results.

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Jung Keun Ahn, Antonella Antonelli, Giuseppina Anzivino, Emile Augustine, Laura Bandiera, Jianming Bian, Francesco Brizioli, Stefano De Capua, Gabriella Carini, Veronika Chobanova, Giancarlo D'Ambrosio, John Bourke Dainton, Babette Dőbrich, John Fry, Alberto Gianoli, Alexander Glazov, Mario Gonzalez, Martin Gorbahn, Evgueni Goudzovski, Mei Homma, Yee B. Hsiung, Tomáš Husek, David Hutchcroft, Abhishek Iyer, Roger William Lewis Jones, Mai Katayama, Yuto Kawata, Eun-Joo Kim, Chong Kim, Takeshi Komatsubara, Katsushige Kotera, Michal Kreps, Gianluca Lamanna, Cristina Lazzeroni, Samet Lezki, GeiYoub Lim, Sanghoon Lim, Chieh Lin, Farvah Mahmoudi, Victoria Martin, Karim Massri, Toru Matsumura, Luigi Montalto, Matthew Moulson, Hajime Nanjo, Matthew Needham, Siavash Neshatpour, Tadashi Nomura, Daiki Ogawa, Keita Ono, Monica Pepe, Letizia Peruzzo, Jacopo Pinzino, Dan Protopopescu, Claire Prouve, Thomas Reddel, Joseph Redeker, Daniele Rinaldi, Marco Romagnoni, Angela Romano, Armine Rostomyan, Jack Sanders, Diego Martínez Santos, Ivano Sarra, Artur Shaikhiev, Koji Shiomi, Ryota Shiraishi, Mattia Soldani, Marco Sozzi, Benjamin Stillwell, Yi-Ting Su, Joel Swallow, Yasuhisa Tajima, Adam Tomczak, Yu-Chen Tung, Yau Wah, Rainer Wanke, Hiroaki Watanabe, John Wendel, Tong Wu, Maresa Wynd, Guang Yang. 2025-01-22. Proposal of the KOTO II experiment. https://arxiv.org/abs/2501.14827

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