Preliminary Studies of the KM3NeT Physics Sensitivity

Sebastian Kuch, Rezo Shanidze

KM3NeT Collaboration Meeting

Pylos, Greece, 16 - 18 April 2007

Introduction/Motivation

What is the minimal flux of high energy cosmic neutrinos which can be detected with KM3NeT detector ?

What is the minimal flux which is necessary for discovery of neutrino point sources ? - How does KM3NeT sensitivity depends on detector configuration (geometry, OM) and environmental (site) parameters ?

New data for NEMO site:

G.Riccobene et al, Astroparticle Physics, 27 (2007), 1

‘Deep seawater inherent optical properties in the Southern Ionian Sea

’.

- How does the sensitivity depends on KM3NeT performance parameters, for example energy and angular resolution ?

R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece 2

What to expect ?

Sensitivity: Upper limits of cosmic neutrino fluxes when event rates are comparable with background (no signal detected) Detection with given significance level ( for example 5 s ) ratio of detected events to the standard deviation from expected background events is larger then given significance level • Upper limit scales ~linearly with detector effective area/detection time.

• Detection with given significance scales as ~square root from the effective area/detection time C. Distefano (for NEMO- km 3 ), astro-ph/0608513 NEMO-km 3 : 9 x 9 lines (towers), 5832 x 10’’ PMT, Line=680 m.

d(line)=140m, d(storey)=40m 18 storeys/Line, 4 PMT/Storey Absorption length 68 m (440nm), 30 kHz optical noise R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece 3

After WP2 Meeting in Marseille

WP2@Marseille, October 2006: • A few detector models were selected for the sensitivity studies, according to the results of simulations in Erlangen.

This selection covers the different geometry concepts as well as different photo-detection systems.

• A note on benchmark neutrino fluxes for optimization of KM3NeT detector design was released by WP2 group. KM3NeT-Physics/2007-01 . • First very primary estimation of limits on the high energy cosmic neutrino diffuse flux and neutrino fluxes from point sources were obtained . R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece 4

Selected KM3NeT Detector Models

Different geometries: Cuboid, ring1, clustered1 (with cyl. Multi-PMT configuration) Different storeys: cuboid with ANTARES story and ANTARES 20” ‘Example’: cube2 configuration with spherical multi-PMT storeys (21x3”) Cluster 1 Cuboid geometry Ring 1 R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece 5

Benchmark Neutrino Fluxes

KM3NeT Physics/2007-01 NOT an exhaustive list of potential sources, rather list of recommended ‘typical’ fluxes : • Atmospheric neutrino flux • Neutrinos from dark matter annihilation (talk by H.Motz) • Neutrino fluxes from Galactic sources • Diffuse neutrino flux from extra-Galactic sources (Waxman-Bahcall flux ) • GZK Neutrinos KM3NeT detector sensitivity was considered to muon neutrino charged current events (muon events) for diffuse neutrino flux and fluxe from point sources.

R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece 6

Atmospheric Neutrino Flux

4 different models for the atmospheric neutrino flux are included in the ANTARES software: Volkova, Bartol, Honda and Fluka models.

Bartol

was used in this study, according to WP2 recommendations.

flux R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece 7

Assessment of Diffuse Flux Limits

Detector (Storey) Cuboid (cyl) Cluster 1 (cyl) Ring 1 (cyl) Cuboid (ANT) Cuboid (20” ANT) Cuboid 3 (sph) Optimal E n cut (TeV) Flux limit (

x 10 -9 E 2 GeV -1 m -2 s -1 sr -1

) Minimal (ratio) 1.55 (1.00) 1.72 (1.11) Moderate (ratio) 1.58 (1.00) 1.73 ( 1.10) Selected (ratio) 2.27 (1.00) 2.68 (1.18) 1.62 (1.05) 1.57 (1.01) 1.54 (0.99) 1.64 (1.04) 1.60 (1.01) 1.57 (0.99) 1.54 (0.99) ~370 1.56 (0.99) 2.31 (1.02) 2.31 (1.02) 2.31 (1.02) 2.30 (1.01) ~500 cyl – cylindrical storey (3” PMT), sph – spherical store (21 x 3” PMT), ANT-ANTARES storey Diffuse flux sensitivity is similar (5% level) for the considered detector models, except clustered model. The limits are obtained for neutrino energies above 10 5 GeV, where effective areas of different detector models start to converge. R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece 8

Neutrino Fluxes from Point Sources

Two methods were applied in the point source studies: 1) An upper limit estimated for the generic point source with E -2 neutrino flux as a function of declination 2) Event rates calculated for selected HESS sources, with neutrino flux calculated from measured gamma flux. The sky-map of the H.E.S.S. catalogue sources (33 sources).

R.Shanidze, S.Kuch

VHE g and corresponding n fluxes for HESS J0835-455. (Vela X) .

A.Kappes et al., astro-ph/0607286 KM3NeT, Pylos, Greece 9

Neutrino Fluxes from Point Sources

For the “generic neutrino point sources” : • Neutrino flux is of E -2 type.

