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

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: 1 10 0.044 1.3 H_7081_20 info_OM: 3 xi, yi, zi, Qi, fi Flykt-OM ( 21 x 3” PMT) PMT type: 1 3 0.0039 0.5 pm2 info_OM: 21 R.Shanidze, O.Kalekin/ KM3NeT WP3-Meetiing on Optical Modules, Genova, 9-11/4/2008

PMTs / Optical Modules/ Storeys in the Erlangen optimization studies The PMTs used in the Erlangen MC simulations: 1) Standard: 10” Hamamatsu R7081 2) Small: 3” 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

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, 10 < 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

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

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

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

MC event time and K40 background rate Deep-sea neutrino detector: the hit rates are defined from K40 K40 hits in ANTARES MC ( K40 3545 500 ) 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

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

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

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

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

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

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