Effects of architectural and environmental issues on a km3 detector

R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

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

The environmental effects

R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

Simulation INPUT

ANTARES codes modified for km3 detectors + LNS improvements

- surface 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

The NEMO geometry

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’’

40m

20m

R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

Trigger

2/2

2/4

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+r/vlight difference in time in different PMT

Local coincidences

3/4

R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

Trigger and background rates

35 kHz 60 kHz 2/4 3/4 2/2

1.5p.e. 2/2 3/4

2/4 3/4 2/2

Median vs EMedian vs E Median vs E

Aeff vs E Aeff vs E Aeff vs E

• 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

120 kHz

R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

Effective muon area vs background rates

Even with local coincidence trigger (3/4) a stronger and stronger effective area reduction is observed with increasing 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

R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

Effects of abs

abs 70m @450 nm abs 50m @ 450 nm

At muon energy lower than 3TeV effective areas higher than 20%

Aeff (70m)/Aeff (50m) vs E

Aeff (

ab

s 7

0m

)/A

eff (

ab

s 5

0 m

)

Aeff vs E

The ratio

20 kHz sc 50m @~450 nm -

R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

The architectural comparison

R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

The architectural comparison

Compromise between performance and technical feasibility

Performance-> Good angular resolution and effective areas for

•Up-going muons (E 102108 GeV) in the whole angular rangeSeveral 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

The geometries

40m

20m

5832 PMT81 stringsString height 680m (18floors/string) V= 0.88 km3

String-dh_140_20NEMO_140 String-d_125_165800 PMT100 stringsString height 912 m (58 PMT/string)V= 1.15 km3

5832 PMT81 stringsString height 680m (18floors/tower)V= 0.88 km3

R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

The effective muon areas vs E

string-dh_140_20 string-d_125_16 NEMO_140

35 kHz background – abs 70m@450nm

Up-going muons

R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

Angular resolution vs

Up-going muons

E 102 103 GeV E 103 104 GeV

VerticalHorizontalThe “string” detectors show a worst angular resolution for near vertical muons

Q. Cut applied

string-dh_140_20 string-d_125_16 NEMO_140

R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

Muon effective areas vs neutrino energy

NEMOdh-140 RETd-125 RETdh-140

Median of rec vs cos

35 kHz background – abs 70m@450nm

Up-going E-2 muon neutrino spectrum

NEMOdh-140RETdh-140

Ratio =

1 TeV < Ev < 10 TeV

VerticalHorizontal

R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

Down-going muons

35 kHz background – abs 70m@440nm

Down-going muons (moon shadow)

The “string-d_125_16” detector shows a worst angular resolution and Aeff for down-going muons

string-dh_140_20 string-d_125_16 NEMO_140

R. Coniglione, KM3NeT, Marseille 11-12 October ‘06

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 E =104 GeV.

Comparison of effective muon areas as a function of abs 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 E < 104 GeV up-going muons with

<35° -> A reconstruction strategy adapted to each particular geometry can improve the detector performance.