Cosmic Ray physics is one of the fundamental key issues and an essential tool of astroparticle physics that aims, in a unique way, to address many fundamental questions of the non-thermal Universe. Recently, Ultra-High Energy Cosmic Rays (UHECR) witnessed anisotropy thanks to the results obtained by the Pierre Auger Collaboration published in Science (2007). These results have opened a new window onto the Universe and have pointed out the physics potential of this field that can be achieved by an upgrade of the performance of current ground-based instruments or with new space-based missions, as the JEM-EUSO space telescope.
The Extreme-Universe Space Observatory (EUSO) project is a downward looking telescope, which will be located at the Japanese Experiment Module (JEM), on board the International Space Station (ISS) and called then JEM-EUSO. This challenging mission will search the full-sky for cosmic ray particles with energies greater than 7x1019eV, in the UHECR and Extremely High Energy Cosmic Rays (EHECR) domain, at the frontier of the known Universe. JEM-EUSO will work very much like the Pierre Auger Observatory in Argentina, which detects from ground fluorescent showers of secondary particles, produced by UHECR which traverse the Earth’s atmosphere followed by a final flash as the particle hit detectors on the Earth. JEM-EUSO will pioneer from space the observation of these extensive air showers (EAS). Towards the ZeV range
The main scientific goal of JEM-EUSO is to open the charged-particle astronomy channel in the EHECR domain by sampling huge statistics of more than 1000 events up to the ZeV scale in 3 to 5 years lifetime. This large number of events will allow the directional identification of individual sources and the determination of their spectra. The JEM-EUSO telescope can reconstruct the incoming direction of cosmic rays with accuracy better than several degrees. The observed geometrical area on ground is nearly a circle with roughly a 250 km radius and the monitored atmospheric volume is, assuming the 60-degree field of view about 1 Tera-ton while the target atmospheric volume for upward neutrino events can exceed 5 Tera-tons. This large volume makes the possibility of neutrino observation a highlight. Other objectives of the mission include the detection of photons at such extreme energies and the study of galactic and extragalactic magnetic fields. Recent observations suggest that about 95% of the Universe´s energy lies in the dark sector. This sector is comprised of dark matter, a form of non-luminous matter and dark energy whose origin and composition is unknown. Dark matter seems to make up 23% of the Universe and it possibly consists of new exotic particles that interact very weakly with ordinary matter. JEM-EUSO aims to address that issue searching for new exotic particles and will test Super Heavy Dark Matter (SHDM) models as well as relativity at the highest energies never detected so far.
| JEM-EUSO is a downward looking telescope project, which will be onboard the International Space Station (Credit JEM-EUSO collaboration).
The JEM-EUSO refractive telescope is an extremely fast, highly pixelated, large-aperture, super-wide Field-of-View (FoV ±30°) digital camera. It comprises two double-sided curved Fresnel lenses and a diffractive plane, to observe the time and space resolved atmospheric fluorescence tracks produced, in the near UV range (330-400 nm) by the extensive air showers, with 2.5 μs time resolution and about 0.75 km spatial resolution (0.1º). The focal surface of the JEM-EUSO telescope is formed by about 6,000 photomultipliers with nearly 200,000 pixels. The technological key issues of JEM-EUSO are mainly the implementation of the new lens material and an improved optical design, detectors with higher quantum efficiency and an improved algorithm for event trigger. The JEM-EUSO collaboration is presently an international joint effort of 12 countries (Japan, USA, France, Italy, Germany, Switzerland, Russia, Republic of Korea, Mexico, Spain, Poland and Slovakia) and about 200 researchers. It is being conducted by RIKEN and the Japan Aerospace eXploration Agency (JAXA). Europe, with a long-standing tradition in the previous EUSO plays a key role with Seven countries involved. JEM-EUSO is currently completing the Phase A/B of JAXA design study and it will be launched in 2013-2015 by the Japanese H-IIB rocket and conveyed to ISS by the transfer vehicle HTV. The overall estimated cost of the JEM-EUSO telescope is around 150 M€. Opening an ultra-high energy window on an unexplored Universe could reserve exciting surprises. Onboard ISS, JEM-EUSO will be ready for surprises at the ZeV scales. |
The atmosphere as a detector
 Before reaching the Earth’s surface, cosmic rays interact with the constituents of the atmosphere, changing their nature and energy. A large variety of secondary particles, which decay or make new collisions, is produced. So, a cosmic ray getting into the atmosphere gives birth to a particle shower that can be detected. The atmosphere plays then a crucial role in the detection of cosmic rays, which can be studied from the secondary particles they produce. | Submitted by Andrea Santangelo & María Dolores
Rodríguez Frías for the JEM-EUSO Collaboration. >> JEM-EUSO website |
Cosmic rays getting into the atmosphere give birth to a particle shower that can be detected by ground detectors… Or even by a space telescope! This is the challenge of JEM-EUSO...
