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  理工学術院総合研究所   兼任研究員

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• 2006年01月

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  エルランゲン大学   理学部   物理学専攻  

• 2000年09月

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  エルランゲン大学   理学部   物理学  

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• エルランゲン大学   理学博士

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• 2018年04月

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  早稲田大学   理工学術院（国際理工学センター）   准教授（任期付）

• 2014年04月

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  2018年03月

  早稲田大学   理工学術院国際教育センター   助教

• 2013年06月

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  早稲田大学   理工研究所   次席研究員

• 2013年06月

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  2014年03月

  早稲田大学   理工研究所   次席研究員

• 2013年04月

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  2013年05月

  早稲田大学   理工研究所   助手

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  ドイツ物理学会

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  日本物理学会

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• 素粒子、原子核、宇宙線、宇宙物理にする理論

• 素粒子、原子核、宇宙線、宇宙物理にする実験

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• Cosmic-ray signatures of dark matter from a flavor dependent gauge symmetry model with neutrino mass mechanism

  Holger Motz, Hiroshi Okada, Yoichi Asaoka, Kazunori Kohri

  Physical Review D   102 ( 8 )  2020年10月

  　概要を見る

  © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3. We propose an extension to the Standard Model accommodating two families of Dirac neutral fermions and Majorana fermions under additional U(1)e-μ×Z3×Z2 symmetries where U(1)e-μ is a flavor dependent gauge symmetry related to the first and second family of the lepton sector, which features a two-loop induced neutrino mass model. The two families are favored by minimally reproducing the current neutrino oscillation data and two mass difference squares and canceling the gauge anomalies at the same time. As a result, we have a prediction for neutrino masses. The lightest Dirac neutral fermion is a dark matter candidate with tree-level interaction restricted to electron, muon and neutrinos, which makes it difficult to detect in direct dark matter search as well as indirect search focusing on the τ-channel, such as through γ-rays. It may however be probed by search for dark matter signatures in electron and positron cosmic rays, and allows interpretation of a structure appearing in the CALET electron+positron spectrum around 350-400 GeV as its signature, with a boost factor ∼40 Breit-Wigner enhancement of the annihilation cross section.

  DOI

• Interpretation of the CALET Electron+Positron Spectrum concerning Dark Matter Signatures

  H. Motz, Y. Asaoka, S. Bhattacharyya

  Proceedings of Science   ICRC2019 ( 533 )  2019年07月

• Analysis of CALET Data for Anisotropy in Electron+Positron Cosmic Rays

  H. Motz, Y. Asaoka, for, the, CALET collaboration

  Proceedings of Science   ICRC2019 ( 112 )  2019年07月

• Direct Measurement of the Cosmic-Ray Proton Spectrum from 50 GeV to 10 TeV with the Calorimetric Electron Telescope on the International Space Station

  O. Adriani, Y. Akaike, K. Asano, Y. Asaoka, M. G. Bagliesi, E. Berti, G. Bigongiari, W. R. Binns, S. Bonechi, M. Bongi, P. Brogi, A. Bruno, J. H. Buckley, N. Cannady, G. Castellini, C. Checchia, M. L. Cherry, G. Collazuol, V. Di Felice, K. Ebisawa, H. Fuke, T. G. Guzik, T. Hams, N. Hasebe, K. Hibino, M. Ichimura, K. Ioka, W. Ishizaki, M. H. Israel, K. Kasahara, J. Kataoka, R. Kataoka, Y. Katayose, C. Kato, N. Kawanaka, Y. Kawakubo, K. Kohri, H. S. Krawczynski, J. F. Krizmanic, T. Lomtadze, P. Maestro, P. S. Marrocchesi, A. M. Messineo, J. W. Mitchell, S. Miyake, A. A. Moiseev, K. Mori, M. Mori, N. Mori, H. M. Motz, K. Munakata, H. Murakami, S. Nakahira, J. Nishimura, G. A. De Nolfo, S. Okuno, J. F. Ormes, S. Ozawa, L. Pacini, F. Palma, P. Papini, A. V. Penacchioni, B. F. Rauch, S. B. Ricciarini, K. Sakai, T. Sakamoto, M. Sasaki, Y. Shimizu, A. Shiomi, R. Sparvoli, P. Spillantini, F. Stolzi, J. E. Suh, A. Sulaj, I. Takahashi, M. Takayanagi, M. Takita, T. Tamura, T. Terasawa, H. Tomida, S. Torii, Y. Tsunesada, Y. Uchihori, S. Ueno, E. Vannuccini, J. P. Wefel, K. Yamaoka, S. Yanagita, A. Yoshida, K. Yoshida

