Event reconstruction for KM3NeT/ORCA using convolutional neural networks

The KM3NeT research infrastructure is currently under construction at two locations in the Mediterranean Sea. The KM3NeT/ORCA water-Cherenkov neutrino detector off the French coast will instrument several megatons of seawater with photosensors. Its main objective is the determination of the neutrino mass ordering. This work aims at demonstrating the general applicability of deep convolutional neural networks to neutrino telescopes, using simulated datasets for the KM3NeT/ORCA detector as an example. To this end, the networks are employed to achieve reconstruction and classification tasks that constitute an alternative to the analysis pipeline presented for KM3NeT/ORCA in the KM3NeT Letter of Intent. They are used to infer event reconstruction estimates for the energy, the direction, and the interaction point of incident neutrinos. The spatial distribution of Cherenkov light generated by charged particles induced in neutrino interactions is classified as shower- or track-like, and the main background processes associated with the detection of atmospheric neutrinos are recognized. Performance comparisons to machine-learning classification and maximum-likelihood reconstruction algorithms previously developed for KM3NeT/ORCA are provided. It is shown that this application of deep convolutional neural networks to simulated datasets for a large-volume neutrino telescope yields competitive reconstruction results and performance improvements with respect to classical approaches

Event reconstruction for KM3NeT/ORCA using convolutional neural networks

The KM3NeT research infrastructure is currently under construction at two locations in the Mediterranean Sea. The KM3NeT/ORCA water-Cherenkov neutrino de tector off the French coast will instrument several megatons of seawater with photosensors. Its main objective is the determination of the neutrino mass ordering. This work aims at demonstrating the general applicability of deep convolutional neural networks to neutrino telescopes, using simulated datasets for the KM3NeT/ORCA detector as an example. To this end, the networks are employed to achieve reconstruction and classification tasks that constitute an alternative to the analysis pipeline presented for KM3NeT/ORCA in the KM3NeT Letter of Intent. They are used to infer event reconstruction estimates for the energy, the direction, and the interaction point of incident neutrinos. The spatial distribution of Cherenkov light generated by charged particles induced in neutrino interactions is classified as shower-or track-like, and the main background processes associated with the detection of atmospheric neutrinos are recognized. Performance comparisons to machine-learning classification and maximum-likelihood reconstruction algorithms previously developed for KM3NeT/ORCA are provided. It is shown that this application of deep convolutional neural networks to simulated datasets for a large-volume neutrino telescope yields competitive reconstruction results and performance improvements with respect to classical approaches

Study of the discovery potential of the KM3NeT/ARCA neutrino telescope to the diffuse astrophysical high energy neutrino flux

