1. Optical Modules in the KM3NeT optimization studies in Erlangen
Rezo Shanidze, Oleg Kalekin
KM3NeT WP3 Meeting on Optical Modules
9-11 April 2008, Genova

2. Introduction: OM/PMT properties in the ANTARES MC
In the ANTARES software (gendet):
OM : 1 or more PMT (info_OM). PMT position in OM is defined
by 5 parameters: 3 coordinates + 2 angles
Each PMT is defined with 5 parameters (PMT_type) :
1-type identifier, 2-diameter (inch) , 3-PMT photocathode are(m2),
4-TTS (ns), 5-PMT name
Example of OM/PMTs from Erlangen simulations (S.Kuch, PhD thesis):
ANTARES (10” PMT)
PMT_type: H_7081_20
info_OM: 3
xi, yi, zi, Qi, fi
Flykt-OM ( 21 x 3” PMT)
PMT type: pm2
info_OM: 21
R.Shanidze, O.Kalekin/ KM3NeT WP3-Meetiing on Optical Modules, Genova, 9-11/4/2008

3. PMTs / Optical Modules/ Storeys in the Erlangen optimization studies
The PMTs used in the Erlangen MC simulations:
1) Standard: 10” Hamamatsu R7081
2) Small: ” Photonis XP53X2
OM/storey:
with large PMT
a) OM with one 10” PMT
b) Two OMs with 10”PMT
c) ANTARES type with 3 OMs
d) ANTARES type with 6 OMs
with Multi-PMT OM
e) Storey with 3 cylindrical OMs
f) Storey with spherical OM:
36 or 42 PMTs
g) Storey with spherical OM:
21 PMTs.
R.Shanidze, O.Kalekin/ KM3NeT WP3-Meetiing on Optical Modules, Genova, 9-11/4/2008

4. The large number of the different KM3NeT models:
MC Data in Erlangen
MC data produced in Erlangen (with the modified ANTARES software):
Gendet g GENHEN g km3 g RECO
For each detector configuration, 2 x109 simulated events :
nmN CC interactions:
E-1.4, < En < 107 GeV, -1 <cosQn<1
Data sample for the reconstruction:
~ 8 x104 events / configuration (10 data files )
The large number of the different KM3NeT models:
limited statistics per configuration
Different selection steps, for the stored MC data:
Minimal: requests six signal hits and two storeys.
Reconstructed (selected): event is reconstructed by the modified
ANTARES algorithm.
R.Shanidze, O.Kalekin/ KM3NeT WP3-Meetiing on Optical Modules, Genova, 9-11/4/2008

5. Neutrino effective areas vs. KM3NeT configuration
MC simulations in Erlangen: ( the different OMs for the same geometry configuration)
The differences in PMT/OM are important for the energy region <10 TeV . a b
The neutrino effective areas (a) and their ratio (b) for the detectors with
homogeneous (cuboid) configuration and the same photocathode area.
(The detectors with ANTARES storeys and different multi-PMT configurations).
[ From S.Kuch, PhD thesis, fig 8.24 (selected) ]
R.Shanidze, O.Kalekin/ KM3NeT WP3-Meetiing on Optical Modules, Genova, 9-11/4/2008

6. from S. Kuch ( PhD Thesis, Chapter 8, Photo-detection layouts)
Brief Summary on Photo-detection layouts
from S. Kuch ( PhD Thesis, Chapter 8, Photo-detection layouts)
Storeys with many small PMs (MultiPMT storey) provide advantage at
energies below a few TeV (depending on selection), mostly due to the
higher quantum efficiency of the small PMs.
Despite the smaller TTS of the small PMs, the angular resolution in not
significantly better for detectors with MultiPMT storeys.
The geometry of the arrangement of the PMs in a storey has almost
no influence on the detector performance
A simplification of the readout method for the MultiPMT storeys does
not reduce the effective area significantly above a few TeV.
Detectors with many storeys carrying few PMs are superior to detectors
with few Storeys carrying many PMs, as a higher density of storeys provides
better (coincidence) purity and therefore better reconstruction results.
R.Shanidze, O.Kalekin/ KM3NeT WP3-Meetiing on Optical Modules, Genova, 9-11/4/2008