  Physical Review Letters   122 ( 18 ) 1102  2019年05月  [査読有り]

  　概要を見る

  © 2019 authors. In this paper, we present the analysis and results of a direct measurement of the cosmic-ray proton spectrum with the CALET instrument onboard the International Space Station, including the detailed assessment of systematic uncertainties. The observation period used in this analysis is from October 13, 2015 to August 31, 2018 (1054 days). We have achieved the very wide energy range necessary to carry out measurements of the spectrum from 50 GeV to 10 TeV covering, for the first time in space, with a single instrument the whole energy interval previously investigated in most cases in separate subranges by magnetic spectrometers (BESS-TeV, PAMELA, and AMS-02) and calorimetric instruments (ATIC, CREAM, and NUCLEON). The observed spectrum is consistent with AMS-02 but extends to nearly an order of magnitude higher energy, showing a very smooth transition of the power-law spectral index from-2.81±0.03 (50-500 GeV) neglecting solar modulation effects (or-2.87±0.06 including solar modulation effects in the lower energy region) to-2.56±0.04 (1-10 TeV), thereby confirming the existence of spectral hardening and providing evidence of a deviation from a single power law by more than 3σ.

  DOI PubMed

• The CALorimetric Electron Telescope (CALET) on the International Space Station: Results from the First Two Years of Operation

  Asaoka, Y, Adriani, O, Akaike, Y, Asano, K, Bagliesi, M. G, Berti, E, Bigongiari, G, Binns, W. R, Bonechi, S, Bongi, M, Bruno A, Brogi, P, Buckley, J. H, Cannady, N, Castellini, G, Checchia, C, Cherry, M. L, Collazuol, G, di Felice, V, Ebisawa, K, Fuke, H, Guzik, T. G, Hams, T, Hasebe, N, Hibino, K, Ichimura, M, Ioka, K, Ishizaki, W, Israel, M. H, Kasahara, K, Kataoka, J, Kataoka, R, Katayose, Y, Kato, C, Kawanaka, N, Kawakubo, Y, Kohri, K, Krawczynski, H. S

  EPJ Web of Conferences   208 ( 13001 )  2019年05月

  DOI

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• Updated Constraints on Dark Matter Annihilation and Decay from CALET Data

  Motz H, 浅岡陽一, 鳥居祥二, Bhattacharyya, S

  日本物理学会 2018年秋季大会   (信州大学松本キャンパス) 

  発表年月： 2018年09月

  　概要を見る

  Installed on the ISS in August 2015 and taking data since October of that year, CALET (CALorimetric Electron Telescope) is directly measuring the electron+positron cosmic-ray spectrum up into the TeV-region with fine energy resolution and good proton rejection. The updated results of the measurement published in [O. Adriani et al. PRL 120, 261102] have been analyzed for signatures of Dark Matter. Limits on annihilation and decay of Dark Matter for selected Dark Matter models and propagation conditions were calculated. For this, the local electron and positron spectra were modeled with an analytic parametrization, including a term representing the flux from nearby pulsars as the extra electron-positron- pair source responsible for the positron excess. This parametrization is fitted to CALET electron+positron data and the positron-only flux measured by AMS-02, yielding a good fit quality. The expected Dark Matter flux for various annihilation and decay channels has been calculated with PYTHIA and the calculation of propagation to Earth was calculated numerically with DRAGON. This flux is added to the parametrization with an increasing scale factor until the fit quality reaches the 95%CL threshold, thereby obtaining a limit on the annihilation cross-section or lifetime of the tested Dark Matter candidate. By including systematic uncertainties with known energy dependence in the fitting function as corrections, the limits were improved compared to treating all error components as random errors.

