An expected performance of Dubna neutrino telescope for search for high-energy astrophysical neutrinos by detection of high-energy cascades Zh.-A. Dzhilkibaev, INR (Moscow), for the Baikal Collaboration Rome, September 14, 2015

First Demonstration Cluster “DUBNA” (April 2015) String section, 12 OMs R ~ 40 m L~ 345 m Final Layout 192 OMs at 8 Strings 2 Sections per String 12 OMs per Section DAQ-Center Cable to Shore Acoustic Positioning System Instrumentation String with detector calibration and environment moni- toring equipment Two LED beacons for interstring calibration Active depth 950 – 1300 m Instrumented volume 1.7 Mt Cable MEOC - OE Cable Buoy Station - Instrumentation string - DAQ center

Cascades Detection Mode Cherenkov radiation cascades muon Cascades from νe,τ & νμ(NC): Point-like, strongly anisotropic light-source - cascade size proportional to ~lnE  (but LPM-effect for >20PeV!) Light intensity proportional to neutrino energy ~ E∙ 108 γ/TeV Detection efficiency strongly depends on environment properties (water/ice). Angular resolution ~3°- 15° High energy resolution ~10-20% Cascade curve

Environment properties (Baikal) Light absorption: Labs ~ 20 – 25 m Light scattering: Ls ~ 30 – 50 m Dispersion of light velocity negligible Light background: 15 - 40 kHz Scattering function: <cosθ> ~ 0.88

Background for astrophys. neutrino Cascades from atm. muons (down-going) Atm. neutrinos (~E-3.7) (e/μ ~ 1/20)

Optical module (OM) Angular sensitivity Quantum efficiency Glass pressure-resistant sphere VITROVEX (17”) OM electronics: amplifier, HV DC-DC, controller Mu-metal cage PMT R7081HQE : D=10”, ~0.35QE Elastic gel 2 on-board LED flashers: 1…108 pe., 430 nm, 5 ns Angular sensitivity Quantum efficiency

Generation procedure: Cascade vertex r(x,y,z) within ~0.3 km3 volume and direction Ωn Neutrino (e, μ, τ): Energy selection – uniform log10E distribution passing through Earth up to vertex point (CC, NC) – survival probability (due to CC) - final energy (due to NC) Interaction in r(x,y,z) and cascade energy Esh generation Light propagation in water and OM-response OM-response table Npe(μ,j,t,ρ,z) for point-like cascade Integration along cascade length

z ρ OM response table Npe (m,j,t,z,r) MC-simulation Wg r z Wr q m=cosq 350nm <lg < 600 nm La, Ls, v, (lg) n=  exp(-x/La) t = t(v) –t0(vmax) j Wr Wg Scattering point ρ z 0 < r <300 m; -300 m < z < 250 m OM response table Npe (m,j,t,z,r)

Iterative procedure - OMs with residual δt > 15 ns are excluded and reconstruction is repeated Npe(m,j,z,r)

External calibration laser: Operation - 2014 Laser based light-source External calibration laser: 480 nm light pulses Five fixed intensities: ~1012 – 61013  / pulse (~10 PeV – 600 PeV shower energy) - Distances: 50 – 250 m. .

Reconstruction of laser-light source position Laser and OMs coordinates from data of acoustic positioning system Time offsets of OMs from LED calibration Iterative reconstruction procedure – OMs with residual δt > 15 ns are excluded from analysis Multiplicity of rejected OMs Multiplicity of hit OMs after reconstruction

Reconstruction accuracy (median value) of laser position ~3 m Distances between reconstructed and true laser position Reconstruction accuracy (median value) of laser position ~3 m Reconstructed vertical laser coordinate Accuracy of vertical coordinate about of 1.5 m

Reconstruction of laser-light source position reconstructed ~100 m

Laser intensity reconstruction Distributions of reconstructed laser intensities External calibration laser: - 480 nm light pulses; Five fixed intensities: ~1012 – 61013  / pulse (~10 PeV – 600 PeV shower energy) - Distances: 130 – 250 m. Average values of reconstructed intensities for four light source output series . I, 1012  /pulse I1 I2 I3 I4 Cluster 40 12 4.7 1.8 I1 Reconstruction accuracy ~ 10 %

Cluster performance for cascades detection Distance between generated and reconstructed vertices Reconstruction of a cascade vertex: Iterative procedure- OMs with residual δt > 15 ns are excluded and final Nhit is obtained for following analysis. δr = |rrec – rgen| ~ 2 m (median value) Nhit > 10 Averaged by E-2 e spectrum Energy resolution for cascades: δE/E ~ 30% , averaged by E-2 e spectrum Averaged by E-2 e spectrum Nhit > 10

Directional resolution for cascades: Distribution of mismatch angles Directional resolution for cascades: Median value of mismatch angles ~ 3°- 4° depending on energy and cuts Nhit > 10 Cumulative distribution Nhit > 10

Selection criteria based on hit multiplicity Cascade energy distributions Flux ~E -2 : F(Nhit>20)/F(>10) = 0.51 Flux ~E -2.3 : F(Nhit>20)/F(>10) = 0.36 Flux ~E -3.7 : F(Nhit>20)/F(>10) = 0.06

Neutrino Effective Area IceCube GVD-Cluster e Events per Year from IC-flux (E2FIC=3.6·10-8 GeV cm-2s-1sr-1) ~1 Event/Year (>100 TeV) ~ 10 events/Year

Atmospheric muons MC-sample corresponding to 341 life days Vertex reconstruction filter: -270< z rec<200 m, (OMs location: -172.5  +172.5 m) Hit channel multiplicity distributions 1 – after vertex reconstruction 2 – after vertex reconstruction quality cuts 1 2

Cluster performance for cascades detection Sensitivity on one flavor E-2 flux (preliminary, without systematics) Applied cuts: Nhit > 20 (after vertex reconstruction) Vertex reconstruction filter: -270< z rec<200 m (OMs location: -172.5  +172.5 m) Erec > 100 TeV Expected number of events for 1 year exposition: Signal: 1 ev. from astrophysical IC flux (3.6x10-8 GeV cm-2 s-1 sr-1) Background: 0.05 ev – atm. ; 0.05 ev. – atm. μ 5 σ discovery potential for IC neutrino flux with E-2 spectrum

Conclusion First GVD-Cluster has be deployed in 2015 in Lake Baikal ~ 30% energy resolution and ~ (3° - 4°) angular resolution for cascade detection is expected About 1 IC astrophysical neutrino event is expected in 1 year data sample with Esh > 100 TeV for events with Nhit > 20

GVD-Cluster: Neutrino Effective Area Cut on number of hit OMs after vertex reconstruction significantly suppresses background atm. neutrinos Events per Year from IC-flux (E2FIC=3.6·10-8 GeV cm-2s-1sr-1) Applied cuts: Nhit > 20; Erec > 100 TeV ~1 Event/Year (>100 TeV)

Search for High-Energy Cascades With NT200 large effective volume  Cascades produced below NT200: Arrival times were used for vertex reconstruction: Δr/r ~ 7% PMT amplitudes were used for energy and derection reconstruction: δlgE ~ 20%, ψmed ~ 4.5° Results of laser light source position and intensity reconstruction prove an efficiancy of used methods. g g  („BG“) m

Extra cuts for ν events separation: 1038 days (April 1998 – February 2003 Zenith angle distribution Energy spectrum Extra cuts for ν events separation: Esh > 130 TeV (40 < θ < 180) & Esh > 10 TeV (θ > 90)