7. The Reference Detector
15 x 15 strings
( 95 m)
37 storey (8325 OMs)
16.5 m
1 Multi-PMT OM
21x 3’’ PMT
Total number of PMTs:
174825
Instrumented
volume
1.05 km3
Max m-track length (time) in KM3NeT ~ 2 km (7 msec)
R.Shanidze, O.Kalekin/ KM3NeT WP3-Meetiing on Optical Modules, Genova, 9-11/4/2008

8. MC event time and K40 background rate
Deep-sea neutrino detector: the hit rates are defined from K40
K40 hits in ANTARES MC
( K )
i i
Event time in MC :
a time interval between
muon hits + 2DtK40
DT= (tmax – t min) + 2DtK40
MC event time:
Dt ~ 1 ms ( at low energies )
rate/PMT ± Dtk4o time(ns)
Reconstructed m
R.Shanidze, O.Kalekin/ KM3NeT WP3-Meetiing on Optical Modules, Genova, 9-11/4/2008

9. MC event reconstruction vs. event time
The events :”seen” in the detector for a long time ( > 5 msec) are reconstructed with ~100% efficiency.
An event time is correlated with
a neutrino energy in the event.
R.Shanidze, O.Kalekin/ KM3NeT WP3-Meetiing on Optical Modules, Genova, 9-11/4/2008

10. Flykt-OM in Erlangen MC simulations
Configuration for “Flykt -OM” used in a reference detector (S. Kuch) :
Angle Qij(o) between 3” PMTs in the Flykt-OM
Configuration Flykt-OM with
21 PMTs used MC simulations.
C(2,21) = 210 PMT pairs.
R.Shanidze, O.Kalekin/ KM3NeT WP3-Meetiing on Optical Modules, Genova, 9-11/4/2008

11. The OM hits and coincidences
Purity of single hits and coincidences are very different.
a) Number of PMT hits per event vs. neutrino energy
b) Coincidence of signal and K40 hits in the Flykt-OM (1) a b
K40 hits
K40 hits
1) The correlated hits from the K40 decays are not considered in the current MC
R.Shanidze, O.Kalekin/ KM3NeT WP3-Meetiing on Optical Modules, Genova, 9-11/4/2008

12. Flykt-OM vs. Background
The mean number of Flykt-OMs
with the PMT hits as a function
of the neutrino energy.
The background hits
are significantly reduced
after taking OMs with:
a) at least 2 hits/PMTs
b) Dt < 5 ns for at least
one pair of PMT hits.
In addition angular information
of PMT in the OM can be used.
OM ( > 1 PMT)
OM (Dt < 5 ns)
R.Shanidze, O.Kalekin/ KM3NeT WP3-Meetiing on Optical Modules, Genova, 9-11/4/2008

13. Bioluminescence vs. Optical Module
From I.G. Pride et al., The potential influence from marine animals
on a deep sea underwater neutrino telescope array
in the Mediterranean sea
Prediction of frequency of bioluminescent events - dominant source is
a stimulated bioluminescence:
impact s-1 = A x v x r
A – max. cross-sectional area of a sphere
v - current velocity
r - density ( number of bioluminescent sources m-3)
It is assumed that each impact will result in at least one flash from
bioluminescent organism.
( other sources: spontaneous and entrained bioluminescence)
To minimize the stimulated bioluminescence background:
minimize surface of the detector elements and OM spheres
For fixed photocathode area maximize ratio R= APMT/AOM ratio
R Flykt-OM = 1.86 RANTARES ( Flykt-OM: 21 x 3” PMT )
R.Shanidze, O.Kalekin/ KM3NeT WP3-Meetiing on Optical Modules, Genova, 9-11/4/2008

14. For the same geometry configuration and the total photo-cathode area
Summary
For the same geometry configuration and the total photo-cathode area
the neutrino effective area with the different PMT/OM/ Storeys shows
significant differences only in the neutrino energy region < 10 TeV.
At low energies detectors with the larger number of storeys, (the larger
number of the local coincidences for m- track reconstruction), have
significantly larger effective area.
Flykt-OM (multi-PMT OM) may have additional features, which should be
studied. For example
- Bkg. rejection with a help of time and angular information from PMTs.
More MC statistics are necessary for the study of different features of
Flykt-OM.
Dedicated MC are necessary to study an effect of the correlated K40
hits in Flykt-OM for the m-reconstruction.
R.Shanidze, O.Kalekin/ KM3NeT WP3-Meetiing on Optical Modules, Genova, 9-11/4/2008