Periodic Reporting for period 1 - LEANOR (Detecting Low-Energy Astrophysical Neutrinos with KM3NeT/ORCA: the Transient Neutrino Sky at the GeV Scale)
Período documentado: 2019-10-08 hasta 2021-10-07
LEANOR takes place of multi-messenger astronomy (MMA), a new, multidisciplinary approach, which combines electromagnetic observations, neutrinos, and gravitational waves in view of understanding the most energetic phenomena in our Universe. While astrophysical sources have been studied using light for centuries, the possibility to observe them through different messengers has been made possible in the past 10 years with the first observation of high-energy astrophysical (HE) neutrinos in IceCube and the first detection of gravitational waves by LIGO and Virgo.
Neutrinos play a special role in MMA: being neutral and weakly interacting particles, they can travel over cosmological distances, without being deflected by magnetic fields nor absorbed by matter and radiation. The unique scientific value of measuring cosmic neutrinos has motivated the advent of neutrino telescopes in the last decade. These telescopes challenge the smallness of the interaction rates through the instrumentation of large volumes to detect the Cherenkov light emitted by secondary particles produced in neutrino interactions with the water or the ice. The largest operating neutrino telescope, IceCube, is a 3D matrix of sensors deployed over a volume of 1 km^3 deep in the ice of the South Pole. The next-generation detector of comparable size, KM3NeT, has started construction in the Mediterranean Sea.
Large neutrino telescopes have been working towards the identification of the astrophysical sources producing high-energy astrophysical neutrinos. While recent multi-messenger observations suggest that blazars may be the first identified sources of high-energy neutrinos, other popular candidates are gamma-ray bursts (GRBs), the brightest electromagnetic events observed in the Universe. The observation of a short GRB in coincidence with the gravitational wave event GW170817 confirmed the hypothesis that such events are produced by binary neutron star mergers. The joint observation of a neutrino signal would be another breakthrough. So far, none of the neutrino searches revealed a significant signal.
HE neutrino telescopes are optimized for the TeV-PeV range. At lower energies, neutrino experiments have focused on the characterization of the atmospheric neutrino flux. The GeV energy domain remained poorly explored in terms of astrophysical observations, but as astrophysical neutrino fluxes typically exhibit a power-law decrease with energy, one can expect that neutrino telescopes sensitive to such low energies (LE) could allow us to probe larger neutrino fluxes and possibly identify new astrophysical neutrino sources!
ORCA is the low-energy branch of KM3NeT. It is optimized for the detection of neutrinos in the 5 – 100 GeV range, mainly focusing on fundamental neutrino physics. The ORCA digital optical modules (DOMs) rely on the innovative KM3NeT design featuring 31 small photosensors in one glass sphere. The first ORCA detection unit (DU), a flexible line about 350m high and supporting 18 DOMs equally spaced by 9m, has been installed in September 2017 offshore Toulon, France. In June 2022, 10 DUs have been deployed on the ORCA site.
LEANOR proposed to enlarge the science scope of ORCA by turning it into a GeV neutrino telescope and seized this experimental opportunity to develop an innovative, promising and cost-effective way to observe astrophysical GeV neutrinos, with two main objectives:
-develop the potential of ORCA to detect LE astrophysical neutrinos: LEANOR could not only demonstrate the feasibility of astrophysical neutrinos searches with ORCA in the GeV range, but also contributed to the improvement of astrophysical neutrino detection at lower (MeV) and higher (GeV-TeV) energies!
-promote low-energy neutrinos as new promising messengers to study the Extreme Universe: LEANOR led to the first constraints on the GeV neutrino flux using IceCube for gravitational wave candidates detected by LIGO and Virgo. LEANOR also led to the development of multi-detector techniques that significantly enhance the potential of low-energy astrophysical neutrino detection.
Neutrinos play a special role in MMA: being neutral and weakly interacting particles, they can travel over cosmological distances, without being deflected by magnetic fields nor absorbed by matter and radiation. The unique scientific value of measuring cosmic neutrinos has motivated the advent of neutrino telescopes in the last decade. These telescopes challenge the smallness of the interaction rates through the instrumentation of large volumes to detect the Cherenkov light emitted by secondary particles produced in neutrino interactions with the water or the ice. The largest operating neutrino telescope, IceCube, is a 3D matrix of sensors deployed over a volume of 1 km^3 deep in the ice of the South Pole. The next-generation detector of comparable size, KM3NeT, has started construction in the Mediterranean Sea.
Large neutrino telescopes have been working towards the identification of the astrophysical sources producing high-energy astrophysical neutrinos. While recent multi-messenger observations suggest that blazars may be the first identified sources of high-energy neutrinos, other popular candidates are gamma-ray bursts (GRBs), the brightest electromagnetic events observed in the Universe. The observation of a short GRB in coincidence with the gravitational wave event GW170817 confirmed the hypothesis that such events are produced by binary neutron star mergers. The joint observation of a neutrino signal would be another breakthrough. So far, none of the neutrino searches revealed a significant signal.
HE neutrino telescopes are optimized for the TeV-PeV range. At lower energies, neutrino experiments have focused on the characterization of the atmospheric neutrino flux. The GeV energy domain remained poorly explored in terms of astrophysical observations, but as astrophysical neutrino fluxes typically exhibit a power-law decrease with energy, one can expect that neutrino telescopes sensitive to such low energies (LE) could allow us to probe larger neutrino fluxes and possibly identify new astrophysical neutrino sources!
