ICRC 2013: from Earth to the Galaxy and beyond

At the traditional dinner party they danced to samba music while holding caipirinhas. During the day, the more than 700 physicists who attended the 33rd Cosmic Ray Conference (ICRC 2013) in Rio de Janeiro listened carefully during the 400 scheduled talks in a variety of plenary and parallel sessions on 2–9 July. Instead of caipirinhas, they held laptops and notepads as they focused on the important findings and data presented at the first ICRC to be held in South America.

Organized under the auspices of the International Union of Pure and Applied Physics (IUPAP) and its C4 Commission on Cosmic Rays, ICRC 2013 was hosted by the Centro Brasileiro de Pesquisas Físicas – an institute of the ministry of science, technology and innovation – the Federal University of Rio de Janeiro and the Brazilian Physical Society. It was sponsored by the National Council for Scientific and Technological Development (CNPq), the Coordination for Improvement of Higher Education Personnel (CAPES) and the Research Support Foundation of the state of Rio de Janeiro (FAPERJ).

The location in South America was not the only “first”. The organization of the 33rd ICRC had a scientific programme committee for the first time, consisting of leading experts in solar and heliospheric physics, cosmic-ray physics, gamma-ray astronomy, neutrino astronomy and dark-matter physics. Also for the first time, ICRC included research on dark matter as a main branch of the programme. For this reason, ICRC 2013 adopted the subtitle “The Astroparticle Physics Conference”. This might also become the C4 Commission’s new name, as Johannes Knapp, the commission’s chair, announced during the closing session. The commission organized a poll during the nine days of the conference in which all registered participants could vote on changing the name from “Cosmic Rays” to “Astroparticle Physics”. The majority voted for the change and the commission is now consulting IUPAP on the matter. To maintain tradition, the conference’s main title – ICRC – will remain unchanged.

In neutrino research, the IceCube experiment has some thrilling results

ICRC 2013 was certainly a success. During the plenary session on results from the Pierre Auger Observatory, Antoine Letessier-Selvon of CNRS and Université Pierre et Marie Curie presented evidence of what could be called “the muon problem”. It concerns the conflict between the prediction from Monte Carlo simulations of the number of muons in the surface Cherenkov detectors and the value extracted from the experimental data, which is about a factor of 1.5 higher. Letessier-Selvon argued that a change in composition at higher energies is not sufficient to explain the discrepancy.

The ground-based gamma-ray experiments HESS, MAGIC and VERITAS have added new gamma-ray sources – both in the Galaxy and beyond it – to the catalogue, which now totals about 150 sources. Teams at the northern-hemisphere observatories reported flaring of the blazar Mkn 421 in April this year, while MAGIC registered another flare in November 2012, in IC 310 – an extra-galactic source that it had previously discovered. Miguel Mostafa of Colorado State University presented the results of the “first light” – in fact, gamma rays – in the High Altitude Water Cherenkov Observatory installed at an altitude of 4150 m in Mexico. It is designed to detect ultra-high-energy gamma rays and is sensitive to energies above 300 GeV. With approximately only one third of the detector in operation, the collaboration was still able to present their view of the Mkn 421 flare of April.

In neutrino research, the IceCube experiment has some thrilling results. Spencer Klein of the Lawrence Berkeley National Laboratory and the University of California, Berkeley presented the 28 events that were detected with energies above 50 TeV, which include the previously revealed events above 1 PeV (CERN Courier July/August 2013 p5). Klein also spoke of the observation of another very-high-energy event in the ongoing analysis of 2012 data – but its characteristics remain “top secret”.

Another highlight of ICRC 2013 was the presentations by Nobel laureate Sam Ting and the Alpha Magnetic Spectrometer (AMS) collaboration of the first results from two years of AMS-02 operation on the International Space Station (ISS). The main goal is to perform a high-precision, large-statistics and long-duration study of cosmic nuclei, elementary charged particles and gamma rays. At the conference the collaboration presented high-precision measurements of the fluxes, ratios and anisotropies of electrons and positrons, as well as first results on proton and helium fluxes (CERN Courier October 2013 p22).

Moving further out in space, Ed Stone from Caltech presented the saga of the Voyager 1 spacecraft, launched in 1977, which is now at the edge of the solar system. The data clearly show a “wall” characterizing the heliosheath. It is astonishing that Voyager 1 is still collecting data after all these years – with an on-board computer of the 1970s and a power source that is still very much alive having passed through the harsh environment of Jupiter and Saturn. Stone was seen not only by the conference participants but also by the 40 million viewers who watched an interview with him during a popular programme on Brazilian TV.

The parallel sessions included presentations on a plethora of new projects ranging from next-generation imaging air-Cherenkov telescopes, represented by the Cherenkov Telescope Array, to the Extreme Universe Space Observatory onboard the Japanese Experiment Module (JEM-EUSO). To be installed on the ISS, JEM-EUSO is designed to measure ultra-high-energy cosmic rays through the fluorescence of the extensive air showers that they produce – an expression of optimism in the future of the field.

The 34th ICRC meeting will be held at The Hague, the Netherlands, in July 2015 and will be followed two years later by the 35th meeting in Busan, Korea. Although there will be no samba or caipirinhas, there will surely be the same level of results and commitment from astroparticle physicists worldwide.