Simulation of a hybrid optical, radio, and acoustic neutrino detector

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Simulation of a hybrid optical, radio, and
acoustic neutrino detector

• Justin Vandenbroucke
• with D. Besson, S. Boeser,
• R. Nahnhauer, P. B. Price

IceCube Collaboration meeting, Berkeley March 23,
2005
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The goal

• EeV neutrinos, particularly GZK neutrinos, could
  be a valuable source for astro- and particle
  physics
• IceCube or Auger could detect 1 GZK neutrino per
  year, but
• 10 GZK events/yr would give a quantitative
  measurement including energy, angular, and
  temporal distributions allowing tests of cosmic
  ray production models and new physics
• Other projects (e.g. ANITA, SalSA) are actively
  seeking this goal. Should IceCube also seek it?

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Why a hybrid extension to IceCube?

• Like Auger and detectors at accelerators, use gt1
  technique monitoring the same interaction region
• Difficult to reach 10 GZK events/yr with optical
  alone
• At EeV, radio and acoustic methods could outdo
  optical
• Detecting events in coincidence between 2-3
  methods more convincing than detections with one
  method alone
• Coincident events allow calibration of the radio
  and acoustic methods with the optical method
• Hybrid reconstruction gives superior energy and
  direction resolution than with one method, or
  allows reconstruction of coincident events that
  cannot be reconstructed with one method alone
• Extended IceCube could be pre-eminent neutrino
  telescope at all cosmic energies?

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EeV fluxes

• Z-burst and topological defect models predict
  large EeV fluxes but are observationally
  disfavored
• The GZK flux is a fairly conservative EeV source
• Optimize the hybrid detector for a high rate of
  events from the Engel, Seckel, Stanev (ESS) GZK
  flux model, but
• Do not only seek GZK events. Measure whatever is
  there at EeV and design to detect events over a
  wide energy range
• Then the IceCube observatory measures the
  neutrino spectrum over 10 orders of magnitude!

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The ESS GZK flux model
zmax 8, n 3 Unclear which ?? to use
(unclear effect on star formation rate) For now
use the lower rate
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First-pass simulation keep it simple

• Assume exactly the 2? downgoing neutrinos make it
  to the detector, independent of energy, within
  our 1016 - 1020 eV range
• For radio and acoustic assume the LPM effect
  completely washes out signal from EM component of
  ?e CC events, so
• For all flavors and both CC and NC we detect only
  the hadronic shower, with
• Esh 0.2E? for all events, independent of
  energy
• Generate incident directions uniformly in
  downward
• 2?, and vertices uniformly in a fiducial
  cylinder
• At each of a set of discrete energies, expose
  each of the 3 detector components to the same set
  of Monte Carlo events

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An example hybrid array
Optical 80 IceCube 13 IceCube-Plus holes at a
1 km radius Radio/Acoustic 91 holes, 1 km
spacing 5 radio 200 acoustic receivers per
hole
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Optical simulation

• Check Halzen Hoopers rate estimate with
  standard simulation tools run a common event set
  through optical radio and acoustic simulations
• For now, only simulate the muon channel (later
  add showers)
• Propagate muons with mmc
• Use amasim with MAM ice (no layering)
• Local coincidence trigger 10 coincidences with 2
  out of 5 in 1000 ns
• For optical-only events, apply Nch gt 182 to
  reject atmospheric background
• Do not apply Nch requirement when radio or
  acoustic also triggers

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Optical Effective volume
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Muon track length
Count
Length (km)
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Radio simulation

• Dipole antennas in pairs to resolve up-down
  ambiguity
• 30 bandwidth, center frequency 300 MHz in air
• Effective height length/?
• Radio absorption model based on measurements by
  Besson, Barwick, Gorham (accepted by J. Glac.)
• Trigger require 3 pairs in coincidence
• Use full radio MC

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Predicted depth (temperature)-dependent acoustic
absorption at 10 kHz
In simulation, integrate over absorption from
source to receiver
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Acoustic pancake contours
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Acoustic event rate depends on S/N and hole
spacing
Trigger 3 strings hit ESS events per year
RMS Noise (mPa) Hole spacing, km (91 string hexagonal array) Hole spacing, km (91 string hexagonal array) Hole spacing, km (91 string hexagonal array) Hole spacing, km (91 string hexagonal array)
RMS Noise (mPa) 0.25 0.5 1 2
5 1.7 2.6 4.5 4.0
2 3.6 5.5 9.6 9.1
1 5.6 8.6 15 15
Need low-noise sensors (DESY) and low-noise ice
(South Pole?) Frequency filtering may lower
effective noise level For hybrid MC, set
threshold at 9 mPa
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Acoustic neutrino direction and vertex
reconstruction
- With 3 strings hit, its easy - Fit a plane to
hit receivers. - Upward normal points to neutrino
source. - Within that plane, only 2D vertex
reconstruction is necessary, done by intersecting
2 hyperbola determined by 3 arrival times.
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Acoustic angular resolution
Resolution due to pancake thickness expose array
(0.5 km hole spacing) to isotropic 1019 eV ?
flux, determine hit receiver, fit plane to hit
receivers, compare plane normal with true
neutrino direction
Result (not including noise hits)
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Hybrid reconstruction

• Typical UHE vertices are outside the optical
  detector - optical might measure muon energy at
  detector but needs muon energy at vertex and
  doesnt know the vertex
• Get the vertex from radio/acoustic shower
  detection. Combining them gives good energy and
  pointing resolution
• Very little radio or acoustic scattering - hits
  are always prompt and timing information
  straightforward
• So hybrid sets of 4 receivers hit (e.g. 31, 22,
  211) may be sufficient for vertex
  reconstruction using time differences of arrival
• Different radiation patterns between the methods
  leads to non-degenerate hit geometry for good
  reconstruction
• Not a problem that timing resolutions are
  different
• Put them on the same footing by multiplying by
  respective signal velocities (position
  resolutions are comparable)

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O, R, A independent effective volumes
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Coincident effective volumes

• - RA, AO, ORA curves in preparation
• Preliminary results
• RA overlap 10-30
• AO overlap 10

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Event rates
Log(E/eV) ESS Events per year with E? gt E ESS Events per year with E? gt E ESS Events per year with E? gt E ESS Events per year with E? gt E
Log(E/eV) Optical (muons only) Radio Acoustic R-O hybrid
16.5 0.6 8.1 7.6 0.4
17.5 0.4 8.0 7.6 0.4
18.5 0.1 4.7 7.6 0.2
19.5 0.0 0.7 1.3 0

• cf. Halzen Hooper IceCube-Plus muon rate 1.2
• These results depend on a wide parameter space
• - Acoustic ice properties and noise level
• Optimizing the array (eg hierarchical spacing
  such as adding R/A receivers to the optical
  holes) could increase rates (factor of 2?)
• Adding the optical shower channel will increase
  rates.
• First results are encouraging.

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91 radio/acoustic strings for lt 20 of the
IceCube cost?

• Holes 3 times smaller in diameter and 1.5 km
  deep
• Don LeBar (ICDS) drilling estimate 33k per km
  hole length after 400k drill upgrade (cf. SalSA
  600k/hole)
• Sensors simpler than PMTs
• Cables and DAQ Only 5 radio channels per string
  (optical fiber). 200 acoustic modules per
  string, but
• Send acoustic signals to local in-ice DAQ module
  (16 sensor modules per DAQ module) which builds
  triggers and sends to surface
• Acoustic bandwidth and timing requirements are
  easy (csound 10-5 clight!)
• Acoustic bandwidth per string 0.1-1 Gbit, can
  fit on a single ethernet cable per string