• Constraints on Dark Matter Annihilation and Decay from CALET Data

  Motz H, 浅岡陽一, 鳥居祥二, Bhattacharyya, S

  2018 TeV Particle Astrophysics conference   (ベルリン) 

  発表年月： 2018年08月

  　概要を見る

  Installed on the ISS in August 2015 and taking data since October of that year, CALET (CALorimetric Electron Telescope) is directly measuring the electron+positron cosmic-ray spectrum up into the TeV-region with fine energy resolution and good proton rejection. The latest published total electron+positron spectrum is analyzed for Dark Matter signatures. Limits on annihilation and decay of Dark Matter are calculated by fitting the expected flux from Dark Matter on top of a parametrization of the astrophysical background spectrum to both CALET data and the positron flux measured by AMS-02. Starting from a purely astrophysical scenario with a nearby pulsar as the origin of the positron excess, the spectrum from Dark Matter annihilation or decay, which is numerically calculated with DRAGON, is added, and its scale-factor increased until the fit quality reaches the limit threshold. The flux from Dark Matter is calculated for multiple Dark Matter candidates with varying mass, yielding limits on annihilation cross-section or lifetime as a function of Dark Matter mass for each. In addition to presenting these Dark Matter limits and their comparison with results from other Dark Matter detection methods, possible interpretations of the spectrum measured by CALET including a contribution from Dark Matter will be discussed.

• Implications for Dark Matter and Pulsar Contributions to the Positron Excess from CALET Data

  Motz H, 浅岡陽一, 鳥居祥二, Bhattacharyya, S

  日本物理学会 第73回年次大会(2018年)   (東京理科大 野田キャンパス) 

  発表年月： 2018年03月

  　概要を見る

  Installed on the ISS in August 2015 and taking data since October of that year, CALET (CALorimetric Electron Telescope) is directly measuring the elec- tron+positron cosmic-ray spectrum up into the TeV-region with fine energy resolution and good proton rejection. The results of the measurement as pub- lished in [O. Adriani et al. PRL 119, 181101] have been analyzed for signatures of Dark Matter. Limits on annihilation and decay of Dark Matter for selected Dark Matter models and propagation conditions were calculated. For this, the local electron and positron spectra were modeled with an analytic parametrization, includ- ing a power law with exponential cut-off representing a nearby pulsar as the extra electron-positron-pair source responsible for the positron excess. The parametrization is fitted to CALET electron+positron data and the positron- only flux measured by AMS-02, showing good agreement. The expected Dark Matter flux for various annihilation and decay channels has been calculated with PYTHIA and propagated DRAGON, and is added to the parametrization with an increasing scale factor until the fit becomes excluded at 95%CL, thereby obtaining a limit on the annihilation cross-section or lifetime of the tested Dark Matter candidate. Limits for generic channels and selected Dark Matter candi- dates as a function of Dark Matter mass are presented and compared to those from other experiments. The CALET electron+positron spectrum shows structures, and especially a step around 400 GeV is better modeled if a flux from Dark Matter is added to the parametrization than without the Dark Matter term. The possibility of such a partial contribution of Dark Matter to the positron excess is discussed. Furthermore, a 3-body decay of fermionic Dark Matter is shown to be a possible cause of the positron excess without additional contributions from pulsars. While this scenario is strongly constrained by the Fermi-LAT diffuse gamma measurement, 800 GeV mass Dark Matter may be a candidate compatible with this γ-ray flux measurement. Based on simulated data for five years of CALET data-taking, the capability to discern the decaying Dark Matter model from a generic pulsar source scenario is shown.

