| 1. |
T. Araki, K. Asai, H. Otono, T. Shimomura, Y. Takubo, Search for Lepton Flavor Violating Decay at FASER, J. High Energ. Phys. 2023, 145 (2023), https://doi.org/10.1007/JHEP01(2023)145, 2023.01. |
| 2. |
H. Fukuda, H. Otono, S. Shirai, Searching for the QCD axion with the proposed International Linear Collider beam facility, Phys. Rev. D 106 (2022) 5, 055029, https://doi.org/10.1103/PhysRevD.106.055029, 2022.09. |
| 3. |
FASER Collaboration, The tracking detector of the FASER experiment, Nucl. Instrum. Methods Phys. Res., A, https://doi.org/10.48550/arXiv.2112.01116, 1034 , 166825, 2022.07, FASER is a new experiment designed to search for new light weakly-interacting long-lived particles (LLPs) and study high-energy neutrino interactions in the very forward region of the LHC collisions at CERN. The experimental apparatus is situated 480 m downstream of the ATLAS interaction-point aligned with the beam collision axis. The FASER detector includes four identical tracker stations constructed from silicon microstrip detectors. Three of the tracker stations form a tracking spectrometer, and enable FASER to detect the decay products of LLPs decaying inside the apparatus, whereas the fourth station is used for the neutrino analysis. The spectrometer has been installed in the LHC complex since March 2021, while the fourth station is not yet installed. FASER will start physics data taking when the LHC resumes operation in early 2022. This paper describes the design, construction and testing of the tracking spectrometer, including the associated components such as the mechanics, readout electronics, power supplies and cooling system.. |
| 4. |
H. Fukuda, N. Nagata, H. Oide, H. Otono, S. Shirai, Cornering Higgsinos Using Soft Displaced Tracks, Phys. Rev. Lett., 10.1103/PhysRevLett.124.101801, 2020.02, Higgsino has been intensively searched for in the LHC experiments in recent years. Currently, there is an uncharted region beyond the LEP Higgsino mass limit where the mass splitting between the neutral and charged Higgsinos is around 0.3–1 GeV, which is unexplored by either the soft di-lepton or disappearing track searches. This region is, however, of great importance from a phenomenological point of view, as many supersymmetric models predict such a mass spectrum. In this Letter, we propose a possibility of filling this gap by using a soft microdisplaced track in addition to the monojet event selection, which allows us to discriminate a signature of the charged Higgsino decay from the standard model background. It is found that this new strategy is potentially sensitive to a Higgsino mass of ≲180(250) GeV at the LHC Run2 (HL-LHC) for a charged-neutral mass splitting of ≃0.5 GeV.. |
| 5. |
E. Kpatcha, I. Lara, D. E. López-Fogliani, C. Muñoz, N. Nagata, H. Otono, R. Ruiz De Austri, Sampling the 𝜇𝜈SSM for displaced decays of the tau left sneutrino LSP at the LHC, Eur. Phys. J. C, 10.1140/epjc/s10052-019-7412-1, 79 (2019) no.11, 934, 2019.11. |
| 6. |
FASER Collaboration, FASER’s physics reach for long-lived particles, Phys.Rev. D, 10.1103/PhysRevD.99.095011, 99, 095011, 2019.05, FASER, the ForwArd Search ExpeRiment, is a proposed experiment dedicated to searching for light, extremely weakly-interacting particles at the LHC. Such particles may be produced in the LHC's high-energy collisions in large numbers in the far-forward region and then travel long distances through concrete and rock without interacting. They may then decay to visible particles in FASER, which is placed 480 m downstream of the ATLAS interaction point. In this work, we describe the FASER program. In its first stage, FASER is an extremely compact and inexpensive detector, sensitive to decays in a cylindrical region of radius R = 10 cm and length L = 1.5 m. FASER is planned to be constructed and installed in Long Shutdown 2 and will collect data during Run 3 of the 14 TeV LHC from 2021-23. If FASER is successful, FASER 2, a much larger successor with roughly R ~ 1 m and L ~ 5 m, could be constructed in Long Shutdown 3 and collect data during the HL-LHC era from 2026-35. FASER and FASER 2 have the potential to discover dark photons, dark Higgs bosons, heavy neutral leptons, axion-like particles, and many other long-lived particles, as well as provide new information about neutrinos, with potentially far-ranging implications for particle physics and cosmology. We describe the current status, anticipated challenges, and discovery prospects of the FASER program.. |
