1. Use of floating surface detector stations for the calibration of a deep-sea neutrino telescope G. Bourlis, N. A. B. Gizani, A. Leisos, A. G. Tsirigotis, S.E. Tzamarias In the framework of the KM3NeT Design Study

2. The General Idea… Angular offset Efficiency Resolution Position Physics ? C.R. composition UHE ν - Horizontal Showers Veto atmospheric background – Study background Use of EAS detector stations for the calibration of KM3NeT

3. ~4km ~20km Isotropic on the top of the atmosphere BUT … α~10 Range of muon in water

4. Floating stations EAS Calibration Method - The Concept A floating array of EAS detectors can be used as a sea-top calibration infrastructure, on top of the KM3NeT neutrino telescope. Such an array can detect atmospheric showers and the collected data can be used for the reconstruction of the direction and the estimation of the impact parameter of the shower axis. Cosmic showers with energies above 10 14 eV contain energetic muons able to penetrate the 4000m deep sea water and reach the KM3NeT detector. The comparison of the reconstructed muon track parameters with the estimated shower axis: Atmospheric Muon Underwater Neutrino Telescope 1.Reveals any possible systematic angular error of the neutrino telescope and, 2.Provides the absolute position of the undersea detector.

5. The SeaTop Detector – HELYCON Station Triangulation  Shower Direction The EAS array used in this study consists of floating HELYCON (HEllenic LYceum Cosmic Observatories Network) scintillation counters. Each HELYCON station includes a GPS antenna, digitization and control electronics and the data acquisition system controlled by a PC. A single station is able to detect atmospheric showers initiated by cosmic particles of energy more than 10 14 –10 15 eV. The reconstruction of the shower axis is based on the measurement of: a) the arrival times and b) the amplitude of the detector signals. GPS Scintillator- PMT DAQ ~20 m 1 m 2 Station Server

6. Scintillator 2 Scintillator 3 GPS timestamp Station Server Scintillator 4 Scintillator 1 1 m 2 active area scintillation counter. The ReadOut system is based on a HPTDC chip, designed at CERN,with 5 analogue inputs. The input signals are compared to six adjustable thresholds and the corresponding times of the PMT waveform-threshold crossings are digitized with an accuracy of 100ps. The synchronization between the HELYCON stations relies on the GPS time- signal which is incorporated in the data. The EAS Charged Particle Detector - DAQ

7. CORSIKA (Extensive Air Shower Simulation) GEANT4 (Scintillation, WLS & PMT response) Simulation Tools to describe the detector response DAQSIM (DAQ Simulation) HOUANA (Analysis & Shower Reconstruction) The CORSIKA air shower simulation software is used to produce air showers, initiated by cosmic ray particles entering isotropically the upper atmosphere. Detector response, trigger formation, digitization and the Data Acquisition System is simulated by the specific HELYCON MC package. The events produced by the simulation are stored using the same format as the experimental data and they are analyzed in exactly the same way as real events.

8. Calibration and Test Results Scintillator A Scintillator B Lead discriminators Inputs Trigger Charge (in units of mean p.e. charge)  Data - Monte Carlo Prediction Response to a MIP ΔT [ns] Local time resolution Slewing Resolution Global time resolution and slewing 21 pes mean <10% variation

9. Shower reconstruction – Timing Corrections χ 2 minimization curvature thickness Plane wave Hypothesis

10. Time corrections Arrival Time Delay [ns] Deposited Charge [MIP] Statistical Error [ns] Deposited Charge [MIP] curvature thickness

11. Observations of Extensive Air Showers - Resolution The performance of HELYCON in detecting and reconstructing showers has been studied by operating a system of eight HELYCON detectors in the laboratory. group A σ A MC =4.5 ο ±0.5 o, group B σ B MC =5.2 ο ±0.6 o, all six detectors σ 6 MC =3.5 ο ±0.3 o. These resolutions can be evaluated solely from the real data, by comparing the results obtained by the two detector groups (A and B) on an event by event basis. The distribution of the difference (Δθ=θ Α -θ Β ) of these two estimations of the zenith angle has a spread of σ DATA =7.2 ο ±0.2 ο. This spread is consistent with the above MC predictions of the detector resolution: MC Estimated resolution σ= 7.2 ο ±0.2 ο