ORCA is the low-energy branch of KM3NeT. It is optimized for the detection of neutrinos in the 5 – 100 GeV range, mainly focusing on fundamental neutrino physics. The ORCA digital optical modules (DOMs) rely on the innovative KM3NeT design featuring 31 small photosensors in one glass sphere. The first ORCA detection unit (DU), a flexible line about 350m high and supporting 18 DOMs equally spaced by 9m, has been installed in September 2017 offshore Toulon, France. In June 2022, 10 DUs have been deployed on the ORCA site.
LEANOR proposed to enlarge the science scope of ORCA by turning it into a GeV neutrino telescope and seized this experimental opportunity to develop an innovative, promising and cost-effective way to observe astrophysical GeV neutrinos, with two main objectives:
-develop the potential of ORCA to detect LE astrophysical neutrinos: LEANOR could not only demonstrate the feasibility of astrophysical neutrinos searches with ORCA in the GeV range, but also contributed to the improvement of astrophysical neutrino detection at lower (MeV) and higher (GeV-TeV) energies!
-promote low-energy neutrinos as new promising messengers to study the Extreme Universe: LEANOR led to the first constraints on the GeV neutrino flux using IceCube for gravitational wave candidates detected by LIGO and Virgo. LEANOR also led to the development of multi-detector techniques that significantly enhance the potential of low-energy astrophysical neutrino detection.
With LEANOR, Gwenhael De Wasseige explored the potential for LE neutrino detection in KM3NeT. A major showstopper to achieve this goal is the presence of bioluminescent species at the bottom of the Mediterranean. She used data science to identify the different components of the environmental noise (no, not all the fishes emit light in the same way!). She was able to isolate the signal produced by LE neutrino interactions from that of the environment, both in the GeV and MeV ranges. The results were presented during VLVnT2021 conference. She also contributed to develop searches targeting GeV-TeV astrophysical neutrinos in KM3NeT. As ORCA was still small during her MSCA, Gwenhael also used IceCube to search for a LE neutrino counterpart from gravitational wave events detected by LIGO and Virgo, leading to the first constraints in this energy range derived with IceCube. The results were described in a paper submitted to PRD.
Despite COVID, LEANOR could significantly improve the potential of KM3NeT to detect LE neutrinos, and already explored this energy range using IceCube.
LEANOR also made Gwenhael realized that the most promising approach to explore the Universe with LE neutrinos is to combine different detectors. She developed novel approaches enhancing the scientific outputs for a variety of transient sources. These results were presented during VLVnT2021.
Despite COVID, LEANOR could significantly improve the potential of KM3NeT to detect LE neutrinos, and already explored this energy range using IceCube.
LEANOR also made Gwenhael realized that the most promising approach to explore the Universe with LE neutrinos is to combine different detectors. She developed novel approaches enhancing the scientific outputs for a variety of transient sources. These results were presented during VLVnT2021.
Despite COVID, LEANOR was a success. Searching for LE neutrinos is challenging, especially when neutrinos are hidden in bioluminescence signals. LEANOR could demonstrate the feasibility of such searches by disentangling the signature of LE neutrinos from environmental backgrounds, paving the way to future LE neutrino searches in KM3NeT, but also in the future IceCube-Upgrade that will be equipped with similar sensors. While LE neutrinos were mainly used for particle physics, they are now recognized by the community as promising messengers to study the Universe in great part due to LEANOR.
LEANOR contributed to popularize neutrino astronomy: Gwenhael organized the contest ‘Draw me a neutrino’, where participants drew a neutrino based on general information about this particle and how to detect it. She received more than 500 drawings from 16 countries. She could measure the impact of the contest: 60% of the participants learnt about neutrinos for the first time, and 86% of them discovered the existence of the KM3NeT project with the contest.
She collaborated with Donald Fortescue, professor at the Californian College of the Arts, San Francisco. They developed an instrument that is sensitive to the environmental conditions as ORCA. The so-called Bathysphere is a KM3NeT glass sphere containing hemispherical bells, a microphone, and a camera. The deployment of the instrument happened in September 2021. The sphere and the accompanying video will be part of an exhibition at the Center for Craft in Fall 2022 and then travel in USA/Europe.
The MSCA had a strong impact on Gwenhael's career. In 2020, she received a LabEx UnivEarthS exploratory grant and was invited to be researcher ‘In the Spotlight’ in EuroPhysics News. At the end of her MSCA, Gwenhael became professor at UCLouvain, Belgium and started her own group. She pursues the various efforts initiated in LEANOR. In Fall 2021, she received the prestigious Francqui Start-Up Grant to help her in these efforts.
LEANOR contributed to popularize neutrino astronomy: Gwenhael organized the contest ‘Draw me a neutrino’, where participants drew a neutrino based on general information about this particle and how to detect it. She received more than 500 drawings from 16 countries. She could measure the impact of the contest: 60% of the participants learnt about neutrinos for the first time, and 86% of them discovered the existence of the KM3NeT project with the contest.
She collaborated with Donald Fortescue, professor at the Californian College of the Arts, San Francisco. They developed an instrument that is sensitive to the environmental conditions as ORCA. The so-called Bathysphere is a KM3NeT glass sphere containing hemispherical bells, a microphone, and a camera. The deployment of the instrument happened in September 2021. The sphere and the accompanying video will be part of an exhibition at the Center for Craft in Fall 2022 and then travel in USA/Europe.
The MSCA had a strong impact on Gwenhael's career. In 2020, she received a LabEx UnivEarthS exploratory grant and was invited to be researcher ‘In the Spotlight’ in EuroPhysics News. At the end of her MSCA, Gwenhael became professor at UCLouvain, Belgium and started her own group. She pursues the various efforts initiated in LEANOR. In Fall 2021, she received the prestigious Francqui Start-Up Grant to help her in these efforts.