| 7. |
I. Lara, D. E. Lopez-Fogliani, C Muñoz, N. Nagata, H. Otono, Looking for the left sneutrino LSP with displaced-vertex searches, Phys. Rev. D, 0.1103/PhysRevD.98.075004, 2018.10. |
| 8. |
H. Ito, O. Jinnouchi, T. Moroi, N. Nagata, H. Otono, Searching for Metastable Particles with Sub-Millimeter Displaced Vertices at Hadron Colliders , JHEP , 10.1007/JHEP06(2018)112 , 2018.06. |
| 9. |
H. Fukuda, N. Nagata, H. Otono, S. Shirai, Higgsino Dark Matter or Not: Role of Disappearing Track Searches at the LHC and Future Colliders, Phys. Lett. B, 10.1016/j.physletb.2018.03.088 , 2018.06, Higgsino in supersymmetric standard models is known to be a promising candidate for dark matter in the Universe. Its phenomenological property is strongly affected by the gaugino fraction in the Higgsino-like state. If this is sizable, in other words, if gaugino masses are less than O(10) TeV, we may probe the Higgsino dark matter in future non-accelerator experiments such as dark matter direct searches and measurements of electric dipole moments. On the other hand, if gauginos are much heavier, then it is hard to search for Higgsino in these experiments. In this case, due to a lack of gaugino components, the mass difference between the neutral and charged Higgsinos is uniquely determined by electroweak interactions to be around 350 MeV, which makes the heavier charged state rather long-lived, with a decay length of about 1 cm. In this letter, we argue that a charged particle with a flight length of O(1) cm can be probed in disappearing-track searches if we require only two hits in the pixel detector. Even in this case, we can reduce background events with the help of the displaced-vertex reconstruction technique. We study the prospects of this search strategy at the LHC and future colliders for the Higgsino dark matter scenario. It is found that an almost pure Higgsino is indeed within the reach of the future 33 TeV collider experiments. We then discuss that the interplay among collider and non-accelerator experiments plays a crucial role in testing the Higgsino dark matter scenarios. Our strategy for disappearing-track searches can also enlarge the discovery potential of pure wino dark matter as well as other electroweak-charged dark matter candidates.. |
| 10. |
The ATLAS Collaboration, Search for long-lived, massive particles in events with displaced vertices and missing transverse momentum in sqrt(s) = 13 TeV pp collisions with the ATLAS detector, Phys. Rev. D, 2018.03. |
| 11. |
H. Ito, O. Jinnouchi, T. Moroi, N. Nagata, H. Otono, Extending the LHC Reach for New Physics with Sub-Millimeter Displaced Vertices, Phys. Lett. B, 2017.08. |
| 12. |
N. Nagata, H. Otono, S. Shirai, Cornering compressed gluino at the LHC, JHEP, 2017.03. |
| 13. |
菊池 結貴子, 江崎 和音, 中島 悠, 石川 遼子, 伊與木 健太, 正田 亜八香, 音野 瑛俊, マニアの社交場「BAP cafe」:“狭く深いサイエンスカフェ”の魅力, Japanese Journal of Science Communication, 20: 3-13, 2017.01. |
| 14. |
中島 悠, 江崎 和音, 菊池 結貴子, 宮武 広直, 安藤 康伸, 生出 秀行, 横山 広美, 音野 瑛俊, 大学院生出張授業プロジェクト(BAP) : 9年間の継続的活動を通じた分析と展望, Japanese Journal of Science Communication, 21: 59-75, 2017.06. |
| 15. |
Otono Hidetoshi, LiNA – Lifetime of neutron apparatus with time projection chamber and solenoid coil, Nuclear Instruments and Methods in Physics Research Section A, http://dx.doi.org/10.1016/j.nima.2016.05.042, 2016.09, Among measurements of the neutron lifetime, there is a 1% difference between proton-counting and neutron-counting methods. In this paper, a new electron-counting method with a magnetic field aiming for a 0.1% accuracy is proposed, which would possibly allow to resolve the current discrepancy between the different neutron lifetime measurements.. |
| 16. |
Otono Hidetoshi, New probes for bino dark matter with coannihilation at the LHC, Proceedings of Science, 2015.09, It has been widely known that bino-like dark matter in supersymmetric theories suffers from over- production. The situation can be improved if the gluino or wino has a mass of O(10) GeV heavier than the bino, sufficiently reducing the bino abundance through co-annihilation. In this scenario, the gluino decays to the bino via squark exchange, and the wino decays to the bino via higgsino exchange. In split SUSY models favoured after the Higgs discovery, the intermediate particles in these decays would be much heavier than gauginos, suppressing the decay of the gluino and wino. This, in addition to the small mass differences, results in long lifetimes for the gluino and wino. We show that searches performed at the LHC for long-lived particles with displaced vertices offer a powerful method to test this scenario.. |
