ICRR young researchers' workshop

15 Jul 2026, 09:00 → 16 Jul 2026, 18:00 Asia/Tokyo

Large Seminar Room 601 (Kashiwa) (Kashiwa)

The two-day workshop has successfully concluded.
Thank you very much for your participation!

Please complete the survey by July 23.
https://forms.gle/gy28AKHxZAQyZodm9

Purpose

The workshop is dedicated to establishing the interconnections between young researchers from different research groups and fields at ICRR.

Style

This year's workshop is held at the Kashiwa campus, and in-person participation is preferred in order to have fruitful discussion.

Remote connection can be setup if necessary. Please let us know whether you attend the workshop onsite or online in your registration process. The Zoom link is below.

Zoom link: https://u-tokyo-ac-jp.zoom.us/j/86181338028?pwd=iusayO8JklhEEpDtKrHFm3qGKmM95Y.1

Meeting ID: 861 8133 8028

Passcode: 122139

※Please do not share this link publicly.

Banquet

Although there will be no banquet, you are welcome to join the ICRR Summer Party on July 16 if you're interested. If you are willing to join the party but didn't pay for the party yet, please contact the recreation committee (Seiya Nozaki: nozaki@icrr.u-tokyo.ac.jp).

Registration

You can make your registration process from the bottom of this page. Please complete your registration if you join this workshop.

Target

Postdocs, project assistant professors, assistant professors, and students.

Observer

Faculty members.

Wednesday, 15 July

09:50 → 10:00 Opening

Convener: chiaki hirose

ICRR_YRW_260715.pdf

10:00 → 11:00 Session 1: Telescope array

Convener: Chenghao Zhu

10:00 Ultra-High-Energy Cosmic Rays and the Telescope Array Experiment

The year 1912 marked the beginning of modern astroparticle physics, when Victor Hess discovered penetrating radiation of extraterrestrial origin. Since then, the energy frontier of cosmic rays has steadily expanded. In 1962, a primary cosmic ray with an energy of about 100 EeV was observed for the first time. However, more than 60 years after that observation, many fundamental questions about ultra-high-energy cosmic rays remain unresolved.

As part of the effort to address these questions, the Telescope Array (TA) experiment was established as an international collaboration in which Japanese universities and research institutes, including the Institute for Cosmic Ray Research, have played an important role. Since 2008, TA has been observing ultra-high-energy cosmic rays as the largest ultra-high-energy cosmic-ray observatory in the Northern Hemisphere. In recent years, its extension project, TA×4, has been deployed to increase the exposure at the highest energies.

In this talk, I will first review the history of ultra-high-energy cosmic-ray observations, and then present recent results from the TA experiment. Finally, I will briefly introduce proposed next-generation ultra-high-energy cosmic-ray observatories, such as GCOS.

Speaker: Heungsu Shin

10:45 Discussion

11:00 → 11:20 Coffee break

11:20 → 12:20 Session 2: Tibet-ASγ/ ALPACA

Convener: Heungsu Shin

11:20 Recent Results from the Tibet ASγ Experiment: Gamma-Ray Observations and a Related Study on Cosmic-Ray Composition

This presentation introduces three recent peer-reviewed papers related to the Tibet ASγ experiment published in 2025–2026. The first presents a study of the ultra-high-energy γ-ray halo surrounding the Geminga pulsar, providing new constraints on the magnetohydrodynamic turbulence around the source. The second demonstrates the experimental verification of a convolutional neural network (CNN)-based gamma/hadron separation method for TeV gamma-ray observations. The third reports a Monte Carlo simulation study of elemental cosmic-ray energy spectra using the Tibet Air-Shower and Muon Detector Arrays with the Bayesian unfolding method, demonstrating the feasibility of elemental spectrum reconstruction around the knee region.

Speaker: Ginga Imaizumi (ginga@icrr.u-tokyo.ac.jp)

2026_ginga_imaizumi_young.pdf

11:50 Review on Recent Progress and Status of the ALPACA Experiment

Andes Large area PArticle detector for Cosmic ray physics and Astronomy (ALPACA) experiment is a planned extensive air shower experiment aiming for very high energy gamma ray sources in the southern sky. The full array will combine surface detector array with underground muon detector for gamma / hadron discrimination. Currently the prototype, ALPAQUITA surface array has been constructed and is operating since April 2023. In this brief talk, I will introduce the scientific motivation, detector concept and current status of underground muon detector construction with emphasis on cosmic-ray observation results obtained with prototype array.

Speaker: Futatsu Sugimoto (ICRR)

ALPACA_2607ICRRyoungresearcherWS.pdf

12:20 → 13:50 Lunch Break (Free discussion encouraged)

13:50 → 14:50 Session 3: CTA

Convener: Ryo Higuchi

13:50 CTA group general talk

Cherenkov Telescope Array Observatory (CTAO) is the next-generation very-high-energy gamma-ray observatory. Our group has been contributing to the commissioning of the telescopes since years. In this presentation, we report activities of our group and the status of the CTAO commissioning and construction.

