The latest results from the ANTARES neutrino telescope will be presented regarding the search for a diffuse high energy neutrino flux, the analysis to identify astrophysical neutrino point sources and the various searches for multimessenger coincidences between neutrinos and other cosmic probes, like photons or gravitational waves. KM3NeT, the new generation of underwater neutrino telescopes, is currently under construction in the Mediterranean sea. Thanks to its large size and improved detection capabilities, KM3NeT will open new perspectives in neutrino astronom

Versari, F.

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DOI 10.1393/ncc/i2019-19080-3Colloquia: EuNPC 2018IL NUOVO CIMENTO 42 C (2019) 80KM3NeT and ANTARES status and resultsF. Versari(1)(2) on behalf of the ANTARES and KM3NeT Collaborations(1) INFN, Sezione di Bologna - Bologna, Italy(2) Università di Bologna - Bologna, Italyreceived 5 February 2019Summary. — The latest results from the ANTARES neutrino telescope will bepresented regarding the search for a diffuse high energy neutrino flux, the analysisto identify astrophysical neutrino point sources and the various searches for multi-messenger coincidences between neutrinos and other cosmic probes, like photonsor gravitational waves. KM3NeT, the new generation of underwater neutrino tele-scopes, is currently under construction in the Mediterranean sea. Thanks to itslarge size and improved detection capabilities, KM3NeT will open new perspectivesin neutrino astronomy.1. – IntroductionNeutrino astronomy is the youngest branch of astroparticle physics. TeV neutrino as-tronomy is even younger, since only recently the IceCube detector provided the first everobservation of high energy neutrinos of cosmic origin [1]. This has opened a new windowof observation on the Universe. The observation of neutrinos of extra-terrestrial origincan solve a fundamental question in astroparticle physics: the origin, the sources and theacceleration mechanisms of charged cosmic rays. Since neutrinos could be produced inthe dense environment surrounding the acceleration site, they can directly point to thecosmic ray source and accelerator. A possible way to detect high energy neutrinos usinghuge volumes of transparent natural material such as ice or sea water was proposed byMarkov in 1960 [2]. High energy neutrinos undergoing weak interactions with one of thenucleons of the medium would produce charged particles. Cherenkov photons induced bythese charged particles that travels through a medium, can then be detected by a latticeof photomultipliers. Given the low cross section of νN interactions and the predictedastrophysical neutrino fluxes, the typical size of the detector should be of the order ofkm3.2. – Mediterranean neutrino telescopesThe ANTARES [3] neutrino telescope is a three-dimensional array of 885 photomulti-pliers (PMTs) distributed over 12 vertical lines 450 m long, installed in the MediterraneanCreative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 F. VERSARI on behalf of the ANTARES and KM3NeT COLLABORATIONSSea, 40 km off-shore Toulon, France, anchored 2475 m below the sea level. The detectorhas been operated in partial configurations since March 2006 and was completed in May2008. It is taking data continuously since then. The time and the position of the photonsproduced by the charged particles generated in neutrino interactions are detected by thePMTs and used to reconstruct the direction and the energy of the interacting neutrinos.KM3NeT is a future research infrastructure comprising the ARCA and ORCA detec-tors [4]. The former will be located about 100 km off-shore from the coast of Portopalodi Capo Passero, Sicily, Italy at a depth of 3500 m and is designed for the investigation ofhigh energy neutrino astrophysics and the search for the sources of cosmic neutrinos. Thelatter will be located close to the ANTARES site about 10 km apart from it and is opti-mised for the study of low energy neutrino oscillation physics and for the measurement ofthe neutrino mass ordering. Both detectors will use the same technology. In particular,photons will be detected with Digital Optical Modules (DOM), a sphere resistant to highpressure that contains 31 PMTs. The DOMs are arranged in a vertical string called De-tection Units (DU) and the difference between ARCA and ORCA is the relative distancebetween the DOMs and between the DUs, sparser in ARCA and denser in ORCA. TheARCA detector will be built in two phases: the first phase, already funded, will consistin 24 strings, 3 of them were already deployed and the construction will be completedin 2019. The second phase, partially funded, will consist on two building-blocks (BB),each one made of 115 DUs to reach an instrumented volume larger than 1 km3 and willbe done approximately by the end of 2021. The ORCA detector will have two phaseslike ARCA: in the first one, already funded, 6 DUs will be deployed and one of them isalready under the sea. The second phase will consist in one BB of 115 DUs.There are two event topologies that can be identified in a high energy neutrino tele-scope: track -like and shower -like events. The track events are produced when a muon isgenerated in a charge current (CC) interaction of a muon neutrino in the proximity of thedetector. Thanks to the long muon range the direction of the interacting neutrino canbe reconstructed with an angular resolution that is below 1◦ for ANTARES and in theorder of 0.1◦ for KM3NeT-ARCA. Shower events are produced when an electromagneticand hadronic cascade are generated in a neutral current interaction (NC) of a neutrinoindependently from its flavor, or in a charge current interaction (CC) of an electron ortau neutrino. All the energy of the cascade is deposited