The 20th International Symposium on Very High Energy Cosmic Ray Interactions (ISVHECRI 2018) was held in Nagoya, Japan, on 21–25 May. More than 120 attendees from 19 countries discussed various aspects of hadronic interactions at the intersection between high-energy cosmic-ray physics and classical accelerator-based particle physics. The 65 contributions reflected the large diversity and interdisciplinary character of this biennial series, which is held under the auspices of the International Union of Pure and Applied Physics.
In his opening address, Sunil Gupta paid a tribute to Oscar Saavedra, one of the leading scientists and founders of the ISVHECRI series, who passed away in 2018. Following the long tradition of this symposium series, the main topic was the discussion of particle physics of relevance to extensive air showers, secondary cosmic-ray production, and hadronic multi-particle production at accelerators. This time, the symposium expanded its coverage of multi-messenger astrophysics, especially to neutrino and gamma-ray astrophysics. Many talks were invited from the Pierre Auger Observatory and Telescope Array, as well as from IceCube, Super-Kamiokande, CTA and HAWC, and space-borne experiments such as AMS-02, Fermi and CALET.
Participants discussed how many open questions in high-energy astroparticle physics are related to our understanding of cosmic-ray interactions from the multi-messenger point of view; for example, the relevance of production and propagation of positrons or antimatter for indirect dark-matter searches, or of atmospheric-neutrino production for neutrino oscillations or neutrino astronomy.
Showcasing several models of high-energy cosmic-ray interactions, and their verification by accelerator measurements, was also a highlight of the symposium. The event offered a unique opportunity for developers of major cosmic-ray interaction models to gather and engage in valuable discussions. Other highlights were the talks about accelerator data relevant to cosmic-ray observations, reported by the teams behind CERN’s large LHC experiments as well as smaller fixed-target experiments such as NA61. Emphasis was put on forward measurements by ATLAS, CMS, LHCb and LHCf, including first results from the SMOG gas-jet target measurements of LHCb (see “Fixed-target physics in collider mode at LHCb“).
A public lecture, “Exploring the Invisible Universe” by Nobel Laureate Takaaki Kajita, attracted more than 250 participants, which was complemented by a tour of the nuclear emulsion lab of Nagoya University to see state-of-the-art emulsion technology. The progress in this technology was clearly visible when Edison Shibuya and others recalled the early days of studying cosmic rays with emulsion chambers and Saavedra’s related pioneering contributions.
There were many discussions on future studies of relevance to cosmic-ray interactions and astroparticle physics. Hans Dembinski discussed prospects in the near and far future in collider experiments, including possible proton–oxygen runs at the LHC and a study of multi-particle production at a future circular collider. The cosmic-ray community is very enthusiastic about a future proton–oxygen run since, even with a short run of 100 million events, charged particle and pion spectra could be measured to an accuracy of 10% – a five-fold improvement over current model uncertainties that would bring us a crucial step closer to unveiling the cosmic accelerators of the highest energy particles in the universe.
The next ISVHECRI will be held in June 2020 at Ooty, the location of the RAPES air-shower experiment in India.