• No energy cut, energy range corresponds to simulated energy interval 10 < E n < 10 7 GeV. • Event rates calculated in an angular area, with 2 x angular resolution ( DQ n (E n )), at E=1 TeV (error dominated by kinematics) • 2D effective area A eff (E n , Q n ) used in the calculations and ANTARES location is assumed for the detector . R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece 10

Visibility of Point Sources

Zenith angle of a source viewed from the detector is defined by detector latitude (

LAT

), source declination ( d ) and hour angle (

HA

) .

sin(

Q

)=sin(

d

)·sin(LAT)+cos(

d

)·cos(LAT)·cos(HA) HA =

Hour angle, 1

day: 0 < HA < 2

p Source below horizon HESS J1713-3935, d =-39 o ANTARES site R.Shanidze, S.Kuch

HA (0-2 p ) 2D Effective area A(E, Q ) at moderate selection level. (cube2, with sph.) KM3NeT, Pylos, Greece 11

Assessment of Point Source Flux Limits

a b c Limits for the point sources with E -2 neutrino flux. Calculations for the selected detectors models and 2 different criteria: a) selected/reconstructed events b) moderate criteria (6 hits /6 storeys) R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece 12

Flux Limits vs Selection Criteria

Note that KM3NeT limits are very preliminary ! Presented plot indicates what can be achieved with 1km 3 detector at ANTARES site, with optimistic assumptions. Neutrino flux limits (very preliminary!) for point sources evaluated as a function of source declination, for the cuboid detector with cyl. storeys, at different selection steps. ANTARES limit is plotted for the comparison. R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece 13

Comparison of the Flux Limits

Note that KM3NeT limit is very preliminary ! Presented plot indicates what can be achieved with 1km 3 detector at ANTARES site, with optimistic assumptions. Comparison of the neutrino flux limits vs. source declination obtained for example detector, to the limits from experimental data (MACRO, AMANDA) and the other neutrino telescope projects (ANTARES, IceCube). R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece 14

Summary

•

KM3NeT sensitivity has been considered for the detector models selected from the simulation studies in Erlangen, corresponding to different geometrical layouts and photo-sensors.

•

Upper limit of cosmic neutrino diffuse flux (E -2 ) was estimated for selected detectors using Bartol model for atmospheric neutrino flux. The upper limit is similar (within 5%) for all detectors, except clustered one (0.9 CL).

•

Upper limits for the point sources were estimated for E -2 neutrino flux model as function of source declination.

R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece 15

What is still missing:

Outlook

•

Energy estimation of the selected/reconstructed muon neutrino events. Important for diffuse flux limit calculation. Can be used in the optimization of the point source analysis.

•

Dedicated event selection and reconstruction.

•

Dependence on site parameters, like optical properties of the selected site, 40 K background.

•

Cross-check of the obtained results with different methods / groups.

16 R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece

Event Rates from HESS J1713-397

Expected number of events from HESS J1713-397 (SNR RX J1713.7-3946) for different detector models and selection steps. (E n > 1TeV, T= 1 year) Detector mean number of events / number of atmospheric events Minimal Moderate Selected Cuboid 1 (cyl) Cluster 1 (cyl) Ring 1 (cyl) Cuboid (AN) Cuboid (20” AN) Cuboid3 (sph) 2.7 /10.7

1.7 / 6.5

2.5 / 9.7

2.6/ 9.8

3.2/12.7

2.8/10.9

2.4/9.1

1.7/6.3

2.3/8.7

2.2/8.3

2.9/11.6

2.6/10.1 0.8/2.9

0.8/2.9 0.9/3.4

0.9/3.1

0.9/3.1

0.9/3.2

cyl – cylindrical storey (3” PMT), sph – spherical store (21 x 3” PMT), AN-ANTARES storey (10”) R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece 17

Current Limit ( Point Sources )

Flux model: F

(E

n

)= k

n

E -2

Current AMANDA limit: k n  ~ 10 -7 ( GeV -1 cm -2 s -1 ) KM3NeT ?

IceCube (1 year): 5 s :

7 10 -9

90% c.l.:

2 10 -9 E -2 E -2

T.Montaruli, astro-ph/0608140 R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece Astropart.Phys. 20(2004), 507 astro-ph/0305196 18

Preliminary Diffuse Flux Limits

Comparison of the calculated KM3NeT diffuse flux limits to the current experimental data and upper limits of ANTARES and the Waxman-Bahcall flux expectation R.Shanidze, S.Kuch

KM3NeT, Pylos, Greece 19

Assessment of Flux Limits

Cosmic neutrino flux limits (for diffuse and point like sources) for considered detector models were calculated in Feldman-Cousins approach, assuming Poisson statistics for the signal and background neutrino events. The event rates (for T=1 year) were calculated from the corresponding effective areas . ( more in: S.Kuch, Ph.D thesis, FAU-PI1-DISS-2007-01 ).

Example

for the diffuse flux calculations: integrated events rates for the diffuse (signal) and atmospheric (background) neutrino fluxes as a function of threshold energy for the Cuboid detector (cyl.).

N limit – is an upper limit of signal events obtained from background event rates in Feldman-Cousins approach. KM3NeT, Pylos, Greece 20 R.Shanidze, S.Kuch