| 17. |
Otono Hidetoshi, on behalf of neutron lifetime experiment at J-PARC, Development of time projection chamber for precise neutron lifetime measurement using pulsed cold neutron beams, Nuclear Instruments and Methods in Physics Research A, 10.1016/j.nima.2015.08.006, 2015.11, A new time projection chamber (TPC) was developed for neutron lifetime measurement using a pulsed cold neutron spallation source at the Japan Proton Accelerator Research Complex (J-PARC). Managing considerable background events from natural sources and the beam radioactivity is a challenging aspect of this measurement. To overcome this problem, the developed TPC has unprecedented features such as the use of polyether-ether-ketone plates in the support structure and internal surfaces covered with 6Li-enriched tiles to absorb outlier neutrons. In this paper, the design and performance of the new TPC are reported in detail.. |
| 18. |
The ATLAS collaboration, Search for massive, long-lived particles using multitrack displaced vertices or displaced lepton pairs in pp collisions at sqrt(s) = 8 TeV with the ATLAS detector, Phys. Rev. D, 10.1103/PhysRevD.92.072004, 2015.10, Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. This article presents the results of a search for events containing at least one long-lived particle that decays at a significant distance from its production point into two leptons or into five or more charged particles. This analysis uses a data sample of proton-proton collisions at sqrt(s) = 8 TeV corresponding to an integrated luminosity of 20.3 fb^{−1} collected in 2012 by the ATLAS detector operating at the Large Hadron Collider. No events are observed in any of the signal regions, and limits are set on model parameters within supersymmetric scenarios involving R-parity violation, split supersymmetry, and gauge mediation. In some of the search channels, the trigger and search strategy are based only on the decay products of individual long-lived particles, irrespective of the rest of the event. In these cases, the provided limits can easily be reinterpreted in different scenarios.. |
| 19. |
Natsumi Nagata, Otono Hidetoshi, Satoshi Shirai, Probing Bino-Wino Coannihilation at the LHC, JHEP, 10.1007/JHEP10(2015)086, 2015.10, We study bino-wino coannihilation scenario in the so-called spread or mini-split supersymmetry. We show that, in this model, a neutral wino has a macroscopic decay length in a wide range of parameter space. This characteristic feature could be observed as a displaced vertex plus missing transverse energy event at the LHC. In this paper, we study the current constraints and future prospects on the scenario based on the displaced vertex search performed by the ATLAS collaboration. It is found that a sizable parameter region can be probed at the 8 TeV LHC run. This search strategy will considerably extend its reach at the next stage of the LHC running, and thus play a crucial role to examine a possibility of bino dark matter in the mini-split type supersymmetric models.. |
| 20. |
Natsumi Nagata, Otono Hidetoshi, Satoshi Shirai, Probing Bino-Gluino Coannihilation at the LHC, Phys. Lett. B, 10.1016/j.physletb.2015.06.044, 2015.09, It has been widely known that bino-like dark matter in the supersymmetric (SUSY) the- ories in general suffers from over-production. The situation can be drastically improved if gluinos have a mass slightly heavier than the bino dark matter as they reduce the dark matter abundance through coannihilation. In this work, we consider such a bino-gluino coannihilation scenario in high-scale SUSY models, which can be actually realized when the squark-mass scale is less than 100–1000 TeV. We study the prospects for exploring this bino-gluino coannihilation scenario at the LHC. We show that the searches for long-lived colored particles with displaced vertices or large energy loss offer a strong tool to test this scenario in collider experiments.. |
| 21. |
Otono Hidetoshi, and ATLAS collaboration, Search for the bbbar decay of the Standard Model Higgs boson in associated (W/Z)H production with the ATLAS detector, JHEP, 10.1007/JHEP01(2015)069, 01, 069, 2015.01. |
| 22. |
Otono Hidetoshi, and ATLAS collaboration, Operation and performance of the ATLAS semiconductor tracker, Journal of Instrumentation, doi:10.1088/1748-0221/9/08/P08009, 9, P08009, 2014.08. |
