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\title{The Borexino experiment at the INFN- CNAF}

\author{Alessandra Carlotta Re$^1$\\ \small{on behalf of the BOREXINO collaboration}}
\address{$^1$ Universit\`{a} degli Studi di Milano e INFN Sezione di Milano, Milano, IT}
\ead{alessandra.re@mi.infn.it}

\begin{abstract}  %OK
Almost all the energy from the Sun is produced through sequences of nuclear reactions that convert hydrogen into helium. Five of these 
processes emit neutrinos and represent a unique probe of the Sun's internal working.
Borexino is a large volume liquid scintillator experiment designed for low energy neutrino detection, installed at the National 
Laboratory of Gran Sasso (Assergi, Italy) and operating since May 2007. 
Given the tiny cross-section of neutrino interactions with electrons ($\sigma ~ \approx 10^{-44}\,-\,10^{-45}~\mathrm{cm}^2$, for the
solar neutrino energy range), the Borexino expected rates are very small. Despite that, the exceptional levels of radiopurity made possible 
for Borexino to accomplish not only its primary goal but also to produce many other interesting results both within and beyond the Standard 
Model of particle physics, helping a better understanding of the neutrino's features
\end{abstract}
 
\section{The Borexino experiment} %OK
The Borexino experiment is located deep underground (3,800 meter water equivalent) in the Hall C of the National Laboratory of Gran Sasso (Assergi, Italy), and measures
solar neutrinos via their interactions with a target of 278 ton organic liquid scintillator. The ultrapure liquid scintillator is contained inside a very thin transparent nylon vessel of 8.5 m diameter. 

Solar neutrinos are detected by measuring the energy and position of electrons scattered by the neutrino-electron elastic interactions. 
The scintillator promptly converts the kinetic energy of the electrons by emitting photons, which are then detected and converted into electronic signals by 2212 photomultipliers (PMT) mounted on a concentric 13.7 m diameter stainless steel sphere.

The Borexino detector was designed exploiting the principle of graded shielding: an onion-like structure allows to shield from external radiations and from radiations produced in the external layers. The requirements on material radiopurity increase when moving to the innermost region of the detector.

Starting from 2007 and through years, the Borexino \cite{ref:BxLong} experiment has been measuring the fluxes of low-energy neutrinos (neutrinos with energy $&lt;3$ MeV), most notably those emitted in nuclear fusion reactions and $\beta$ decays along the pp-chain in the Sun. 
 

\section{The Borexino recent results} %OK
On January 2018, the Borexino collaboration released a detailed paper \cite{ref:BxMC} about the Monte Carlo (MC) simulation of its detector and the agreement of the MC output
with the detector's acquired data. The simulation accounts for absorption, reemission, and scattering of the optical photons, tracking them until they either are absorbed or reach the photocathode of one of the photomultiplier tubes. These simulations were used and still are used, to study and reproduce the energy response of the detector, its uniformity within the fiducial scintillator volume relevant to neutrino physics, and the time distribution of detected photons to better than 1\% between 100 keV and several MeV. This work has been foundamental to all the Borexino analysis so far done.

On October 2018, the collaboration published on Nature \cite{ref:BxNuSol} the latest solar neutrino result concerning a comprehensive measurement of all fluxes of the pp-chain solar neutrinos. This work is a milestone for solar neutrino physics since it provides the first, complete study of the solar pp-chain and of its different terminations in a single detector and with a uniform data analysis procedure. This study confirmed the nuclear origin of the solar power and provided the most complete real-time insight into the core of our Sun so far.

The Borexino analysis is now focused on the possibility to measure the interaction rates of the rare CNO solar neutrinos.


\section{The Borexino computing at CNAF} %OK
The INFN-CNAF currently hosts the whole Borexino data statistics and the users' area for physics studies. 

The Borexino data are classified into three types: 
\begin{itemize}
\item {\bf raw data~} Raw data are compressed binary files with a typical size of about 600 Mb corresponding to a data taking time of $\sim$6h. 
\item {\bf ROOT files~~~~} ROOT files are files containing the Borexino reconstructed events, each organized in a {\tt ROOT TTree}: their typical dimension is  $\sim$1Gb. 
\item {\bf DSTs~~~~~~~} DST files contain only a selection of events for the high level analyses.
\end{itemize}
 
Borexino standard data taking requires a disk space increase of about 10 Tb/year while a complete Monte Carlo simulation of both neutrino signals and backgrounds requires about 8 Tb/DAQ year.

The CNAF TAPE area also hosts a full backup of the Borexino rawdata.

Our dedicated front-end machine ({\tt ui-borexino.cr.cnaf.infn.it}) and pledged CPU resources (about 1500 HS06) are used by the Borexino collaboration for ROOT files production, Monte Carlo simulations, interactive and batch analysis jobs. 
Moreover, few times a year, an extraordinary peak usage (up to 3000 HS06 at least) is needed in order to perform a full reprocessing of the whole data statistics with updated versions of the reconstruction code and/or a massive Monte Carlo generation.

\section{Conclusions} %OK
Borexino has been, so far, the only experiment able to perform a real-time spectroscopy of neutrinos from almost all the nuclear reactions happening in the Sun. Near future goals are mainly focused around improving its current limit of the CNO neutrino flux and possibly measure it. While the amount of CPUs resources needed is expected to remain quite stable, during next years the Borexino collaboration will increase its disk space requests so to successfully complete its challenging and very rich physics program.

\section*{References}
\begin{thebibliography}{9}
\bibitem{ref:BxLong}  Bellini~G. {\it et al.} 2014~{\it Phys. Rev. D} {\bf 89} 112007.
\bibitem{ref:BxMC}    Agostini~M. {\it et al.} 2018~{\it Astropart. Phys.} {\bf 97} 136.
\bibitem{ref:BxNuSol} Agostini~M. {\it et al.} 2018~{\it Nature} {\bf 562} 505.
\end{thebibliography}
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