• Limits on Dark Matter and Nearby Astrophysical Sources from the CALET Electron+Positron Spectrum

  Motz H, 浅岡陽一, 鳥居祥二, Bhattacharyya, S

  CosPA, International Symposium on Cosmology and Particle Astrophysics, 2017   (Yukawa Institute for Theoretical Physics, Kyoto University) 

  発表年月： 2017年12月

  　概要を見る

  Installed on the ISS in August 2015 and taking data since October of that year, CALET (CALorimetric Electron Telescope) is directly measuring the electron+positron cosmic-ray spectrum up into the TeV-region with fine energy resolution and good proton rejection. The results of the measurement so far have been analysed for signatures of a nearby SNR or Dark Matter. Limits on annihilation and decay of Dark Matter for selected models and propagation conditions were calculated by fitting a combined parametrisation including an increasing Dark Matter term to the total electron+positron flux measured by CALET and the positron flux measured by AMS-02. Also the contribution from the Vela SNR to the flux in the TeV-region was studied and with an equivalent method constraints on the injected cosmic-ray energy derived.

• Measurement of Electron Anisotropy with CALET

  Motz H, 浅岡陽一, 鳥居祥二, Bhattacharyya, S. for, the CALET collaboration

  日本物理学会 2017年秋季大会   (宇都宮大学 峰キャンパス) 

  発表年月： 2017年09月

  　概要を見る

  The ISS-based Calorimetric Electron Telescope (CALET) is directly measuring the energy spectrum and direction distribution of electron+positron cosmic-rays well into the TeV-region. The measured events are analyzed for a possible dipole anisotropy as could be caused e.g. by emission from a nearby supernova remnant. The methods for deriving limits on the anisotropy from the reconstructed events, as well as the procedures to take into account the non-uniform exposure to the sky and possibly inhomogeneous acceptance of the detector are explained. Preliminary results for the measured anisotropy and upper limits in several energy ranges are presented.

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• Search for a Combined Spectrum and Anisotropy Signature of the Vela SNR with CALET

  2020年  

  　概要を見る

  This project comprised the refinement of previous work on Dark Matter Search using  cosmic-ray spectra measured by CALET (electron+positron) and AMS-02 (positron-only), as well as in initial steps towards the goal of identifying a signature of the Vela SNR in CALET data.The study of signatures from a flavor-dependent gauge-symmetry dark matter was updated, including among other items a comparison with current and future neutrino observations, concluded by publication in PRD and presentations in a JPS meeting and at the Kashiwa Dark Matter symposium.  Concurrently, a method to study the emission of electron cosmic rays from the nearby Vela SNR quantitatively was developed. The expected spectrum from Vela is calculated, normalized to a total emission energy of 10^48 erg. By re-scaling this flux in a fit with a flexible background model, best fit interpretations and upper limits were derived, depending on parameters of the Vela SNR, as well as the cosmic-ray propagation conditions. First results with this  method based on the spectrum published by the CALET collaboration in 2018 were presented at the annual JPS meeting. It was shown that CALET limits the emitted energy by Vela to within a factor four  from the proposed value of 10^48 erg.

• Investigating Structures in the CALET Electron+Positron Spectrum as Dark Matter or Pulsar Signatures

  2019年   Yoichi Asaoka, Hiroshi Okada, Kazunori Kohri

  　概要を見る

  The electron+positron spectrum measured by CALET features structures which could be signatures of individual astrophysical point sources, or alternatively Dark Matter (DM) annihilation or decay.This was investigated using a parametrized model assuming initially a single pulsar as the source of the positron excess fitted to the CALET electron+positron spectrum and the AMS-02 positron-only spectrum. Addition of multiple pulsars, or alternatively the flux from DM annihilating partly through the electron-positron channel can improve the fit significantly by modeling a step-like structure around 350-400 GeV (presented at ICRC 2019 and published in its proceedings). Also presented were updated limits on the DM annihilation/decay rate which are competitive for electron and muon channel, while DM search by gamma-rays favors the tau-channel.An extension of the Standard Model by U(1)_e-mu gauge symmetry was investigated, finding a DM candidate particle interacting only with electron and muon, with the structure in the CALET spectrum being compatible with its signature (result paper uploaded on arxiv).  Another topic investigated was the anisotropy of the electron-positron flux, calculating an omni-directional limit on dipole anisotropy (presented at ICRC2019 and JPS autumn meeting).

