Showing papers by "Tsuyoshi Nakaya published in 2021"

Neutron-antineutron oscillation search using a 0.37 megaton-years exposure of Super-Kamiokande

Abstract: As a baryon number violating process with $\Delta B=2$, neutron-antineutron oscillation ($n\to\bar n$) provides a unique test of baryon number conservation. We have performed a search for $n\to\bar n$ oscillation with bound neutrons in Super-Kamiokande, with the full data set from its first four run periods, representing an exposure of 0.37~Mton-years. The search used a multivariate analysis trained on simulated $n\to\bar n$ events and atmospheric neutrino backgrounds and resulted in 11 candidate events with an expected background of 9.3 events. In the absence of statistically significant excess, we derived a lower limit on $\bar n$ appearance lifetime in $^{16}$O nuclei of $3.6\times{10}^{32}$ years and on the neutron-antineutron oscillation time of $\tau_{n\to\bar n} > 4.7\times10^{8}$~s at 90\% C.L..

Search for neutrinos in coincidence with gravitational wave events from the LIGO-Virgo O3a Observing Run with the Super-Kamiokande detector

Abstract: The Super-Kamiokande detector can be used to search for neutrinos in time coincidence with gravitational waves detected by the LIGO-Virgo Collaboration (LVC). Both low-energy ($7-100$ MeV) and high-energy ($0.1-10^5$ GeV) samples were analyzed in order to cover a very wide neutrino spectrum. Follow-ups of 36 (out of 39) gravitational waves reported in the GWTC-2 catalog were examined; no significant excess above the background was observed, with 10 (24) observed neutrinos compared with 4.8 (25.0) expected events in the high-energy (low-energy) samples. A statistical approach was used to compute the significance of potential coincidences. For each observation, p-values were estimated using neutrino direction and LVC skymap ; the most significant event (GW190602_175927) is associated with a post-trial p-value of $7.8\%$ ($1.4\sigma$). Additionally, flux limits were computed independently for each sample, and by combining the samples. The energy emitted as neutrinos by the identified gravitational wave sources was constrained, both for given flavors as well as for all-flavors assuming equipartition between the different flavors, independently for each trigger and by combining sources of the same nature.

Measurements of $\bar{\nu}_{\mu}$ and $\bar{\nu}_{\mu} + \nu_{\mu}$ charged-current cross-sections without detected pions nor protons on water and hydrocarbon at mean antineutrino energy of 0.86 GeV

Abstract: We report measurements of the flux-integrated $\bar{ u}_\mu$ and $\bar{ u}_\mu+ u_\mu$ charged-current cross-sections on water and hydrocarbon targets using the T2K anti-neutrino beam, with a mean neutrino energy of 0.86 GeV. The signal is defined as the (anti-)neutrino charged-current interaction with one induced $\mu^\pm$ and no detected charged pion nor proton. These measurements are performed using a new WAGASCI module recently added to the T2K setup in combination with the INGRID Proton module. The phase space of muons is restricted to the high-detection efficiency region, $p_{\mu}>400~{\rm MeV}/c$ and $\theta_{\mu} 200~{\rm MeV}/c$ and $\theta_{\pi} 600~{\rm MeV}/c$ and $\theta_{\rm p}<70^{\circ}$" is required. In this paper, both of the $\bar{ u}_\mu$ cross-sections and $\bar{ u}_\mu+ u_\mu$ cross-sections on water and hydrocarbon targets, and their ratios are provided by using D'Agostini unfolding method. The results of the integrated $\bar{ u}_\mu$ cross-section measurements over this phase space are $\sigma_{\rm H_{2}O}\,=\,(1.082\pm0.068(\rm stat.)^{+0.145}_{-0.128}(\rm syst.)) \times 10^{-39}~{\rm cm^{2}/nucleon}$, $\sigma_{\rm CH}\,=\,(1.096\pm0.054(\rm stat.)^{+0.132}_{-0.117}(\rm syst.)) \times 10^{-39}~{\rm cm^{2}/nucleon}$, and $\sigma_{\rm H_{2}O}/\sigma_{\rm CH} = 0.987\pm0.078(\rm stat.)^{+0.093}_{-0.090}(\rm syst.)$. The $\bar{ u}_\mu+ u_\mu$ cross-section is $\sigma_{\rm H_{2}O} = (1.155\pm0.064(\rm stat.)^{+0.148}_{-0.129}(\rm syst.)) \times 10^{-39}~{\rm cm^{2}/nucleon}$, $\sigma_{\rm CH}\,=\,(1.159\pm0.049(\rm stat.)^{+0.129}_{-0.115}(\rm syst.)) \times 10^{-39}~{\rm cm^{2}/nucleon}$, and $\sigma_{\rm H_{2}O}/\sigma_{\rm CH}\,=\,0.996\pm0.069(\rm stat.)^{+0.083}_{-0.078}(\rm syst.)$.