Speaker: Seiya Nozaki (ICRR)

20260715_YRW_CTA.pdf

14:05 Flash talks on their research

In this sub-session, we will have flash talks on their own topics by young researchers. If you want to discuss with them, please feel free to contact them during the coffee break!

Nanaki Itakura (M1): WaCoT & NGC1068 review
Kai Morita (M2): VHE Gamma-Ray Observations of the PeVatron Candidate V4641 Sgr with LST-1
Sogo Ito (M2): Systematic Uncertainties in Flux Estimation for Large-Zenith-Angle Observations with LST-1
Habib Mondal (postdoc): Pushing the Horizon: Flat Spectrum Radio Quasars with LST-1
Zhipeng Zhang (postdoc): From LACT to LST
Mitsunari Takahashi (project assistant professor): How should we record research with self-made software?

Speakers: Habib Ahammad Mondal, Kai Morita, Mitsunari Takahashi, Nanaki Iwakura, Sogo Ito (Nagoya University), ZHIPENG ZHANG

0715_nanaki_itakura_YRWS.pdf 20260715_ICRR-YRW_MTakahashi.pdf 2026_July_15_Young_Researcher_Workshop_ZhipengZhang.pdf ICRR-YRW_Sogo_Ito_20260715.pdf YRWS20260715_morikai.pdf

14:41 Discussion

14:50 → 16:00 Session 4: Neutrino / Nucleon Decay / Dark Matter

Convener: Heungsu Shin

14:50 Neutrino Physics with Super-Kamiokande and Hyper-Kamiokande: Recent Progress and Future Prospects

This talk will review recent progress in Super-Kamiokande neutrino research, including oscillation measurements, low-energy neutrino studies and supernova neutrino searches. It will also discuss the current status of Hyper-Kamiokande and its physics goals in neutrino related field.

Speaker: Xubin Wang

xbwang_nu_ICRRyong.pdf

15:13 Status and prospects of the nucleon decay search in Super-Kamiokande and Hyper-Kamiokande

Nucleon decay is a key prediction of grand unified theories (GUTs) and would provide direct evidence for physics beyond the Standard Model. Extensive searches have been conducted by experiments such as Kamiokande and Super-Kamiokande. This presentation reviews the current status of nucleon decay searches and discusses future prospects with the upcoming Hyper-Kamiokande experiment.

Speaker: Takuya Tashiro

YoungResearcher_Tashiro_20260715.pdf

15:36 An Overview of the XENONnT Experiment

The XENONnT experiment is one of the world's most sensitive direct dark matter search experiments, employing a dual-phase liquid xenon time projection chamber to search for rare interactions between dark matter particles and xenon nuclei.
In this talk, I will introduce the scientific motivation, detector design, detection principle, and recent physics results of the XENONnT experiment

Speaker: Kotaro Otsuzuki (Kamioka, ICRR)

2607_ICRR_young_researcher_workship_DM_otsuzuki.pdf

16:00 → 16:20 Coffee break

16:20 → 17:20 Session 5: Obs. Cosmology

Convener: Masayuki Harada

16:20 Cosmic Reionization and Cosmological Parameters

JWST observations of high-redshift galaxies have greatly advanced our understanding of cosmic reionization. Since reionization affects the CMB, I will present our recent results on constraining cosmological parameters using these galaxy observations.

Speaker: Yuta Kageura

16:35 A Scaling Relation of “Little Red Dots” between Halpha and Bolometric Luminosities: Enhanced Halpha Emission Relative to Low-z Type 1 AGNs

We investigate the spectroscopic demography of “little red dots” (LRDs) using 37 objects at z~3–7 compiled from various JWST programs. We identifiy a tight scaling relation between Ha luminosity (L_Ha) and bolometric luminosity (L_bol), which is enhanced by a factor of ~40 in L _Ha relative to that of low-z type 1 AGN. We explore the physical origin of this enhancement based on the classic locally optimally-emitting cloud (LOC) framework, and find that it can be explained by an increase in the broad line region (BLR) covering factor from ~20% (Type 1 AGN) to ~100% (LRDs), together with an increase in the hydrogen column density from N_H~10^23 cm−2 to >10^24 cm−2.

Speaker: Hiroto Yanagisawa

16:50 Early Chemical Enrichment in UV-Bright Galaxies at the Epoch of Reionization Probed by JWST Absorption-Line Analysis

Using JWST/NIRSpec medium-resolution spectra of UV-bright
galaxies at z=7.2-10.6, we investigate interstellar absorption lines to
probe the physical properties of mostly neutral gas and the early
chemical enrichment of galaxies during the epoch of reionization.

Speaker: Minami Nakane

17:05 Statistical Rethinking: overmassive blackhole at high-z universe

We will present a statistical rethinking of the phenomenon that the AGN in the high-z universe tends to have overmassive black holes. The result will be revisited in the aspect of both more stable statistical index and more sources.

Speaker: Chenghao Zhu

17:20 → 18:20 Session 6: Gravitational wave

Convener: Chenghao Zhu

17:20 The current status of the gravitational wave detector KAGRA

KAGRA is a 3 km cryogenic, underground laser interferometric
gravitational-wave detector in Kamioka, Japan, and a member of the
international LIGO–Virgo–KAGRA network. This talk reviews KAGRA's
performance and contribution during the fourth observing run (O4).