within a few meters from theinteraction vertex hence they are reconstructed as point-like source of light, thus pro-viding a poorer angular resolution as compared to the track channel, in the order of∼ 5◦ for ANTARES and ∼ 2 − 3◦ for KM3NeT-ARCA. On the other hand this kind ofevents allow a very precise energy estimation of the interacting neutrino that is ∼ 15%for ANTARES and ∼ 5% for KM3NeT-ARCA.3. – Cosmic neutrino searchesThere are three main strategies to detect a cosmic neutrino, the first one being thesearch for a diffuse high energy neutrino flux where one looks for an excess of high energyneutrinos over the atmospheric neutrino background, without any request on the neutrinodirection in the sky.Using nine year of the ANTARES data a search of a diffuse flux [5], like the onediscovered by the IceCube experiment [1], has been performed. The result of the analysisis shown in the left and central plots of figure 1. Here a slightly excess of events, bothin the track and shower channels, of 33 events, when 24 ± 7 were expected from thebackground, has been found. After a maximum-likelihood fit of the energy estimatorsKM3NET AND ANTARES STATUS AND RESULTS 3Fig. 1. – Left and middle: distribution of reconstructed neutrino energy for the track andshower channels in the ANTARES diffuse flux analysis [5]. The uncertainties, depicted as ashaded area, take into account the detector efficiency and the water properties systematics.Right: significance as a funcion of time for the detection of the IceCube diffuse flux using theKM3NeT-ARCA detector in the phase two configuration [4].distributions the hypothesis of a null cosmic flux has been excluded with a significanceof 1.6σ. In the right plot of figure 1 is shown the significance as a function of time forthe detection of an IceCube-like diffuse flux with the ARCA detector with two buildingblocks. With the two building blocks of KM3NeT-ARCA, the IceCube-like diffuse fluxwill be observed with a 5σ significance in only six months.The second strategy observe cosmic neutrinos is the so-called point source search.In this case a correlation between the neutrino direction and the position of an alreadyknown astrophysical object is searched for. The results of the ANTARES point sourceanalysis, that uses a 9 year data sample and both the track and shower channel andinvestigate 106 astrophysical candidate neutrino sources, is shown in the left plot of figure2. No significant evidence of cosmic neutrino sources has been found [6]. Nevertheless,these searches provide the most sensitive limits for the predicted neutrino fluxes for alarge fraction of the Southern Sky region. The KM3NeT-ARCA [4] detector will improvethe ANTARES sensitivity by an order of magnitude as shown in the right plot of thefigure 2.The third strategy to find cosmic neutrinos is the multimessenger approach. TheFig. 2. – Left: ANTARES sensitivity and limits, as a function of the declination, to the astro-physics candidate neutrinos sources [6]. Right: Estimated sensitivity for point like sources as afuncion of the declination for a 6 years observation with the KM3NeT-ARCA detector in phasetwo configuration [4].4 F. VERSARI on behalf of the ANTARES and KM3NeT COLLABORATIONSFig. 3. – Distribution of ANTARES events in the right ascension and declination coordinatesaround the position of TXS 0506+056 [7]. The read point denotes a shower-like event, whereasthe blue points indicate track-like events. The size of the circle around each event indicate theassociated angular error.search is done by sharing information with various detectors ranging from electromagneticobservatories (optical, radio, X-ray, gamma-ray) to cosmic rays and gravitational wavedetectors. The goal of this kind of search is to detect neutrinos from transient phenomenatherefore using a space-time coincidences between the different probes, which heavilyreduces the background contamination. An example of a multimessenger analysis doneby ANTARES is the one done in blazar TXS 0506+056. The 22 of September 2017IceCube recorded a neutrino with an arrival direction consistent with this blazar [8]that was observed to be in flaring state. This source has been investigated using theANTARES data but no muon neutrino candidate event has been found within 3◦ aroundthe IceCube neutrino directino within ±1hr centered on the event time. A point sourcelike search has been done with ANTARES looking to the blazar as a candidate neutrinosource and in figure 3 are shown the neutrino candidate event. No significant excessabove the expected backgound is found [7].4. – Conclusions and PerspectivesThe ANTARES neutrino telescope continues taking data and producing relevantphysics results after 10 years of continuous data taking. It produced solid results fromvarious searches of astrophysical neutrino emission and it has a very active multimessen-ger program. KM3NeT, the new generation of Mediterranean neutrino telescopes, willbenefit from the best practice coming from the ANTARES experience and will be sooncompetitive in astrophysical neutrino searches and in the basic neutrino physics.REFERENCES[1] AARTSEN M. G., Phys. Rev. Lett., 113 (2014) 101101.[2] MARKOV M.A., Proceedings Int. Conf. on HE Phys., (1960) 183.[3] AGERON M. et al., Nucl. Instr. Meth. A, 656 (2011) 11-38.[4] ADRIAN-MARTINEZ S. et al., J. Phys., G43 (2016) no.8, 084001.[5] ALBERT A. et al., The Astro. Jour. Let., 853 (2018) L7.[6] ALBERT A. et al., Phys. Rev. D, 96 (2017) 082001.[7] ALBERT A. et al., The Astro. Jour. Let., 863 (2018) L30.[8] AARTSEN M. G. et al., Sci, 361 (2018) 10.1126.

KM3NeT and ANTARES status and results

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KM3NeT and ANTARES status and results

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