Even though Cosmic Rays were discovered more than a century ago, the acceleration mechanisms of protons and heavier nuclei to ultra high energies still remain unknown. Being charged they are deflected by magnetic fields so they can not reveal the astrophysical objects responsible for their acceleration. Nevertheless, at the astrophysical objects where cosmic rays are accelerated, neutrinos are also produced. Neutrinos, being neutral, are not deflected by magnetic fields and they are not significantly absorbed by the interstellar medium, so, when detected, they can point back to their production sites. Neutrino telescopes are being deployed in the sea, in lakes and in the ice of Antarctica. They instrument large volumes of medium (water or ice) and they detect neutrinos indirectly by detecting Cherenkov light produced by neutrino-induced charged particles.KM3NeT is a collaboration building the next generation neutrino telescopes in the Mediterranean Sea. Currently two detectors are being deployed by KM3NeT; the ORCA - Oscillation Research with Cosmics in the Abyss detector, which aims to study the fundamental properties of neutrinos as well as the ARCA - Astroparticle Research with Cosmics in the Abyss telescope. The main science objectives of the ARCA telescope are the detection of neutrinos from astrophysical sources and the measurement of the diffuse astrophysical high energy flux. In this thesis a study of the discovery potential of the KM3NeT/ARCA telescope to the diffuse astrophysical high energy neutrino flux using High Energy Starting Events (HESE) is presented. The use of HESE comprises a novel approach for the KM3NeT collaboration. In Chapter 1 the production mechanisms of Cosmic Rays and astrophysical neutrinos are described. The detection principle of neutrino telescopes, the background for underwater neutrino telescopes as well as the major existing neutrino telescopes are presented in Chapter 2. The KM3NeT collaboration is described in Chapter 3 as well as the KM3NeT detectors. In Chapter 4 GRBNeT - a project that designed, built and successfully deployed an autonomous prototype neutrino detector is discussed. In the following chapter the tools used in KM3NeT to perform Monte Carlo simulations of the detector response to signal and background events as well as the reconstruction tools are detailed. CORSIKA program, which is the most widely used tool to simulate atmospheric showers, has been used in order to create a sample of background atmospheric events for the ARCA telescope. These efforts are detailed in Chapter 6. A novel tool, MAMBA rejection, created in order to select High Energy Starting Track events inside ARCA telescope and reject those track events that enter the detector, is described in Chapter 7. Moreover a sensitivity and a discovery potential analysis of ARCA to the diffuse astrophysical high energy neutrino flux using High Energy Starting Track events is described. Furthermore, a sample of background atmospheric events simulated with CORSIKA has been used to demonstrate the power of the self-veto effect (the rejection of atmospheric