Underwater neutrino telescopes in the Mediterranean: from the GeV to the PeV neutrino energies

1. Underwater neutrino telescopes in the Mediterranean:from the GeV to the PeV neutrino energies E. Tzamariudaki NCSR Demokritos status report • the projects • objectives • trigger studies: a status report • GRBNeT • plans / outlook

2. high energy neutrino observation: motivation ν andγproduced in the interaction of high energy nucleons with matter or radiation cosmic ray acceleration yields neutrinos and gammas with similar abundance and energy spectra neutrinos: unique messengers

3. KM3NeT objectives • investigate neutrino “point sources” in the TeV energy regime • galactic Supernova Remnants, Microquasars • extragalactic Active Galactic Nuclei, Gamma Ray Bursts • High-energy diffuse neutrino flux • Field of view includes the Galactic center and complements IceCube • Optical properties of deep sea water: excellent angular resolution Neutrino cross section is extremely low very large active volume needed Instrumented volume of several km3 exceed IceCube sensitivity

4. high energy neutrino observation • Upward-going neutrinos interact in rock or water • charged particles (in particular muons) produce Cherenkov light in water at 43° with respect to the neutrino direction • light is detected by array of photomultipliers • muon direction is reconstructed using PMT positions and photon arrival times • the Earth provides screening against all particles except neutrinos

5. ANTARES Backgroundsources • cosmic ray interactions in the atmosphere produce andwhose decays produce neutrinos - atmospheric neutrinos • cosmic rays entering the atmosphere produce extensive air showers; a component of which are high energy muons – atmospheric muons

6. trigger • “All-data-to-shore” concept: • for the envisaged photocathode area: total data rate 0.2 Tb/s • total data rate exceeds that of any data storage capacity by several orders of magnitude need to discriminate neutrino (muon) signal from random background “trigger”: minimal number of time-position correlated PMT hits • noise: background from decays and from bioluminescence • keep only events that have a good chance of being reconstructed

7. KM3NeTdetector configuration • 310 strings 130m distance • each string: 20 floors separated by 40m

8. neutrino events no noise with noise trigger level N events N events reco level well reconstructed events

9. definition of the trigger requirements L1pm3 • take advantage of the MultiPMT OM • require at least 5 OMs with 3 hits correlated • in space and time • ( neigbouring or next-to-neigbhouring pmts • within 20ns ) 31 x 3” PMTs • require clusters of hits • apply new filtering algorithms L2 • at least 3 clusters of 3 OMs or 4 clusters of 2 OMs • at least 2 clusters of 3 OMs on the same string (vertical tracks) • cluster of neigbouring strings with neigbouring OMs hit (horizontal tracks)

10. trigger studies: neutrino events no noise with noise N events N events L1 all reconstructed events 2T3 trigger level reco level L2 L1pm3 well reconstructed events L1pm3L2

11. trigger studies: neutrino events no noise efficiency with noise efficiency 2T3 efficiency L2 L1pm3 L1pm3L2 logE (GeV) logE (GeV) ratio of triggered events

12. ORCA: extending to lower energies Low energy option for KM3NeT Phase 1 Mass hierarchy measurement – feasible? • Is a 3-5σ measurement with a ~2Mt detector volume within reach? • Most Long Baseline experiments expect 3-5σ by 2030 Limiting factors: • E and angular resolution ν • systematics

13. ORCA: extending to lower energies Akhmedov – Razzaque – Smirnov paper assuming perfect resolution Mass hierarchy measurement – challenge

14. trigger studies: neutrino events reco level 2T3 efficiency efficiency L2 L1pm3 L1pm3L2 efficiency L1pm2 L1pm2L2

15. trigger studies: atmospheric muon events trigger level N events L1 N events 2T3 L2 L1pm3 L1pm3L2 muon zenith angle use veto layers to check if the atmospheric muon background can be further reduced veto: equip each string 2 OMs at ~100m distance

16. extending to higher energies: GRBs Gamma-Ray-Bursts are short duration emissions of γ-rays associated with extremely violent explosions in the Universe in distant galaxies characterized by the largest luminous energy emissions known detection of x-rays and measurement of the redshift placed GRBs in distant galaxies long bursts (>2s) are associated with the death of a massive star Today at least one GRB is detected each day – data are collected by the Gamma Ray Burst Coordination Network

17. extending to higher energies: GRBs

18. extending to higher energies: GRBs

19. extending to higher energies: GRBs exploit the temporal coincidence of the potential signal from neutrinos from GRBs with the signal from x or γ-ray telescopes the GRBNeT project: construction of an autonomous string (in terms of power and data-handling) to be deployed and take data for ~1 year collaboration of NCSR Demokritos, University of Athens, ELKETHE trigger studies: • suppress the noise from decays • optimize for high suppression of atmospheric muons and low energy muons

20. Plans and outlook KM3NeT • Trigger optimization studies: • very efficient filtering at the trigger level 2 large suppression of noise contribution high efficiency for well reconstructed events ORCA • Trigger optimization studies are ongoing • filtering at the trigger level 2 at the 20% level • investigation of the performance of a veto has started GRBNeT • extend the detection potential at high energies taking advantage of the multi-messenger approach • prove that autonomous strings can be used for a PeV energy underwater neutrino detector • work still in progress…