AB

C

125m

302m421m

DIceCube 22 strings deployed

M. Bothe1, K. Helbing2, T. Karg2, K. Laihem3, R. Nahnhauer1, B. Semburg2, D. Tosi1, Ch. Vogt3, Ch. Wiebusch3 for the IceCube Acoustic Working Group1DESY, Platanenallee 6, 15738 Zeuthen2Bergische Universität Wuppertal, Fachbereich C – Astroteilchenphysik, 42097 Wuppertal3RWTH Aachen, III. Physikalisches Institut, Otto-Blumenthal-Straße, 52074 Aachen

Acoustic Neutrino Detectionin Antarctic Ice

Detection of Ultra High Energy Neutrinos

1. D. Besson et al., Proceedings of the 29th International Cosmic Ray Conference 5 (2005) 21, arXiv:astro-ph/0512604.2. S. Boeser et al., arXiv:0708.2089: Feasibility of acoustic neutrino detection in ice: First results from the South Pole Acoustic Test Setup (SPATS).

References

The SPATS Sensor

SPATS – The South Pole Acoustic Test Setup

2007/08:1 new string (D):- 7 SPATS transmitters- 6 SPATS sensors- HADES

Mean sensitivity: ~1.5 V/PaEquivalent self noise: ~30 µPa

Detection of ultra high energy neutrinos will provide valuable information concerning astrophysics (cosmic ray sources), cosmology (relic particles) and particle physics (neutrino-nucleon cross section). In order to determine distributions, 100 km3 – scale detectors are needed. An optical/radio/acoustic hybrid detector of such scale is predicted to detect more than 10 cosmogenic neutrinos each year [1].Ultra high energy neutrinos interacting in a medium produce electromagnetic and/or hadronic cascades, which dissipate their energy in a very small volume. This leads to local heating of the medium followed by a prompt expansion. An acoustic shock wave propagates perpendicular to the cascade and can be detected with acoustic sensors over several kilometres as a bipolar pulse with a length of several ten microseconds.

Principle of a hybrid neutrino detector

sonic disc

cascadet

p

coherent radio signal

~ km

optical Cherenkov signal

AAL – A Test Facility for Acoustic Neutrino Detection

Inter-string events: Attenuation length• Systematic errors included

• Large scatter due to module-to-module variations

No in-ice calibration of the sensors and transmitters has been possible so far. Increasing statistics will allow us to build ratios of sensor-transmitter pairs and fit the attenuation length.

HADES – A New Sensor Prototype

Three piezo-ceramics and amplifiers in pressure resistant stainless steel housing

Place piezo-ceramic and amplifier outside the steel housing. The housing only contains a voltage regulator board and supports the sensor within the string.

Piezo ceramicØ 2 cm, h 2 cm

Amplifier

The acoustic impedance of the polyurethane coating the piezo and amplifier is matched to ice to maximize signal transmission.

Mean Sensitivity (10-80 kHz): 0.2 V/PaEquivalent self noise (10-80 kHz): 11 mPa

Something nice about Erlangen building HADES

ConclusionsSPATS status• The South Pole Acoustic Test Setup was successfully installed and commissioned in the 06/07 polar season.• All 21 transmitters are working.• 53 out of 63 sensor channels are operationalResults• Ambient noise is stable and Gaussian• Transmitter signals have been recorded between all strings. Amplitudes are an order of magnitude lower than expected.• The current data determine a lower limit on the attenuation length.Outlook• With increased statistics, we will be able to constrain attenuation length.• Implementation of precise timing will allow us to determine the speed of sound and study refraction.• 4th string including new prototype sensors will be deployed this season.

Initial results for the speed of sound in ice. The total achieved accuracy of about 1‰ is limited by the uncertainty in the global positions and size of the sensors.

slope: -2.81 ± 0.01 m/(s·K)

Statistical Error & FitStat. + sys. error

Picture of the IceTop tank inside the cooling container. The freeze control unit is attached to the tank (front)

Perspective view of the IceTop tank inside the cooling container

Perspective view

T min about -2

5 °C

2110

mm

5454 mm (2

0')

2285 mm

Freezing time (d)

Volu

me o

f ic

e (

l)

Layer

of

ice (

cm)

Finite element simulation

FCU data

Ice thickness as function of the freezing time. The freezing process agrees well with a finite element simulation of the tank.

Supporting in-situ tests (see SPATS below) the Aachen Acoustic Laboratory (AAL) aims to provide an appropriate laboratory infrastructure. Main goals are:

• Verification and of the thermo-acoustic sound generation in ice• Development of highly sensitive sensors optimized for ice• Calibration of acoustic sensors in ice

A particular challenge is the realization of sufficiently large volume of perfectly clear ice. Central element is a tank of ~3m3 designed originally for the IceTop air shower detector. The tank is located inside a standard 20' cooling container. Matched to the tank is a freeze control unit which optimizes the freezing process.In an initial run the tank was operated between July and September 2007. 30 sensors were tested in ice at various temperatures. Preliminary results are shown below. As next step SPATS string D sensors will be calibrated prior to their installation at the South-Pole.After the installation of a powerful laser system studies of the thermo-acoustic effect will be done to allow detailed modelling of the sound generation of neutrino induced cascades in ice.

2006/07:3 strings deployed:- 7 transmitters- 7x3 sensor modules