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  1. Effects of architectural and environmental issues on a km3 detector R. Coniglione for the NEMO collaboration Istituto Nazionale di Fisica Nucleare- Laboratori Nazionali del Sud  Effects of environmental parameters on a km3 detector • Optical background • Absorption length •  Architectural effects on the detector effective areas R. Coniglione for the Nemo coll. NIM A 567 (2006) 489-491 R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

  2. The environmental effects R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

  3. Simulation INPUT • ANTARES codes modified for km3 detectors + LNS improvements • surface m generation • muons with E-1 spectrum - isotropic distribution • can radius dmax/2+ 200 m • Capo Passero absorption length (70 m @ 450 nm) • Background 35, 60, 120 kHz with offset 1000 ns • “Aart” reconstruction with different “triggers” (LNS routine for triple local coincidences reco v4r5km3) In order to get a fair comparison, quality cuts on the reconstruction are applied to get similar angular resolution ( 1° at 1 TeV) R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

  4. The NEMO geometry 40m 20m • Characteristics of the simulated km3 detector • Square array - 140 m tower spaced • number of towers 81 • - number of PMTs 5832 • - Dimension: 1.14 · 1.14 · 0.68 = 0.88 Km3 • Tower characteristics: • total height 830 m • instrumented 680 m • number of bars 18 • number of PMTs per bar 4 • bar length 20 m • bar vertical distance 40 m • PMT 10’’ R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

  5. Trigger • The reconstruction procedure is based on a maximum likelihood method • all the hits with amplitude < 0.5 p.e. are rejected • A causality filter with respect to the highest amplitude hit is applied • A linear prefit is applied on a sub-set of hits that passed the following conditions (trigger condition) • (they are part of a local coincidence) OR (hit amplitude >2.5 p.e.) • Local coincidences = hit with 20ns+Dr/vlight difference in time in different PMT Local coincidences 2/2 2/4 3/4 R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

  6. Trigger and background rates Aeff vs Em Aeff vs Em Aeff vs Em 35 kHz 60 kHz 120 kHz • 2/4 • 3/4  2/2 •  2/4 • 3/4  2/2 •  1.5p.e.  2/2 • 3/4 Median vs Em Median vs Em Median vs Em • Trigger effects are strongly dependent on the background rates • Local coincidences (3/4) are relatively more efficient at higher background rate in particular at muon energy lower than 10 TeV R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

  7. Effective muon area vs background rates The best “trigger” for each rate value is applied •  35 kHz - 2/4 local coinc. • 60 kHz – 3/4 local coinc.  120 kHz – 3/4 local coinc Even with local coincidence trigger (3/4) a stronger and stronger effective area reduction is observed with increasing background rates R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

  8. Effects of labs 20 kHz lsc 50m @~450 nm - Aeff vs Em Aeff (70m)/Aeff (50m) vs Em The ratio  labs 70m @450 nm  labs 50m @ 450 nm Aeff (labs 70m)/Aeff (labs 50 m) At muon energy lower than 3TeV effective areas higher than 20% R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

  9. The architectural comparison R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

  10. The architectural comparison Compromise between performance and technical feasibility • Performance-> Good angular resolution and effective areas for • Up-going muons (Em102108 GeV) in the whole angular range • Several architectures were studied with the following constraints: • about 100 structures • about 5000-6000 OM • tower height <1000m • 10” PMT R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

  11. The geometries 40m 20m NEMO_140 String-dh_140_20 String-d_125_16 5832 PMT 81 strings String height 680m (18floors/string) V= 0.88 km3 5800 PMT 100 strings String height 912 m (58 PMT/string) V= 1.15 km3 5832 PMT 81 strings String height 680m (18floors/tower) V= 0.88 km3 R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

  12. The effective muon areas vs Em Up-going muons 35 kHz background – labs 70m@450nm • string-dh_140_20 • string-d_125_16  NEMO_140 R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

  13. Angular resolution vs qm Up-going muons Em 103  104 GeV Em 102  103 GeV Q. Cut applied • string-dh_140_20 • string-d_125_16  NEMO_140 Horizontal Vertical The “string” detectors show a worst angular resolution for near vertical muons R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

  14. Muon effective areas vs neutrino energy NEMOdh-140  RETd-125  RETdh-140 Up-going E-2 muon neutrino spectrum 35 kHz background – labs 70m@450nm Median of qn-mrec vs cosqn 1 TeV < Ev < 10 TeV NEMOdh-140 RETdh-140 Ratio = Horizontal Vertical R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

  15. Down-going muons Down-going muons (moon shadow) 35 kHz background – labs 70m@440nm • string-dh_140_20 • string-d_125_16  NEMO_140 The “string-d_125_16” detector shows a worst angular resolution and Aeff for down-going muons R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

  16. Summary • A study on the possible trigger conditions on a tower based detector has been undertaken -> triple local coincidences are more efficient with increasing background rates. • Stronger and stronger reduction on effective areas with increasing background rates up to Em =104 GeV. • Comparison of effective muon areas as a function of labs shows an improvement higher than 20% for muon energy <3TeV • Architectural study on tower vs string based detector performances indicates that detectors based on strings have a bad angular resolution for Em < 104 GeV up-going muons with qm<35° -> Areconstruction strategy adapted to each particular geometry can improve the detector performance. R. Coniglione, KM3NeT, Marseille 11-12 October ‘06