Can We Listen for Neutrinos ?
T.Sloan
February 7, 2005
Overview
Brief review of Cosmic rays.
Cosmic ray neutrinos - what is our current knowledge.
Current or planned experiments to detect cosmic neutrinos.
Listening experiments - use of ultra sensitive hydrophones
used in characterising the noise from naval vessels to
detect the sound from high energy neutrinos.
1
Review Knowledge of Cosmic Ray Primaries
The energy spectrum of cosmic ray primaries shows several
features.
One sees the “knee” at energy
at
and the “ankle”
eV
The slope changes at the knee and possibly at the ankle .
2
The Ankle - GZK Cut-off at
eV (
J).
Protons at energy above this can produce pions by
interactions with the 3 K cosmic background radiation
with threshold at eV and the
resonance just above threshold.
Therefore energy is always degraded down to this energy as
the primary travels towards the Earth i.e. the GZK cut off.
What do the data say ?
AGASA do not see the cut-off but HiRes may see it. NB
change to energy scale minimises the disagreement.
Curve shows a fit to HiRes data which includes GZK cut-off
expected from a uniform distribution of sources.
3
If there are charged primaries at UHE - are there neutrinos ?
Sources of Ultra High Energy (UHE) Neutrinos
Waxman-Bahcall limit - baryon primaries interact in “thin”
material surrounding the cosmic ray primary source.
The GZK effect
and
from decay of pions produced by
interactions of primaries with Cosmic Microwave
Background radiation (CMB).
Topological Defects and other possibilities beyond the
standard model.
4
Current experimental limits on Neutrino Fluxes
-2
10
E ν2 d φ/dE ν (GeV cm
-2 -1
s sr -1)
Optical Cerenkov
Radio, Acoustic
-3
10
-4
10
GLUE 2003
-5
10
atm-ν
RICE 2003
Baikal νe +νe ,2001
10
FORTE 2003
Auger νe +νµ
-6
Amanda up-νµ ,2003
Auger ντ
Antares :
1yr
3yr
-7
10
-8
Waxman-Bahcall
km3 ⊗ 3yrs
10
GZK
-9
10
10
4
10
5
10
6
10
7
10
8
10
9
Eν
10
10
10
11
10
12
10
13
10
14
10
15
10
(GeV)
Waxman-Bahcall Limit - estimate production from measured
primary spectrum assuming a low density target and
produced from standard ,K production and decay. They
multiply their estimate by a rather arbitrary factor of about
5 and call it a limit (labelled Waxman-Bahcall).
Engel,Seckel and Stanev compute the flux of neutrinos
produced from interactions of UHE protons with the
cosmic background radiation (labelled GZK).
5
16
10
17
Table 1: Attenuation Length
Water
Ice
EM Optical
m
Salt
m
Particles detected
Upward
(Cerenkov)
EM Radio
few km
km(?)
Electron
(0.1-1 GHz)
acoustic
km
large?
large?
(10kHZ)
6
Hadron shower
Acoustic Detection of UHE neutrinos . Using hydrophones
in a water target.
Particle showers contained in a thin cylinder about 10
collision lengths long (
m) and radius
m.
Some of energy converted to sound.
Add up Huygen’s wavelets coherently on a roughly cylindrical
wave front.
Sound propagates out in a pancake shape perpendicular to
the shower axis.
7
Summary in words
Particle shower causes a micro-tidal wave with positive
pressure followed by negative pressure in a time
sec with Fourier components peaking at 10 kHz.
Pressure wave propagates according to wave equation
Time
8
Results for a shower of energy
eV at 1 km from
the shower and in plane perpendicular to the shower.
Far field Radiation pattern
0
10
−1
Pressure (Pa)
10
−2
10
−3
10
−5
−4
−3
−2
−1
0
1
Angle(degrees)
9
2
3
4
5
Need to pick out pulses of bipolar shape from the noise characteristic of hadron shower. All other noise makes a
continuous ring while hadron shower is a bipolar signal.
Noise Man made (e.g. boats), wave and wind at surface,
bionoise (dolphins, snapping shrimps etc.)
Many arrays of very sensitive hydrophones exist which have
been used to “categorise the noise from naval vessels” i.e.
listen for submarines at low frequency.
We think that these hydrophones are sensitive enough to
listen for ultra high energy (uhe) cosmic ray neutrinos
interacting in water.
We do not know enough about noise limitations or how to
calibrate such an array.
An R and D proposal has been funded jointly by PPARC and
the MoD. We will use a hydrophone array in Scotland
(belonging to MoD) the (Acoustic COsmic Ray Neutrino
Experiment - ACORNE).
10
Separating the signal from the noise.
Use a signal processor - on line algorithm.
denz(z)
pulse
A
Acoustic Pulse
1
Inverse Filter
Matched Filter
denz(z)
Discrete Filter
Can this dig out the signal from the noise ?
11
match(z)
numz(z)
numz(z)
White Noise Source
B
C
Scope
Generate a signal and inverse filter to simulate the data
Inverse Filtered
0.4
0.3
0.3
0.2
0.2
0.1
0.1
Relative Pressure
Relative Pressure
Original
0.4
0
0
−0.1
−0.1
−0.2
−0.2
−0.3
−0.3
−0.4
0
5
10
sample
15
−0.4
20
0
5
10
sample
15
20
Add it to the noise (Rona - mean sea state)
Noise with Embedded Signal
4
3
2
Amplitude
1
0
−1
−2
−3
−4
0
100
200
300
400
500
sample
12
600
700
800
900
1000
Put it through the signal processor.
Matched Filter Output
8
6
Amplitude
4
2
0
−2
−4
0
100
200
300
400
500
sample
600
700
Out pops the signal which we simulated.
13
800
900
1000
Does it work in practice ?
The programme - study if the technique is feasible.
To achieve this we propose to
Study the noise from the Scottish array.
Make a hardware hadron shower simulating device.
Use it to fire calibration signals into the sea to see if we
can detect them against the background noise (wind,
man-made and bionoise).
Cross disciplinary team - Signal processing experts (J.
Allen, R. Binns, S. Danaher), Acoustics expert (C.
Rhodes), Particle physicists (Lee Thompson, David
Waters and TS) from UCL, Univs of Lancaster,
Northumbria and Sheffield and from MoD.
14
Log10[E2 dN/dE (GeV cm−2 s−1 sr−1)]
Limits set in pilot experiment.
2
SAUND
0
FORTE
−2
GLUE
Z
−4
RICE
−6
A
AGN
B
TD
WB
−8
−10
8
GZK
10
12
Log10[E (GeV)]
14
16
Dashed curves are estimates of the potential of a
multi-element array NB needed to be sensitive to whole
angular range.
15
Conclusions
Acoustic technique is potentially a viable technique for ultra
high energy neutrino detection - but will need a large array
of hydrophones.
Purpose of the ACORNE project. Do a design and feasibility
study to see if we can improve on the radio techniques.
16