neutrinos, accompanied by muons created at the same atmospheric shower, interacting inside the detector by identifying the muons entering the detector). In Chapter 8 a tool designed to differentiate shower-like from track-like events is detailed. Also, an analysis of the discovery potential of ARCA to the diffuse astrophysical high energy neutrino flux using only shower-like events selected by that tool is presented. The tools described in the previous chapters are combined in order to create a sample of High Energy Starting Events as described in Chapter 9. The discovery potential of ARCA to the diffuse astrophysical high energy neutrino flux using High Energy Starting Events is presented. ARCA is expected to make a 5σ discovery of the diffuse astrophysical high energy neutrino flux with a probability of 50% and 90% in less than 0.5 and approximately 0.8 years, respectively, using High Energy Starting Events.Οι κοσμικές ακτίνες παρατηρήθηκαν για πρώτη φορά πριν από έναν αιώνα, ακόμα όμως παραμένουν ασαφείς οι πηγές και ο μηχανισμός επιτάχυνσή τους, διότι σκεδάζονται από τα μαγνητικά πεδία των γαλαξιών και χάνονται οι πληροφορίες σχετικά με την προέλευσή τους. Παρόλα αυτά αναμένεται ότι στα αστροφυσικά αντικείμενα όπου οι κοσμικές ακτίνες επιταχύνονται σε υπέρ-υψηλές ενέργειες παράγονται και νετρίνο υψηλής ενέργειας. Τα νετρίνο δεν έχουν ηλεκτρικό φορτίο με αποτέλεσμα να μην σκεδάζονται από τα μαγνητικά πεδία και επειδή αλληλεπιδρούν ασθενώς με την ύλη πρακτικά δεν απορροφώνται. Η ανίχνευση, λοιπόν, νετρίνο αστροφυσικής προέλευσης, μπορεί να αποκαλύψει τα αστροφυσικά αντικείμενα όπου αυτά παράγονται και τα οποία είναι υπεύθυνα για την επιτάχυνση των κοσμικών ακτίνων. Συνεπώς τα νετρίνο αποτελούν μοναδικούς φορείς αστροφυσικής πληροφορίας. Τα τηλεσκόπια νετρίνο κατασκευάζονται στα βάθη θαλασσών, λιμνών ή στους πάγους της Ανταρκτικής, καταλαμβάνουν πολύ μεγάλους όγκους και ανιχνεύουν τα νετρίνο έμμεσα, καθώς ανιχνεύουν την ακτινοβολία Cherenkov που εκπέμπουν τα φορτισμένα σωματίδια τα οποία παράγονται κατά την αλληλεπίδραση των νετρίνο με την ύλη. Το πείραμα KM3NeT κατασκευάζει ανιχνευτές νετρίνο νέας γενιάς. Υπό τη σκέπη του πειράματος αυτού ποντίζονται δύο ανιχνευτές νετρίνο στα βάθη της Μεσογείου θάλασσας, ο ανιχνευτής ORCA - Oscillation Research with Cosmics in the Abyss του οποίου ο κύριος επιστημονικός στόχος είναι η μελέτη των βασικών σωματιδιακών ιδιοτήτων των νετρίνο και το τηλεσκόπιο νετρίνο ARCA - Astroparticle Research with Cosmics in the Abyss. Οι κύριοι επιστημονικοί στόχοι του τηλεσκοπίου ARCA είναι η ανίχνευση νετρίνο από αστροφυσικές πηγές καθώς και η μελέτη της διάχυτης αστροφυσικής ροής νετρίνο υψηλής ενέργειας. Στην παρούσα διατριβή παρουσιάζεται η μελέτη της δυνατότητας ανακάλυψης της διάχυτης αστροφυσικής ροής νετρίνο υψηλής ενέργειας με το τηλεσκόπιο KM3NeT/ARCA, χρησιμοποιώντας γεγονότα υψηλής ενέργειας που αλληλεπιδρούν εντός του ανιχνευτή. Η χρήση τέτοιων γεγονότων αποτελεί μια καινοτόμο προσέγγιση για το πείραμα KM3NeT. Η παρούσα διατριβή αποτελείται από εννέα κεφάλαια. Στο Κεφάλαιο 1 παρουσιάζονται οι μηχανισμοί επιτάχυνσης των κοσμικών ακτίνων και τα