Search for Neutrinos in Coincidence with Gravitational Wave Events from the LIGO-Virgo O3a Observing Run with the Super-Kamiokande Detector

Abstract: The Super-Kamiokande detector can be used to search for neutrinos in time coincidence with gravitational waves detected by the LIGO–Virgo Collaboration (LVC). Both low-energy (7–100 MeV) and high-energy (0.1–105 GeV) samples were analyzed in order to cover a very wide neutrino spectrum. Follow-ups of 36 (out of 39) gravitational waves reported in the GWTC-2 catalog were examined; no significant excess above the background was observed, with 10 (24) observed neutrinos compared with 4.8 (25.0) expected events in the high-energy (low-energy) samples. A statistical approach was used to compute the significance of potential coincidences. For each observation, p-values were estimated using neutrino direction and LVC sky map; the most significant event (GW190602_175927) is associated with a post-trial p-value of 7.8% (1.4σ). Additionally, flux limits were computed independently for each sample and by combining the samples. The energy emitted as neutrinos by the identified gravitational wave sources was constrained, both for given flavors and for all flavors assuming equipartition between the different flavors, independently for each trigger and by combining sources of the same nature.

First measurement using a nuclear emulsion detector of the ν μ charged-current cross section on iron around the 1 GeV energy region

Abstract: We report the flux-averaged $ u_{\mu}$ charged-current cross sections on iron using an emulsion-based detector exposed to the T2K neutrino beam in the J-PARC neutrino facility. The data samples correspond to 4.0$\times$10$^{19}$ protons on target, and the neutrino mean energy is 1.49$\,$GeV. The cross section was measured to be $\sigma^{\mathrm{Fe}}_{\mathrm{CC}} = (1.28 \pm 0.11({\mathrm{stat.}})^{+0.12}_{-0.11}({\mathrm{syst.}})) \times 10^{-38} \, {\mathrm{cm}}^{2}/{\mathrm{nucleon}}$. The cross section in a limited kinematic phase space of induced muons, $\theta_{\mu} 400 \, {\rm MeV}/c$, on iron was $\sigma^{\mathrm{Fe}}_{\mathrm{CC \hspace{1mm} phase \hspace{0.5mm} space}} = (0.84 \pm 0.07({\mathrm{stat.}})^{+0.07}_{-0.06}({\mathrm{syst.}})) \times 10^{-38} \, {\mathrm{cm}}^{2}/{\mathrm{nucleon}}$. These results are consistent with previous values obtained via different techniques using the same beamline, and it is well reproduced by current neutrino interaction models. These results represent a significant advance for precise measurements of the neutrino-nucleus interactions around the 1$\,$GeV energy region.

First T2K measurement of transverse kinematic imbalance in the muon-neutrino charged-current single- π+ production channel containing at least one proton

Abstract: This paper reports the first T2K measurement of the transverse kinematic imbalance in the single-$\pi^+$ production channel of neutrino interactions. We measure the differential cross sections in the muon-neutrino charged-current interaction on hydrocarbon with a single $\pi^+$ and at least one proton in the final state, at the ND280 off-axis near detector of the T2K experiment. The extracted cross sections are compared to the predictions from different neutrino-nucleus interaction event generators. Overall, the results show a preference for models which have a more realistic treatment of nuclear medium effects including the initial nuclear state and final-state interactions.