• Analysis of the CALET Electron+Positron Cosmic-Ray Spectrum for Dark Matter Signatures

  2018年   Saptashwa Bhattacharyya

  　概要を見る

  This project focused on the scientific analysis of data from the CALET cosmic-ray detector on the ISS for signatures of Dark Matter.Previously calculated limits on Dark Matter annihilation and decay from CALET data were refined. The limit calculation is based on a parametrization of the spectra from astrophysical sources fitted to CALET (electron+positron) and AMS-02 (positron-only) data, to which the expected flux from Dark Matter is added until the model is excluded, yielding a limit.The parametrization of the pulsar source assumed to cause the positron excess was improved from a generic power law with exponential cut-off to a semi-analytically calculated spectrum for individual known pulsars.  The combined spectrum of multiple pulsars fits significantly better than a single pulsar, modelling better a step-like spectral structure at 350 GeV.Alternative to multiple pulsars, a Dark Matter explanation is also possible, assuming a single pulsar background, which is also applicable to a step at 1 TeV not explainable by nearby pulsars.A model of leptonic three-body Dark Matter decay as the only source of the positron excess was published in a refereed journal after improving the discussion of constraints from gamma-ray observation.

• Numerical Calculation of Cosmic Ray Anisotropy

  2017年   Bhattacharyya Saptashwa

  　概要を見る

  This research project advanced the scientific analysis of data from the CALET cosmic-ray detector on the ISS with regard to anisotropy of the flux and signatures of Dark Matter Annihilation and decay. Using numerical simulation, reference models for the interpretation of the CALET data are created. The anisotropy of the cosmic ray electron+positron flux measured with CALET was analyzed, confirming the reliability of the analysis methods previously tested on Monte Carlo simulations. On the field of indirect Dark Matter search, limits on Dark Matter annihilation and decay were calculated from published CALET data.  A weak hint at what could be a signature of Dark Matter annihilation or decay was studied, since additional flux from Dark Matter was found to slightly better model a step structure in the spectrum than the power-law background from astrophysical sources alone.Furthermore,  leptonic three-body decay of Dark Matter as the sole cause of the positron excess was investigated. It was shown that a parameter space both for this Dark Matter model, as well as the single-pulsar model exists with current CALET data, but that the two cases could be separated with full statistics of  5-year CALET data.

• Precise Cosmic-Ray Simulations to Support CALET Data Analysis

  2016年   Bhattacharyya Saptashwa

  　概要を見る

  The expected anisotropy in electron+positron cosmic-rays was calculated using numerical methods,  to study a possible anisotropy signature from the Vela SNR, and its detectability with CALET. For these calculations, the code DRAGON was extended to extract the anisotropy information near the solar system from the cosmic-ray distribution on the spatial grid, on which the calculation is done. As the required finely binned grid requires a PC with large RAM, the hardware procured from this project grant was essential in accomplishing this. Based on these calculations, the sensitivity of CALET to anisotropy of the electron+positron flux was studied, and expected limits on the dipole amplitude calculated. To enhance the sensitivity, an analysis method assuming a fixed direction of the dipole towards Vela was tested, and it was shown that a possibility to find a significant signal exists.Using similar numerical calculations, the signature of Dark Matter decay in cosmic-rays and its background were studied. Specifically, leptonic 3-particle decay of Dark Matter was investigated as a potential source of the positron excess and it was shown that CALET has potential to discern this Dark Matter decay from a nearby pulsar causing the positron excess.

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