αστροφυσικά αντικείμενα που αναμένεται να παράγουν νετρίνο υψηλής ενέργειας. Στην συνέχεια στο Κεφάλαιο 2 περιγράφεται η αρχή ανίχνευσης νετρίνο υψηλής ενέργειας, το υπόβαθρο των υποθαλάσσιων τηλεσκοπίων νετρίνο καθώς και τα σημαντικότερα εν λειτουργία τηλεσκόπια νετρίνο. Το πείραμα KM3NeT και οι ανιχνευτές νετρίνο ORCA και ARCA παρουσιάζονται στο Κεφάλαιο 3. Στο Κεφάλαιο 4 περιγράφονται οι δραστηριότητες του ερευνητικού έργου GRBNeT στα πλαίσια του οποίου σχεδιάστηκε, κατασκευάστηκε και ποντίστηκε επιτυχώς αυτόνομος ανιχνευτής νετρίνο. Στο επόμενο κεφάλαιο παρουσιάζονται τα εργαλεία λογισμικού που χρησιμοποιούνται στο πείραμα KM3NeT για την προσομοίωση της απόκρισης του τηλεσκοπίου νετρίνο ARCA σε γεγονότα σήματος και υποβάθρου. Για την προσομοίωση ατμοσφαιρικών καταιονισμών σωματιδίων το πιο διαδεδομένο πρόγραμμα είναι το πρόγραμμα CORSIKA το οποίο χρησιμοποιήθηκε για την προσομοίωση γεγονότων υποβάθρου για το τηλεσκόπιο ARCA. Στο Κεφάλαιο 6 αναλύονται αυτές οι δραστηριότητες. Στο Κεφάλαιο 7 περιγράφεται ένα καινοτόμο εργαλείο, το MAMBA rejection, το οποίο δημιουργήθηκε για την αξιόπιστη επιλογή γεγονότων νετρίνο με την υπογραφή τροχιάς που αλληλεπιδρούν εντός του όγκου του τηλεσκοπίου ARCA και για την ταυτόχρονη απόρριψη γεγονότων τροχιάς που εισέρχονται σε αυτό. Επίσης αναπτύσσεται η μελέτη της ευαισθησίας του τηλεσκοπίου και της ικανότητας ανακάλυψης της διάχυτης ροής νετρίνο υψηλής ενέργειας αστροφυσικής προέλευσης, χρησιμοποιώντας γεγονότα τροχιάς που αλληλεπιδρούν μέσα στον όγκο του. Τέλος χρησιμοποιώντας προσομοιωμένα γεγονότα ατμοσφαιρικών καταιγισμών με το πρόγραμμα CORSIKA, καταδεικνύεται η αξία του self-veto effect, δηλαδή της απόρριψης ατμοσφαιρικών νετρίνο, τα οποία συνοδεύονται από ατμοσφαιρικά μιόνια που δημιουργήθηκαν στον ίδιο ατμοσφαιρικό καταιονισμό, και τα οποία αλληλεπιδρούν μέσα στον όγκο του ανιχνευτή λόγω της ανίχνευσης των εισερχομένων μιονίων. Στη συνέχεια, στο Κεφάλαιο 8, αναπτύσσεται άλλη μια καινοτόμος μέθοδος η οποία αναπτύχθηκε για την επιλογή των γεγονότων καταιγισμού και τον διαχωρισμό τους από τα γεγονότα τροχιάς. Επίσης αναλύεται και η μελέτη της ικανότητας ανακάλυψης της διάχυτης ροής νετρίνο υψηλής ενέργειας αστροφυσικής προέλευσης από το τηλεσκόπιο ARCA χρησιμοποιώντας μόνο γεγονότα καταιγισμού επιλεγέντα με την προαναφερθείσα μέθοδο. Τα εργαλεία που παρουσιάστηκαν στα δυο προηγούμενα κεφάλαια μπορούν να συνδυαστούν με αποτέλεσμα την επιλογή γεγονότων υψηλής ενέργειας που αλληλεπιδρούν μέσα στον όγκο του τηλεσκοπίου ARCA. Στο Κεφάλαιο 9 παρουσιάζεται η εν λόγω ανάλυση καθώς και η μελέτη της ικανότητας ανακάλυψης της διάχυτης ροής νετρίνο υψηλής ενέργειας αστροφυσικής προέλευσης από το τηλεσκοπίου ARCA χρησιμοποιώντας αυτά τα γεγονότα. Το τηλεσκόπιο ARCA αναμένεται να προβεί σε ανακάλυψη με επίπεδο σημαντικότητας 5σ με πιθανότητα 50% και 90% της διάχυτης ροής νετρίνο υψηλής ενέργειας αστροφυσικής προέλευσης σε λιγότερο από 0.5 χρόνια λειτουργίας και σε περίπου 0.8 λειτουργίας αντιστοίχως, γεγονότα υψηλής ενέργειας που αλληλεπιδρούν μέσα στον όγκο του. Τέλος, το Κεφάλαιο 9 αποτελεί την κατακλείδα της παρούσας διδακτορικής διατριβής

