1. 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

2. 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

3. 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

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

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

6. 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

7. 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

8. z ρ OM response table Npe (m,j,t,z,r) MC-simulationWg 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)

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

10. External calibration laser:
Operation
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. .

11. 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

12. 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

13. Reconstruction of laser-light source position
reconstructed
~100 m

14. 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 %

15. 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

16. 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

17. 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

18. 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

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

20. 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:  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

21. 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

22. 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)

23. 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

24. 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)