12. Trigger Detectors >1.5 mip Detectors of groups A.and.B > 0.5 mip’s zenith angle [degrees] Trigger Detectors > 1.5 mip Detectors of groups A.and.B > 1.5 mip’s α=9.4±0.2 Observations of Extensive Air Showers

13. - Three Floating Stations operating independently above KM3NeT - Distance between stations 150m - 16m 2 Scintillator Each Station SeaTop Detector – Station Setup 19m 5m 1 m 2 Scintillation Counter Station

14. Single Station Detection Efficiency Efficiency Events A hit is considered when there is more than 4 mips deposited charge on a counter

15. Muon Propagation μ track km3 Geant Simulation (propagation & Energy Loss) Accepted if muon with E>2TeV goes through km3 Zenith angle < 13 deg Detector response simulation and Muon Track Reconstruction

16. Monte Carlo Studies- Outlook 10 14 - 5·10 15 eV E~ 10 14 - 5·10 15 eV: 2500 showers/m 2 /year Single station detection: 360m 2 geometrical area (effective area depends strongly on selection cuts) E> 10 16 eV: 1 shower/m 2 /year TO BE STUDIED 35% of the detected showers include a muon which arrives at the Neutrino Telescope (depth 4000m) with an energy >300GeV General Remark: 3 stations operating for 10 days can identify an angular offset of the KM3NeT with an accuracy of 0.05 o Specifically…..

17. Investigation for a systematic angular offset of the KM3NeT We use EAS that contain at least one energetic muon reconstructed by the KM3NeT and compare the estimated zenith angles of the shower axis and the muon track on an event by event basis. The difference between these two angles should follow a normal distribution with mean zero. A possible statistically significant deviation from zero indicates that the estimations of the KM3NeT suffer from a systematic angular offset. The spread of this distribution expresses the calibration resolution per shower event.

18. σ1(na)σ1(na) A eff (n a ) [m 2 ] nana nana Investigation for a systematic angular offset of the KM3NeT Calibration resolution per single shower event (degrees) n a : minimum number of active detectors per shower event Effective area of a floating detector station The calibration resolution per single shower decreases when events with more active detectors are selected because the reconstruction accuracy of the shower’s direction improves. However, the requirement of more active detectors per event results to a reduction of the effective area of the floating detector array.

19. minimum number of active detectors per shower event. Investigation for a systematic angular offset of the KM3NeT The calibration resolution, σ c (n a ), in identifying a possible angular offset in the neutrino telescope estimations using the three floating detector arrays, is: For 3 EAS detector stations and 10 days of operation the calibration resolution has a minimum for n a ≤5. The proposed calibration system will be able to measure a possible zenith angle offset with an accuracy of ~0.05 o. σ c (n a ) [degrees] nana

20. Charge parameterization AGASA parameterization (S. Yoshida et al., J Phys. G: Nucl. Part. Phys. 20,651 (1994) Parameters depend on (θ, Ε, primary) “Mean particle density registered by an active counter”

21. Determination of the KM3NeT Absolute Position The resolution in estimating the (X-Y) coordinates of the under-water detector, as a function of the number of active detectors, using: (a) single reconstructed EAS and (b) showers collected by three floating arrays during 10 days of operation. The proposed technique can estimate the absolute position of the neutrino telescope with an accuracy ~0.6m. nana (a) nana (b)

22. Conclusions The operation of 3 stations (3x16 counters) for 10 days will provide: The determination of a possible angular offset of the KM3NeT with an accuracy ~ 0.05 deg The determination of the absolute position of the KM3NeT with an accuracy ~ 0.6 m Efficiency vs Energy and Zenith angle…

23. 1 km 2 km SPASE air shower arrays  calibration of AMANDA angular resolution and pointing !  resolution Amanda-B10 ~ 3.5° spase-amanda IceCube IceTop

24. The Underwater Neutrino Telescope – Working Example 125m IceCube Geometry 9600 OMs looking up & down in a hexagonal grid. 80 Strings, 60 storeys each. 17m between storeys MultiPMT Optical Module 20 x 3” PMTs (Photonis XP53X2) in each 17” Optical Module