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KM3NeT: a project for an underwater cubic kilometre neutrino telescope

The KM3NeT consortium aims at developing a deep-sea research infrastructure in the Mediterranean Sea. The construction of a multi-cubic-kilometre Cherenkov telescope for neutrinos with energies above 100 GeV is the principal KM3NeT goal.

ethan-garner
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KM3NeT: a project for an underwater cubic kilometre neutrino telescope

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  1. The KM3NeT consortium aims at developing a deep-sea research infrastructure in the Mediterranean Sea. The construction of a multi-cubic-kilometre Cherenkov telescope for neutrinos with energies above 100 GeV is the principal KM3NeT goal KM3NeT: a project for an underwater cubic kilometre neutrino telescope R. Coniglione INFN-LNS for KM3NeT collaboration • Introduction • Main objectives • The KM3NeT Technical Design Report • Telescope physics performance • New developments • Summary

  2. KM3NeT and the international context High energy neutrino telescope world map Antares Taking data in its final configuration (12 lines) since may 2008. 5 lines data analyzed and ready to be published ANTARES, NEMO, NESTOR joined efforts to prepare a km3-size neutrino telescope in the Mediterranean Sea: KM3NeT IceCube IC79 taking data since 2010 IC59 data analysis started

  3. The KM3NeT consortium includes 40 Institutes from 10 European Countries (Cyprus, France, Germany, Greece, Ireland, Italy, The Netherlands, Rumania, Spain, U.K.) The KM3NeT consortium • KM3NeT Design Study (DS) -> define the telescope design and outline the main technological options • Approved under the 6° FP (funded by EC for the period 2006-2009) • Conceptual Design Report (CDR) published in 2008 (http://www.km3net.org/public.php) • Activity of DS culminated with the publication of the Technical Design Report (TDR) that outlines the main technological options for the construction, deployment and maintenance of a deep sea neutrino telescope (http://www.km3net.org/public.php) (TDR contents frozen in November 2009) • KM3NeT Preparatory Phase (PP) -> define legal, governance and funding aspects, production planes for the detector elements, infrastructure features and prototype validation will be also defined • Approved under the 7° FP (funded by EC for the period 2008-2012)

  4. Motivation for the high energy neutrino detection • Neutrino will provide unique info on High Energy Universe • on the origin of UHE cosmic rays (astrophysics, cosmology and particle physics) • on the high energy gamma production mechanism (hadronic and/or leptonic) • on the source dense inner core • Neutrino observation can be connected with the observed gamma fluxes for sources with low matter density while new high density sources can be observed

  5. KM3NeT main objectives • Central physics goals: • Investigate neutrino “point sources” in the 1-100 TeV energy regime • galactic ->Supernova Remnants, Microquasars… • extragalactic -> Active Galactic Nuclei, Gamma Ray Bursts • Complement IceCube field of view • Exceed IceCube sensitivity • Other important physics items: • - High energy diffuse neutrino flux detection • - Indirect search of Dark Matter • - Neutrino particle physics aspects • Exotics (Magnetic Monopoles, Lorentz invariance violation, …) • Interdisciplinary research • geophysics, oceanography, marine biology, … • Implementation requirements: • • Construction time ≤5 years • • Operation over at least 10 years

  6. KM3NeT sky view 2p downward coverage assumed At the Mediterranean sea latitude the source visibility can be less than 24h >25% >75% • KM3NeT complements the IceCube field of view • KM3NeT observes a large part of the sky (~3.5p)

  7. Interaction point m  n Neutrino detection principle • Upward-going neutrinos interact in rock or water (nm is the golden channel for astronomy) • Emerging charged particles (in particular muons) produce Cherekov light in water at 43° with respect to the neutrino direction • Light detection by array of photomultipliers • From photon arrival times and PMT positions is possible to reconstruct the muon direction gc 43° Detection volume of the order of5 km3 to exceed IceCube sensitivity by a substantial factor

  8. Technical items • The telescope consists of 3D array of photo-sensors supported by vertical structures (DU) connected to a seabed with a cable network • The construction of a deep sea neutrino telescope is technically highly challenging • Very high pressure • Environment chemically aggressive • Deployment operation safe, robust and precise • Requirements • Cost-effective • Reliable • Producible • Easy to deploy • Technical items • Optical Modules • Front-end electronics • Readout, data acquisition, data transport • Mechanical structures, backbone cable • General deployment strategy • Sea-bed network: cables, junction boxes • Calibration devices • Shore infrastructure • Assembly, transport, logistics • Risk analysis and quality control

  9. Other issues addressed in the Design Study • Site characterization: • • Characterization of the site and measure of the water properties • optical background, currents, sedimentation, water properties (absorption and scattering lengths….) • Simulation: • Detector performances (sensitivity and discovery fluxes) optimizing the detector parameters • - Earth and Sea science requirements: • • Define the infrastructure needed to implement multidisciplinary science nodes (marine biology, geology/geophysics, oceanography, environmental studies, alerts, …)

  10. Optical modules Two alternative solutions in the TDR for OM Multi-PMT Optical Module 31 small PMTs (3-inch) inside a 17 inch glass sphere Single-PMT Optical Module 8-inch PMT with 35% quantum efficiency inside a 13 inch glass sphere Evolution from pilot projects • 31 PMT bases (total ~140 mW) • Cooling shield and stem First full prototype ready at the end of 2010

