The Joint Experiment Missions for Extreme Universe Observatory comprises a collection of complementary missions dedicated to pioneering technologies and techniques for a future space-based multi-messenger observatory which will have sufficient sensitivity and exposure to measure properties of extremely rare ultra-high energy (E>50 EeV) cosmic rays and very high energy (E>100 PeV) neutrinos. Here we describe a general-purpose software framework designed to facilitate detailed simulation and reconstruction of events observed by the various missions using both detection of fluorescence and Cherenkov light produced when cosmic ray or neutrino-induced extensive air showers traverse Earth's atmosphere. The software builds on a framework developed by the Pierre Auger Collaboration. We describe the techniques used to organize contributions from numerous collaborators, manage an abundance of configuration information, and provide simple access to time-dependent detector and atmospheric information. We also explain how we support a multitude of computing platforms, provide fast installation and maintain the broad testing coverage required for stability of the large and heterogeneous code base. We provide a few examples of simulated and reconstructed data gathered by some of the JEM-EUSO missions, including the EUSO-SPB2 instrument.

NA61/SHINE (SPS Heavy Ion and Neutrino Experiment) is a multi-purpose experimental facility to study hadron production in hadron-proton, hadron-nucleus and nucleus-nucleus collisions at the CERN Super Proton Synchrotron. It recorded the first physics data with hadron beams in 2009 and with ion beams (secondary 7Be beams) in 2011. NA61/SHINE has greatly profited from the long development of the CERN proton and ion sources and the accelerator chain as well as the H2 beamline of the CERN North Area. The latter has recently been modified to also serve as a fragment separator as needed to produce the Be beams for NA61/SHINE. Numerous components of the NA61/SHINE set-up were inherited from its predecessors, in particular, the last one, the NA49 experiment. Important new detectors and upgrades of the legacy equipment were introduced by the NA61/SHINE Collaboration. This paper describes the state of the NA61/SHINE facility — the beams and the detector system — before the CERN Long Shutdown I, which started in March 2013.

The steeply falling end of the cosmic ray spectrum now extends up to ≈ 3 × 10 eV (see Ref. [1] for a recent survey), three orders of magnitude higher than the highest energy achieved by hadron colliders. Direct measurements using sophisticated equipment on satellites or high altitude balloons are limited in detector area and in exposure time. Ground-based detectors with large apertures make such a low flux detectable after a magnification effect in the upper atmosphere. Namely, the incident cosmic radiation interacts with atomic nuclei of the air molecules and produces extensive air showers which spread out over large areas. This indirect method of detection bears a number of serious difficulties in the interpretation of the recorded data. In particular, since many variables are involved the processes describing the shower development are intrinsically complicated, numerical simulation of the giant cascades has to be performed. The most important source of fluctuations in Monte Carlo simulations such as corsika [2] and aires [3] are the depth and characteristic of the first few inter-

Water Cerenkov detectors have proved to be superb devices for the study of cosmic air showers [1], and will constitute major components of future experiments such as the Pierre Auger Observatory [2]. Monte Carlo simulation of the response of such detectors to signal and background processes is crucial for proper interpretation of the data and to aid in development of reconstruction and analysis algorithms. To address these needs, experiments have prepared dedicated detector simulations [3]. There may be advantages, however, in exploiting some of the efforts which the High Energy Physics (HEP) community has directed at this problem. The geant3 package [4], for example, was developed in order to provide HEP experiments with generic tools for simulating the passage of particles through matter, but it also found substantial usage in the medical and biological sciences and in astronautics, and in fact has been studied for use in simulating water Cerenkov detectors for the Auger experiment [5]. In 1996 CERN initiated the geant4 project [6] with the goal of reproducing all the functionality of geant3 using an Object Oriented approach, as well as addressing some of the shortfalls of the older program. We have begun investigating the suitability of geant4 for the problem of simulating water Cerenkov detec-

The steeply falling end of the cosmic ray spectrum now extends up to ≈ 3 × 10 eV (see Ref. [1] for a recent survey), three orders of magnitude higher than the highest energy achieved by hadron colliders. Direct measurements using sophisticated equipment on satellites or high altitude balloons are limited in detector area and in exposure time. Ground-based detectors with large apertures make such a low flux detectable after a magnification effect in the upper atmosphere. Namely, the incident cosmic radiation interacts with atomic nuclei of the air molecules and produces extensive air showers which spread out over large areas. This indirect method of detection bears a number of serious difficulties in the interpretation of the recorded data. In particular, since many variables are involved the processes describing the shower development are intrinsically complicated, numerical simulation of the giant cascades has to be performed. The most important source of fluctuations in Monte Carlo simulations such as corsika [2] and aires [3] are the depth and characteristic of the first few inter-