results from saund study of acoustic ultra-high-energy neutrino detection justin vandenbroucke...

Results from SAUND

Study of Acoustic Ultra-high-energy Neutrino Detection

http://saund.stanford.edu

Results from SAUND

Study of Acoustic Ultra-high-energy Neutrino Detection

http://saund.stanford.edu

Justin VandenbrouckeUniversity of California, Berkeley

[email protected]

ARENA Workshop, DESY-Zeuthen, May 18, 2005

Justin VandenbrouckeUniversity of California, Berkeley

[email protected]

ARENA Workshop, DESY-Zeuthen, May 18, 2005

Justin Vandenbroucke ARENA Workshop May 18, 2005

The Tongue of the Ocean (TOTO)


The SAUND-1 array

7 hydrophones on sea floor, spacing ~1.5 km


Integrated livetime

Commissioning run (48 days)

Physics run (147 days)

Fraction of up days

Fraction of all days


Livetime at each adaptive-threshold value

“quiet” times used for analysis


Acoustic pulse simulationExpansion of basic kernel written by N. Lehtinen

Given a detector position (r,) relative to the shower, calculate P(t):

Use Learned’s prescription to integrate over the energy density of the shower (in the time domain)

The code can simulate water, ice, and salt. Input: X0, Ecrit, RMoliere, vsound, Cp,

At this energy, LPM effect lengthens electromagnetic shower to O(1 km), so assume hadronic contribution dominates

Use hadronic shower parametrization (gamma functions), based on Alvarez-Muñiz & Zas, Phys. Lett. B 434 (1998) (includes LPM effect on sub-showers)

Assume constant inelasticity: Ehad.sh = 0.2 E for all flavors, both NC and CC

Apply sea-water absorption directly in the time domain using Learned’s “smearing function” technique


Simulated neutrino pulses

1050 m transverse distance from

shower

longitudinal distance z forward from shower max

Eshower = 1020 eV

t (s)


Pancake contours

Labeled by Log10(E/GeV)


Over several km, refraction is significant!

unrefracted (+5 to -5 degrees)

refracted


How to calculate refracted ray paths

- Divide ocean in layers, but don’t use Snell’s law directly (zeroth order, c constant in each layer)- Use c = c0 + h*z (first order, c linear in each layer)- In such layers, paths follow arcs of circles:

€

Rcurvature =dc

dz

1

c

⎡ ⎣ ⎢

⎤ ⎦ ⎥

−1

- In ocean, Rcurvature is O(100 km) >> path lengths, so do we care?- Yes: Deviation is quadratic in path length:

€

−y = R − R2 − x 2 ≈x 2

2Rx

y

So for R=100 km, x=5 km: y=125 m > pancake thickness

ray emitted horizontally

See Boyles, “Acoustic Waveguides: Applications to Oceanic Science” for a nice algorithm:


Neutrino pancakes are refracted

E = 3 x 1021 eV


Shadow zone due to refraction

Rays from shadow zone cannot reach central phone


Focusing/defocusing due to refraction?

Slight focusing. Contours give intensity focusing factor for various source locations as seen at central hydrophone.


Require:1) Events obey causality: tij dij /vsound + 10%2) Geometry consistent with pancake (flat circle!) shape:

Accepted:

Rejected:

Event topology cuts

No hitHit


Source localization: 2 algorithms1) AnalyticalTime-difference-of-arrival, TDOA (for homogeneous media):- Each independent pair of receivers constrains source to hyperboloid- 4 receivers gives 3 hyperboloids intersecting in 0, 1, or 2 source points- 5 receivers gives unambiguous location (in the case of 2 solutions)- An exact analytical solution exists using d = ct for each receiver:- Combine them into a matrix equation and use Singular Value Decomposition [Spiesberger & Fristrup, American Naturalist 135, 1 (1990)]

2) Grid-based- For grid of source locations, use measured c(z) to calculate ray path to each receiver location, integrate travel time- From source-receiver times for N receivers, calculate N-1 independent time differences of arrival- Compare to measured time differences, best match gives best grid point- Linearly interpolate tij grid locally around best grid point

But in ocean c = c(z)


Localization: Monte Carlo and Data (Top View)

• 1014 GeV MC

• 1015 GeV MC

• 1016 GeV MC

data


Monte Carlo and Data (Radial View)

• 1014 GeV MC

• 1015 GeV MC

• 1016 GeV MC

data


Background Rejection

Cut Events remaining1. Online triggers:a) Digital filter ..................................................................... 64.6 Mb) Correlated noise ............................................................ 20.2 M2. Quality cuts:a) Offline rethresholding..................................................... 7.23 Mb) Offline quiet conditions.................................................. 2.60 Mc) ∆t0 > 1 ms .............................................................…..…. 2.56 M3. Waveform analysis:a) Remove spikes ........................................................….... 2.03 Mb) Remove diamonds..................................................…..... 1.96 Mc) fe > 25 kHz..........................................................….….…. 1.92 M4. Coincidence building:a) Coincidence ..........................................................……....... 948b) Localization convergence.......................................……….. 795. Geometric fiducial region….………………………………........0


Flux limits

A/B represent 1-year limits from hypothetical large arrays (367 1.5-km strings, spaced 0.5/5 km apart)

SAUND not optimized for neutrinos.


ConclusionsThe first large-area, large-livetime search for acoustic neutrino signals has been completed.

Code has been written to simulate P(t) at arbitrary location, with absorption, for various media.

DAQ, triggering, adaptive thresholding, noise rejection, and reconstruction strategies have been developed.

Over multi-km distances in the ocean, refraction is important!

A neutrino flux limit has been calculated. It is not competitive, but is from an entirely different signal production and detection mechanism: complements the radio limits.

The ocean has been characterized as a target material, but there is room for improvement: phase information, signal processing, analysis techniques, environmental (site) variation. Needs SAUND-2 and other efforts!

Ethr in the ocean seems to be unavoidably high - are there any fluxes here?

Onward to other materials!


The SAUND-1 Collaboration:• Academic:• G. Gratta (Stanford) N. Lehtinen (Stanford)• S. Adam (Stanford, now Cornell) T. Berger (Scripps)• M. Buckingham (Scripps) Y. Zhao (Stanford)• J. Vandenbroucke (Stanford, now Berkeley)• with help from N. Kurahashi (Stanford)

• US Navy:• D. Belasco J. Cecil• D. Deveau D. Kapolka• T. Kelly-Bissonnette

More information: see http://saund.stanford.edu and Vandenbroucke et al, ApJ 621:301-312 (2005)

results from saund study of acoustic ultra-high-energy neutrino detection justin vandenbroucke...

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