Speaker: Shoichi Oshino (ICRR)

17:40 Direct Wave and Review of gravitational wave data analysis

Gravitational waves emitted as a binary black hole merges and settles into a stationary state are called ringdown gravitational waves, which provide key clues to exploring the nature of strong gravity. These waves are conventionally modeled by a superposition of damped oscillations known as quasi-normal modes (QNMs). Recently, the potential contribution of a "direct wave" component has been debated, but its mechanism remains largely unknown. We clarify this mechanism through an analysis based on black hole perturbation theory. Furthermore, we review recent studies from gravitational wave data analysis groups.

Speaker: Keiichiro Kubota

Kubota_GWDA_ICRR_Young_Researchers'_Workshop_2026.pdf

18:00 Robust Inference of the Binary Black Hole Spin Population Using Gravitational-Wave Data

The spin population of binary black holes (BBHs) provides key insights into their formation channels. Recent gravitational-wave (GW) observations have suggested the presence of spin subpopulations and correlations between spin and other BBH parameters. However, the limited measurability of spins in certain regions of the parameter space can bias the inference of the underlying spin population. We propose a new inference method to mitigate this limitation, demonstrate its performance using simulations, and apply it to real GW data to infer the underlying BBH spin population.

Speaker: Kazuya Kobayashi

slide_ICRR_ECR2026_v2.pdf

18:20 → 18:30 Wrap-up of Day 1 &announcements for Day 2

Thursday, 16 July

09:50 → 10:50 Session 7: High energy astrophysics

Convener: Naohiro Osamura

09:50 Cosmic-Ray Acceleration on supernova remnant shocks

Supernova remnants (SNRs) have been considered as the sources of the bulk of Galactic cosmic-ray (CR). Recently some evidences of extended gamma-ray emission are reported by e.g. LHAASO and H.E.S.S. and this emission infers the existence of particles escaping from accelerating region of SNRs.
In this work, we solve one-dimensional diffusion-convection equation coupled with analytical solutions for shock dynamics, to obtain the time evolution of phase-space distribution function of CR. As a result, the time evolution of CR acceleration still increases even after the age of 10kyrs in our models, and this behavior is largely affected by environment of SNRs.

Speaker: Ryosuke Kobashi

YRW2026-HEA-kobashi.pdf

10:20 Cosmic-Ray Transport in Interstellar Medium

Cosmic rays are a key probe of high-energy astrophysical phenomena across a broad wavelength range, from radio to gamma rays, and may also play an important role in regulating galaxy evolution. However, how cosmic rays are transported in and around galaxies, and how they feed back on gas and magnetic fields, remain poorly understood. To investigate these two aspects of cosmic rays in a unified framework, we are developing a numerical code that treats cosmic-ray transport and dynamical feedback self-consistently. Recent improvements to the code have enabled us to stably follow the long-term evolution of star-formation-driven winds interacting with cold gas clouds under more realistic physical conditions. In this talk, I will present an overview of the code and discuss numerical results on how cosmic-ray transport affects the dynamical evolution of cold gas clouds in the galactic halo.

Speaker: Ryohei Inamoto

10:50 → 11:20 Coffee break

11:20 → 12:20 Session 8: Theory group

Convener: Ryosuke Kobashi

11:20 Evanescent operator contribution to radiative correction to QCD theta parameter at two-loop level in the BMHV scheme

This talk studies a three-loop contribution to the electron EDM induced by CP-violating Yukawa couplings of new $SU(2)_L$ multiplets.
These couplings generate the electroweak Weinberg operator at two loops, whose one-loop insertion can yield an electron EDM larger than the SM contribution even for TeV-scale new particles.
The paper also compares this three-loop effect with the usual two-loop Barr–Zee contribution when the SM Higgs has new Yukawa interactions.

Speaker: Naohiro Osamura

ICRR_Osamura_2607.pdf

11:40 Cosmic String in Multi-step Symmetry Breaking

Cosmic strings are promising sources of a stochastic gravitational wave background that can be probed by pulsar timing arrays and future interferometers. In this talk, I discuss metastable cosmic strings formed through multi-step symmetry breaking, focusing on their internal structure and its implications for gravitational wave observation.

Speaker: Aken Bun

po.pdf

12:00 Thermal leptogenesis における reheating temperature のベイズ推定

本発表では、type-I seesaw模型に基づく熱的レプトジェネシスにおいて、再加熱温度の自然性をベイズ推論により評価する。ニュートリノ振動データと宇宙のバリオン非対称性を同時に課すことで、成功するレプトジェネシスが単に可能かではなく、パラメータ空間でどれほど典型的かを定量化する。

Speaker: Shotaro Ieyasu

WorkShop_Ieyasu.pdf

12:20 → 12:50 Wrap-up of ICRR YRW 2026 / photo session

Convener: Chiaki Hirose

ICRR_YRW_260716.pdf