Abstract
Given the good performances in terms of geometrical acceptance and energy resolution, calorimeters are the best suited detectors to measure high energy cosmic rays directly in space. However, in order to exploit this potential, the design of calorimeters must be carefully optimized to take into account all limitations related to space missions, due mainly to the mass of the experimental apparatus. CaloCube is a three years R&D project, approved and financed by INFN in 2014, aiming to optimize the design of a space-borne calorimeter by the use of a cubic, homogeneous and isotropic geometry. In order to maximize detector performances with respect to the total mass of the apparatus, comparative studies on different scintillating materials, different sizes of crystals and different spacings among them have been performed making use of Monte Carlo simulations. In parallel to this activity, several prototypes instrumented with CsI:Tl cubic crystals have been constructed and tested with particle beams (muons, electrons, protons and ions). Both simulations and prototypes showed that the CaloCube design leads to a good particle energy resolution (< 2% for electromagnetic showers, < 40% for hadronic showers) and a good effective geometric factor (> 3:5 m2 sr for electromagnetic showers, > 2:5 m2 sr for hadronic showers). Thanks to these performances, in 5 years of operation it would be possible to measure the ux of electrons+positrons up to some tens of TeV and the uxes of protons and nuclei up to some units of PeV/nucleon, hence extending these measurements by at least one order of magnitude in energy compared to the experiments currently operating in space.
Highlights
IntroductionPrecise measurements of flux and composition of cosmic rays are needed to understand the mechanisms responsible for their production, acceleration and propagation
Precise measurements of flux and composition of cosmic rays are needed to understand the mechanisms responsible for their production, acceleration and propagation. These measurements can be performed directly in space or indirectly at ground. In the former case, the highest energy achievable is limited by the typical constraints in terms of mass (∼ 1 − 5 t) and life time (∼ 5 − 10 y) of a payload: being the cosmic rays flux very steep, it is difficult to collect enough statistics at high energy
It is possible to collect enough statistics up to the endpoint of the spectrum, but the properties of the cosmic rays must be reconstructed indirectly from the air showers detected at ground: because the hadronic interaction models used for this purpose have large systematics, these measurements of flux and, in particular, composition are affected by large uncertainties
Summary
Precise measurements of flux and composition of cosmic rays are needed to understand the mechanisms responsible for their production, acceleration and propagation. These measurements can be performed directly in space or indirectly at ground In the former case, the highest energy achievable is limited by the typical constraints in terms of mass (∼ 1 − 5 t) and life time (∼ 5 − 10 y) of a payload: being the cosmic rays flux very steep, it is difficult to collect enough statistics at high energy (this is for example the case of protons above the knee region, located between 1015 and 1016 eV). Assuming 5 years of operations, they must have a good energy resolution σE/E (< 2% for electromagnetic showers, < 40% for hadronic showers) and a good effective geometric factor Geff 1 (> 3.5 m2sr for electromagnetic showers, > 2.5 m2sr for hadronic showers)
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