The CSES space mission, originated from an international collaboration between Italy and China, aims at monitoring the perturbations induced by electromagnetic emissions in the ionosphere, magnetosphere and Van Allen Radiation belts and investigating possible correlations with seismic events. More in general, CSES mission will investigate the structure and the dynamic of the topside ionosphere, the coupling mechanisms with the lower and higher plasma layers and the temporal variations of the geomagnetic field, in quiet and disturbed conditions. Data collected by the mission will also allow studying solar-terrestrial interactions and phenomena of solar physics, namely Coronal Mass Ejections (CMEs), solar flares and cosmic ray solar modulation. CSES satellite has been launched on February 2nd, 2018. Expected lifetime is 5 years.
\end{abstract}
\section{The Scientific Objectives}
The lithosphere-atmosphere-ionosphere coupling is a complex subject involving many physical effects and interactions that occur from the Earth surface up to the magnetosphere. The investigation of such coupling mechanisms - and in particular of the, partially unknown, behavior of the iono-magnetosphere transition region - is of fundamental importance for Earth remote sensing, monitoring of the near-Earth electromagnetic environment and studying of natural hazards. A great part of these effects is caused by natural non-seismic and anthropogenic electromagnetic emissions, but of particular relevance are the electromagnetic disturbances associated with the seismic activity that can produce ionospheric perturbations as well as the precipitation of particles from the Van Allen belts, observed before, during and after earthquakes of medium and strong magnitude. All of these phenomena must be distinguished from those induced by sources external to the geomagnetic cavity and by atmospheric events. In fact, an important role in controlling the dynamic of the topside ionosphere is played by the Sun – that generates (regular and irregular) variations of the lithosphere-ionosphere-magnetosphere parameters by impulsive events as solar Coronal Mass Ejections and Solar Flares – as well as by tropospheric activity (lightning, TLE, etc.). More info can be found in \cite{web}.
\section{High Energy Particle Detector}
The High-Energy Particle Detector (HEPD), developed by the INFN, detects electrons, protons and light nuclei. The main objective is to measure the increase of the electron and proton fluxes due to short-time perturbations of the radiation belts caused by solar, terrestrial and anthropic phenomena. The energy range explored is 3 - 100 MeV for electrons and 30 - 200 MeV for protons.
The instrument consists of several detectors. Two planes of double-side silicon microstrip sensors placed on the top of the instrument provide the direction of the incident particle. Just below, two layers of plastic scintillators, one thin segmented, give the trigger; they are followed by a calorimeter, constituted by other 16 scintillators and a layer of LYSO sensors. A scintillator veto system completes the instrument.
\section{HEPD Data}
The reconstruction occurs in three phases, which determine three different data formats, namely 0, 1 and 2, with increasing degree of abstraction. This structure is reflected on the data-persistency format, as well as on the software design. Raw data as downlinked from the CSES. They include ADC counts from the silicon strip, detector, from trigger scintillators, from energy scintillators and from LYSO crystals. ADC counts from lateral veto are also there, together with other very low-level information. Data are usually stored in ROOT format. Level 1 data contain all detector responses after calibration and equalization. The tracker response is clustered (if not already in this format at level0) and corrected for the signal integration time. All scintillator responses are calibrated and equalized. Information on the event itself like time, trigger flags, dead/alive time, etc… are directly inherited from level 0. Data are usually stored in ROOT format. Level 2 data contain higher level information, used to compute final data products. Currently the data are transferred from China as soon as they are downlinked from the CSES satellite and are processed at a dedicated facility at ASI Space Science Data Center (ASI-SSDC \cite{ssdc}) and then distributed to the analysis sites includind CNAF.
\section{HEPD Data Analysis at CNAF}
Level2 data of the HEPD detector are currently produced daily in ROOT format from the raw files. Once a week they are transferred at CNAF, using gfal-tools for the analysis team to be used. Raw data are transfered also to the CNAF facility on weekly basis and will be transferred to the tape storage. Most of the data analysis software and tools have been developed to be used at CNAF. Geant4 MC simulations are currently ran at CNAF by the collaboration, the facility proved to be crucial to perform, computational intensive, optical photons simulations needed to simulate the light yield of the plastic scintillators of the detector. Most of the software is written in C++/ROOT while several attempts to use Machine Learning and Neural Networks tecniques are pushing the collaboration to use more frequently Python for the analysis.
\section*{References}
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%\bibitem{iopartnum} IOP Publishing is to grateful Mark A Caprio, Center for Theoretical Physics, Yale University, for permission to include the {\tt iopart-num} \BibTeX package (version 2.0, December 21, 2006) with this documentation. Updates and new releases of {\tt iopart-num} can be found on \verb"www.ctan.org" (CTAN).