Diffuse Supernova Neutrino Background search at Super-Kamiokande with neutron tagging

Abstract: K. Abe, 43 C. Bronner, Y. Hayato, 43 K. Hiraide, M. Ikeda, S. Imaizumi, J. Kameda, 43 Y. Kanemura, Y. Kataoka, S. Miki, M. Miura, 43 S. Moriyama, 43 Y. Nagao, M. Nakahata, 43 S. Nakayama, 43 T. Okada, K. Okamoto, A. Orii, G. Pronost, H. Sekiya, 43 M. Shiozawa, 43 Y. Sonoda, Y. Suzuki, A. Takeda, 43 Y. Takemoto, A. Takenaka, H. Tanaka, S. Watanabe, T. Yano, S. Han, T. Kajita, 43 K. Okumura, 43 T. Tashiro, J. Xia, G. D. Megias, D. Bravo-Berguño, L. Labarga, Ll. Marti, B. Zaldivar, B. W. Pointon, 47 F. d. M. Blaszczyk, E. Kearns, 43 J. L. Raaf, J. L. Stone, 43 L. Wan, T. Wester, J. Bian, N. J. Griskevich, W. R. Kropp, S. Locke, S. Mine, M. B. Smy, 43 H. W. Sobel, 43 V. Takhistov, 43 J. Hill, J. Y. Kim, I. T. Lim, R. G. Park, B. Bodur, K. Scholberg, 43 C. W. Walter, 43 S. Cao, L. Bernard, A. Coffani, O. Drapier, S. El Hedri, ∗ A. Giampaolo, † M. Gonin, Th. A. Mueller, P. Paganini, B. Quilain, T. Ishizuka, T. Nakamura, J. S. Jang, J. G. Learned, L. H. V. Anthony, D. Martin, M. Scott, A. A. Sztuc, Y. Uchida, V. Berardi, M. G. Catanesi, E. Radicioni, N. F. Calabria, L. N. Machado, G. De Rosa, G. Collazuol, F. Iacob, M. Lamoureux, M. Mattiazzi, N. Ospina, L. Ludovici, Y. Maekawa, Y. Nishimura, M. Friend, T. Hasegawa, T. Ishida, T. Kobayashi, M. Jakkapu, T. Matsubara, T. Nakadaira, K. Nakamura, 43 Y. Oyama, K. Sakashita, T. Sekiguchi, T. Tsukamoto, Y. Kotsar, Y. Nakano, H. Ozaki, T. Shiozawa, A. T. Suzuki, Y. Takeuchi, 43 S. Yamamoto, A. Ali, Y. Ashida, ‡ J. Feng, S. Hirota, T. Kikawa, M. Mori, T. Nakaya, 43 R. A. Wendell, 43 K. Yasutome, P. Fernandez, N. McCauley, P. Mehta, K. M. Tsui, Y. Fukuda, Y. Itow, 29 H. Menjo, T. Niwa, K. Sato, M. Tsukada, J. Lagda, S. M. Lakshmi, P. Mijakowski, J. Zalipska, J. Jiang, C. K. Jung, C. Vilela, M. J. Wilking, C. Yanagisawa, § K. Hagiwara, M. Harada, T. Horai, H. Ishino, S. Ito, H. Kitagawa, Y. Koshio, 43 W. Ma, N. Piplani, S. Sakai, G. Barr, D. Barrow, L. Cook, 43 A. Goldsack, 43 S. Samani, D. Wark, 38 F. Nova, T. Boschi, F. Di Lodovico, J. Gao, J. Migenda, M. Taani, S. Zsoldos, J. Y. Yang, S. J. Jenkins, M. Malek, J. M. McElwee, O. Stone, M. D. Thiesse, L. F. Thompson, H. Okazawa, S. B. Kim, J. W. Seo, I. Yu, K. Nishijima, M. Koshiba, ¶ K. Iwamoto, K. Nakagiri, Y. Nakajima, 43 N. Ogawa, M. Yokoyama, 43 K. Martens, M. R. Vagins, 7 M. Kuze, S. Izumiyama, T. Yoshida, M. Inomoto, M. Ishitsuka, H. Ito, T. Kinoshita, R. Matsumoto, K. Ohta, M. Shinoki, T. Suganuma, A. K. Ichikawa, K. Nakamura, J. F. Martin, H. A. Tanaka, T. Towstego, R. Akutsu, V. Gousy-Leblanc, ‖ M. Hartz, A. Konaka, ‖ P. de Perio, N. W. Prouse, S. Chen, B. D. Xu, Y. Zhang, M. Posiadala-Zezula, D. Hadley, M. O’Flaherty, B. Richards, B. Jamieson, J. Walker, A. Minamino, K. Okamoto, G. Pintaudi, S. Sano, and R. Sasaki