  11. Optical modules Two alternative solutions in the TDR for OM Single-PMT Optical Module Advantages • Multi-PMT Optical Module • Advantages • photocathode surface greater than 3 8-inch PMTs • insensitive to the Earth’s magnetic field -> no mu-metal shielding • single-photon from multi-photon hits separation • information on the arrival direction of Cherenkov light-> better track reconstruction • large angular acceptance • good timing response • well known technology

  12. Front-end electronics: Time-over-Threshold Common solutions in the TDR for the front-end electronics

  13. Detection Units Three alternative solutions in the TDR for DUs Triangular arrangements of OMs with single-PMTs or multi-PMT Evolution of the ANTARES storey Slender string Vertical sequence of multi-PMTs OMs Flexible tower with horizontal bars equipped with single-PMTs or multi-PMT OMs Simulations indicate that local 3D OM arrangement resolve ambiguities in the reconstruction of the muon azimuthal angle

  14. Deployment strategy Common deployment strategy in the TDR • Main deployment concepts • Compact package • Self unfurling • Connection to seabed network by Remotely Operated Vehicle The packed flexible tower (20 storey) Spherical deployment structure for string with single OM with multi-PMT Successful deployment test in February 2010 Successful deployment test in December 2009

  15. KM3NeT: an artistic view Detection Units Primary Junction box Secondary Junction boxes Electro-optical cable

  16. Simulations: optimization studies Examples for the flexible tower Optimization of Detection Unit separation Bar length optimization ratio of the effective area relative to 3m ratio of the effective area relative to 100m Low energy region 100GeV<En<500 GeV Quality cuts applied DWm-mrec~ 2° (close to the DWn-m) Point like sources 3TeV<En<100 TeV Quality cuts applied DWm-mrec~ 0.4° (close to the search cone radius) Diffuse flux studies & GRB En>100 TeV No quality cuts applied DWm-mrec  0.9°

  17. Simulations: optimization studies Sensitivity ratio for point like source - 1 year – d =-60° Flexible tower Bar length Detection unit separation Final bar length choice is a compromise between physical performance and technical constraints 180 m preferred DU distance

  18. Simulation results A detector with a total cost of about 220M€ is required to surpass the performance of IceCube by a substantial factor Full KM3NeT detectors made of the three DU configurations at the same cost were considered in the simulations Sensitivity to point source (flux E-2) vs declination for one year of observation time Black Slender string Red Flexible tower Green Triangles Similar sensitivity per euro for the three configurations

  19. KM3NeT: effective area & resolution Detector resolution Median of DW n-mrec Neutrino effective area median of the q n-mdistribution Kinematics ☐Quality Cuts applied (0.2°@30TeV) Quality Cuts optimized for sensitivity m q n-m n

  20. KM3NeT: sensitivity & discovery Sensitivity and discovery fluxes for point like sources with a E-2 spectrum for 1 year of observation time KM3NeT sensitivity 90%CL KM3NeT discovery 5s 50% IceCube sensitivity 90%CL IceCube discovery 5s 50% 2.5÷3.5 above sensitivity flux. (extrapolation from IceCube 40 string configuration) unbinned method binned method |Observed Galactic TeV-g sources (SNR, unidentified, microquazars) F. Aharonian et al. Rep. Prog. Phys. (2008) Abdo et al., MILAGRO, Astrophys. J. 658 L33-L36 (2007)  Galactic Centre

  21. “bar” option with horizontal extent and 6 8-inch PMTs Optimised design and plan for extensive deployment tests defined Study of the advantages offered by a “hibrid” solution DU with horizontal extent Multi-PMT Optical Module Multi-PMT option Needs validation of technology and integration procedures Common development of the multi-PMT Optical Module and its implementation on the tower Optimization of simulation of the detector performance ongoing Developments after the TDR In the recent months developments towards a technology convergence on a unique design

  22. Flexible tower DU with 6 13” spheres: stacking concept Height = 1.43 m

  23. Flexible tower DU with 2 17” OM: preliminary storey design

  24. Summary • A design for the KM3NeT neutrino telescope complementing the IceCube field of view and surpassing it in sensitivity by a substantial factor is presented • The required sensitivity can be achieved within an overall budget of ≈ 250 M€ • Staged implementation, with increasing discovery potential, is technically possible • Convergence process toward a unique technical design under way • Development plan for qualification of a pre-production model of the detection unit defined • Remaining technical decisions have to be taken within the next spring • Readiness for construction expected at the end of the Preparatory Phase (march 2012) • Installation could start in 2013 and data taking soon after

  25. The end

  26. Simulations: optimization studies Sensitivity ratio for point like source - 1 year – d =-60° Flexible tower Bar length Detection unit separation a=-2 a=-2.2 Final bar length choice is a compromise between physical performance and technical constraints 180 m preferred DU distance

  27. Theta versus declination Below the horizon Mediterranean sea latitude 36° Above the horizon Near the horizon the effect of Earth absorption is reduced for high energy neutrinos +50 +40 0 +20 -10 -20 -30 d=-40 -50 -60 -70 -80

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