Transcript Simulation of Particle Cascades for the Acoustic Detection

Diving For Neutrinos
( How to use the sea as a Calorimeter… )
AGN - Black Hole
proton
e+
Enveloping Radiation
p, e-

Jonathan Perkin
University of Sheffield
Acoustic Cosmic Ray Neutrino Experiment
Ultra High Energy Cosmic Ray
(UHECR) neutrinos…
• Cosmic ray protons can interact with ambient radiation
to produce associated flux of neutrinos (previous slide)
• Above a certain threshold, CR protons will interact
with CMB photons (GZK effect)
p + e- + e
p + CMB →  → N + 
 + 
e+ + e + 
• “Guaranteed” flux of cosmogenic neutrinos
17/07/2015
Jonathan Perkin
Lake Louise Winter Institute
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• GZK effect should produce a cut-off in CR spectrum
1020 eV = 2.4x1034 Hz
= 1.6x108 erg
= 170 km/h
tennis ball
s equivalent is 3x105 GeV
• There is a discrepancy between existing experiments –
AUGER to settle this.
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Jonathan Perkin
Lake Louise Winter Institute
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Acoustic Cosmic Ray Neutrino Experiment
Ultra High Energy Cosmic
Ray (UHECR) neutrinos…
(using the sea as a calorimeter…)
neutrino
Sea / Ice
Ice /
Salt
PMT Array
Optical
Cerenkov
Sea / Ice / Salt
Cascade
Antenna
Array
Radio
Cerenkov
muon
neutrino
Attenuation ~50m
E few × 103GeV
17/07/2015
Hydrophone
Array
Cascade
Acoustic
Pressure
Waves
neutrino
Attenuation few km
E few × 106GeV
Jonathan Perkin
Lake Louise Winter Institute
Attenuation ~10km!
E > 1010GeV
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Acoustic Cosmic Ray Neutrino Experiment
How to detect UHECR
neutrinos
Generation of Acoustic Signal
Temperature
dt2
h
t
17/07/2015
Acoustic Cosmic Ray Neutrino Experiment
• Fast thermal energy deposition
(followed by slow heat
diffusion)
• Results in a nearinstantaneous temperature
increase and material
expansion giving rise to an
"acoustic shock" sound pulse d2
Time
• This pressure pulse is related to
the double derivative of the
(essentially) step function of the
temperature rise and leads to a
characteristic expected bipolar
pulse shape
• h is defined by the properties of
the medium, t is defined by the
transverse spread of the shower
Jonathan Perkin
Lake Louise Winter Institute
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Generation of Acoustic Signal
Acoustic Cosmic Ray Neutrino Experiment
For E = 1020eV, 99% of the
cascade energy is contained within a
cylinder of length 10m and radius
20cm.
•The energy deposition can be
considered as a continuous distribution
of individual heating centres
•Radiation is emitted coherently along
the cascade axis – leading to a
confinement of the signal to a narrow
pancake due to a superposition of
wavelets.
This is analogous to the diffraction of
light through a narrow slit
17/07/2015
Jonathan Perkin
Lake Louise Winter Institute
10m
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Simulation of Large Scale Array
Acoustic Cosmic Ray Neutrino Experiment
Basic approach:
• Take a parametrised acoustic signal - amplitude is a function of
incoming neutrino energy and direction
• Calculate the expected signal at each hydrophone in the array
taking into account attenuation, etc.
Place cuts at each
hydrophone at a very
conservative threshold
that corresponds to one
false alarm per 10 years
according to the known
sea state
•Visualisation of the response of a hypothetical array of
1260 hydrophones.
17/07/2015
Jonathan Perkin
Lake Louise Winter Institute
Record only those
hydrophones above
threshold and within the
plane of the acoustic
“pancake”
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Array Potential Performance
•
• Energy reconstruction via a c2
technique where the energy seen
on the hydrophones is compared
to that predicted from the
parametrisation
• Some effects still to be added,
results look promising
Best fit at log10E=14.82
17/07/2015
• (Actual – reconstructed)
x position of the vertex
• Y and Z look similar
• Avoid symmetry in array
geometry
Jonathan Perkin
Lake Louise Winter Institute
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Acoustic Cosmic Ray Neutrino Experiment
A reconstruction package has been written to reconstruct the incoming
neutrino position, direction and energy. NB PRELIMINARY RESULTS
Energy Simulator
Acoustic Cosmic Ray Neutrino Experiment
• Short duration laser pulses → energy deposition at
any given point is a delta function in time
• Path length limited by reflecting
element → angular spread of the
acoustic pulse mimics that of the
shower
• Extra (de)focussing optics
to control lateral spread
of the energy deposit →
 Optical wavelength
ensures the pulse shape
chosen to give
and frequency
absorption length
spectrum mimic
in water similar to
shower length that of a
effective coupling
shower
of optical energy
May use alternate light sources to thermal energy
– e.g. High Power LED
17/07/2015
Jonathan Perkin
Lake Louise Winter Institute
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Test Beam Results
Thermoacoustic signals have been recorded from
proton test beam interactions at accelerators
(Sulak et al., NIM 161 (1979) 203)
Agreement within 2 between simulation (solid
line) and experiment (points) indicates that the
observed pressure wave could be primarily of
thermoacoustic origin.
17/07/2015
Jonathan Perkin
Lake Louise Winter Institute
Typical signals
from the two
hydrophones in the
linac experiments –
clear bipolar signal
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Other Acoustic Activities
The SAUND collaboration, operating
the AUTEC hydrophone array in the
Bahamas has published first results
from the array in astro-ph/0406105
Array consists of 7 hydrophones
Analysis method involves selecting 5-fold co-incidences
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Jonathan Perkin
Lake Louise Winter Institute
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Thanks for your attention
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Jonathan Perkin
Lake Louise Winter Institute
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Backup Slides
17/07/2015
Jonathan Perkin
Lake Louise Winter Institute
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Signal Attenuation
• The acoustic signal detected at the
hydrophone is modified by 3 factors:
1. geometric (1/r) attenuation,
2. angular spread using parametrisations of the modelled spread (using
Fraunhofer diffraction theory) fit to 2 Gaussians (hydrophones more than 5
degrees out of the pancake plane are not considered)
3. attenuation due to the medium - again from studying the acoustic signal as a
function of the distance from the source and the water properties. Performed
on matched filter output
Angular spread
Medium losses
17/07/2015
Jonathan Perkin
Lake Louise Winter Institute
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Backgrounds (physical & biological!)
UHE Cosmic Rays should not mimic the signal:
–UHE protons have a very low probability of reaching the Earth
without interacting, they produce many lower energy muons that
have a significantly lower dE/dx
–UHE muons have a far lower dE/dx. If they decay (v. unlikely:
bgct >> D ) they may give rise to an UHE electron that can
mimic the acoustic signal but this is interesting in its own right!
Bio-noise is less obvious
and a subject for study in
this proposal, however in
deep water:
–Most bio-noise is expected to come
from close to the surface in which
case
•refraction carries sound away from
detectors
•linear phased arrays will aid
background rejection
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Jonathan Perkin
Lake Louise Winter Institute
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