Supernova Model Discrimination with Hyper-Kamiokande

Abstract: Core-collapse supernovae are among the most magnificent events in the observable universe. They produce many of the chemical elements necessary for life to exist and their remnants -- neutron stars and black holes -- are interesting astrophysical objects in their own right. However, despite millennia of observations and almost a century of astrophysical study, the explosion mechanism of core-collapse supernovae is not yet well understood. Hyper-Kamiokande is a next-generation neutrino detector that will be able to observe the neutrino flux from the next galactic core-collapse supernova in unprecedented detail. We focus on the first 500 ms of the neutrino burst, corresponding to the accretion phase, and use a newly-developed, high-precision supernova event generator to simulate Hyper-Kamiokande's response to five different supernova models. We show that Hyper-Kamiokande will be able to distinguish between these models with high accuracy for a supernova at a distance of up to 100 kpc. Once the next galactic supernova happens, this ability will be a powerful tool for guiding simulations towards a precise reproduction of the explosion mechanism observed in nature.

Low energy radioactivity BG model in Super-Kamiokande detector from SK-IV data

Abstract: The radioactivity background are among the most dangerous background for low energy neutrino analysis in Super-Kamiokande (SK), like the solar neutrino analysis. Among them, the main contribution is coming from $^{222}$Rn, which is spread in the detector's water due to the water source and to the photo multiplier (PMT) emanations. Up to now, its exact distribution in the detector was not known. Using our knowledge of the radon concentration in the detector water, and the SK-IV solar data, we developed a model of the radon distribution in the detector. The uncertainty on the Rn concentration associated with this model was estimated to be $\sim0.1$ mBq/m$^{3}$

Search for tens of MeV neutrinos associated with gamma-ray bursts in Super-Kamiokande

Abstract: A search for neutrinos produced in coincidence with Gamma-Ray Bursts(GRB) was conducted with the Super-Kamiokande (SK) detector. Between December 2008 and March 2017, the Gamma-ray Coordinates Network recorded 2208 GRBs that occurred during normal SK operation. Several time windows around each GRB were used to search for coincident neutrino events. No statistically significant signal in excess of the estimated backgrounds was detected. The $\bar u_e$ fluence in the range from 8 MeV to 100 MeV in positron total energy for $\bar u_e+p\rightarrow e^{+}+n$ was found to be less than $\rm 5.07\times10^5$ cm$^{-2}$ per GRB in 90\% C.L. Upper bounds on the fluence as a function of neutrino energy were also obtained.

New Methods and Simulations for Cosmogenic Induced Spallation Removal in Super-Kamiokande-IV.

Abstract: Radioactivity induced by cosmic muon spallation is a dominant source of backgrounds for $\mathcal{O}(10)~$MeV neutrino interactions in water Cherenkov detectors. In particular, it is crucial to reduce backgrounds to measure the solar neutrino spectrum and find neutrino interactions from distant supernovae. In this paper we introduce new techniques to locate muon-induced hadronic showers and efficiently reject spallation backgrounds. Applying these techniques to the solar neutrino analysis with an exposure of $2790\times22.5$~kton.day increases the signal efficiency by $12.6\%$, approximately corresponding to an additional year of detector running. Furthermore, we present the first spallation simulation at SK, where we model hadronic interactions using FLUKA. The agreement between the isotope yields and shower pattern in this simulation and in the data gives confidence in the accuracy of this simulation, and thus opens the door to use it to optimize muon spallation removal in new data with gadolinium-enhanced neutron capture detection.

Search for Tens of MeV Neutrinos associated with Gamma-Ray Bursts in Super-Kamiokande.

Abstract: A search for neutrinos produced in coincidence with Gamma-Ray Bursts(GRB) was conducted with the Super-Kamiokande (SK) detector. Between December 2008 and March 2017, the Gamma-ray Coordinates Network recorded 2208 GRBs that occurred during normal SK operation. Several time windows around each GRB were used to search for coincident neutrino events. No statistically significant signal in excess of the estimated backgrounds was detected. The $\bar u_e$ fluence in the range from 8 MeV to 100 MeV in positron total energy for $\bar u_e+p\rightarrow e^{+}+n$ was found to be less than $\rm 5.07\times10^5$ cm$^{-2}$ per GRB in 90\% C.L. Upper bounds on the fluence as a function of neutrino energy were also obtained.