Knowledge and Technology Transfer in KM3NeT

The status of the construction of the KM3NeT detector components and the experience gained from the detector units deployed underpin the dissemination of innovative technological solutions to industry, Institutions and other potentially interested parties. KM3NeT is now entering a phase during which the design of the detector elements is being finalized and testing procedures for controlling the quality of the different components are settled. In addition, a few KM3NeT detection units have been deployed successfully and many more are coming, data have been recorded and are currently being analysed. The maturity and scalability of the technological solutions developed or modified by KM3NeT has been demonstrated and therefore justifies their exposure to relevant technology developers or users

Analysis of High Energy Starting Events with the KM3NeT/ARCA detector

KM3NeT is a research infrastructure housing the next generation neutrino detectors in the depths of the Mediterranean Sea. The ARCA detector, which is currently under construction, is optimized for neutrino searches from astrophysical sources as well as measurements of the diffuse high energy astrophysical flux. The unambiguous detection of neutrinos of extraterrestrial origin by IceCube has led to the first measurement of a high energy astrophysical neutrino flux. The cutting-edge technology used for the design and construction of KM3NeT Digital Optical Modules along with the properties of sea water allow for a measurement of the neutrino direction with an unpresidented resolution for both track and cascade events. Taking advantage of this angular resolution a method to differentiate track and shower events and a method to reject the atmospheric muon background from track-like events were developed and combined to select a sample of high energy starting events. An analysis for the discovery potential of KM3NeT/ARCA for a diffuse astrophysical neutrino flux using these events is presented

Analysis of High Energy Starting Events with the KM3NeT/ARCA detector

KM3NeT is a research infrastructure housing the next generation neutrino detectors in the depths of the Mediterranean Sea. The ARCA detector, which is currently under construction, is optimized for neutrino searches from astrophysical sources as well as measurements of the diffuse high energy astrophysical flux. The unambiguous detection of neutrinos of extraterrestrial origin by IceCube has led to the first measurement of a high energy astrophysical neutrino flux. The cutting-edge technology used for the design and construction of KM3NeT Digital Optical Modules along with the properties of sea water allow for a measurement of the neutrino direction with an unpresidented resolution for both track and cascade events. Taking advantage of this angular resolution a method to differentiate track and shower events and a method to reject the atmospheric muon background from track-like events were developed and combined to select a sample of high energy starting events. An analysis for the discovery potential of KM3NeT/ARCA for a diffuse astrophysical neutrino flux using these events is presented

Energy reconstruction of high energy muon and neutrino events in KM3NeT

KM3NeT will be a European deep-sea infrastructure of neutrino telescopes covering a volume of several cubic kilometers in the Mediterranean Sea aiming to search for high energy neutrinos from galactic and extragalactic sources. This analysis focuses on muons coming from neutrino charged-current interactions. In large water Cherenkov detectors the reconstructed muon is used to approximate the neutrino direction and energy, thus providing information on the astrophysical neutrino source. Muon energy estimation is also critical for the differentiation of neutrinos originating from astrophysical sources from neutrinos generated in the atmosphere which constitute the detector background. We describe a method to determine the muon and neutrino energy employing a Neural Network. An energy resolution of approximately 0.27 has been achieved for muons at the TeV range

Energy reconstruction of high energy muon and neutrino events in KM3NeT

KM3NeT will be a European deep-sea infrastructure of neutrino telescopes covering a volume of several cubic kilometers in the Mediterranean Sea aiming to search for high energy neutrinos from galactic and extragalactic sources. This analysis focuses on muons coming from neutrino charged-current interactions. In large water Cherenkov detectors the reconstructed muon is used to approximate the neutrino direction and energy, thus providing information on the astrophysical neutrino source. Muon energy estimation is also critical for the differentiation of neutrinos originating from astrophysical sources from neutrinos generated in the atmosphere which constitute the detector background. We describe a method to determine the muon and neutrino energy employing a Neural Network. An energy resolution of approximately 0.27 has been achieved for muons at the TeV range

KM3NeT front-end and readout electronics system: hardware, firmware, and software

he KM3NeT research infrastructure being built at the bottom of the Mediterranean Sea will host water-Cherenkov telescopes for the detection of cosmic neutrinos. The neutrino telescopes will consist of large volume three-dimensional grids of optical modules to detect the Cherenkov light from charged particles produced by neutrino-induced interactions. Each optical module houses 31 3-in. photomultiplier tubes, instrumentation for calibration of the photomultiplier signal and positioning of the optical module, and all associated electronics boards. By design, the total electrical power consumption of an optical module has been capped at seven Watts. We present an overview of the front-end and readout electronics system inside the optical module, which has been designed for a 1-ns synchronization between the clocks of all optical modules in the grid during a life time of at least 20 years