Search for cosmic neutrino point sources & extended sources with 6-21 lines of KM3NeT/ARCA

Search for cosmic neutrino point sources & extended sources with 6-21 lines of KM3NeT/ARCA NeuTel workshop Padua, Italy September 30th, 2025 KM3Neutrino Telescope / Astroparticle Research with Cosmics in the Abyss is a neutrino observatory, currently being build at the bottom of the Mediterranean Sea. It can do multi-flavour astronomy (𝜈𝜈𝑒𝑒, 𝜈𝜈𝜇𝜇, 𝜈𝜈𝜏𝜏), has subdegree angular resolution, is sensitive in a large energy range[MeV -PeV], and can probe many different type of 𝜈𝜈-sources. Its location in the Northern hemisphere provides a good view of the Galactic Region The KM3eT/ARCA detector 30-9-2025 Search for cosmic neutrino sources with KM3NeT/ARCA 2 KM3-230213A 30-9-2025 Search for cosmic neutrino sources with KM3NeT/ARCA 3 The ultra-high-energy cosmic neutrino(KM3-230213A) detection by KM3NeT, not only demonstrates the detector’s capability to detect neutrinos at the highest energies, but also reinforces the scientific potential of KM3NeT/ARCA in probing extreme astrophysical environments. * KM3NeT Collaboration: Observation of an ultra-high-energy cosmic neutrino with KM3NeT. Nature, 2025, 638.8050: 376-382. Neutrino astronomy Astrophysical neutrino sources are cosmicray accelerators. The two main machanisms of highenergy neutrino production are: (1) When cosmic rays interact with matter (hadronuclearinteractions): 𝑝𝑝+𝑝𝑝 →𝑝𝑝+𝑛𝑛+𝜋𝜋+ 𝑝𝑝+𝑝𝑝 →𝑝𝑝+𝑝𝑝+𝜋𝜋0 𝑝𝑝+𝑛𝑛 →𝑝𝑝+𝑛𝑛+𝜋𝜋0 𝑝𝑝+𝑛𝑛→𝑝𝑝+𝑝𝑝+𝜋𝜋− (2) When cosmic rays interact with photons (photohadronicinteractions): 𝑝𝑝+𝛾𝛾 →Δ+→𝑛𝑛+𝜋𝜋+ 𝑝𝑝+𝛾𝛾 →Δ+→𝑝𝑝+𝜋𝜋0 While the neutral pions decay into 𝛾𝛾-rays: 𝜋𝜋0→𝛾𝛾+𝛾𝛾, neutrinos are produced in the decay of the charged pions: 30-9-2025 Search for cosmic neutrino sources with KM3NeT/ARCA 4 𝜋𝜋+→𝜇𝜇++𝝂𝝂𝝁𝝁 𝜋𝜋+→𝜇𝜇+→𝑒𝑒++𝝂𝝂𝒆𝒆+� 𝝂𝝂𝝁𝝁𝜋𝜋−→𝜇𝜇−+� 𝝂𝝂𝝁𝝁 𝜋𝜋+→𝜇𝜇−→𝑒𝑒−+� 𝝂𝝂𝒆𝒆+𝝂𝝂𝝁𝝁 Neutrino Astronomy *IceCube Collaboration: Observation of high-energy neutrinos from the Galactic plane. Science, 2023, 380(6652), 1338-1343 In their respective energy ranges the sources NGC 1068 and TXS 0506+056 contribute no more than 1% to the overall diffuse flux of astrophysical neutrinos.* 30-9-2025 Search for cosmic neutrino sources with KM3NeT/ARCA 5 Candidate sources 106 sources are selected based on: GeV –EeVinformation from other neutrino experiments, cosmic ray experiments as well as optical measurements in the range -90°< 𝜹𝜹< 40°for which KM3NeT has > 35% visibility (after cut of upgoing + horizontal). The 19 extended sources are tested assuming a Gaussian with spread (σ) equal to their extension [0.1°−2.2°], and assumed to be circularly-symmetric. 30-9-2025 Search for cosmic neutrino sources with KM3NeT/ARCA 6 Event selection Signal definition: A cosmic neutrino with an outgoing muonreconstructed better than 1°. Basic event selection criteria (“pre-cuts”): 1. Select horizontal/up-going tracks (𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃tkr >−0.1), 2. Select events with high number of hits used in the reconstruction (𝑁𝑁ℎ𝑖𝑖𝑖𝑖𝑐𝑐 >20), 3. Select events with good fit quality (based on likelihood of reconstruction) (lik >50). Additional selection criteria for the ARCA6-8 sample: 1. Select horizontal/up-going events passing the shower reconstruction (cos 𝜃𝜃shw >−0.1). Additional selection criteria for the ARCA19-21 sample: 1. Select evens with a long track length (len >100m), 2. Select events with an energy above 100 GeV (𝐸𝐸>100 GeV), 3. Select events with good fit quality (based on likelihood of reconstruction) (lik >101.8), 4. Select events estimated to have a small error in its reconstructed direction (𝛽𝛽0>10−2.25), 5. Boosted decision tree (BDT > 0.9996). Background estimation: made with scrambled data. Very High Energy event KM3-230213A*removed from data sample. 30-9-2025 Search for cosmic neutrino sources with KM3NeT/ARCA 7 * KM3NeT Collaboration: Observation of an ultra-high-energy cosmic neutrino with KM3NeT. Nature, 2025, 638.8050: 376-382. Event selection in numbers Precuts Final cutlevel ARCA6-8 ARCA19-21 ARCA6-8 ARCA19-21 Data 119313 293965* 15742 1544* Muons 125314 334902 13278 150 Atm nu 921 3798 750 863 Cos nu 12 32 912 Cos signal (with muon, Within 1 degree) 312 210 MC tot 126246 338731 14038 1025 Muon_contamination 99% 99% 95% 15% Signal efficiency 83% 78% 30-9-2025 Search for cosmic neutrino sources with KM3NeT/ARCA 8 Data are taken with 6 -21 lines, between May 2021 and Sept. 2023. After event selection, the ARCA19-21 data sample has a muon contamination of 15%. A cosmic neutrino flux of 𝝓𝝓𝒄𝒄𝒄𝒄𝒄𝒄 𝝂𝝂+� 𝝂𝝂=𝟏𝟏.𝟐𝟐⋅𝟏𝟏𝟏𝟏−𝟒𝟒 𝑬𝑬𝝂𝝂 𝐆𝐆𝐆𝐆𝐆𝐆 −𝟐𝟐 GeV-1 m-2 s-1 sr-1 per flavour yields 21.4 cosmic neutrino events in the full ARCA6-21 sample, of which 12.1 contain a muon and are reconstructed with <1°accuracy. Datasample after event selection 30-9-2025 Search for cosmic neutrino sources with KM3NeT/ARCA 9 * KM3-230213A removed KM3NeT dataset Number of events ARCA 6 4205 ARCA 8 11537 ARCA 19 182 ARCA 21 1361* ARCA6-21 total 17285